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ALTERNATIVE CONVEYANCE SYSTEM REPORT
VACUUM SYSTEMS
RICH NARET
CD
HEADQUARTERS LIBRARY
ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
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AI iiiONAii'v'i i :HNVI T'AIJI :; :;V:,IIM i AI r.)
IIVM-.'V(!W Hi AI ll::h>MAM VI i ;i INVI-YAWl'li: SYl
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4 Myhh:'. vr; RCM i i l.y
!:i i'M-.lii-r
C. Vacuum Systems
1. Histoi-y
a. System Types
b. System Comparison
Services
Collection Piping
Vacuum Station
c. Summary
2. Simplified System Sketch
a. Basic System Sketch
b. Components
Services
Collection Piping
Vacuum Station
c. Operation
3. Potential Applications
4. Extent of Use in the U. S.
5. Myths vs Reality
/S/AZ.6T
1).
SwK-ilH i.)iiy:i by Si-.-wer;*
1 . ,l ,n rnp:i 3 f i ed f'-Jy F. ti=-m I J- -r-icr ipi. r.on
a. Har-;i.i: f->ywt''|:Jfn '•ikft-.r.h
h.. r;rimponfvril".a
f.. ripp-r. •=)!•. inn
?. Pnl-r-rih-i a") App I T f:at. i i >ru::
I:l. l-xt^nt. nt I lr-;« in i.h<-' it S.
4.. Myhhw vs Uoril.it.y
F. l :ompnr-i sson wi l.h Cnnven 11 nn.< i I :i • IJ < •« :t.; i in Sy-.-il..
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I 'K'l SSI iK't SI Wi
SYS i i- MS HIIWNI
III. VACUUM SEWER SYSTEMS
A.
B.
C.
D.
Introduction
System Plan and Elevation Views
Description of All System Components
1. Services
2. Collection Piping
3. Vacuum Station
System Design Considerations
X. Hydraulics
a. Design Flows and Their Variabilities
Average Daily Flows
Peak Flows
Design Flows
h. Minimum Flow Velociti.es in Pipes
c. Applicable Equations
Static Losses
Friction Losses
2. Mains, Services, and Building Sewers
a. Mains
Geometry
Pipe Sizing
Routing
Trench Section
Pipe Materials
b. Services
Geometry
Pipe Sizing
Routing
Trench Section
Pipe Materials
c. Building Sewer
3. Valve Pit Settings
a.' General
Fiberglass Settings
Concrete Settings
b. Appurtenances
Anti-Flotation Collars
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4. Vacuum Valves
a. General
Model 0
Model S
b. Appurtenences
External Breather
Auxiliary Vent
Cycle Counter
5, Division Valves and Cleanouts
a. Division Valves
b. Cleanouts
6. Odors and Corrosion
7. Vacuum Station Design
a. Component Sizing
Vacuum Pump Sizing
Discharge Pump Sizing
Collection Tank Sizing
Reservoir Tank Sizing
System Pump-Down Time
b- Typical. Component Specifications
Vacuum Pumps
Discharge Pumps
Vacuum Tanks
Standby Generator
Station Piping
Motor Control Center
Level, controls
Telephone Dialer
Vacuum Gauges
Vacuum Recorder
Sump Valve
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E.
Const-ruction Con si. derations
1. Line Changes
2. Grade Control
3. Service Connect:! ons
4. Equipment Substitutions
5, Testing
a. General
b. Vacuum Station
c. Collection Piping
6. Past Construction Problems
F. Operation and Maintenence Considerations
O&M Manual
Staffing Requirements
&. General Information
b. Operator Responsibility
Operator Training
Spare Parts Inventory
As-Built Drawings and Mapping
Maintenance
a. Normal Maintenance
b. Preventive Maintenance
c. Emergency Maintenance
7. Record Keeping
8. Troubleshooting
9. Evaluation of Operating Systems
a. Early Vacuum Systems
b. Recent Vacuum Systems
General Information
Design/Construction Data
Q&M Data
c. Summary
3.
4.
5.
6.
10.
•Past Operating Problems
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G. System Casts
1. Construction Costs
2. O&M Casts
a. Labor
b. Clerical
c. Power
d. Utilities
e. Transportation
f.' Supplies/Maintenance
g. Miscellaneous Expenses
h. Equipment Renewal & Replacement
i. Future Service Connections
3. User Charges/Assessments
H- System Management Considerations
1. Homeowner Responsibilities
2. Sewer Utility Responsibilities
3. Other Entd.ti.es
:;MAI i m AMI IIM i;kAvrr» ::Y:;;u M i
V. HKSIliN i XAHPi I
2. Vacuum Sewer System •*-
;< MIIU-I i I I )"i •THin^tf'-r l-if •"(vi ty My
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Q_F F_!_G_U_R_I_S_
Fig.
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ft ft ft ft i
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.* Description Chapter Section
Li] jendahl -Electrol ux Vacuum System
Vacuum Toi let
Colt-Envirovac Vacuum System
AIRVAC Vacuum System
Major Components of a Vacuum Sewer System
Valve Pit/Sump Arrangement
Upgrade/Downgrade/Leve 1 Transport
Diagram of a Typical Vacuum Station
Early Design Concept-Reformer Pockets
Current Design Concept-Pipe Bore Not Sealed
Sample Gravity Sewer System
Vacuum Assisted Gravity Sewer
Basement/Valve Pit/Main Relationship
Typical Layout-Vacuum Sewer System
Water System/Vacuum System Similarities
Plan & Profile View-Typical Vacuum Line
Plan & Profile View-Typical Valve Pit
Auxiliary Vent Location
. Lift Detail
Line Diagram of a Typical Vacuum Station
Liquid Ring Vacuum Pump-Cross Section
Sliding Vane Vacuum Pump-Cross Section
AIRVAC Calculation Form
Static Loss Determination in a Lift
Spigot Adaptor Detail
Crossover Connection Detail
Typical Fiberglass Valve Pit Setting
Shallow Fiberglass Pit Arrangement
Typical Concrete Valve Pit Setting
Typical Concrete Buffer Tank
Typical Concrete Dual Buffer Tank
Anti-flotation Collar Detail
Model D Valve
Model S Valve
Early External Breather Detail
Alternative External Breather Det-eil
AIRVAC External Breather Detail
Auxiliary Vent Detail
Division Valve with Gauge Tap Detail
Access Point Detail
NPSHa Calculation Diagram w/Typical Values
Typical Elevations of Level Control Probes
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30 Effect of Temperature Change on
Vacuum Testing
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__L_I_S_T___Q_F___T_A_B_L_E_S.
Tablg_* ; Descrj.pt ion
1 Vacuum Collection System Parameters
2 Vacuum Station Parameters
3 Summary of System Types
4 Conditions Conducive To Vacuum
Sewer Selection
5 Operating Vacuum System in The U.S.
***********»s**s*s«ss*****«***«*s»****s*******s**sx
1 Recommended Lift Height.
Main Line Design Parameters
3 Guidlines for Determining Line Slopes
4 Governing Distances for Slopes Between I.
5 Maximum Flow for Various Pipe Sizes
6 Maximum Number of Homes Served For
Various Pipe Sizes
7 Typical Requirements For Separation
Of Sewer Lines From Water Lines
8 Service Line Design Parameters
9 Situations That Dictate The Use Of
Concrete Valve Pit Settings
10 Vacuum Station Design Nomenclature
11 "A" Factor For Use In Vacuum Pump Sizing
12 Discharge Pump NPSH Calculation Nomenclature
13 Typical Values For NPSH Calculations
14 Values of Vo For A 1.5 Minute Cycle % Qmin
For Different Peaking Factors
15 Spare Parts List Per Every 50 Valves
16 Specialty Tools And Equipment
For Co3lection System
17 Specialty Equipment For Vacuum Station
18 Operating Systems Visited in 1.989
19 General Information On Operating Systems
20 Design/Construction Data-Collection System
21 Design/Construction Data-Vacuum Station
22 Operation 4. Maintenance Data-General Tnfo
23 Operation &. Maintenance Data-ManKmirs/Year
24 Operation fc. Maintenance Data-Power/Year
25 Operation 4 Maintenance Data-MTBSC
26 Classification of Operating Problems
27 Typical O&M Cost Components
28 Manhour Estimating Factors
29 Vacuum Station Power Consumption
Estimating Factors
30 Typical Renewal And Replacement Factors
31 Annual Budget Example
Chapter
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t. OVERVIEW OF ALTERNATIVE CONVEYANCE SYSTEMS
C. VACUUM SYSTEMS
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S E C T I I!) N C
.y_A_C_U_y_M S_Y_S_!_E_M_S_
1..
n
Vir r:o I I r-i :t."i nn '••.yr-tir-mn WOKO pat,«nt.r.'ri in t.h^
t ln::i fr.r;d in "t HMH, whi-'n Adrian I .F; Mar1 qua rid invt"-inl/»->d ;=i system «'i1
GRwage co I l.^cti.nn h F t »?r:V.fn3 nx ) i.t'i r:ant, i..ia 1=f'i=!K"Rnr:e« flmnng t;h«Ki=? "in t.t^ffuss of design
noncwpt.:^. Th« major' di 1;1-er-en(~F'r:; 1 i 1=? .in hhr- «xt.finfc t.o w
i.he Kysl.enis use SHpar-aL*? blar:k ( t.oi ].r»t. ) and gray ( t,he ba
wat.f;?f oo'l. Xpr:t.i on man ns. E I writ-K-n'] ux ufseK .H :;vepaK'^t,i"- system t'-or
t.hp?«e nouK'f.es ; f-.nvi.K"ovrtr: usi>;-:5 vfirsnurn t.rn if-'f.R «nd on« rn.iin; <;inrJ
ATFJVAi: and Var:— O— I er; hnkc^ t,hi;i ruiKmal hi-iuKi-'--! u;> I rJ noinhi n«ri
w«-Hf-;t'.es>. Dt.hef di 1:1"eKf=;n( :»-•«; KV- I .i1'.^ 1,ri hh« lnr:at/iori ni~ i.h«
gravn by/ vacuum .1 nt.ftrl^icR ^nd V.o t.h»- di=?Fsi >.jn of- pump?:, va I v»-.-n,
li.nRS, etc.
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The t. i 1 Jendahl —F l.ectro'l ux system war-: fi r ~st used in the
Bahamas in the late 1.9BO" s (Figure? 1J. In thi r-; concept,
separate black and gray water r:nl!l.«';cti on mains arf* MRecl.
Blrink water refers tn ti-ri.let w.Hfitr-JM and gray water T rin'l udwfs
a III nther domestic: wiit-jti--;water. Tho blru:k water T r? di sr:l"ia»".3i-'d
to on«=c o1: tho vacuum ma:ins thrnuj^h i:< vacuuid toilet (Figure ^'}
while th« gray water enterr, the otl'ter through the ur.e <.it a
J3pe«r:ia 11 y designed vacuum valve.. The separate vacuum main«
are connected to the vacuum station. l-or critically wate>—
r-short areas, such as the Bahamas, the reduction in toilet
wast i'1 water volume war; a definite t:actor in the Fse3.ecti.nn of
vacuum transport.
TRANSPORT POCKETS
VACUUM PUMP —
BLACK WATER
"COLLECTION TANK
BLACK WATER
VACUUM MAIN
GRAY WATER T «—CRAY WATER VALVE
COLLECTION TANK ' GRAY WATER VACUUM MAW
TO TREATMENT FACOJT1ES
BUFFER
VOLUME
FTl'ilJRF 1
i TI .TFNDAHt -i-i FT:TROI..MX
VAilltllM SFWFR SYSTFM
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VACUUM TOILET
JL
.FLUSHING
MECHANISM^
--VACUUM
| MAIN
DISCHARGE VALVE
FIGURF ?
VACUUM Trm.F'1
A Vac—Q—Tec system, serving the I ake of the- Woods
development near Frederickssburfl, Va. was the first resident.-Lai
vacuum collection system in the United States. This syst-.em
uses r:onoepts of the L13 jendahl system hut has many Important
d"i Inferences. The Vac.—0—Tec system requires no i nsa.de vacuum
ho.i 1 ets or vacuum plumbing. This system employs a single
combined black and gray water collection main. large? (750
gaJ. ) storage tanks are required at each residence. Finally,
an external power source is required for each valve since they
are electrically operated. In addition to the i ake of the
Woods system, several other Vac- Q-Tec residential systems-; h.ivf
been used by private developers.
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The Colt.—Fnvi.rovac system Is the direct descendant of the
l.i.1 Jendah'l-Fleotrolux f>yr-:tem (Figure 3)- The Holt, system at
South Seas Plantation near Fort- Meyers, F1_a. serves '.-in
r err! derices.. The houses have separate blank and gray water
pj umb ing., Ihe black water piping fVorn the vacuum trn'iet jcnru
the yray water vacuum piping i.mmedi.i:ite!J.y dowru:l.rearn nf the
gray water valve. A si.ngle pipe with the combined oontent?;
transports the wastewater to the vacuum station.
GRAY
WATER-
VALVE
COLLECTION TANK-
TRANSPORT POCKET
•VACUUM MAIN
TO TREATMENT^
FAOUTIES
I (GURK :-.<
t;rii.T-4:Nv.runvAC:
VACUUM ^hWFW SYfJTFM
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ATRVAC markets & pneumatics 1.1 y controlled and operated
vacuum valve which is used for cornbi ne*d gray «=tnd hi ack water
systems (Fi.gurr-- 4). The AIRVAC syntern a I "I own foe use of
con van hi cm a 1 plumbing in the house, w:i t-.h the wciKbewater
f"J owina by 9K~avi hy to a i":arnhn n«d sump/valve pit. Thw valve
starts its cycle when it senses approximately 10 ga.llonra has
accumulated in the sump. It apr-.*nr-- f'ar a few secondK, which i R
enough to evacuate the contents of thw sump ats we I..I as allow
atrnospherd.c air to enter t.h« system. The sewayR/a i r «n xturo
travels to the vacuum station.
AIRVAC' s f::i rr;t system was inntallwd -in Mathwws r;ourthous«4,
:i n 1970. Since then AU3VAC \-\HK more than 30 add i t:i ona 1
m operating i.n the United Stater-; with many more cui-rent'l y
being planned, designed, or in oririKtruction.. ATRVAH has also
been very active in the foreign market with apeati.ng systems
in Australia, Canada,. Japan, Holland, and some other Furopeem
Countri es.
VACUUM PUMP
RESERVE TANK
COUECnON TANK 1
VACUUM
VALVE
TRANSPORT POCKET
VACUUM MAM
SEMMGE PUMP
TO TREWVEKT
FACUflES
F TGI IRl- 4
ATRVAH
VAt'UIUM SFWI-IV SYSTEM
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'"'• -..'y*^ '•'.''' ' 'OUILid.C!! f"H
Fach nl:: t,h«=« 'four s;yr?1",»=?ms have- unique? d^wi ctn fi:.-iil.urr':~., The
I he* wahor navi ng tV-viiMi re-* ol t.ht* I ..... I r*cLrpri I ux .-*•' at-; mur;h a'.-\ 'S'f p^ri'i^nt. inf; t.hft hnLa I in .1
ilninh l,l'n-' L.U::P' <")i v.inuum t.n~i It •).---.. A 1 IV'v'Ai ;
«uid Van -U •- Tp»r: Kystenis c..:an hr~> .-i I Lf'>t-(-.>i1 t'-O ;-n:r:
Blank: 1 • 1./5?"
& 'S" ; ;^r ay :: 1-' "
A :r-; pvr: «r,!
Single iiu-rin., '.-I
4", & R" : I'Vi:..
f special "')"
Si.ns'l« tna'in,
A " - PVi ;
Con ven tiorii-^"I Pnwuma t,i i"
pi ijriih.ln«3 va'l vn
Set cnn-Pi ;;| • Singift main,
urahion wi t.h ^ ",'"'", & •"'" '
pr-ol-.i U- PVi:, r-:cil v,^r.!.
wr- I H CM-- "II"
t' i rig
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Var:uum va I V^K ap<-jK«4t;e .:i«.i1.nrn.-i Line I "I y., b;:t';;(•••.! on l.bf
l uftH-f Ot" b"lfn:k fit" iSK'i-iy writer bwlrind t,bt--- v,-Tiv<:>. Prciv i rii-ij
t.hrtt. ;-;u1-1:"i rri.»;>nl, V.K:UUKI i ;; available; in t.ht • tii.im., t,br- v.ilvor.
wl I I ripen a1"t.p?r ,-i pn^dei'.^K'ftri nr*rl vnlunif i>f WMr.V.«w,.|t,(.-K"i~.:ii .i;j v.i I v*7' .-if-rn-mlri j..y
is unique in t;h.it. it. r-e«qij-t I'rtf; an f-fxt-i^rna ! r-'«'W^K •»• HH t-h*-' Vrn.niiin
f-:t..af,i on t.l-irrui'.^h an exl-rvn f-;oti rrf" r:rmt..--ic:t'.<; in t.hi-j
COnt.K'oX 1 er.. A raeparat.o r:yc: I i n;^ nindr-f, r:.-n'll<»d Anl.riSj-.-m, c,.iii
b*^ added whi.nh rj-f f«Kf. t "l.^xxbil Uy i-i i l-hf Vat: L^l "iV-n : :y«1,<-tn.
This rrtCK'Jt^ 1 ockr-' out. the anriumulatwd vn i unie -i..yi. I <-> i:oitmi. md
•fVorn ear:l't v.'il. ve,, i^nd r-subsequent. I y op«r"rit,*=«R »•••. ir.b va.l v»-
durin<3 t ow-f i nw p«K-i.ndf5. 1 hi.s f "l.t-.-x i bi 1 t.y ,iliow« t.l-ir; •--.vnl-.Rui
t.r> st.OKe •Plows dtJK'i ng p><=?ak pofi nds .-^nd K"f-1 «-'>i=»{3w t.hern l,ril.i;;K
during 1 nw fJriw p^rindr.. All of th«-> ot.hfti- r3ysV.eMn« inust. br-
de«ignftd t.n handli? pi^.nk l^li'iws. Tbi ?-; -fi^FifcuKM. drir-'r-; howi;vi-<> ,
add cost.s tin t>in b.ir-se sysit.om. AT r;rt, addi. t.'i«inn I np«r.Hl. i n;4
and skilled F>J.rM-:t.ri::ini r:« t-er:bm dans ftfft rf»M'J i rt*ei t.n
man nt.«-»i n t.he moc'i^ complex syt;t,«trir-5
V
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Of?!pt:~;nd'j riot on t;l">6" iiitHnij'I'-n^l-i.it't'r, hl'ir- .-unourit. iff w^il.i-^K"
>-"*n te?»""i nj} tJ-n=» system w t t'-l'i I=>FI <•:(•( va t vi-.- OPI---K ;-rl, i on WIK~I <->K, !
vacuum V.ri'i. I ei". *<"hn i i,t~, af'r>(r'c''x ' i(ii;it,t'j I y (')_ H ho O. 4 cir»3 Inn:-; Fn-
t I i.i:'2l i, wi'i^fea;-: t.hit- pi ii-'ijiru-it. i i:. i I ly r:r»i i l.r ri I 1 (-'d vacuum v.tiv<>
rtditn t. 10 to 1 Fi y«i I Ion:1, pwr i.yiilr-.
II. S. NiiVy r f--Si--.'.;'U'i :l'i hrt:. r fpoKhrjd l,!-i.-iL «-iood 1".K • inspi H- !.
i-:l'u-ir ;-n':t.i~'K "r..'> I. i CM .-ire-- -f-ound wil.ii : :.i it -fri <: i f>n I. inli-'t. .H i r .-mo
fsma'i I p-nouqh «-:'). 149 1 o-iHini-i:". "tor l.l'n=» ,-ivH'i I fibll.i-'' pfi->r-:KiJp-^
di.t-f'eKent'i £*1 tn nvi-'i-'nriiw* hi K-- I iQU'id*:-: 'i nr-r h:i a . fl-ii <:
KISCJU I ts "in fapi i;1 r-ilii;^ t>ri-Nv)k
quir:k"ly at, up:-;hrt-!.un valvt-r:.
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HOI \Jf'.\ lllIM PJI
P i p~i ric) prrit'i I FJP: d'i 1 f'f-'f, nf-jpi-'nrli.ng i in upl ri II, rlriwnhvi I I , S3 gn
rn.Hnua [ wh'i nh i hT-.CK i bier- l.l'n- di--r. i t"^d p-i.pin--j prot'i'1 p-r. in rj^oh
s'i l.u.i I,'I«>n..
I herf' l'u:iv(-! br'i-.'n t.wn <'^'i f 1'i^ff-M-i I. ccinr-.^pt.w usr-rJ in v/rtc
dt->f>:i 'jri. Jn t.|-ii-> 1"i (••;•>!, r:rmr:r^pt, V.l"i«-' hriri"' ci1" t,hu^ pipi-v :i ;•;
r-.Ha"U-'d during r;1,aivi<:: ccmdi V.i < ms. "I h.i r~ ir. .n •.«•-< 'impli <;hf--< I t.hr nugh
hhc iu~r> rrl' i-t=»-^nrm«r prickfahf?. 1 ri t,hi-' (it.l'iwK r':onr:t'p1,, Lhrt b'n»KR of
t.l'H--.' f. i i pe i f. r\>\(\ PUSH | r-»d. Thr.;i grierJ ijrm ng
bht-'f lat.ter pr::i riiri pl.e-
All Fsystwfitf1; ussen PVR pri pe. Bnhh sn1v«=*nt-. -wi-r l.rl and cMFikt.'fci^d
l) IV-ing pipe? h«v« r^i.ir:r:er»sf: u 1 1 y h*=ji=?n u^^i'J., in <=spp>i-:i .1) oaKen,
di.ir:1".T 1 e cuH^t. iron pi.pf=> h.ns hwen uf-.i-?d.
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VACUUM S I AT
Vacuum s;l".;"i t:*i nnr-i, r:niTiei'.'i rni:ir-; trfff>t'rt~'rt t.o /IFJ no I l.or:t, i t iri
r-:> vary f'rrnn iiirimt t-ar:t.i.ir»;ir t.n nmnuf ricLur ei'. '! <-i I. • i (•-• ;'-'
whriwf; t,h(;> varyi n«j i.1c*F,ri «:^n |:i;;ir .•••Hii»r»Li-.if' :-; lit ^'.nc':! i hype-1.
I I pohiT] I i ix «-m«::l linli. vi4K'y l.hf-vir i.if-:«?; rrf' v. KHJIMII KI Tiwr'Vf • l..mi<;:
wi t.h <;'^cl'i i nr:t,,H j I ai'.'i nn, whi'h' V;Hc:-Q- -T «••(-. iinri A FU'VAI i u:;--
r^kK bc-'t-.wp-.-f-.'ti l.hr-' r:n ) .1 r-'dvi ( in V.cink <-ind l.hc-' v.<«:uum
f;. (Nut.e: Tl'ic-.1 l.t-'rin " (••»••?«*•"?!' vr? L.nnk" i ?•; ur:i-d hy .j I I o1 l.ii«--
ffifirtu t"rii : hi.iK f*rft exr:i-.'i;i t. A i F?VAl I wl-n.r:h t"rj }utjr :~~ t,< i t.hi,:"; I., "-ink ,i:-~. .-1
"KTfr.i^rvci i K tank". )
ri-!r-u->r vn: r
i ABI i
i ' y f'i o
f-'.'l ect.m I ux
! -i i I t --En vj reiver:
Vac -IJ T f-^i '
ATPVAf;
_ T * i n k _
S^"F>i5iK'afc« hlai:k ."iric'J <^t-.sy w,-it-.eK
v e s s e "! s . R ft & e r v c> h
-------
ifi.mu 1:t=«i :t.i.trws hav^ plnyed vi inn j in- mli' "in i.h<~-
di.rivt~* i i ipuiMnt. nf VMr:uuffl f>wwi:n' MysjUi^inw. 1 hr-t-- <-• <-iKft « i Pin i"t "i <~,~
d'i r }(•!»' I-TIOC-T: in iivRf«ri|,j raywl'.t-Jiii phi i 'I r issr.ipHy, ilfFii cm r:nn«-.r'|;iLi;
r-:y:'-"l-<->ni i':imi|;»i inwnt.S, HfH'1 rn*«:ir:h«-'r; i Idtilc-' HJ.
Wl ri l.f; •"! I 1 1" rn.it" w^ft* '() yt^Hi r; »i<.^n in i.l~i«» lln.j t;.i -rl
Sti-i !.«?:;. i m I y AIKVAi; riar-; r.:ont.i nuwd t.ri pl;ur(- r I-T--. i ilei il. i •< I
syf-vl'.< 'in" "inl.ri rip<"'K'i!itt. .i on on «ri rt-'^u i .-IK hi.i:'. i :-. '._>( nti»-- ol" l.hr-»
c--.(>- ly :-;ysl'.Miii:; of" Cn!l t'.--|- ri v • i.r'rivai : <-in i'J ar y
I'll
in
No rj*--f?i.pri tn<-iiiii.:«l
In hem r-itv
Nn iJp.'Ri cjn fn.-tii
-------
a. Basic: Oi/s
Figure 5 shows the basic vacuum newer system "layout,,
including the major nomporients. This layout is ba^e'd on an
AIRVAC type of system ;-rinc:t-; it is the innst common.
FIGIIRI- !-)
MAJOR riflMPflNKNTS
OF A
VACUUM SFWFR SYSTKM
-------
A vacuum i-sewer system oonrvi r.to of throe (3) ma.ior
c:i irnponentf;: the vacuum station, the noVI ^oti on pip
the r.ervi cos. Each i ;-~ dec-*< :i-"i hr-»d bo'lriMr.
SffRVTQES
1^1 OWK by gK.'tvit'.y 1:K'om one or" mofi1* hrnnftK "int.o
n 30 J3»5in on holding t-.ink. AK t.ho sewage I evftl ri K*=»J-; Sn
i-,hr-? Hump, ."iir i.R nompn-.'SSi-^d :i r> a sensor- hubt? whi r:h :is
r:onnectr-»d to t-.he va'l.vr- nnnt.ro] l«?r. At. .1 pKfr-^t; point;,
•fchi"? f>«^nr;or rn.p)n.Ti]l.i3 'for the vaciaum v«"i ).ve> Ko open. I he*
va!l v« stayR opien 1:or an adjustable period o1~ tim«^ and
then closes- Ourlnjg. the open cycle, the holding tank
contents ai-e evacuated. The timing cycle i r; •field
adjusted between ft and 30 seconds. Thi?s ti inn- i s
usually set to hold the valve open tor .-i tot -a 3 time
equal, to tw:i r:e the ti.me reQui.red to admit the sewage-
In this manner, atrnospheric fl'ir -is allowed l.o enter the
system behind 'the sewage. Thfc t..i me setting if;
dependent on the val.ve 1 i:ir:ati on s i nee the vat:uunt
avai.labl r» will vary throtj«;^hou t thr-.« sy:::l.i7im, theKvhy
cic:sverni n«g the rate of sewage tr 1 r>w.
-------
Thw vallvF* pit, t.ypi«::;vi I I y i.yj 1 ocHt/i-'d o I nri'3 a prnpechy
11 i rn». '1 ho Vt.il v<-' pi t'./bn"l_d"i I'M;? l-onk arr cHnqi-Miiont- (I" i <:?urr-
fi ) i.« ufujallly nu-iiiU-; crt 1' ~\ tn'M'gl «sra» a I t.hrH.igh cm idl f'i r-rJ
«":c mi :K p't.i-; inanl'ii > 1 (•• r.ivct.1 nnr. l't.-ivr? bi-v<-';n UK<-'<:' I-CIK :-;p< >rri a I
rri t.i.i,--i h~i nnf. ( rloop ham-inonhK, t iriK-^i".- U;-:«?K, (.n r';;:;ii> (••/v.ii :utnn
•i rrl.rtKf-ai .i'., (~'t.i:)- A nnn —hrat )'"i r: I i.ght.wi-: i i^hl, a'l I.IKH mini nr
car:t; i.rcin .lid .1 r- aval l.ahT
-------
GDI I Jrl'-.l DJN PIPJNG
I !• »ft var:tjiji»i i :ol 1 r-n : I, i nn p'i p i n;J) iif-uju-il !y i :< m f-;;i r:t.:: ni
(•>•• :i nnh, arid 4~"iiir:h main;:, M I l.hi HIM! i rnrif <"• KI»M u-ril.
"insl-dl I..-.1 h i nn« H I MI i i nc: I ndr-* 8-lnr.h mari n:-s in Knun* < :.:i;:c-;
h>ma I I (-.'K (3 irioli) irr.i i n:-; (.r;(-«r:l in i';ar I y vac:uuin r-.y».-;l.i MII.. ,
rut iiiii<:3tM' >"(->c:riinn)f-*ni"lf-'i J, «-u:; V-hi-1 ci'isii ?;«riv i nu;-; 1 11" ii iut:ii
4 inch .-iff conn i dt-.'t-vrl Ln t:ur> i n« i cini -f: i c.m I-,.
Rribh .'>i 1 1 vwnt. weldi-i-l C'VC flip*-- .irtrJ i'(jhhrjK- ;?..iMl St-M :t. i t in !),>')- Wl n''rt'' ruhber gHtskHt-.*--! inri? u5-.t--ri, l.|
mur.t. hfi cirfftii 1-ied hy i.ht- inanu t'-u :l.ur'<->r .i<; t'iei.n;:j raji i.vi
frn- vrinuijm swrvi. CP. I hr> man n« «::ife oieru^ral I y 'La if I i-t i
t,he sanift c-;'t ope as i.hf^ g^Mund wi t'.l'i ;=i irri.ni mum slop^'- i'if.
. '.'''£. )• OK UphJ 1 1 t.KiHriKpOKl"., "I 3 1:tvF! i-'lKPf T' I .4«-;<-fd i'.ii
in'i ITJ rnri ^e *-;xi':.:ivrit, i.nri cJnphh ( Fi CIUKW 7). Ther"*.' .-IKI^ nn
itirtr^ in I.HI-S in t'.h»^ fsy?;t'.i-'fii, t'towr-'Vtvj-' ., fii':of-«rir> r:.:s. D-i.v-i.a:i < m valvi-' in.-iirir. t.n .-:i') l.<">w f-'or" i f><">1 t^tinn
wl-ii-'.-n trcmh I erjhiool'.'i n-.j r«K whuvn making K'ppad rs-v P i u«j
va i vrt and Kt'.'sxl'i.tvfnV. wi--jdnf qahe valves h.Hvc;
IKI-
I ^
1!".
-------
UPGRADE TRANSPORT
///=///— ///=/// — //'=///=
FLOW
LEVEL GRADE TRANSPORT
LAY SEWER TO A FALL
Of NOT LESS THAN
0.2V DO NOT ALLOW
POCKETS TO FORM.
DOWNGRADETRANSPORT
FLOW
FTliURF 7
UPW-MOE/OUWNiilMDH/I.FVFL TRANSPORT
-------
M 51 AT TON
The vacuum station !;•:> the heart of 1..h«-» vacuum s^'wer
system* Tt Is similar to a conventic ma!). st-?w«-»ge pumping
station. These stations are typically two (2) r.tciry
ooncre te and hi nek buildings apprnxi.inat.pl y ?'.V x 3O" in
1:!LrH"iK plan. I- qun.prnenh in hhF* ?:V.aV.:i r m iru:::'l mli^r-i .-t
collection tank, a vacuum res*-rvolr tank, v.-icutim puirip^,
sewage pumps, and pump cfinfcro'J.s. ( F"i ijuK-e ft). In
addition, an emergency generator is standard equipment.
whether it be Located within tJ"iFs stat.jnn, outside the
station i.n an eric Losure, OK of the portable, t.rur:k
mounted variety.
The cri'l I. ect :i nn tank, made o'f either steel or
fiberglass?, i K the equivalent to a wet well in a
conventional pumping station. The vacuum reservoi r
tank is connected directly to the col 'lection tank and
nerves as a buffer to reduce the •frequency oP vacuum
pump starts and thereby extend their !l.if:f»- The vacuum
pumps can be either "I i quid ri ng or sliding vam-- type
pumps. These pumps are usually si^ed -fnr 5 to 8 hour;;
per dav run time. I he sewage discharge purnps are nan
clog pumps with sufficient net positive suction head t.n
overcome tank vacuum- Level control probes are
.installed in the cnl'i eotinn tank to regulate the sew.tg^
pumps. Vacuum switches on th*-1 reservoir t.-ink regulat*--
the vacuum pumps. A fault rnon.i horn.ng system alerts the
syt-~tem operator should n J ow vacuum or hi gh «r>wage
level condition occur.
17
-------
VACUUM
PUMP
EXHAUST
POWER
VENTILATOR
FOR TOP
FLOOR
VACUUM RESERVOIR/
TANK
CONTROL
PANEL
VACUUM GAUGE
ISOLATION VALVE
VACUUM PUMPS (2)
' ^\
EQUAUNGJUNES (2)
NJR
FORCE MAM
TO TREATMENT
PLANT
COLLECTION
DISCHARGE PUMPS (2)
L_
T ITillRF K
DIAGRAM OF A
TYPl'llAI VACUUM STA I'TflN
•i r:
-------
Vacuum OK negative pressure sewer systems use vacuum
pumps; ;-it central collection stations t.o evacuate air from
the lines, thus creating a pressure differentia'!. In
negative pressure systems, a pncH.iniat.:i ca.l I y operated valve
serves as the interface hetw*^en hhi^ gravity syr.i.wm •from thr?
ind:t.v:.i dual user and thus vacuum pi pelri nem. Pre«;r.ure «enKorr.
in a wastewater hoil.dina tank opwn and clnse the interface-
valve? to control the flow of wastewater and air into the
vacuum system.
The normal SP*CIUen«":«:-> of operation is as fol-.lciws:
W«sis3tewatp»r from the individual, service flows by
gravity to a holding tank.
As thei level in the holding tank continue;-' to rise.
air is compressed in a small diameter sensor tube.
This air pressure is transrni tted through a tube to the
controller/sensor unit mounted on top of the valve.
The air pressure operates the unit and its integral H-
way valve which applies vacuum from the sewer rnai n to
the valve operator. This opens the interface va!J ve
and activates a field adjustable timer in the
controller/sensor,. After a set time period has
expired, the interface vaJ ve e"loses.
-------
* The wastewater within the vacuum sewer apprnxi mates
the form of a spiral rotating hollow cylinder
traveling at. 15 to 1.8 ft/sec.. Fventually., the
cylinder disintegrates from p:i.pp fri ntri.nri. and the
.liquid flows to low p<:ri nts (bottom nt lifts) In the
pipe"! ine.
* The next liquid i.:yl..i rider and the air behind it will
narr-y the liquid "fVorn the pK^viouw disintegrated
r:yl i riders up river the Raw tonth li.ft« designed i.nto
the system. In th.J FS manner, tl'ie wastewater IK
transported river a series n1~ 3j.1"t:-: tn tl-»e vanuuin
station.
The princip'l.es nf operation of a vacuum «ewe»r system have
not been completely understood. An earl y concept wacs that o1:
liquid plus flow. In this concept, it was assumed that a
wastewater plug completely sealed the pl.pe bore during static
conditions. The movement o1: the plug through the pipe hnre
was attributed to the pressure differential behind and in
front of the plug. Pipe friction would cause the plug to
disintegrate, thus breaking the vacuum. With this being the
situation, reformer pockets were located in the vacuum sewer
to allow the plug to reform and thus restore the pressure
differential (Figure 9). In this concept, the re-establishment
of the the pressure differential for each disintegrated plug
was a major desi.gn consideration.
-------
MAIM
FIGURE a
EARI Y DF.SIRN CONCEPT
REFORMER POCKETS
!„ th. nur«nt *•!«. cnn«Pt. the
~ th-t th- «— *-r *-. not ,
p
pock.*,
,he
Th.
th, pr^tnu-lv
- th.
cond.tinn
peline (Figur. 1O). Tn «H. «nc«*.
.1. the f*. rf . -Pi«l- -"«•••
th. —t— t- -n- t>-
- cyl.n*« ovi- «.
tum of
it, contrdbutix- tn th.
liauid po««n«t n. .lu- -
consji.disrati.on.
n,
-------
AIRSPACE
SEWAGE AT REST
' FIGURE 10
CURRENT DESIGN CONCF'PT
PTPF BORE NOT SFAl ED
Bnfch of the above design concepts are approximations and
, .verw itnplifications of a r:rimpj ex, t.wo-phase flow system. The
, tu-irai:ter of the fXow wi thi.n the vacuum sewer varies
, > msi derably. The plug flow concept, Is probably a rftaf-srmab t e
of hhe flow ^s i.t.".ent.«->rK the syetom, whi-rt (->aw l.h
mcivwtnent nnricept. IK probably a betLeK
.i.•(.••mxi.mafci.on of t.he flow throughout. hh« vacuum mai.n,
1 hf^ significance of the axr as a riri.ving forcw cannot b<^
,.v'«!rt-'fnphaKi ^ed. The atninKphf-iric: air expands w~i th'i n thif ViH.i.n.i
•..•wr*r, thtJi? dr."i.vi.n<3 the I 'i qui d forward. The air affectF! not
, ily the liqui.d in the atsKociated air/liquid slu«3, but al?;o
> -!»•• 1'iqui.d downntream.
-------
*""'-
iable 4 shows {genera"! conditions t.hat are conducive t.o t.hi
selection of vacuum sewers.
TARI. E 4
CIINDT ! TUNS nUNDllC ( VF TTl
VACUUM SEWH-? f-iFIFOTll'IN
Lin stab! t? r-icn Is
Flat V. Rr ra i n
construct-lon
High wahi^r tab 'I «=•
Rock Unusual or
Deep t:>«'iKfiinenl,fr:
Low popu] at.i on density
peirienaw has whown hhat for vanuum nywt.c'ins t.o be norat.-
«1:fectlve. a minimum of 75 t.o 100 nushomers ±s needed
vanuurn station. The average number of nustomer'Q per- s
in systems presently in operation is=i about 200 to 3OO.
are a few systems with fewer than 5O and some with as many OH
200O customers p
-------
*•!•. If ?< tent Q£ U-f-s? i.o. tbs .
Table 5 shows the operati ng res;:J dranti a'] vacuum sower s=syntiams
•in the United States, a55 of Decr-Miiner 1 HftS-L Tl it-*re .-ire anothoi-
dozen or so present, I y i n the r:onstrur:ti on phase, with rnrrre he-ing
planned and designed.
TAHI F 5
LJM._SYSJT:MS JN_.THFtJ.LS-_
T
TIA
TIB
PROJFC1
Marti nghatri
Foxcil :i r f e Fstatns
Country Squire Lakes
Mathews Courthouse
PI ainvi Ile
Fastpoint
Wfs tinoc'i--1 Lan d
Fal.il en Leaf Lake
1 Ipper Fairmont
Uueen Anne' s County
L a F a r g e v i 11 e
Char 1otte
Ohio County-Phase
Ohi o County-Phase
Ohio Coun ty—Phase
Friendly PSD
Central Boaz PSD
Red Jacket PSD
Washington Lands PSD
Cedar Cove
Lake Chautauqua
Laa Marina
Einmonak
Swan Poi.nt
Alton
Whi te House
Morristown
•Lake Manitou
Therewa
Sanford
!-u"iuth Seas P.I an hati 01
No or vi k
8i g Bear I ake
Cert ter town
Stafford Township
Ocean Pines
I ake of- the Woods
Sh i pyac d I'1.'] antations
Pfi I met to
Captai n' n
. P.KOJEQIJJJLJAT TriN_ _ 5
St. Michar-1«. Md,
Ma r t i n ;•• v i "I. I e, T n d-
NoK'th Vernon, ilind.
MathrjwK, Va.
Pil .'ii nv i. 11 e, Fnd..
Far-stpoi n t1., FT a.
Wnr-ttniore'l.arid, Term.
South t ake Tahoe, CA
Somerset Co, , ML)
tJiiRt^n Anru"'* K County. Ml
I al- arjgevi I 1 e, N. Y.
Charlotte, Tenn.
Wheei) i.ng, WVa
Wheeling. WVa
Wheeling. WVa
Friendly, WVa
ParkerKburg. WVa
Red Jacket, WVa
Washington Lands, WVa
Lexington Park, Md.
Cel errin, N. Y.
Norfolk, V,i.
Frnmon.'ik, Al«=iF5ka
Swan Point. Md-
A'lton, Ky
White Hou?-:.«-, "tc-nn..
Mnrri fjt'.owji, N. Y.
l?oc:h*?r;ter, I nd-
ThereNa, N.. Y.
Sanf ord, F 1 a
Fort Mt^yeKft, F.l.i.
Nnorvi k, A i .'irtka
.R.i <3 Ruar i. ake, IIA
C«-?n ter town, K Y
Manal'iawki n, N. ,J .
Reri] i n, Md.
I oc:ur;t l-irrtve. Va.
H t I tun Hi-.-, i-1 11: i an« j., l-:C
Hi I trin Hi-, id i:. ! i-mci, ••«!•
t'.!i' e^-nh-tc:!-,, Va
:;YSTFM
AIRVAC
ATIVVAC
ATRVAC
ATRVAC
AIR VAC:
ATRVAC
A mVAC
A IRVAC
ATRVAC
) A IRVAC
ATRVAC
AIRVAC
A.IRVAC
AIRVAC
AIRVAf:
AIRVAC
AIRVAC
ATRVAC
A IF? VAC
ATRVAC
AIRVAC
ATRVAC
AIKVAC:
A I RVAJ":
AIRVAC
ATRVAt:
AIRVAC
AIRVAC.
AIRVAC
AIRVAC
I-NVTRIIVAC
FNVIROVAi:
FNVIROVAC
FNVIRnVAi:
hMVIROVAC
VAC-Q U -C
VAC P TFC
VAC--O--1FC
VAC-U-fFC
VAC u-Tl-i:
-------
In addition to the* ahnv*-? K'esidRnti a 1 wypjl'.i^fiu-s, si'Vtrtral
•industrial f'ar:.i t i t:i !-.•:> use var:uum ray stem;; to noil I p-nt wastf=*wat«-'r..
Tl-ic?se «:ntnparri *=s .include* t-hi-1 ScoLti l'.--ipn>r I Irnnpany ptil..p and p.-ipx-i-
mi t I .-in MobiU>, Alaharnn w:i t.h 2b AIRVA1"! va Iver;. SLiern meirHjf;ac1l-.ur<^r, J<-^r'ad
Industd *=•«, zi.n many c:hiptinard incfca11ah.-i.ons. Thwsf types of
instal 1 ata.nnp; are beyond the-; scope nf: t.hi.s frrpriKt., and WT 1_1 nrii-.
b «r* a d d r w s s e d,
-------
Many myths exist concerning vacuum sewer : iytjiu-mr... In many
ways a vacuum system is not unlike a convent'! on a I «.|i'avitry
system. Wastewater flows from the individu.il homer, and iitili •»•••;-;
cjKvivi tv to reach the point of connection to the public r-;nwer
The 1 i.ne materials are the s
-------
MY TH:
Vacuum Kewerr-i should not hi-- c:on« i d«-?r<-»d when
natural gravity exists,.
Rt-AI J'TY: Many timer-; a broad view at' an <-i>•(•-.-r :-. 1.i->rrrri n
automatically rules out. vaoiium ^fweri-s ar: an
alternative to he eon wider i-*d.. However, .-1 i: linger
look may reveal many snu-i I I arJvanl,aQi'--r-;, bi"ial., wl ion
r:i insri dered r:o I t.ei:tivp.'.l y, add up to * :••
:>.-iv:i ngs.
A f n ne exanif;) l,e inf l;hn t: nnruirrr.-d i n t.he llhio
Kfuinhy PSO-Phasi' ITA project,, in Wh<-M> I .inq, WV.. In
jech, .it. only siawm«rj loqxr.aA t.ci t,hfj
to UFS« jjravity rjewwrf-;.. Vh>? ai^fta was
rural with resi.d^ntia 1 development fci.l.J nwi .n«i a
creek. ' However, upon nloser rnspir-rifc. j on, it waw
evident that the gravity main would tie requi rod tri
cross the creek in .various p"U With t.he* <:rtT*n-k
bank being 3.0 feet deep and the <-;»•• eek i-.Konj>i n;-i
requiring 3 1~oot of c-.over. the i^ravi I'.y Mt>wt-t- would
have been 'V3 t'eet deep for mo;'-.t u'l ri *•.:•? I i--»n!'4t^i
(Figure 11)..
-------
V V
/ / "7 /
12
7
7~7~1
•BEDPOCk
11
liRAVJTY SI-WFR SYS IFM FXAMPI.
was KoJ id rm::k, tJ'ie en hire 1 ^n^W'i «:rl b
f:av«t3 on wriuld hav*-? tii->«n in r«u:;k. At, i.
rius nt |-.h« syKt.em, a 'M. wt.r»l'..ori wa:-; n»-^rirf
t.o pump t.l'it? r:ftwage fr.i'i a pliini", wlvi v.l't wa« lnr:«-rhf-?rl
abrive t.h« "I.OO yf f:'l rind elevahinn ( K'-j.iqi.ir** 11).
-------
By utilizrri n<3 vacuum, the detiri gner used "lifts" to
raise the main above the bedrock ] evel to a depth
of1 4 OK 5 feet (Figure 12). The vacuum station
V.l'iat wafi required was ncithi n«3 rnore than the "lift
statinn that was required in the «3»',=iivi t.y layout,
with the exception of the flddri t-i cm n1: vacuum
pumps. This additiona I expense w.-is KinrF- th-an
offset by the savings of the line lnKt<=)11..it;i.on.
The "inexpensive" gravi t.y system would hrtve
Kequi.Ked c:Jeep, da.ff i cult exr.:avat:i.nrif. with much
n»r:k. The varrutjrn a'l ternati v*-.- had much shallower
rjxcavations with little r r.i(:;k. In e:>r-:enc.e, the
vacuum system war: installed .=1?: a "vacuum assi.sted-
gravity sewer" with significant cost savings.
BHDOOCK
FIGURE ].?
VAHUUM-ASSISTED
GRAVITY SEWER SYSTEM
EXAMPLE
29
-------
MY I H: Sinr:e vacuum {--sewers are in<-
-------
MYTH:
1 he vacuum pumps must run x'4 hour:--. .~i day to ki-'<>p
var:uum c:m the F?yKtr*m_
RFAI TTY: The? typlo.Hl vacuum Kt..it,ion i ;; dp;s:j cin«<1 Ro'"t.h,-i |- Khr-
vacuum pump;1, < ipftrc-ihi • atn^ut, Fi hourr: «=i day..
MYTH:
" iur; .-unounh nl1 F?rir?r;:jy t,«"i k «=»«-• p
on
IVIrA!.. I I Y : Thft averagw £-;i;'(-;d vAi:uum :;t,at,ion r:rint.,-i-i n« >*O hp
vacuum pumps. r.nnrrj citur-'i ng vin riv^roi;:^ fun h'i me " if
S hours a day and the r-nst nf e-'l.Rct.r ir.:i hy «-it.
$. 08/kwhr, t,hr- monthly nost rcf pow«r fnr tihw
vacuum purnpFi :i K about SI 85. A system thri r-: KI xe
ortn and t.ypi cfll l.y do.n-»s r.ervir^ ?0() to HOO cur-; hrmu^rr.
MYTH: The operation of" a Viii-.uuiii r;y:--.ti
wi th «=t r-.n.l Lf.fift rJw.^r f-'t.1..
a per won
RFAI TTY: Any person 1.1'nt -j ?> mt-M:hanxr:a.lly i.nr:l n.nt'-
-------
MYTH: I t; -the vacuum valve f:a i 1 f., Ke
into rny hou ;-;<•••_
j J 'i har-k up
RFAI.. 1 ! Y r. Vacuum va i ver. can 'tVri I in ei ther tb« • < i|:ien**-< it
i : l.owi >rj poc-:i tvi on. line fall i n<3 "t n l.!pn-j r:1 owed
piOK'j V."i cm w~i II fHsu'l t. i.n Ltcir.kiips. I l~n rs wi«uli'd lrn-r<
ana.l i IIJJOIJF. tri .-i hi nrikfis-TiM nr r-iur cht^f <:n ri;:;i rif a
cjr-.-ivi.t;y spweK. Fnt-i.tjn«t-i-'"J y, 1 .-< i lure in t.hi FS iimrJ
is (-jxb.r ftiMt=f I y r.-u'if.'. A I rwir.1'. <:i I I v^=i I vr-- 1r.Tt 1 uK'tj:>
hctppfn "in thr- i ip^n pns3.t.inn. This? «u".-.-in^ t^hal. t.V'i
var:i.uiiii rrnnt/i niiRin t.o work 1".r> ev<-ir:u up rir--. this f.-ri.Ture P: i mu Lnhes a line hfenk.
I'n this cas« t,hpf t;«-« I. t=?phrm« dialif-r nnt.i f:i »"••:•; hhe
rtpRrfttor' c»1: hhi.s onndi.t.i on, whi.ch ,i f. Q&
r:orr«ot.ed in "I ei-i« i.han iriri hour.
MYTH:
Th« vacuum rrifi i n has t.n be deep ennucjh tin drain 1.1 I
REALITY: Tn a aravi.t.y fn-jwpr i.iynut., ono i"J«eo !:.i."11 ;«-••; nu-• n r. m.iv
tli.ct.cite thw rit'*pLh
-------
u
-
-------
I I. VACUUM SEVER SYSTEMS
A. INTRODUCTION
-------
SECTION
The use ami acceptance a1: a I ternative wastewater
col I eotion ?:yr-;temr-: has; expanded greatly in the last, 2?)
years. Urie of these alternatives, vacuum sewers, bar; been
used 'in Eurnpe for over a 100 yearn. However, 'it ha« hwr-ri
only in fchw I a?-;t /-"S yoacr-i or FSO t-hat, vai::i-iufn tKanspnrt. hart
be? tan ut.i i i j'ftd in hhw ilnit.Rd St.aii.t=JS5. Tn t,h"i. F: r--.l-iort; pi«r i r»rj
nf- time, si grri f:i cant. :i rnpirovement.s have hf-;p?n madt-- in systu.-m
cnmpnnRnhK. In addlVi.on, *-»xp«K"i i-?nc::ft wi t,h npi-?rftt,n ng
Kyst«amsi ha?: led t.ci advannc-ementifj in rlwFii.jgn, r:nnf~t.ruct.i rin,
and op«'^rat-i rina.'J. t.^nhni c^iies, Thf?sw f:ar:V-OK'r: havft all
onnt.fihuted t.n var:uurn sewer syst;efns tiei.n<3 a re.liahle, nnst.-
ef-feoti ve a't tf?nati ve for wasit.ewat.Kr cnnveyance.
Vacuum sewerage ±H a mechanised syjr.t;em nf wast.ewat.er
transport.. Unlike gravity flow, it, ur?es di.ft erent,i ri I air
pressure to move the fsewage. It. requires a central sourne
of power to run vacuum pump?; whi.rrh maintain vacuum on the
cci3 lection nyctem (Fisjure 1). The system risquirer. a
normaH 3.y closed vacuum/gravn ty int.erface valvr.- at each
entry point to seal the linen F.O that vacuum is
• •*
maintained.. These valves, located i.n « pit., open when a
pre«^etermi.,ned amount of sewage accumu tates in the
collecting mirnp. The resulting di f ferenti.al prr-Fssure
between atmosphere and vacuum becomeK the driving force
that propelr: the sewage towards* the vacuum station.
-------
RIVER
FORCE MAIN
t
L
TREATMENT PLANT
c
c
c
Q
1
c
VA
ST
*ji
JK
M-
4
1
UNE B-J
C
a
:
a
£
C
c
d
13
C
a
£1
D
C
L7
* — LINE A
PLAN
FT.lillRF 1
TYPTt.AI. I AYl'ltir
VACUUM S'FWFR SYSTFM
-------
A vacuum system is very similar to a water system,
only the flow is in reverse (Figure ^). This relationship
Mould be complete if the vacuum valve was manually opened,
like a water faucet is manual ly opened. Wi th proper
•*r±
design, construction, arid operation a vacuum system r:.m he
made to equal a water system in terms of rwli. ahi I i ty.
"OHt
moat
PUMP
WUE
OOUEEIION
WIVE
FI6LIRF 2
WAThR SYSTFM/VACUUM SYSTEM STMII ART I TFs
The choice of- collection system type is usually ma
by the consulting engineer in the planning stages. Thi.s
choice is the result «:»1: a cost—ef'feoti veness analysis.
Where the terrain is applicable to a gravity system, the
vacuum system many times is not even considered. Wh i !Uj
gravity may be the cast—effective in these situations, many
small factors considered collectively may resuil t in ."i
vacuum system being the proper choice. Vacuum sewers
should considered where one or more at the Pol. lowing
conditions exist:
*
*
*
*
*
*
*
*
Unstable w
Flat terrain
Rolling land with many small elevation changes
H:i gh water table
Rock
Deep basements
Unusual or rer.tri cted construction ormoi 1 1 ons
Low population derisi.ty
3
-------
Th« advantages of such systems may include substantial
reductions in water use, materials, excavation casts, and
treatment expenses. In short, there is a potential for
overall cost—effectiveness. Specificail ly, the following
advantages are evident: •
* Small pipe sizes, usually 3", 4", 6" and 8" are used.
* No manholes are necessary
* Field changes can easi.ly be made ;HS unforeseen
underground obstacles can he avoided by going over,
under, or around them.
* Installation at shallow depths eliminates the need
for wide, deep trenches reducing excavation costs
and environmental impact.
* High scouring velocities are attained, reducing the
ri sk of blockages.
* Unique design features of system eliminates
exposing maintenance personnel to the risk of H S
2
gases.
* Very nature of the system will not allow major
leaks to go unnoticed resulting in a very
environmentally sound situation.
* The interface valve isolates each home from thi^
man n, making it impossible for system flow to
backup into a house.
* Only one source of power, at the vacuum station, is
required.
* The elimination of infiltration results in a
reduction of sl^-e and cost of the treatment plant,
* The air/sewage mixture enters the sewers at high
velocity with the air providing a high degree of
mixing action of the sewage inside the vacuum
sewers.
* The short detention times in the receiving vessels,
along with the introduction of air, do not allow
for sewage to become septic thereby resulting :i n
the lack of odors.
-------
In Chapter I.C.1, the history of vacuum sewer
technology is discussed. The differences in overall system
philosophy, design concepts, system components, and
marketing approaches of four manufacturers are discussed.
Each of these companies have made significant contributions
to the vacuum sewer industry. Presently, most systems in
operation in the United States are AIRVAC systems. For
this reason, the remainder of Chapter III will focus on the
AIRVAC approach.
-------
I. VACUUM SEWER SYSTEMS
6. SYSTEM PLAN AND ELEVATION VIEWS
-------
SECTIONS
.S_Y_S_!_E_M E_L_A_N A_N_D E_L_E_y_A_I_I_Q_N V_I_E_W_§_
FOB A 8* SERVICE LI*C OK 4' VACUUM MAINOKLT
DC9WH MOFIUS FO« «* ON LANOEH VACUUM MAM ONLY
OF
PLAN AND PHOFUF: VTEW
TYPTCAL VACUUM I. TNE
-------
! « ll
17
PI...AN AND PROFTt.F VTFW
TYPI.I:AI, VALVE PIT
2
-------
ill. VACUUM SEWER SYSTEMS
C. DESCRIPTION OF ALL SYSTEM COMPONENTS
-------
SECTION C
Q_E S_Y_S_I_£_M Q_Q_M_E_Q_N_E_N_I_S.
1.
The services In a vacuum system confvi.st tif; the
f ol I owing components :
* Vacuum valves
* Valve pit/sump
* Buffer tanks
* Auxiliary vent
The vacuum valve provides the interface between the
vacuum in the* onllection piping and the atrnospheri c air in
the building sewer. System vacuum :i n the collect-ion piping
is maintained when the valve is closed. With the valve
opened, system vacuum evacuates the contents of the sump.
The valve is entirely pnuematic by design, and has a 3-inch
opening size. Some states have made this a rninumum size
requirement, as this matches the throat diameter nf the
standard toilet.
Valve pits with sumps are needed to riccopt the wastes
from the house. These consists of two ('^) separate?
chambers. The upper chamber houses the vacuum va'l VR.. The
bottom chamber is the sewage sump into which the building
sewer is connected. These two chambers are sealed from
each other. The combination valve pi t/sump :i s made nf
fiberglass, and is able to wi thstand traf f :i c 1 nads. These
-------
are avaiJab'I.e :i n two (2) d'j t'1"ereni. dephh :-• i xi •:---. should a
deepen settri ng be needed, the friberglaf^; pi t./r;ump
arrangement may he replaced by a r:orir:ri?t.e tnanVni I *••• ^i-.-otvi tin
in wl'iinh i,\rw vnouuin valvft ir. rnot.int,ed.. In t!"ri r. .:ir-ransir-jfnftni"..
fin.} y nrie r:h^mbF?K" exir.t.K. • ****
kK are u?;ed f;r>r l.=(r«;:ie < uit-il.i'mn-'r?- nr wl-ien ,=«
or rjravi hy/v.;ic:uuni 'i rit.eK"t".:-u-:e H « i:li-js-i red, ft ft
wmrld be l,h(-- cafte with n hybrid i.i-inkf;
con^tril. nf- rnantinle s«-*r:tn nns that «=ire c:ur-:l.oin built, to
i.rinl ude f-.timpri. rnu I t.i.p] e valves, and otlioc m \ -;i:< -1 I a
-------
vr>
i ii*it=?
ru?«-"iK
m
A A i nr:h auxi I i .:iKy vent, \ K ~\ ru« t.t-i "I .I t~»f.l tin hhe
hncHF?owner' K servi <".?•' 1 citer;5! ! , rtnwnFstre.-Hm rrl a I 1 i it th*71 riiuJ5>*';;
hf'otpf; ( F"i ;;)UK'i-! pi). Th'i K Vf-.'i'i'h i K n<';jr:fv.'nKc:iK'y hn pr ft vide t,l'i^;
nf: ai K' t.hatv WT VI t"nl I nw hl'io :=:(-• wet vi-",'ri1". lvo hi-* I
.hfitii r: and prnt,^r:hT
i--f--.--)p,cins.. Jn c I 'iiruHt-.ws whore t.eiiipf-'Kal.ureK 1:«11 helriw
("(•'•m^x'i n<;i, 1",l ri . s vent rnuf?l", he lonal'.i^d .-1 mini mum nf' ?()
from tJ'ii-- va I v^' pi h. In t-hi.s manner, Uhe heat I'rorn t.he
Bt-«WHt^iv cinh:-: t.ci warm the •f:ree?ri.ng <:itrnt:if.phori r: a:rr t.hurt
reducing V,hie pnssi h:i . ~l.i t,y nf: freezing of; srimt-! o1: the valve
nnmpnrien hs,
- < VENT NEXT TO HOME
VACUUM MAIN
FIRIIRF Fi
Al IX TI. IARY VFNT I III.:AT 1 ON
-------
The collection piping network r:onsi nts of the
f oj I owi 119 components:
* Pipe
* Fi tting
* I i f tr;
* I >ivi.si an valves
Th« piping network is connecterJ to the individual
valve pits and the collection tank,. Schedule 40. SDR 21 or
SDR 2F; PVH pipe is; used, with SDR 26 being the most
common. Roth solvent-welded and gasketRd joints are
acceptflib I e. Experience has shown there to be 1 ens protil ems
with the ga^keted type? pipe. Where gasketed p.ip-e is used.
the gaskets rnufjt he certi f i ed for use under vacuum
conditions. In special cases, DS'ITP gasketed pipe may he
used, providing the pipe is vacuum tested. Typical sizes
include 3—inch, 4-inr:h, 8-inch and O—inch.
PVC pressure fitti.ngs are needed for directional
changes as well, as for the crossover connections from the
service line to the main line. These fittrings may he
solvent-welded or gasketed. Again, the recent trend is to
avoid solvent-welded fittings where possible.
Lifts, or vertical profile changes, «re used for
uphill liquid transport. These Lifts are generally mad*- in
a sawtooth fashion. A single lift consists of two (2) 45-
degree fitti.ngs connected with a short 1 ength of
(F i gure R).
4
-------
45° PVC SOLVENT WELD,
SCHEDULE 40-DWV
FITTINGS
SCHEDULE 40 OR
SDR2! PVC PIPE.
FIGURE 6
LIFT DETAIL
Since vacuum sewers are exposed to repeated energy
input,:;, pipe movement is possible if proper i nstallati on
practices are not followed. Early systems used concrete
thrust blocks at each fitting. More recent systems hove
been installed without concrete thrust blocking. The
theory behind this is that the pressure is inward rath«r
than outward as would be the case in a positive pressure
situation. However, a more important concern is that each
•fitting is a point of possible joint failure. Failure of
the fitting may occur because of trench settlement rather
than "thrust". For this reason, care must he exercised in
the backfill and compaction operations. Granular backfill
material covering the fitting coupled with mechanical
compaction is a must if thrust blocki ng is to be
eliminated. If thrust blocking is used, a thin plastic
membrane should cover the pipe prior to the concrete pour.
H
-------
Division valves ar^- used for iso I ,nt ion purpose:-;
during troubleshooting. Both plug and rersi lient wt-*dge gate
valves have been used. Recent ssystr-fms have included gauge
taps i.nstalll.ed Just downstrecim i">'f" t:t'n-:j di.vision va.l ve. Thin
gauc|p> tap makf?-s it possi.b'l.t-"" 1:c»r nnr« in<"in to trnubl ershoot
without having to check vacuum at the Ktation. This
greatly reduces emergency maintenance expenr-ses, Lioth f;rom «:<
time and manpower standpoint.
Different pipe lor:«- of
the trench, metal toning wires j^hove the pipe, and color
coding the pipe itself.
-------
3- Vacuum Otafeicjo.
Vacuum stations function as « transfer 1'aci "I i i.y
between a central rrci.Jlwct3.rm point for ail 3 vacuum sewer
11 nes and a pressurised line 1eacl:in9 di rec11 y or i ndTKer:11 y
to a treatment facility. Tl'ie following components
included :i n the vacuum sstati on (Figuft51 7):
* Vacuum p urn PS
* Sewage pump:-;
* Generator
* Collection tank
* Reservoir tank
* Pump r:eintro3ss
* Motoe control center
* Gage^/chrirt rocorrier
* Fault monitoring system
Vacuum pumps are needed to produce the vacuum
necessary for liquid transport. The operational history of
vacuum rsewers indicates that the optimum operating range i«
16—?0 in. Hg. The pumps, however, should have the
capability of providing up to 25-in. Hg as this level is
sometimes neeeded in the troubleshooting process.
Duplicity is a minimum requirement with each purnp capable
of provi.dirig XOO percent of the required air flow (cfrn).
-------
CONTROLS AND
ALARMS
I I TELEPHONE
I 1 ALARM
STANDS
GENERATOR
VACUUM RESERVOIR/
MOISTURE REMOVAL TANK
T AIRCVAC VALVE
SEWAGE COLLECTION
TANK
VACUUM PUMPS
DISCHARGE
PUMPS
V) VACUUM GAUGED
VS ) VACCUM SWITCH
C) COMPOUND GAUGE
VACUUM RECORDE
SIGHT GLASS
N.C. NORMALLY CLOSEC
N.O. NORMALLY OPEN
TREATMENT
PLANT
Fir.URF 7
LINF
I IF A
TYPTCAI VAIUIUM STAT I TIN
-------
Vacuum pumps may be either the Ii.qui.t1 ring or si idin
vane type and must be capable of delivering the specified
cfm at, 20 in. Ha. A liquid ring vacuum pump utiliz.es a
service liquid as a seali nci rned'i urn het;ween an offset.
impeller and the pump r:aa:i ng. As the impeller rap::i ns;,"~'Lht--
sservi.ce liquid is forced against, the pump outer cas:.i nvs by
centrifugal force, and a:i r i.s compressed and forced out. of
the discharge pipe by the eccentric l.i quid action. The
vacuum is created as more a:i r i« drawn in to be
compressed. When liqui d ring pumps are used, rvi 1 is
recommended as the seal liquid. Since the service liquid
continually circulates when the pump is in opereiration, a
service liquid tank must he provided. The tank should be
corrosion resistent and air tight. The tanks are vented
with an outlet to the outsi.de. Since the service liquid
carries a significant quantity of heat away from the pump,
a heat exchanger is required. A liquid ring pump i.s shown
in cr€:iss-secti.on in Figure B.
i'J
-------
.Compound
Gau
Heat Exchanger
In Out
Cooling Water
Drain
Gas/liquid
separator &
service liquid
-I Shut Off
\vaive
Make Up
FIGIIRF e
LIQUID RING PUMP
CRDSS SECTION
S.1 idi.ng--van«=> type vacuum pumps may a I f,i \ kit* used.. For
these types of. pumps an air filter is required. This:
filter is located on the -inlet line between the reservoir
tank and the vacuum pump KO as to rernnve particulate
material which might Otiuse exce«r>ivi-« nmpeller wear it it
were to enter the pump volute. The urse of si i.da ng-van©
vacuum purnpn has -inoreaKed recently. The rea«on for thi 5?
i.« the lower power nnnrsumptn on required for a given pump
10
-------
capaci ty. On the negative si do, the re have been prob 1 ems
reported with the vul.nerabi.lty of these pumps should liquid
be carried into them. In this situation, the pumps are
usually damaged to the point where a replacement pump will
be repaired. By contrast, the liquid ring pump, by Tits
very nature, can usually withstand an accident, of this type
with very .little damage. Design precautions, such as an
electrical I y control.! ed plug valve between the collection
tank and the reservoir tank, can be added to the piping
systecn in order to protect the slidi ng—vane type pumps. A
cross section of a sliding—vane type vacuum pump is shown
in Figure 9.
Fll-illFJF 9
SI ID TNG VANI- PUMP
IIROSS SFCTTflN
-------
^ewage pumps are required to transfer the liquid that
is pulled into the?, collects.an tank by the vacuum pumps; to
its ultimate point of disposal. Dry pit pumps have been
used extensively although submersible sewage pumps located
on guide rails within the collection tank may be usetT'rtS an
alternative?. The rnnst frequently used type o1: purnp have
been the non-clog type. Duplicity is required with each
pump capable erf providing 100 percent of the design
capacity. The level controls are set for a mini.mum of 2
minute:;: pump running time to prevent excessive pump
starting and related increased wear. The pumps should have
shutoff valves on both the suction and discharge piping to
allow for removal during maintenance without affecting the
vacuum level.
Check valves are used on each pump discharge line or
on a common manifold after the discharge lines are joined
to it- Equalising lines, consisti.ng of small diameter
clear PvT: pipe connecting the pump discharge to the
coll ecti.on tank are usually required. The purpose o1- these
equalizing lines are to remove air from the the pump and to
equalise the vacuum acrossed the impeller. Tn acldi ti.nn.
they will prevent the "loss of prime should a check valve
leak. Since thi.s ;setup wi 11 result in a small part of the
discharge flow being -recirculated to the collection tank, a
decreased net pump capacity results.
-------
fterrone 8r Associates, ri..n thei r mast. recent designs,
have eliminated equalizing lines by using horizontal, sewage
pumps with a con tin ou sly flooded auction. This is
accomplished through the use of a ball check valve on the.
pump suction pi ping between the collection tank and tTie
sewage pumps. Prior to using this concept, the d€?si gner
should carefully weigh whether the pumping cost savjngs are
significant enough to risk the posr-iibi li ty of failure of
the ball check and the resulting problems that would occur.
Sewage pumps are typically located at an elevation
significantly below the collection tank to minimize net
positive suction head (NPSH) requirements. l.n conjunction
with NPSH requirements, pump heads are increased by 23 feet
to account for tank vacuum. Both vertical and horizontal.
pumps can be used.
Materials of construction for pumps include cast iron
with stainless steel, shafts, while avoiding aluminum,
bronze and brass. Fiber packing i.s not recommended.
Double mechanical seals which are adaptable to vacuum
S6?rvice should be used.
A standby generator is a must. Tt. ensures the
continuing operation of the system i.n the event of a power-
outage. Standard "generators that'have been used in other
wastewater applications are available from a variety of
manu facturers.
13
-------
The wastewater is stored in the coj.lection tank unlvi I
a sufficient volume accumulates, at which point the tank in
evacuated. It is a sealed, vacuum tight vessel made nf
either fiberglass or steel. Fiberglass tanks are generally
more expensive, but do not require the future maintenance
(painting) of a steel tank. Vacuum, produced by the vacuum
pumps, is transferred to the collects on piping system
through the top part of this tank. The part of the tank-
below the invert of the incoming linos acts as the
wetwe.11. A bolted hatch provides access to the tank should
it be necessary.
Most collection tanks are "located at a "low elevation
relative to most of the components of the vacuum station.
This minimizes the lift required for the sewage to enter
the collection tank, since sewage must enter at or near the
top of the tank to insure that vacuum can be restored
upstream. Many times this results in a deep basement
required in the vacuum station.
A vacuum reservoir tank is located between the vacuum
pumps and the collection tankl It has three functions: (1)
to reduce carryover of moisture into the vacuum pumps; (2)
to act as an emergency reservoir; and (3) to reduce the
frequency of vacuum pump starts. H..ike the collection tank,
it can be made of either fiberglass or steel.
-------
The? vacuum pumps are control led by vam.itjm swi tches
located on the reservoir tank. I lr.ua 1 operating level is 16-
20—in. Hg with a low level alarm of 14-in. H«:j. The sewage-
pumps are control.Led by a probe( ft) located inside of the
collection tank. line method includes using s^ven (77"
probes, one for each of the six (£J) set points of the
pumpii no? cycle and one (1) ar, a ground. Another method
relies on & single probe that is capable of monitoring all
at the set points. ThwsG* probes are the capacitance
inductive type. They require a transmitter/transducer to
f.end a 4-20 mA signal to the control pane.1.
The motor eonto! center houscK all of the motor
starters, overloads, control circuitry, and hiourc> run metv«=»r
tor each vacuum and sewajge purnp. The vacuum chart
recorder, colllecti.on tank level control relays, and the
telephone dialer are also normally located within the motor
control center.
Vacuum gauges are used on all incoming lines as well
as on both the collection tank and the reservoir tank.
Their purpose is to allow the operator to monitor the
system. These gauges are very important in the
troubleshooting procedures. Chart recorders for both the
vacuum pumps as well as the sewage pumps-are needed so that
system characteristics can be estahli shed and mrmi tared.
Like gauges, these recorders are vi tal in ^the
trxiub I eshooting process.
15
-------
A fault riionitar'inci system is neerh-fd to «J f-fK"t the
operator o1r any irresgul «rities;, such as a low vacuum
'level. An automatic telephone dialer ;-;«??rvr-?s t.h.is
Th«3Ke
-------
t
In addition to these spare parts, there are certain
specialty maintenance tools and equipment that are needed.
TABLE 16
SPECIALTY TOOLS AND EQUIPMENT
L
1 ea.
2 ea.
100 ea,
3 ea.
2 ea.
2 ea.
1 ea.
15 ft.
2 ea.
2 ea.
1 ea.
1 ea.
1 ea
Portable vacuum pump
Portable vacuum chart recorders
Vacuum charts
Chart pens
0-20" W. G. magnehelic gauges
0-50" W. G. magnehelic gauges
12 VOLT DC submersible pump
Pump discharge hose
No-hub torque wrenches
Vacuum gauges
Flexible mercury manometer
Controller test box
Pipe locator
The vacuum station also requires spare parts. These
_. •. T-^.'-rrfs'-'rr*..
range from spare pump seals to fuses. Specialty iterns that
should be considered are:
TABLE 1.7
SPECIALTY EQUIPMENT
I
i
1 ea.
1 ea.
2 ea.
2 ea.
1 ea.
r
U
Inductance -probe ' .
Probe transmitter
Probe microprocessor card
Vacuum switch
Vacuum gauge
Auto dialer microprocessor card
10
-------
Especially vital far- the vacuum station are spare:-..
microprocessor—based electronic components. This type of
equipment is used for the level controls and the fault
monitoring systems and is very sensitive to power spikes.
These system components are the two most important parts of
the station, as they essentially operate and monitor the
system. Losing either to some type of failure will cause
short term problems, such as loss of vacuum or discharge
pump malfunctions. Not having spare equipment amplifies
the problem since this would result inr the system being
operated manually. This would require an operator on a
continual basis (until the spare part arrived) to cycle
both the vacuum pumps and the sewage pumps manually.
-------
II. VACUUM SEWER SYSTEMS
D. SYSTEM DESIGN CONSIDERATIONS
-------
SECTION D
S_Y_S_I_E_M Q_E_S_£_G_N C_Q_N_S_I_0_E_R_A_I_I_Q_N_S_
Q £ 3 i. 9 n E. 1 1! w s an d T h e T. r V n r i a h j_ 1 ;i 1 . , i g r,
AVFRAGE DA 1 1 Y Ff.flWS
I- unclfiinFjntii^l t.o the derva gn nt" a r-uvwr-?r «=!yr:t,i?ni i:-;
hhft dftt.«nnn.niiit:i.i:in o1" des.i gn f:"l ciwr;. An a'l .I tiwarir:»> nl" 10O
g^'ilonr? pev i-:;\ipl.t.ii--day (Qpiod) h.=ir» tiFfen nr-u-'d «=ii=i a
!3t;;nc''j'al r"i,i I *~; in t-.he? design ol r:nnv(fnt."i rir»a I F;I->WWK'F;
J3ys:t.e?mn, HOW^VF-K', t.hafc gRn^KV-i I rule- may wl'lriw 1:or mo»'«
•i n f-i 1 hr«tion than mf\y occur when vac:uuni ?;-.ewers etK-w
iiKp-d, and it. allows For some amount of t-.imimere-i «1 and
industrial use that fnay not be present in vaouurn r:ewer
design. Experience with vacuum sewers has-shown a
lower allowance to he more in order. If available.
water use records should carefully he analyser! and a
per capita use established.
During the early stage:-: ot: pressure sewer
development, extensive ~i nveslvi gati.on« were made into
domestic water consumption during periods of ~lnw
outside water use. with the r.-orrel ati on that water
consumption would closely parallel sewer flow. These
stud.i es showed per nap.ita flows rangi ng from 4() to GO
gpcd. Flow measurements w«re made on convent i tm.-il
sewers serving resd dent:i.al. commurn ties during pr-riods
-------
eye ].(••> <"J"i scnarge, and an av^n-aon? l.i.rne p:r-'l.l-.;i net) of n'
©eccmdn, a vacuum vallve Mould tie requi red bo ripen and
c'J nse ">'H times in a irri.nube, wi bh a "repst." ot: only about,
20 seconds hebween r:yc I *-?«. Tl'i i :-; may noi. pr'etti^rit, a
fH'Cit"i!Ltf;in t,o a v«i I ve t.h•(••• I a L'i vc-; l.y oliipji-- t.n t'.hc--
vac:uum Kt.sihi on, nonnpct.ed ho a tt" ina.i'n.. A d i 1"t"ernrit.
a:i t;uat-.i on exir->1,r; t'or ,-i v« I vw ;-il, tvhc:? far frid or l-,h»'-
syKl-ern t.hfit, :i r-: r:nrm F«r: bud t.n a 4" infHii. V. ir:uurji t- f>;-ip( in:;
( tl*«=? atri'I i i'.y of t.hiP' vacuum main t-.n ciuick'ly ror:« ivi--r l,o
l-.hw r-^airu"' Iwvel of vacuum bh«=ib pxi r--.bi~'d pr-i or 'L>'i hl'ii-
cycle) it; n1" ab&jo I u <".•=• :i.nit.>»"iKt.ani':i=! :.i n vcic:uunt SI'-W^K*
df-:si gn- Vacuum f«r-:pnnF.e "i P: a 1:unr:t.i cm of '1 i nf length,
p"i fi(> di.amRt.wr, number c-if r:onruvr.t.i.onj-,, and aniiiunV. erf
'1 i f\; ~i n t.h« sys:br;m.
fihotjl.d a ?;i btuvibinn ex"i.fjb bhat is causf .-f-or
concern, t.hvi--nb
backups until, the val.ve. 'i M capable ol" empl-.y i ng bhe
bank.
-------
NI-S i UN I-1
'lgri f I OWFJ ;=IK<^ maximum flow rati.'« «-"'xper.:t«d t.t i
occur onci? OK" twi <";*•••> P<;?K dd to nixw thf--
vacuum sewwr inairiK .ts w»~' I 1 ,i« th*-- various vacuum
f.tial- 1 nn r:ninpnrient;;-"s. Flow K-at.c-vr-i in i-'xnt-'nr; r>f' dr-'Si gn
flriwr; can i tr:r:ar t.inrler r :*=•(• 'i.n'i ri si t,u«H t/i cms ( SP-T.- I 'r<=T,r;uKt
^^|•..•wf;:•r ::wcl,irin, t;l*rt «s manual, I I
rj«=-'?:i gn 1" I nwr; 'should nnl. hr- S,.-ikr'n ;:if. tihe tTiciximuiii 1V1 nw
in i:\r\ft PKewsufff Si-'Wi-r Kc-'nln on ot tKiif. cn.=«ni.i.-i 1 ,
Rnwrm d«"*ssi'.:K "i hi;>:-; var'J .oi.is r:>t.url i i\';-; of 1:.l.ow v«-*K'tujs
w:turi v<:iT <-?nt dwe'Lling unit,:-. ( fiil)!.)' r. )„ Ttd.s LK araj >!'t:i r;
O
:i n Kriapher [J.U ol' Lh.nt-.
s<"M-;t,ioru Uowne deve U ipert « f-fquc-ita.an for fffshii maUi ng
design ("'low basi?d on hhe number of" I-IOIMOK t.o hr=» K
This fquatri on i.s as fVil 1 OWK:
O =. AN f B
Q - Der-ign flow ( gprn )
A -- - A r-oef-^lci.ent. psel ecfc^H by
f* f\
-------
h. M'iri i JIIUIM l::; I ow Vw'l ric . j_L i w;--. in I ''i (:>>•••.;
The herrn " !=!!=• I i: r: I t^ani n«3 vi--0 oni.hy " r< .-< ! rtrii..i wi l.h l.!-u-
w.'-iLi-^r riar'c 'i <:JK'.. In mari nt..'ri~i n an i.inoh';i'.ru< rl.c-'rl p:i pf ••• I n n<->,
t.l"i.-i1, v<~- 1 1 in.i t;y fvjhrnjlrJ t:t«^ sul""^^ i~: i on I", tvt \.r cinr-r't"^"^" ;:;ir i 1,
t.l'irtl. rn«'iy \w pir^KPrit ri n t'.he w<-if-;tii;'WFii-.c";K , i.n rn-r^vi^rri.
ojct-'awiv pl.'iLincj nn t.h*-- r:r~nwn ''5>(.it>|::u-'nrl pr»:>v"i nun l.y s^hi'.l.f^ti in.'i'ht.r-'K..
Jn hl'ir1 Pri^RMUf't"' Swwprr si:>r:t. i <" nnnclur-'.T nn rc-'ar:hc:'i1 i r: i.hai:. tl'ir-
i-'d rninnnium ve'l i n-.i hy 1 ' cir sr'T 1: n!l i--.'iri-i n«:i •) :; ',-' t-.ri 3
V«->loc::i t-.H err--, i.n i-.hf typical, vacuum ar'wi -K range
15 tn >B •fps, ohvj nusly w^T.l .tbovw hhi-- uri n.i
ne.'l t1 el,** an in a- A r:rirnrnnn t:l,^im f>"
haK n(-'ve»' he«n a h I ockaae reported :i ri « vac
«y«tr-'in. This may be fl K-.3t.hftr st-.rnnr? r: I a j MI ; hnwi-*vr-«r.
the high transport, vwlnci t,i. *••??? fiUflW^f-'t. I. hah hhc
pr ribahi..!. i hy ; rf" h.lnc:ka«3<3s or;i::ait-"K"i ny ;-n'f» i
-------
i (.1£'. :L 1. L- »:< b is V.' L" !'J U. S t-. J Q D f~
An understanding of' thr- vaniiiini l,i-'anr~port pt-'nr:<-T.r.
•i '.-: needed hy the ;~:yr;1>'fri dew i <3n<-;r_ With tht-? r-;aw hrml.ti
pro1"i.J *'•', and a;-:; II on '.3 an no vacuum v;-i 1 vft: .-ire
oporftt. in<3, nri Kifw-'^!:.!'-' l.f.:mr:piir't. 1".."ik'<-»r; p ! .-ir:r?. All
r:(-';wT t.lic
pi pr? 'in thr-?£!i:< nt'.at. i •': rinndi t;'i cins, l-il.t/h-- vacouiri Itisr. • f i nw
a t. r;:-:
i.hr--
is; (-ii":r:umi rig.
Wh*=«n a su1"'f "i r:i erit. vnli.inir- tit F,c-'wa'.:3O af:r:
•| n the sump, l.h,e var:ni.nri VH 1 V^J r;yc: ] t'j«.. I hie
di ffp't'enti aJ pcef;r;nt- f t.h.tt. r-«x-i :;!.:> hc-l,w»'^n t.h
main and atjnowpl'u'K-f--' l:riK<::cw thf-* t:;urnp r:c»nhp«nt:w
m«!»"in. While ar::r:ol,ef-'vit.:i ng, l",h«' y:wwa«3r-J i '"• KMpxd ! ••-•
LKnnsf ofrniffd i.nt/o 1;i:;>ai(i - arid «;rmn nr:r:up i.p*r> only p.^r i'. i-ihui-n he «)>-.-; tv-r
iVom t-.he air to wateK t.«=«keK pK^n^e J.:u-"«3i^ly hhKfiugl'i tl i«"j
action a1; sheaK Fjti-«sr-:«r3. "1 he numrn tude* ot i.hr--
prnpulfsive forces starts tri der: I :i rn-' not i i-rwnh i y whi^n
the vacuum v«il.ve r.'\ nse« hut remain 3 rfipi'irtant ..i:: thu
air continues to expiand within th^ P i P«:J I- ve
fri.oti.on anrJ gravity hr ~i ni^ th«; FH.'waci»-f to r> ••-.-: t
r-;piot.. Another va I v<;^ i:yi:le, at any 1 oc:.'it. i on upstrea
ot~ the low spot, wi II c:ai.t :••>•• thlv; st-'Wtigr-1 to i":ont>i.n»Ji"*
"its movement toward the vii
I I y
ci low
-------
vVir uiiin rjyr-'.l.i-'in:; ,irr- i !<•';•; i •"iru-'d l.o i ipf -r a l.i • i in tvwo
pbiHsr-- «i i r t.i i liquid t'lnwK wi.t.l'i t.bi-a .1 i r h*'? r nci aririri t,hi»d
frit-" .-I l,"i rnc-'f pf?K"t ucl l,wi or-» t,l'i«it. o1: l,bi- I i qui.d llpt>n tyimr-
ot 1.1'n-1 A I I^VAII! va I vr« HK <"i<^ JuKh<:il;il i .• ; hir-ru :(•?, v.-ifi nus ciif1
t.( i 1 i -:|ii i d K'at'i nr-v .;n-"c.' at.l'.a'i ru-ib.l f.p
^•-.
Ni irtna I I y, i.he v«-ir:uiini puinpf-; ,-ir'i • ««.;i. t.i i npt-?r^i.e
i:n-> !',wi"'r-'n IH and l?O—"i.n. H<3 in f v.-u ;i iurii. i'l if.- m i rvi mum
v. irn.d.rni ill 1 1- i - "i n .. Hn f'-'SJU I t.r; .in .4 t".ot'.«"i I iiv.ri l.::ibl<- hr.-.id
It inn i"i1- '1 t'i -f:t--'«^t,. FT VR f-f.-i-.-t rif t.hi F-. I-M •.-td I or. p. -i p.
r r-f<::|t i i Y r-d t'.n npi-VKVit.e bhr; vara.iurn valvcf, I f.iv i n«:j 1 3--f-( »»--t,
,- a-h hh<-' v,::ir:uum st.at. ion
( tvpi «:••"! 1 1 V j.6--in, l-<<3 wh i • ii «••'"(' '• "» I -'• IB-- "hi. cif
tr.^K )
Vv = Vacuum f-"f=?r)u:i r't'-'i bo npofa t.t-- i.i"i»??
(ft- in- Ho
WH hh Vc: — fit-ati.f. LI'IMJ-" + FK-I e.-h i on I i i;-?r;, and t.l"i«
vailuwf? juwt'ist.H t.ut.Pd 'in fcl"«"- .'ibovi-1 ftcjurttion, t.l 11"?
, i nn i r> s'i mp 1 1 f i ed t;o:
fit.atir; !..O::K f f-r i..:t.i <-in l
-------
l-'-igure 1 O i :-i
-------
Static losses are those incurred by unring
lifts, or vertical profile changes. Profile changes
are accomplished by usdng two 4H- degree f ri tt"i ngs
joined by a section of pipe. For efficient USF* of
the energy available, profile changes shou'J d he «s
small as possible. Numerous lifts are recommended
over one large Iri ft. Table 1 shows the recommended
lift height for various pipe sisres;
TABLF 1
REnflMMENDED I...TFT HEIGHT
Liffc-Height
1. 0 ft.
1. 0 ft.
1. 5 ft.
1. 5 ft.
2. 3 ft.
3 in.
4 in.
6 in.
8 in.
10 in.
Static losses are calculated by subtracting the
pipe diameter from the lift height (Figure* 11).
Static Loss = Lift Height - Pipe Diameter
4/Vvc SOLVENT
l€?Hr STW1C UFTFOK
CM£UUOM6 UNE
LOSSES - UFT HBQHT
MMUS WE DWCTER
-ran AU.PVC SEES.
SCHEDULE 4O-WW
WELD. —
v nnwes
FJfitlRF 11
STATIC I OSS DFTERMINATIUN
10
-------
Fricti on loss charts for SDR 21 PVC pipe and a
2:1. air/liquid ratio have been developed by AIRVAC,
and are contained in their design mamual- Friction
*-.
1 riwses are nnly calculated for sewers that are laid
between 0.2% and 2. 0£ fa 1 .1. Fri.c-;ti.on !.| ns-srjp-s in l-wTLr;
greater than 2. 0% are t.o he ignored.
The friction tables, along with the system
nalculation sheets, will give the designer a
conservative result, since the calculation sheets
assume all flow inputs; occur simultaneously resulting
in a cummu I ati ve flow rate. In reality, this? will
rarely occur. Because of the anticipated nature of
the system flow, some engineers have totally ignored
friction losses in some past projects, with
successful operating results. Despi te this success,
ignoring friction losses i.« not recommended.
The hydraulic calculations should commence
including friction, A separate calculation can then
he made to see how much of the total loss is static
versus friction. Assuming proper line sixing has
been done, some liberties may been taken with respect
to friction lasses, depending on the particular
characteristics of the system.. This should on.I y be
done by those with vacuum design and 'operation
experience and in no case, without written approval
of the manufacturer.
11
-------
Ouii l.dio.9
The geometry of a vacuum sewer system :i F;
si «ri 1 ar to that of a water distri bution ssyrat.Rm.
Rat.h»t-fK" than looped, how«vwr, "it; ri s nnrinaVly ~i.n A
dendf ;i f CIKHI pat-t.^rn.
Tfr. .Is des'iK-ah'I.R t.o have the vanuum st.a*vi nn
lacabed as centrally as possible. This lends itself
to & system with multi-branches. This is a very
important, ar> multiple main branches to the vanuum
stat;-i on give added operating flexibility. For
example, with a system having 3 branches serving 300
customers, the worst case soenerio if; that LOO, or
one-third, nf the customers may be without service
while a problem i.s corrected. By contrast, the worst
case scenerio assuming a similarly si.2*ed system with
one branch would have all 300 customers out of
service.
When laying out a vacuum system, the rtesi
should select pipe runs that:
* Minimize lift
* Minimise length .
* Fqualixe flows on each main hran>:h
-------
The? length of on I ler:tiiin lines; .in-" c)< »vt=?i» ned by
twn factors. These are sta tic .I i ft and friction
losses. As previously d"i s«":ussed, tho Ruriirnahlon c;rf:
these two amounts yeru^ra 1 ).y cannot exceed 1.X 1"«=?et.
Due to ^estrfti ntr> planed upon ear:h rir?j?i gn hy
*».
topogfaphy Hnd siswajae 1:.l owr-;, it, i.s i rnpossi bl.e to cri v»
a definite maximum linp; length.. fine opt-ratri.ns Kv^l.^i
has a s:i ngle main l:i ne hranch wx>i~«t
in length.
Vacuum s«=w*?«r design fulejs have been develo
largely as a result ol" f-.tudyins'-T opRKat'i.ng syf
important design parameterra are shown in the
•following table.
TABI.F. 2
Mi.ni.mum distance between lifts V?0 ft.
Mini.mum distance of 0. '2.% slope 50 ft.
prior to a series of lifts
Minimum distance between top of 6 ft.
lift and any crossover connection
Minimum slope 0. 2%
-------
TAR! F :<
I NFS FUR
4" Mainw
6" Mains
* - , P%
* — fif ound (3.1 ripe
* - flO% of pi fie rid n
( between J :i f tr. on Ly )
* -- 0. 2%
* — (5 found r.l.op*=!
* — 40% of1 p-i.pn di
nn 1 y
Tahl.e 4 nhnwa at what. li=>ngt.h t,h« ().*<''' eater than 135 ft. 0. 2% s3 ope
Less than 10O ft. 40% of pipe di.«.
f than 1.00 ft. 0. 2% slope
1.4
-------
ATRVAC has dwve.1 oped a table r«r:orlr|l
~ " ........ ~~
150
54ti
Substi tut-.ri ng the values nf maximum flriw (O)
from Table 5 -i.nt-.n Bowne* s jni.rnp] i f led equation,
(Q-. 5NH-'
than 70.
-------
The valutas in Tab IP* I-J ^should l:it-j uwc'd f nr
planning purposes or as a t-stoiKti n«3 p«.ii nt. f'or th*»
detailed design. In the Latter niise. est/irnatwrl
speci f'S c f'l.nw inputs* alcmy with th«=» 'f;r-;i cti <"»n tatile
j-»hou'ld k»p? used 'in the* hydraul i.e.: «':v-i l.c:u l.atii.nns. A
r;orrer:tly si^ed line will yx.c-> I d a n^lat-i vo I y small
t'K"i r:i;j nn "Loss. '[1% when gni.ng tn thiw next "I •Nr'ger
p i pf=? si^e frinti.nn ] or=ss is cri gn i f i nantly rwducr-d,
Line was mrist likely unrtr->rsi '^t?d.
Experieni:::e has shnwn that th«rrj is little
econorny in using 3—i.nch pipe for riiai.ris. For thif;
reason, 4—inch is thi? mi.ni mum recommended main si z
Iti
-------
In most cases, vacuum sewer mains are located
outside of and adjacent t,o the edge of pavement and
approximately para I J.el to the road or street, which
*•*.
reduces the expenses of pavement, repair and traffic
control. in areas subject to 'unusual, erosion, the
preferred location is often within the paved area.
This location is also favored by some muni c i pali ti es:
as being an area where subfiequerit excavation is I esr--.
1 :ike l.y and more controlled, arid there f~on> ,.i tot ration
more protei-;ted from damage.
fine of the major cost components ot" a v.-ir;uurn
system is the vail ve pit setting. With two or more
homes sharing one setting, overall system
construction costs can be significantly reduced,
resulting in a major cost advantage. To do this,
however, may require the main 1ine to be located in
prj vate property, typically in the back yard. There
are two disadvantages to this type of routing.
First, it requires permanent easements frnm the
property owner, wh'd ch may tie dn f fi.cult to obtain.
Second, it will require the operating personnel to
venture onto private property during preventive and
emergency maintenance, a move which may not be
particularly welcomed. Ihe designer should careful.ly
consider the tradeof f of reduced costs to the K« ici a I
Issues prior to making the final routing dei :i s i on.
17
-------
An advantage ho the aftt* ot vacuum r-;t~'w<">rr; I.;';
that the small diameter PVf'l pipe used is flexi bio and
c:an he easi.3 y routed around oh star.::! e«. Thin feature
allows vacuum sewers to foil 1 ow a windi ng path as
nr*ci»r!S«ry. '!>if pi.pe shnu3.fi tip bent in a 1 ong K-ad-i t.is
T'-r
if- possible, not in a radius l««s than that
n=fi:nmutendpd by the pipe manufacturer. In the
section nf tha c manual, Bowne prenents an
from the llni -Bell Handbook of PVI ; Pipe in
which the minimum radius of b«ndin
-------
1 I'll-.- separati on of vacuum sewers from water
supply mains and laterals often requires the vaci
sewer he buried deeper than would be required for
other reasons. In most instances the separation
requirements are dictated by state health
departments. These requirements may vary from state
to state. A table from the Pressure Sewer section of
this manual rthows typical requirement:::: for sower
'.line/water line sepa.ti.an. arid is repeater! below:
TABLE 7
TYPICAL REQIITREMENTS
FOR
SFf:'ARATri)N OF SEWER LINES FRl IM WA.IER I TNES
Parallel Locate sewer as far ias practi.nal from
ins ta'l 1 «^ti ons water main. Minimum Keparat'i t m "1O
feet- rf sewer is r-.loser than 1.0 feet
from wateK main, sewer "it: to he
located 12 inches lower th.m tl'ie water
main. In some jurisdi r.t. i ont-~.. wl i«n
closer than 10 feet, sewer T r> to hr> nf
water •main material.?; or ennfirswrJ.
Other jurisdictions allow water and
sewer dn the same trench if the sewer
is 1.2 inches lower.
Crossi rigs Crossing is to be as near! y
perpindicular aK practical- Sewer to
be 12 inches "lower than wati'-r main.
Some jurisdictions require that no
joints he imed in the sewer main
w:i thin 10 feet of the crasssi r>g-
-------
Prrit i I ?if\ of the mains should always tn:' shown on
the plans. Slopes, Vine si ;res and lengths, r:u"J vert and
utility crossings, inverts, and surface replacements
are typi call y shown nn the prot'iI.es (See Sf*r:tion B).
Cul vwct. and ut;-i'1 ::i..V.y crciss'i ngn c'll'fcftn di (:1-.^l.f
nurnr^KouR vari at/i ("inr; 'i n t;l"ie dept.h n1: hur.i al ot" vacuum
sewer mains, with, many K'«su'l V.i nci Ka!.ti'T arid ;->ummri t'.r-; in
the? pipeline p>K'nf:i. I e.. 1 In'l :i ki-.1 pr e:~;nure mrcinr-;, whi-'n- ,-ri K
acc:i.imu!l ate:?; at a suuim:i t t-f •cit.ii.ri ng an air relwa«(-> vt-ilvr-.
vacuum sewwrs arp nnt a'Ftwctwd hy hri gh pni.ntis nn th^
pfofxTe. The-? sags, however, may pren^rit a pKoh"! oni, a:-:
they typically w:.i "LI. add 1 i •ft to the systwm. Fn
addition, if not dorn gnt--d and r:nns;trijr:tc»d prriperly, .=>
Kag may tf-ap* sewage at I r»w f low p«=»rinds blrmki ng o f-f
the low part of the sww«r. When vari atinnss aft*
regarded a« detrimental, reaches of the vacuum sewRr
main may he placed at a particular depith tn allow for
the crossing w.i thiout using a lift.
To minimd.Tre damage to the vacuum newer main
caused by subsequent excavation, route markers are
sometimes placed adjacent to the main, warning
excavators of its presence. Accurate as—constructed
plans are helpful in identi-Fying the pipeline location,
* •*
and a cable buried with the main can be induced with a
tone so the main can be field located using common
utility locating equipment..
-------
A warni rig tripo marked "vacuum sewer" "i'.-. r-oineti tm-'r;
placed sha'l low Ly in the pi.pel.,i ne trench ho -further
notify excnvwtors. When thr* tapp; :i n p'l .-iced 1 nwi--K :i n
the tffnch, w. 9- , adjacent to t.he pipe, at Is; ru=«"l led an
^p-,
"id€?nt~i f l.cat"i cm" tripe. The tap<;> nan h>"; m«tali.xftd nn :i t
can hi-- d(=»t*3f:hr-«d with iiti .1 i ty 'locating devx«;eK.. Most
bap*-':> nannot. he i ndur-.ed wltl'i a bone .-it. a ni gni 1~i r:.inh
c1«=rpth, so rnetali.^i^d tapi7? should he pi ar:t?d «ha'l 1 uw'l.y to
tip; di?tnctr.'d. Jt :i F; also vp^Ky important to rnak^ sure
thf=- tapi^ doer; not be>oome folded or twisted during its
FI'| acwmrant or the detectable surface arr-m will hi-?
rednoerl.
21
-------
Trenching may be accomp.1 i.shed ussin«3 a
wheel trencher, or chain type trencher. The cho:i r:e air
•*•(•,.
equipment is usually dictated by the contractor based
on the material to tie excavated as well aw topography
and available working space.
Imported material termed "pipe zone baekfi I ~l " js
often planed to surround the main several Inches ~i f
material excavated from the trench is regarded an
unsuitable for use as that material. Pipe ?one
backfill is usually granular, such as pea gravel or
coarse sand. Fine sand or soil is' generally not as
desirable as it bulks, rather than flows, into place
under the pipe haunching.
The remaining backfilH material required is often
specified by the agency controlling the road or street,
especialy if the mains are located within the pavement.
In some cases H lean cernent-sand slurry is used
for backfill. This option i.s particularly attractive
when a trencher is used, the mains are located within
the pavement, and prompt restoration for traffic
• '*
] is important.
-------
IE RIALS
PVC or A8S thermop} astic pipe ace riorrn.'i I ly usi-ri
•for vacuum sewers. In certain cases. DCIH has also
been used, assuming the joints have been tested .m<1
found suitable for vacuum service..
The most common PVI"! nia'ins are* Iron p i p*=* «i 7I5-
(IPS) 200 psi working pressure rated. st.i;«nd«rd
dimension ratio 21 (Class 200 SDR 91 PVC). Cl,,ss 1 t'-U),
SDR 26 PVC h»as ulso been used. From a pressure
standpoint, the lower class pipe is acneph.-itij.o.
However, thinner wall pd.pe is more ".likely to be damaged
during installation. Further, there is Little cost
savintgs between SDR 2H and SDR 2f> when the excavation,
backfill, and surface restoration are considered. For
these reasons. Cl 200, SDR 21 is recommended..
PVC pipe hao a high coefficient of thermal
expansion; about TH/8-i.nch of length variation for 100
feet of pipe per 10 degrees Farenheit change i.n
temperature.
-5
Coefficient i n/in/oF =* 3. 0 x 1O
Considerable temperature changes wi1J he
experienced during pipeline ri nstal ~\ ation, and some
degree of temperature change will occur rluri.n«:i
operation, with climate changes and effluent
temperature changes. To reduce expansion and
contraction induced streirsses, flexible elastomeri o
-------
joint ("rubber" ring" joint) pipe i« preferred t.o be
used. If solvent wejded joint pipe is ur;ed, the pipe
manufacturers: recammendritinns fur i nwtaT 1 at, inn
rr-^ardi.niqi hf~«inper«:it.ure trjcmfjidefat.innR nhould be
*TV
tn'i:i owed. The l.lni~8e:il. Handbook ot= PVC Pn.pe a f r?o
pK-rivides: gu:idartr:e as to proper pract.lcen.
In the past, the f i ttri ngF; mowt often »jr-~.ed were
the pso.lvent-wel d. Drain, Wa^te and Vent (OWV) type.
These types are more common3y available than ganketed
joint •fittings (one major Line component, the wye
required "for each connection to the main, i r-? not even
made in gaskefced PVC). Expansion and contK.-ii :ti on,
while a concern if the entire system were so..! vent-
welded, are allowed for in the main Tine pipe joint.;-,
which typically are igasketed.
-------
i.s a rnnv^ t.nword «-j'J Inn nr-it.'i ng all
«olvent—welding. At. J.^asst, rrt:< one majoK- 1:-i t;l;i ng
manu1~a<":t,cJK4«K is oon;=H rt^K"! ng making 9^s-;k«l;«d wyc»
fn.ttings. Unt.il thri r; happeriK, sornr-? ricintract.iirs an-?
•*-,
urging Kp'Lgot, adapt.«Kr; (an adapter •fit.t.ri.ng l-.hai. r:rin h«*
si"ilvent. wRldf-fd :i n a control .1. ed envn fonm«nt, ini.o «ach nf
i'.hf thin^F* I r*g?i n1: t.he wy« r'tnnul hinfl in a Ofrirskr-l.^d Jn i ri 1%
at. each nt- hhe t.hrrje 1 »-?g;- (Figure 1V)..
SPTGC1T ADAPTOR DETAII
-------
Vannum sewer nervi ce lines run "from the varri.umi
ma in to the valve pit;. Typi '-ft '1.3. y these line*?, are near
and parallel t.n property 1 "i np-c-T. 'If ei ther the v.ilvr--
p:i t or main tine i :-: nn private property. t,l -IP? f5P»f v i i :>-.-
"t i n<^ I i kowi ne will ti«=f on pri.viihf* piT»p«»r"t,y.
Ft. in grind prorrtvi i~-.e> t;i"i hnldl y ^i * I iJ nwrk t.h^
loont.'inn rr|- t,l-iw F5ervi.r:F- line wi t,h properly .:i fierrl. i t"i r'l.i
l.-iV,l"i i:i t;«w days prior l%ri -i risl-a 1 I. at-.i.nn. 1'h i n rai^rvePJ «:=!
a reminder i;<~» t.hie prnpRrhy ahrmt". hhe i nt,»-»nrjp-d iin.vtlvion
«'md infty n^usw t.r'i*-* prriFi«rt;y nwnc?r to rftnrngni y.f.i RMrnw
rif.-.=ij;3on thfit hl"i*^ lonati.on Kf'ni'iu I d be changer! 'j I. nl PSI-I
f-Terver: as? an ridvannp? nohi.r:^ to nei.ghhors i f property
liner? arc* in douht.
Mrmt; muni CT pa I i hi er-; prel"r»r loc«*tn.nsj tl-it--- F5t-»rvir:o
l.i n« whi^rp- it will not he driven ov^r. Othi-;r:;:,
how^vr-r, prwtV-?r lor:atiny t.hft srtrvi cf I i.nR within tht~-
paved dri..vew«riy. I hi? r^asnrri n<3 i.«s th«t RufciR^quent
t?x«::c»vflt.xon and a SKoni.fitted riania'.^t-' to t,lr\f> :-;r-i-"v i i :«•: IT <••»•• i •-,
• -•*
I.«RS 11 k«=-l y wi thi.n the paved ««< :t,n on.
S«r"v i.r:i=; 1 i nc.'R should he "loc.ated dn.r.t;«-mt. frc>\n
potable water lines to reduce the poi-:sSi hi I :i l.y i it or or* p.
r:cm taini riciti on. I l"i<^y r?bnu1.d alrso be dxr-at.t-mt f-roni utiii-«r
biu-ied utilities? it1 possible, dee to thf-- pris«i kii I I ty nam .t •
i ir repair of t.i"iot~.<'; ut'i j i ti ef-"s.
-------
A31 connect.! ons to the ma .in, r;« I led crossover
connections, are made "over the top" (Figure 33). This
is accomplished using a vert:i oa I. wye arid a long radius
elbow. Due to the restraints placed upon the depth of
sewers by the connecting sewers entering "over "the
top", engineers should consider the ground cover
required on these connections at the design stage.
9O°
TURKJED
WVC.
Ttr
FIGURE 13
CRfJSStlVFR CONNECTION DETAIL
Table 8 gives design parameters when lifts are
required in the service line.
TABLE 8
Minimum distance from
lift to valve pit
Minimum distance from
lift to crossover
Minimum slope between li.fts
5 ft.
ft.
2 -:i n or
0.2% (Larger)
-------
ino lines typically are ;'•(•--inch in diameter.
An exception to this occurs when a buffer tank i s
**>.
used.. Buffer hanks are used for large flows which wi II.
result in frecjuf^nt valve cycles.. To mai.nta:in grmcl
var:uum rr-^ponse at, the hijl^fef tank, a fi-innh servrit^e
1 in« is
The UKF? o'f r:ha:i.n — type trenhhec-R is nortn-'t:! ines
speci-fd.ed for service .line installation where «n:i I.
types allow as they r:ause lefsR dn sruption to thr»
property owner* s yard than does a hackhoe. Rnnky SOT Is
and some clayey sod Is that will not self clean from the
trencher teeth may he impractical, to excavate using) ,-<
trencher.
Street crossings are often ar:r:orftp"l ished by the
bore method :i n which an auger is used and a steel
casing is pushed in the refsultincj opening under the
street. The casing acts as a sleeve for the service
line that is installed inr-nde. fit her"- street crussi n««
are "free bored" by the use of a "hog". Open cutting
of the street is done where boring is impractical.
-------
Service lines in vacuum system;-; are huri i?.'«'j a
rninirmjm of 30— i nches, since tr.he vacuum line that exi ts
the valve pi t, does so at a depth of '?7~i nches.
if a trencher i FJ u«;sF*d, t*i«r;rid-i ng nnd hackfi 13 is
ussua'J 1 y native m.^terla"! t.=i k*:-'n i~rnm the trench
exr:avi=iti.on- When th« :-~.ervi f.c-t l:i.nf;?s arw :i n»ta!l 1 «d tindt'
tr\=i veiled way« OK- when rnnk f-.'xc:«"ivatlrin 'i « en< :ou n I. e (•'>•? rj,
snm:njnd"i n«3 the rjer-vi.i~:e 1 1 ne wi th -i rnpn;n''ted F<::i pe
bar:k1-±l 1 i.s advi sed,
Many nnntreictorF1. UPJO a hankhoe I'nr t!-ie se
'1 :i ne excavation. The rear-inn For thri F: i« sample; a
backhoe IK reciuT.red 1:or the excavatinn rrF the valve pit
whi r:h typically i.s located clnwe to the main sewer.
Many times thi.s rer>u"ltK in river— excavati on" of the
service line trench. Over-excavation, coupled with the
/
use of fittings which are typically required between
the valve pit and main, is a recipe for future problems
if proper bedding and hackfi.il I material is riot used.
Since the native material and intended contractor
equipment i.s not always known, it is recommended that
the contract documents specify surrounding the service
II ine with i reported pi pe vane backf 3 '1 "I -
As with the vacuum sewer mai.ris, Class ?00, SDR 2'l
PVC pipe typically is used for the service liners..
Solvent-welded f)WV fittings are used, although rubber
ri n
-------
c. Build i rtg__ Sewer £
The term building sewer refers to the gravity
•flow pipe extending from the borne to the valve pit.
setting. In many cases., state or 'local authorities
regu Late installations of building newer?;.. "I l-ir? Uniform
P l.umbi.n«5 ("Iridp i ?; often ref ererined.
For res:.i.dent:J a 1 pservi r:i», the building sewer
shou.l.d be 4~inr:hi and fi I.ope r:nnti.nouFsl y dnwnwnr-d at; «
rate of not less th«n 1 /4—i nr:h per foot (^--perrrent
grade). Desirably, the valve pi t setti.ng should foe
Donated near thie hnnie so the hui.il di ng sewer i s short.
wi.th j,esi:; need for mnintenance and 'I er?R opportunity 1:or
i..rif i..ltrati.on. l.:i.ne si.. Tie for cominerci.a I. users w:i. 1 !1
depend on the amount of flow, wi.th a minimum
recommended si.zre of 6-i.nehes.
Fiends should be avoided in building sewers, and a
cleanout used for each aggregate change in direction
exceeding 135 degrees.
Infiltration via leaking building sewers has been
common, as has the connection of roof or yard drains.
A quality inspection during homeowner connection :i'.>
•advised to determine if these situations exist. Tf so.
steps should be taken to require their elimination
prior to .final! homeowner connection.. "•
-------
To minimise the r i <:k i>t: dam.'igie hi i t.h«: 1::i herciJ a?•?:•;
valve pit, during homeowner connecti on to the system, a
stub—out pipe rrf rsu ff:i rri erit I erngtvh ( typi oa'TJ y
I'i—1:eet) tVorn the valves p:j 1. -is r i^fMimmRndi^rl. Tri
convftnt-i ona I ijKavi hy K«wers;, F T'A e i i >:<:.! tn 1 'i t.y ends <::*t
t.he wyw, with the* «^Kavrity ;-:wrvi r:^ pip*-- hen ri«g f*n
pi ni---!-j..ci:i h"l.<-? i t»-»rn. I I'lt"- fioint^ r't^wfjorrinq won.Id Hiigi^enb i.h.'-il.
f.-1 'i ciitri.'l 'i.ty ;i ri a v
-------
3. Valve Pit Settings
a.
General
The premariuf actured, fiberglass type of valve
pit setting is by far the most common. This type of
setting is comprised of four main parts; the bottom
chamber (sump), the top chamber (valve pit), the
plate that separates the two chambers (pit bottom).
and the lid (Figure 1.4).
FIGURE 14
TYPICAL FIBERGLASS
VALVE PIT SETTING
32
-------
Wastes from the borne is transmitted >•«'> the sump
vi a the building sewer. This sewer enter•«; the* sump
"Itt" above the sump bottom. Up to four separate
building sewers can he connected t.o one r--.unip, each at.
•»-.
9O d«-»!3^ees tci one anuth^r. A t.=i(:if*rt?d sl'i^ini-- IK (.ir-ii^rt
to f ac:i lit.atR the btnrrklH 1 1 iri;^ pKru-:edi.(KR.
The r-:umps have a wall thi <":)-'nt. h«=f.i s^hts ;
H()-::i nchies and 5fi4—i.nnhwf?. Both HK'^ IH i nr:hi»jc: in
di anif ter at the bottom and HH i nchew in di ainr-'i-er at
the top, with the smaLler sixe hav:i.n<;( .=i capacity of
55 gallons and the larger one lOO-ga'l lonr:.
The valve pit houses the vacuum va J ve it.Fielf.
Tt ip manufactured by the filament wi.ndi ng f.i.tartrglasr?
process with a wall!! thickness of i-J/1.6" and is
sui table for H20 traffic loading. The valve pit ri K
36—inch diameter at the bottom and i.s i:nnir:af1y
shaped to allow the fitting of a ?'3 1 /'? inch diameter
clear opening cast iron frame and cover a I. the top.
The depth is 4J?—inches. line >* :i.nch diameV.er opening,
with an elastomer seal.., is pre—cut, trr accept.- t,h*-- H--
i rich vacuum pservice line.
-------
cleb iron
The pit hot bom i r-; made ot' reinforced f:i berg I awr>
that is 1/4" thick nt the edges and 5/1 h"" thick in
bhe center. Tl iese bottoms are molded by bhe resin
inject process;. Valve pib bottoms are provided with
hoj.es pre—cut for the !'-(--i noh suction line, 4 inch
f arid bhe sump securing holt,
,ween the vaj ve pi b bobbmn ami hi n">
fie.Id using a wilicone or butyl.
I l'ii-a pi i. bottom has ft lip which
pit bo r-; imply rest on top ol" it.
;.ov<"'K T! and frames;, desi gned 1 cir HV'O
traffic loading, nee l.ypical'ty used. ihe it
weight, is generally HO pounds and tl-ie 1 H d w«
about 100 pounds. When .•=> Lighter 1 i d i.r-> de;~.i red,
such as in nan traffic ?•; i.hi.iat.;:i ons, a I i ghb weitght
aluminum or cast iron 1 id may be utsed. These byper-:
of lids do nob have frames, bub rather are fitted t-.o
bhe valve pit through the use of two .f-bolts. Thetse
It.ids should nII ear I y he marked "Nan —Traffic"
A shallower arrangement is possible, if so
desired (Figure 15). This arrangement would he ur^ed
in areas where high <^roundwaber or poor soils exist
and depth of the building sewers are very shoI low.
-------
TRAFFIC OR NON-TRAFFIC
, COVERS AVAILABLE
MASS CONCRETE
FIBERGLASS VALVE FIT
FOUNDATION BLOCKS (4)
S" SUCTION UME
FIBERGLASS SUMP
FTGURF IS
SHAI.LflW FIBERGLASS
VALVK PIT SETTING
-------
Certain situations call "for the use erf concrete
valve pi. t settings, These are described :i n labile 9.
lABt E 9
S T II I AT 1 1 INS THAT I) T CT ATF
* When the deepest fiberglass setti ng IPS
not sufficient to accept the building
Wt'ien .'H 'LaKge f Low 'is
requi.K3 no 1"1riw
* When an Interface bet-.wftp?n two system
typ«t? (e.g., pressure and vacuum) is
needed.
The deepest 1L'i. berg]. ass swttd na ir. 8— feet deep.
The building sewer depth at the vaTve pit setting. is
therefore Limited tn 6. 5— feet, since the bui l.ding
sewer enters 18-inches above the bottom. Should a
deeper setting he required, a concrete? val.ve pit
setting may be used. The maximum recommended depth
for a concrete pit is .10 feet.
These type of settings are typi.call y
constructed of 4— foot diameter manhri "!.«•••• sections, wi th
the bottom section having a pre— poured 1.8— i nch
diameter sump (Figure .16). Tt as very important that
all Joints and connections be water tight to
eliminate groundwater ri nf i U.rati.on. Equally
important 3 s the need for a we'1 1 designed pipe
support system, since tl-iese tanks are open from top
to bottom. The support hardware should be of
stainless steel or plastic.
-------
STErPS
OR MORB
ALUM. PIAMONP
ME5H PLANK W/
SgRATEO TOP
WORtvl
FL&XI&L6 PLASTIC
PIPE 3£CTIOKJ«9
W/
TOP £ BOTTOM
COKJC. F-IUU
FT.GURF 1.6
TYPTCAL C11NCRE1F.
VAI..VE PIT SETTING
Earla.er in this section, t=,he «ystem hvdrauli.ns
were discussed, with the sen«ral conclusion that 1.H-
feet of sysstem loss wa« avan 3 .atil.e; 13-f-eet for the
collection piping «nd S- feet fnr the valve
operation. The S—'feet generaJ !l.y corresponds to the
amount of" !l if t reciuired to evacuate the sump
contents, assuming Lhe deepest fiberglass valve pit-
setting is used. Increasing this amount wri It result
in a decreased amount .war I.ah I e for the collection
system. Depending on the specific location of th«s
-------
d»?ep fsetti ng required, thus engineer may opt to serve
the home by other" methods. Should a deep concrete
setting still, he the choice, the engineer' should
receive written approval of the manufacturer.
For large 'flows that require attenuation,"'a
buffer tank should be used. Buffer tanks are
typical! ly used for schools, apartments, nursing
homes, arid other" large users. They are designed with
a small operating sump in the lower portion, with
additional emergency storage available in the tank.
Like the deep concrete va'l ve pit settings, the
buffer tank is typically constructed of 4-foot
diameter manhole sections, with the bottom section
having a pre-poured 18-inch diameter sump (Figure
17) The same water tightness and pipe support
concerns apply to the buffer tank.
FTGURF 17
TYPICAL I::UNI::RFTF
BUFFER TANK
-------
When an i nter t'rico between two system typej-t -in
needed, a duaJ buffer hank should he used. For
example, a hybri d r-;yf:ti-'iii may tie uwed, with vacuum
r-:ewers J-jervin;::! t^l'ic cnn.jrir'i t'.y til' t.l'ie r-:Rf-'v:i r-.e* aK'e;-i nnct
pKeKsuK"e Kewer;:; «er'vi n-;^ t'J'u-1 1~r "i n^e?:.. A1. snnie prrint.,
a 1".r;-inr;l tion wi. I.I he ni->f.»diVfi'J hi-jtween iA ie pr't-^finure t 11 iw
and vacuum f I ow.
A dual hu 1 1"er t,.=ink rip; wi mri \..&r~ bn .1 ht.i1:1-e>' Uanl--,
with the exnephi on i.hah it i R I af^eK tn annnrnndr^l.e
two vacuum vaJvef-; (Figtire 1H). Thes;e t«nk;-. typically
uti.il-t7p« 5-toot di arnet.ec nu:mhn1 e Keoti..nns. .
t- I liURf- 1 H
TYl'ICAL IXINCRFTF
DUAI HliFF'FR TANK
Dual buffer tank« may «"l.r.n be used if the
single buffer tank doeri not have the capacity for the
large flows. A si.ng'l H huffer tank har: a '.:U) gi
capacity while a dual, buffer tank has a fiO g
capfiici.ty.
-------
b.
A P. E> y. £ fe © Q tJ Q C- K '2
Anti—t I ohrit.i i.in r:o I 1 fir Ft ;HKe psometi HIPS?; uned on
the 'Fi.herciJ. i-iRp; v.*i'.]vw pit. swhhi ngr; (F'igur"7* "1H)-
B(~iuy;-inc:y I':;H I nu I rit. i nns sshmLtld bin done ho psi^i-1 "i 1: l;h»=fy
."if-;t: Hxpftfi^nnfi has rthnwri 1-hah t.he^f3
on.11 .'IKS ar« uruial ly rioi1. n«-v«=»dp»d. Should l.h^y be used,
,-;;=,r-p, mijp.t; be taken duri.np) the v.'il.ve pi 1% i riKfca!!'l.afci.nn
tUF. ponr- bidding rind hankf i 11 may "lead to sett. I ernent-,
pt^ob.l enifs. Set.V, I en»ent; of t>he i::oncKet.e K:inj:j rno?5t.
"I :i ke I y wi.11 resuTI t in damage to the building a
and/i IK l-.hr-- pit i tpse'l -f.
F1RURF 1R
ANn:-Fi..r.riATThN HOLLAR
4O
-------
a. General
The AlRVAH vacuum valve oper.it.es wn thout the
use of e I ec;t.ri.ci ty, I hi"' valve j ss varxiurn operated tin
open i ng and sprang /.IKS is ted on closing, Sysstern
vacuuin p»nsurt?f; pa si. t:i ve valve seal.-! rig..
'I he val. vws hav« a H--i nr:h up^na n<3 and arc-1 rnricj*--
i:d scheduJ.e 8C) ABS and h.nve stai riles a sstRFj'l Khat-fcr.,
dw'l K"Ln hear"! ncjs «=ir^d 13!! .-it-;l-omi->r ae«=i1,PJ. The va I vw is
equipped wi.fch a rn] 1 "i ng di.aphK'.:rim t.yp»=f vanuum opf^ra hor"
and i.s capable o1* civ«t^crimi ng all r5«a1in«j 1'-<:in'.«5: and
of~ opening us"i.ng vamium iVniti tl'ie downst.K'eani S3 d« nf
the valve. All maherd al.s of t.he valve are r:hieitn.r:a!l ly
resistant, to sewage and -i t-tr. gases.
The control iFtr/sensnr H.s the k«=»y r.ompnnent of
the vaJ.ve. This nlevioe re I i.er-i on three foroes for
its operation: pressure, vanuum and atmosphere. An
the sewage leve!l rlrses .in the sump, it comprwssns air
in the sensor tube. This pressure initiates the
opening, of the valve by nvercnming r-ip»r:i.n3 tension in
the controller and activated a three-way valve. llnce
opened, the three—way vr« I ve allows t>ie
controller/sensor to take v.nr-uurn from"' the d
41
-------
side of t,he valve arid ctpp.'I y .it to the a<.;t-.ua l-rir
chamber to fu'1 l.y open the valve.. The
contro Ller/J>en«or i.r-i capable of iriai .ntan n:i IT^ f,l"i»v v;-i 1 VP
1:u"l !l y rifii'fn f:rif n fixed period of1 t~d rni-\ whi r:h 't •:•:
.'id Juoi.ati I R nvi=>K" a range rif- ;-i t.«"i 1 ()--t;si-»nnnds. At:l.€-r
t.hf; time pe.f~i.nd KHS wlappsed, atmi'irsn't'iefir air :i f;
adnri tted to the actuatrir chamber pfrnn tt1. i n;::| r.:prina
assisted c'ltising n1- the va'lve. All materi a I r: rif the
r:ontrn I J,er/sensor are 1:nbri.cated frcnn ft pl.aKt.~ir: r»K
elashnmer that :i r. chemir:a'!.it.y resistent to we wage and
ri.ts gases.
Two typen of" vacuum valves are ava'i "I ahl e: hhe
Model. D valve and the Model S valve. I he val ver?
are physical l.y identical., but re.ly on «"H d i 1~"tT;reri t
pi pi ng/pJ.umbH. ng arrangrtrnerit for the-j *-' wm-rct-'- of
atmnspheri r: ai.r needed for proper controller
operation.
-------
MI. inn ..i) ..VAI.VF
As fit.fltF'fl <=?;:ir I :i.ei--, nne of Ivhe- t-.
rtsqurJ red 1:or t'.hc~; prop) >r cipt^rat.xon <'if: t,
•is atmossphi^ri r: ;;rj r. I l*uv> Model 15 vft'l v«*
at,mosph«r'i r: a'i f i-.hroue^ wh i c-.h IK
an external tin •at.ht-'K pi pi-; (t-ifi(nrp? x?O).
F> cr>nt,r r
lvK t;FiS.
r:onn (•••«-.:
BREATHER DOME
LOCATED ABOVE
FLOOD LEVEL
ofuvrrr
w HOMES
rsucnoHUNE
^ I I Gt !RF VO
MODFI. 0 VAI VF
-------
The Model 0 valve .is the most. reliable type
since there is lit Kile nhanee of water entering the
con trailer. However., some di«like this; type of
arrangement her: a urn-- of aesthete as. Some 1:ear
vandalism o1n the external hreather, whiof'i would have
a detri mental 6?1~fei":t on system operation. Experience
has shown that these are B^tTQeiyed proh'l ems, rather
than actual prob'l erm-;.
44
-------
Ml IDE!.. S VALVE
Th« Mode] S valve is a "ssump—verited" valvf=-.
One of the three r:<-inhra"Ll.er tubes is connp*cbf"'rt t-.n hhe
c.leanout./Kt3ni3nr pn p:ri..nc|. Th:.i s pi.pd.ng Rxt-ends :jnt;r> t,he
lower surnp, whxch is connp?ct.«d fco the? hui l.di.na
sewer. The kiui.'Lding sewwr is open fco atrnnspherir: air
through the 4 -inch auxiUlary vent (Figure i?1. ).
MASS COMCftETE
OMVTTY SEWERS
FMOM 14 HOMES
FTlqLIRF 21
MJIDhl S VAI VE
I" . f
-------
While el.'i.Kn nating some of; the concerns
associated with the external breather, the Model S
valve has potential problems of its own.
First, it is absolutely necessary that the sump
be air and watertight.' Should system vacuum he' XWFSS
than 5"-Hg, for whatever reason, the valve will, not
operate. Sewage will continue to fill the surnp.. Tf
the surnp is watertight, it will become pressurised,
with a "bubble" of air trapped at the top of the
sump. When sufficient vacuum is restored, the bubble
of air will be used by the controller in the valve
closing process. However, should water completely
f i.l 1 the bottom pump in the same s< :enerio, the valve
will open and stay open since it will lack the
atmospheric air needed for closure. This open valve
will cause a loss of system vacuum, which may affect
another valve at a different location in a similar
fashion.
Second, the installation of the homeowner* s
buiding sewer becomes more critical. A belly in the
building sewer will trap water and riot allow the free
flow of atmospheric air.
-------
Some engineers have experimented with a bl.end
of the two concepts, by utili ^ing a breather that
gets its air from th« fcQB chamber. This has been
successful i n areas where there i s rm chance for
surface water to enter the top'nhamber. The rtangef
is that water may enter the top stmip f i 1 ling it to a
level above the breather. This water will di reotl y
enter the controller and cause problems with valve
cl.osure.
In either the Model 0 or Model S valve, water
in thw top chamber is of1 no concern, assuming the
controller itself is watertight. To prevent water
•from entering the top chamber has proven to be a
difficult task- For this reason, venting from tht=
top- chamber is discouraged.
Changes in materials, pipe si^es, and supports
have resul ted in a more aestheti.cal 1 y p1.e?asi ng and
vandal proof external breather. Because the Model f)
arrangement is less susceptible to problems than the
Model S. it is th«=? recommended type.
Since the two valve types are physically
identical, it xs possible to cnnv»rt from a Model S
to a Model D, and vice versa, with little effort.
47
-------
h.
The external breather has heen d:i.snuB^fcfi n the
previous section. An early version of this included
an 1--1/'P" gal vanri.zed pipe «xt-,Rndi ng 2 t.o 3-f-««i-. above
near t,hfi? valve pit, setting (Figure 2.V).. A
r dome* is; needed t,o prevent c. 1 riga'i n<3 IVom
small insects. This size ol" pipe was neoewwary for
it to tie self supportiriig. Tri addi hi.nn, :i t was
thoujght to tie less susceptibJ.e to damage. This
arrangernnt haK been successfully used in many of the
operating vacuum systems, a 'I though some perceived
prob.l.erns with aesthetics and vandalism still exist.
FT (JURE ^T-J
PARLY HXPERNAI RRFATICR DFTATI
48
-------
Some engineers have detai. 'J eel an external
breather that uses small*?*" diameter galvanized pipe
(typically 3/4"). This pipe, and the breather dome.
is damped to a 4" x 4" past that lr; driven into the
ground near th«=? va'l vw pit settinpt (F'i.jjmri* 'A'A), Th;i;
fsli ves the arrangement a more permanent look, while
also adding protection to the hreather.
-4X-4 TRCATEQ
PO^T
"TOP
Z'-C" MIM.
LOCATE
OUTRIDE.
CXCAV'M
1-IN&
ATTACHCD TO
FIGHRF 93
ALTERNATIVE F.XTF.RNAI. HRtATHFR DFTAII.
-------
AIRVAC allrao o-fferp: i'n cnlor a I sn
t.n i tss appearance.
. FIGURF ?A
AIRVAC
ALTFRNATTVF FXTFRNAt BRFATHF.R
No matter what, arrangement. -IPS u«ed, two Items
require attention. f-ir^t, the ent.ri.rr-? p-ip-ing sywtwm
•from the dam*? to the connection at the controller
must he watertight. Second, the piping munt slope
toward the valve pit swtt.i ri<^.
FiO
-------
AUXILJ.ARY_VFNT
A 4-inch PVf! vent i.R required on the building
sewer. The: purpose is to provide a sufficient amount;
of air to ant as the driving force hehind the liquid
that, is evacuated from the lower sump I s«e Chapter I,
Swnti.rm G. 3. r: for a d;i . «nus« i on on system operation).
Wi.th a Model J:i valve, a si?fr:ondary function is to
provi df-- the nenenrr-ary atmospheric:: ai.r for proper
r-.ontro'] ler operation.
The auxiliary vr*nt i.c-~. made of 4-inch PVC pipe
and fittings (Figure 2S). Most entities require it
to tie located against a permanent structure, nuch as
the house or a wall. To pirevent valve freezing in
cold cld.mates, the vent should be a minimum of ?0—
feet from the valve pit setting, thereby allowing the
warmth from the newage ti me to warm the air.
MCIURE OR fOST
180 BEND
COUP1MB
FROM CUSTCUOt
< MSEKWE
•< - 4BKMD
ORMIY UNE
rtWcusroia
___^ TOMOMf
F 11^11IVS ^Kt
AliXll 1AIVY VFNI OF I All
-------
To monitor the number of va'lve cyol.es, a cycle
counter is availabl e_ This device is designed for
mounting directly on the vacuum valve or the va*l ve
p:i t wain. The unit-, is enclosed ri r> a watertight
hour-ring wi th a clear nylon top.
With this device, a.t, "is por:r-j:t.h"l.e t.n monitor the
number nf cycle?; of a particular valve, l~lyc:1.f>
counters typically are utilijred where a large water
use i.s expected in order to determine if the valve i.s
reasonably capable of keeping up with the flow.
Some entitites use the cycle counter as a
metering device. Knowing the number of cycles and
the volume per cycle, one can estimate the amount of
sewage through the vacuum valve over a given period,
Others use the device as a method of
determining illegal storm connections to the vacuum
sewer,. The flow through the valve can he estimated
and compared to metered water use. From this, it is
possible to conclude if ex.traneous water is entering
the vacuum sewer and generally in whi^t amounts.
Tt i.s not necessary to have a cycle counter for
each valve, (unless, of course, they are being used
as metering device for hi 1 I.ing purposes), «s they are
small and can ear.:i ..I y he moved from location to
location. It is recommended that the spare parts
list include cycle counters. (See Section K. 4)
-------
Qiy.i§ion Met lysis sod G3*@
Division valves are used on vacuum sewer mains
much as they are on water mains. Plug valves and
resilient. seated gate valves have both tmen
successfully used, although care must, he exercised in
t.he selection process to insure Keliahi "H fr.y ( ?>ee
Chapter F of this Section for a di.scurasn.rin on parat
operating prohlemr. with plug valves). typical
locations for division valves are at branch/main
intersecti.ons^ at both sides of a bridge crossing,
both sides of areas of unstable soil, and at periodic
intervals on long routes. The intervals vary with
the Judgement of the engineer, but typically range
from 1, 500 to 2, OOO feet.
The valves should be capable of sustain:!. ng a
vacuum of 24" Hg. Contract specifications should
call for a certi f ied test from an independent.
laboratory to very this.
-------
The body, bonnet, closure element, and trun:ionr;
should be fabricated of cast, iron equal to ASTM A12fi
Class 8, with the «-.l.osure element being covered with
a precl.si.nn molded Buna—N •facing to act as the
rersi ,l,.i ent seating surface. The mating surface ~shou I d
he ninety (90%) percent pure nickel polished tr» a
fourteen (1.4) RMS finish.
Valves 4-inches and smaller may be direct
actuated while all six—inch and larger valves should
be provided with gear actuators.
The operating nuts should be of cast imn equal
t.n ANSI A126 Class B, The connecting pin or key
should be stainless steel. Aluminum nuts are not
acceptab3 e.
The valves should be installed in a valve box
con-forming to local! codes, with the operating nut be
extended to a position where it accessible with a
standard valve wrench. .
-------
Recent; dec-signs havf» incll uded a gauge tap,
lo.cat.ed on the downstream side of the division valve
(Figure 26). Its purpose is to a] "low vacuum
monitoring by one man in the 1:3e'l.d, ^.ithr'r" t.l'ian
requiring two rneri (one t.o operate the va.lve i n'"thp?
"f':i el.d and one to read the? vac-.uuin gc-i<3i-j at t)-iR vacuum
si.a tion ).
CAST IRON
VALVE BOX
* COVER
CIRCULAR CONCRETE
COLLAR (TYPICAL)
VALVE BOX
r x
CONC. BLOCK
VALVE BOX
3/r BARB CA?
ADAPTOR W/ffl^
3/< FPT
COUP FITTING
SOR-7 200
POLYETHELENE
1UBMC
MPT
COUP. FITTING
SADDLE TAP
F1GURF ^fi
m: vis TON VAIVF
WITH GAUGF TAP OF-'I A [I
HFi
-------
h.
f:!l eanouhw
(Tj eanout.w, called acc«sf> prnnhs -in vacuum sewer
t.ernrLno l.ogy, have heen used in the pa;-;t;.. The? if use
i.s no longer recommended, KT nr:*=- accenH t.ci tif«F? vacuum
main can b*-".1 gained at. any valve pi \... rJrnne fstahe
codesj may require ar;(::er-;;> paint.R t.o he T.nt>t,."< I I ed. \f
so, t.hey should he constructed as shown in Figure '?'7..
FTGIJRF 2Y
Ai:i:ESS POINT DFTATL
-------
Odors
There are very few r»drir prohl ems reported w~i th vacuum
sewers. There are three contri .huti ncj factor's responssi hi e
for this: 1 ) the system is Kepi "I ed, ? ) air n r-i i nl-rnriurred in
gr^ah volumes at each fl.ow input and H) det-.«ntir>n ta mws .= •*
1 K> fps. These factors result in a short detention times,
which also aids in the prevention of septic sewnge.
-------
n
There if; one except. "i ons to the above di rtcuss: i rin cm
odors: when concrete buffer tanks are used. Unlike the
fi berg 1 ass settings, these tanks are open from the sump to
I. he top of the pal;. Operating perr-jonnp"! iiu.tf5t. br- canvl'ul nf:
SPrw^'f gas hulldup i.n l-.hesse tankr-:
mc-ri nt.i=>n«noe*, ajthnuyh t,he voluinw
t.cinl< usually l.r, nrit', I i-ifge «nriugh t'.c~i prnrturin cJiincic-'K'! n.i";
levels of l-iydr rigen su.l 1'::i.de. A.'lsn. tJ-ir-'sr-? t.ypes ri'fr tankra
typ'ica'lly a>'e usswd tn a tt,wnua I;P« 1 afge 1~lnw^.,, which «"11owr;
t-ht? K«?«Wci;3e ninre t.:i me t;n t;urn wepfcri.c. I'hn r-5 drier; not pr"efS«=»nt;
a inajnr problem, si.m~.fr> thte se?a "I c-?d PVl"! mains arr? tjni=i1"1"i=!cr:i',i"-'iJ
by J5«ptic Kfriwaj^e.
Al J of the system par-tvs &r& »si hhwr PVi';, ARS, I;NP,
fubbef, of shan.n].es5«3 st.F*el., which arw corrosi.on rp?:-;:i r-s ten t.
Aes S5uoh. ooc'rnsi.on has not bewri a p^obl t-'in i n vacuum SCWRKC.
The accumulation of grease i P; a causw for concern in
convention lift stations. «n wel"! as in some grinder pump
syst«3m;3. This grease builds up on lc?vel controls and on
the side of the basins. Because* the puitipr- typica.l ly pump
down to a point about an inch above the pump suction, it is
difficult to pump all of the grease frrim the sumps. As
such, grease traps- are typically r+--jqu:i.r ed -i ri applications
such as restaurants to prevent pump p i.uggi rig.
Grease does not present, a problem in vacuum sewf-'rs-
Wheri the sewage is evacuated from the sump, ' i,he ?;ur:r,i nn
pulls floatable grease into the vacuum mains. Since the
sewage moves through the mains in very high v»»1 «•«-: i ti en,
there is litt'le opportunity for grease to Viu'i 3 «J up anywhere
i n the system.
-------
J n Table 1.1), nomerv: I nture u.ssod in the station
design if. given.
TARI F 10
VACUUM STATTflN
DffS I I'-iN Nl IMENC;l._ATI
Q max St,;it,iQn pftak 1"1 nw (y
Qa Station .rivwra
-------
VACUUM PUMP ST7TNI-J
To Rx^e t.hf vacuur^jaumps, the* ^n'l l.own n«J) fdrmu I a is ur-swd:
Qvp= A x Urnax/7. 5 gal/1~h
"A"
fs are shown in Table 1.1
1ABI.F 11
"A" FAHTHR
Fi:il? USE TN
VACUUM PUMP SIZING
- 3, oooft
a. ooi~ 5, ooo ft
5, 001- 7. 000 ft
7, 001-1O, 000 ft
10, 001-12, 000 ft
Over 1.2, 000 ft
5
R
7
8
9
11
The minimum recommenrtwd vacuum pump si^e is 1 FiO nfm.
60
-------
r- To si.s:e t;he discharge pumps, use the fol.il owing
1 " formula:
[~ Qdp = Qrnax = Qa x Peak Factor •»•
(Typical peak factors range from 3.0 to 4.0)
The TDH is cal oulated using the following
j formula;
i
TDH = Hs + Hf -»• Hv
i
i
i .
,. TDH i s calnuli=ited ur>in«3 standard procedures f«>r
i
force mains. However, ^^ead attributed to overnomj ny
i the vacuum in the noll.eotion tank (Hv) mu«t also be
considered. This value is usually 23 feet, whinh is
r
I equivalent to 20" Hg (typical upper operating
value). Since Hv will, vary depending on the tank
- vacuum level (16-2O" Hg, but possitO« to operate at
1 much lower and higher leveHs during problem periods)
it is prudent to avoid a pump with a flat
f '
; capaca ty/head curve.
Where possib'l e, horizontal sewage pumper s^lO^J^l-^
i
i. he used as they have 1 RSJK rsurrtion loesses compared to
r vertical pumps. To reduce the risk of vortexing in
the collection tank, the pump suction line should be
?" larger than the discharge line. Sewage pump
L
shafts should- be fitted with double mechanical shaft.
seals with the sea!l chamber pressurised with light
j-- oi.l.
'-
-------
Net pnssi ti.ve suction head ( NPSH ) calou1 ations
e important in the discharge pump selection
process. In 1 abl e 12, nomencl.ahi.JK(=> used in the NPSH
calculations is given.
TABLE 12
ARriF PUMP
NPSH OAiai.H.ATlGN NOMFNOI. ATHRF
Term__
NPSHa"
ha
havt
V max
hs
hvpa
hf
NPSHr
heq
Net-, positive suction head available (ft.)
Head available due to atmospheric pressure
(ft)
Head avail able du« to atmrispheric pressure
at liquid level less vacuum in collection
tank (ft)
Maximum collection tank vacuum (ft)
Depth of sewage above pump centerline (ft)
Absolute? vapor pressure of sewage at its
pumping temperature' (ft)
Friction loss in suction pipes (ft)
Net positive suction head required by the
pump selected (ft)
Vacuum equalising head provided by 1"
equalising lines (ft)
Typical values are shown in Table
TABLE 13
TYPICAL VAI.UFS
Term
ha: .
Sea level
500 ft above sea level.
1OOO ft above sen level
40OO ft above se.-=i 1 evel
V max:
IB" Hg
20" Hg
hs
hvpa
hf
heq
Typical
33. 9 1-t
33. 2 ft
3?. 8 ft
P9. 4 ft
18. 1 ft
22. B ft
1.O ft (min)
0. 8 ft.
2. 0 ft (for vert, pump )
3. 0 ft (min)
-------
r
To calculate NPSHa. use the fallowing formulas:
NPSHa = havt 4- hs - hvpa + heq
havt = ha - V max
NPSHa must foe greater than NPSHr """
NPSHa and TDH should be calculated for both the
high and low vacuum operating levels and compared to
the NPSHr at the corresponding point on the
head/capacity curve.
r
L
IT
r
C
L
Figure 28 is a diagram for calculation of NPSHa
in a vacuum system.
hi - VMX
(10.81)
I
VACUUM TANK *
HIGH 20* Hg (22.6*
LOU 16- Hg (18.1*)
topi (0.78')
hf (*'}
NPSHA (12' «1o.)
_.. ..£ J:
!• EQUALIZUC LIME
WOt AT AU TIMES
SQWtt
FIGURE 28
NPSHa CALCULATION DIAGRAM
WITH TYPICAL VALUES
-------
J-
r
The operating volume of the collection tank is
the sewage accumulation required to restart the
discharge pump. It usually is sized so that at
minumum design flow the pump will operate once every
15 minutes. Thus is represented by the following
formula:
Vo
= 1.5 x Qmin/Qdp x (UJdp - Qmin)
where:Qmin = Qa/2
Qdp = 0 max = Qa x Peak Factor
L...
Table 14 gives the value of Vo for a 15 minute
cycle at Qmin for different peaking factors.
TABLE 14
VALUES OF Vo
FOR A 15 MINUTE CYCLE & Qmin
3.0
3.5
4.0
Vo
2. 08 x Qmax
1. 84 x Qmax
1. t>4 x Qmax
64
-------
r
r"
[
L
f^STt
The total volume of the collection tank should
be 3 times the operating volume with a minimum
recommended sizre of 400 gallons? (Vt = 3 x Vo).
After sizing the operating volume, the designer
should check to ensure an excessive number of pump
starts per hour will not occur. This will happen
when the sewage inflow to the tank is equal to half
the pump capacity.
When designing the coJ lection tank, the sewage
pump suction lines should be placed at the lowest
point on the tank and as far away as possible from
the main line inlets. The main line inlet elbows
inside the tank should be turned at an angle away
from the pump suction openings.
p.
u- • it may be larger.
The recommended size of the reservoir tank for
most applications is 400 gallons. In special, cases,
...... 65
t_ _. ... - .
-------
SYSTEM PUMP-nriWN TTMF
r
After the vacuum pump, cr.oll ect.n.on tank, and
reservoir tank are sn.?:f»d, system pump-down. time for
an operating range of lh"" to ?Q" Hg shouJ.d be
checked. This calculation will show the amount. o1
time :it will take the Reler:ted vacuum pumps to
evacuate (pump-down) the collection piping from lh'"
Hg to 20" Hg. This formula is shown below:
t -- (0.045 cfnjrmiQl l'^Z3._yE;_±-i.yGt:-yol_i_yr t
gal Ovp cfm
(-
!1
L
where :t = System pump-down time (mn'.n)
Vp = Volume of collection system piping (gal)
Vet - Volume of collection tank (gal)
Vo = Operating volume of collection tank (gal)
Vrt = Volume of reservoir" tank (gal)
Ovp = Vacuum pump capacity (cfm)
In no oaese should "t" be greater than 3 minuter
nor less than 1 minute. -I-f greater than 3 minutes,
the size of the capacity--of the vacuum pumps should
•. -—:••-.-•-
be increased until -"-t~" is less than 3 minutes. Tf
"t" is less than- It minute, the size of the reservoir
tank should be increased.
-------
gns
L
c
[
Vacuum pumps may be either the sliding-vane or
f~ " ' the liquid-ring type (See Chapter TTI. C. 3 for a
I
discussion on the differences between types). In
either case, the pumps should be aiv—cooled and have
l._
an end (ultimate) vacuum of 29.3" Hg minimum at sea
r
j level. The pumps should be capable of contn nous
.- operation. Duplicate pumps, each capable of
delivering 10O% of the required air flow (cfm),
(
; should be provided.
Lubrication should be provided by an integral.
fully recirculating oil supply. The oil separation
P system should also be integral. The entire pump.
^ motor, and exhaust should he factory assembled and
f tested unit mounted on vibration isolators and should
L.
not require special mounting or foundation
) considerations.
[7 . . G7
-------
Both vertical and horizontal discharge pumps
are acceptable, although the latter is recommended
due to lower suction lasses than with vertical
pumps. Duplicate pumps, each capable o'f del 3 vering
the design capacity (gpm) at the specified TDH (ft)
should he used.
Each pump should he equipped with an enclosed,
non-clog type, two port, grey iron impeller,
statically and dynamically balanced, capable of
passing a 3" sphere. The impel").er should be keyed
and fastened to a stress proof steel shaft by a
stainless steel lockscrew or locknut. Pumps should
have an inspection opening in the discharge easing.
The pumps should be fitted with double
mechanical shaft seals. A pressuri/rer mounted on
each pump and connected to the seal chamber is
required to maintain a pressurized supply of light
lubricating oil in the seal chamber.
Fach pump should be coupled to its driving
motor by a grey iron bracket with machined rabbet
fits and a flexible coupling. Stainless steel shaft
sleeves are to be supported by sealed ball bearings
in a one piece grey iron frame. Eaolv pump should be
a base mounted unit with a cast iron base.
A certification from the pump manufacturer that
the pumps are suitable for use in a" vacuum sewerage
installation is required.
68
-------
r
I
i
I
L
[
[
r.
Equalizing lines are to be installed on each
pump. Their purposes is to remove air from the pump
and equalize the vacuum acrossed the impel!! er. HI ear
PVH pipe is recommended for use as small air leaks
and blockages will he clearly visible to the system
operator. On small discharge pumps (generally less
than 1.00 gpm), the equalising lines should be fitted
with motorized full port valves which close when the
L.
pumps are in operation.
r .
69
-------
Two vacuum tanks are required for each station:
the collection tank and the reservoir tank. Basic
construction of the tanks is similar, differing only
in size, shape, and type and location of the
openings. Roth steel and fiberglass tanks are
acceptable.
Steel tanks should he of a welded construction
and fabricated from not less than 1/4" thick steel
plates. The tanks should be designed for a working
pressure of 20" Hg vacuum and tested to 28" Hg
vacuum-
Each tank is to be furnished with the .required
number and si?:e of openings, manways. and taps, as
shown on the plans.
The tanks should he sand-blasted and painted at
the manufacturer* s location and painted as follows:
Internally: One coat of epoxy primer and two
coats of coal tar epoxy.
Externally: One coat of epoxy primer and one
coat of epoxy finish.
Each tank should be supplied complete with
sight glass and its associated valves-
Fiberglass tanks may he substituted using the
same specifications. Fiberglass tanks are to have
150 psi rated flanges.
70
-------
! STANDBY GENERATOR
^
j The standby generator should be capable of
provlding 100% standby power for the station
i «-.
i operation. It typically is located inside the
'.' ' ' station, although generators located outside the ,
station in «n enclosure are also acceptable.
L
This item includes piping, valves, fittings?,
pipe supports, fixtures, drains, and other work
involved in providing a complete installation.
Station piping includes all piping within the
station, connecting piping to the vacuum reservoir
tank, collection tank, vacuum sewer lines, and force
mains.
.....
Wastewater, vacuum, and drain lines larger than
4" should be cast iron, ANSI B16. 1. 125 psi for
exposed installations. For buried Installation.
mechanical joint. ANSI A21. 11. AWWA Clll. cast iron
should be used. Fittings should be flanged and
mechanical joint as appropriate (ANSI AS1. TO, AWWA
C110). One-eighth inch (1/8") thick red rubber
gaskets should be used on all flanges. Vacuum lines
1^ as well as other line*? under 4" should be Schedule 80
[" " PVC. Building sanitary drains are to be PVU fJWV pipe
< _
and fittings.
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The piping should be adequately supported to
prevent sagging and vibration. It also should be
installed in a manner to permit expansion, venting
and drainage.
Far fiberglass tanks, all pipi.ng must be
supported so that no weight is supported by the tank
flanges. Flange bo3.tr. should only be tightened to
the manufacturer" s recommendations. Provisions must
be allowed for inaccurate opening alignment.
All shut-off va3 ves fitted within the
collection station should he identical, to those used
in the collection system piping, with the exception
that they be flanged.
Check valves fitted to the vacuum pi ping are to
be of the 125 Ib. bolted bonnet, rubber flapper,
horizontal' swing vari.ety. Check valves are to be
fitted with Buna-N soft seats.
Check valves fitted to the sewage discharge
piping are to be supplied with an external, lever and
weight to ensure posits ve closing. They also should
be fitted with soft rubber seats.
On the. upstream side of e^ch side of each
vacuum ©ewer isolation valve, a vacuum gauge of not
less than 4-1/2" diameter should be installed.
Gauges should be positianed so that they are easily
viewed when the isolation valves are operated.
Diaphram seals should not fcie used with compound
gauges. Snutabers are recommended for all compound
and pressure gauges.
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MQIQR-CQNIRQL.CENIER
j The Motor Control Center (MCC) Is to be
t
manufactured, assembled, wired, and tested by the
I factory i.n accordance with the latest issue of NEMA
I ' ' Publication ISC2-322, for Industrial Controls and
Systems. The vertical section and the individual
I units shall bear a UL label, where applicable, as
i
evidence of compliance with UL Standard 84H.
I Wiring inside the MCC is to be NEMA Class IT.
j Type B. Where Type 8 wiring is indicated, the
terminal blocks should be located in each section of
j the MCC.
i
The enclosure should be NFMA Type 12-Wifch-
I fiasketed Doors- Vertical sections shall be
constructed with steel divider side sheet assemblies
* formed or otherwise fabricated to eliminate open
f framework between adjacent sections or full—length
1. - -
bolted-on side sheet assemblies at ends of the MCC.
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The MCC should be assembled in such a manner
that it is not necessary to have rear accessibility
to remove any internal devices or components. AIT
future spaces and wireways are to he covered by blank-
doors.
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The discharge pumps anri alarms are controlled
by seven (7) probes insi.de the collection bank..
These probes are 1/4" stainless stee.J with a PVl";
coating. The seven positions are an foljOWP:
1. Ground probe
2. Both dn.wcharge pumps r.t.op
3. Lead discharge pump start.
4. Lag discharge pump start
5. High l_eve".l alartn
G. Reset •frit-- prrihf? tt7
7. High level nut-off: stops a!11 discharge
pumpp (auto position only) and vanuum
pumps (auto and manual, position*?)
t
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Figure 29 give??; apprnxi mate -elevations of
prohes in the collection tank relative to the
discharge pumps and incoming vacuum mains.
An acceptable alternative to the seven probes:
ifj a single capaci tanr:e—i.ndur:ti ve type pKTihe r:apat:i1
of monitoring »!l.l. Keven -set points. Thif* type of
prohe requi.res a transmi tteK/transdi^cer to r?end a 4
2O mA signal to the MO!":..
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VACUUM COLLECTION TANK
r INCOMING VACUUM
AT LEVEL OF BOTTOM
OF MET ELBOWS
ON VACUUM SEWERS
PROBE f7
ST MM FROM
BOTTOM OF
INLET TO TOP
OF DISCHARGE
PUMP VOLUTE
15-2< ABOVE
ABOVE
PROBE §5
PROBE fcTO
TIME OF
ABOVE
DISCHARGE PUMPI
GROUND
ABOVE TANK
-1
FIHllRF 29
TYPIT:AI RLFVATTHNS
OF I.EVFl. nriNTROI. PRORES
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IELEPHQNE-QIALEB
A voice communication—type automatic telephone
dialing alarm system should be mounted on a wall
adjacent. to the MI'IC. The system should he self-
contained and capable of automatically monitoring tip
ho four Independent alarm conditions.
The monitoring system sho.Tl, upon the opening
of any one alarm point, access the telephone 1ines.
wait for the dial tone, and begin to dial the first
of four field programmed telephone numbers. The
system will then deliver a voice message indicating a
two digit station number and the fault status at that
station. The message will be repeated a preset
amount of times with sufficient space between
messages to allow the called individual to
acknowledge receipt of the call. Acknowledgement of
the message is accomplished by pressing a TOUHH TONF*
key on the telephone between messages. Fol lowing thr;
acknowledgement, the system will vocalise a sign—off
and hang up. The system then enters a 30 minute
delay to allow adequate time for follow-up measures
to be taken. - -
If, during the delay, another fault occurs, the
system will begin recalling. Additionally, the
system can be called at any time, from a standard
telephone, whereupon it will answer the call and
deli.ver a vocalised message indicating the station
number arid fault status at the location.
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If the delay elapses and fault.?? still exist.
the system will begin dialing in 1 minute intevals
! attempting to deliver the fault message. If no
acknowledgement is received, the system will hang up,
I
L wait 60 seconds, and ca~l1 the next priority number.
i After dialing the last priority number, the system
I.
wil 1, j f rieoessary, return to the f irst priori ty
number and repeat the sequence indefi nitely.
If the monitoring sysem is to be hours^ri in th«
r
[ MCC, provi.sions must be made to isolate the system
r . from interference, . .
The monitoring system should be provided with
j continously float charged batteries for 24 hours
I
standby operation in the event of a power outage.
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VAGUUM..GAUGES
All vacuum gauges should he specified to have
stainless steel bourdon tube and socket and to be
provided with 1/2" bottom outlets. Polypropylene or
stainless steel ball valves should be used as gauge
cocks.
Vacuum gangers should be provided at the
following locations:
On the side of the vacuum reservoir tank
in a position that is easily viewed from
the entrance door.
On the collection tank in a position that
is easily viewed from the stairway
leading to the basement.
On each incoming main line to the
col.lect.ion tank, immediately upstream of
the isolation valve on the line. These
gauges should be in a position above the
incoming main lines that is easily
from the operating position of the
isolation valves.
The connection from the i ncnming main lines to
the vacuum gauges should b« made of PVH or f:PVf:
pipe. Copper pipe is not to be used for this
purpose.
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The MCC should contain a 7-day circular chart
recorder with a minimum chart diameter of 12 inches.
The recording range is to be O—flO" Hg vacuum, w;i th
the 0 position at the center of the chart. The chart
recorder is to have stainless steel bel !l
The basement of the vacuum station should be
] provided with a 15" x IS" x 1.2" deep sump to collect
i.
washdown water. This sump will be emptied by a
r~
'L vacuum valve that is connected by piping to the
r collection tank. A check valve and eccentric plug
valve should be fitted between the sump valve and th»=?
f collection tank.
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L SECTION
Construction of a vac:uum sewer system is similar to
conventional systems. Utilizing small, diameter pipes in shallow
L trenches and having the ability to avoid underground obstacles
r~ virtually at will makes this type of construction attractive to
contractors. There are, however, certain inherent construction
problems associated with vacuum sewers.
L.
It is imperative "that inspection be performed by those with
i —
{ a thorough knowledge of vacuum sewer technology. . The desj gn of
the system and its hydraulic limits must be understood.
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I Unforeseen, underground obstacles are a reality i n
,— sewer line construction. Water and. gas lines, storm
L~ sewers, and culverts at unanticipated locations all. may
f present difficulties during construction. Natural
I . -. ... . ....
underground conditions, such as rock, water, or sand also
may present more problems than anticipated. With the
"straight line, constant grade" nature of gravity sewer
L- construction, these obstacles usually result in field
j~ changes.
These field- changes may include installing an
additional manhole.' It may also entail removing and
relayi.ng part of the pipe at a di f f erent grade. Depending
on the specifics, the line change may also result in a
grade change which could affect the depth and grade of the
entire gravity sewer system. Another lift station may have
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to be installed. Alterations at the treatment plant may he
required. Unfortunately, this scenerio is all too common.
The end result is an increase in contract price through a
change order.
One key advantage of vacuum sewers is the flexibility
they allow for line changes during construction.
Unforeseen, underground obstacles usually can be avoided
simply by going under, over or around them. There may be
cases where line changes will be necessary, due to
hydraulic limitations. However, the likelihood of this is
greatly reduced with the flexibility vacuum sewers aD.lowZ
One must be very carefuD not to make change for the
sole sake of making construct!.on easier. F.very line change
should be carefully evaluated for its effect on the
performance of the overall system. Will the change
increase the amount of lift in the system (and ultimately
result in increased power costs)? Will the change result
in an undesirable hydraulic condition at a key location in
the system? How will the owner be affected? Will the
change put the pipeline in a location that the owner's
equipment cannot reach? Will i t result in operational
problems in the future? All. of these concerns must be
weighed against, the potential construction cost savings
prior to a change being authorized.
Line changes are made through the uso' of . f i tti.ngs.
No 90-degree bends should be used in vertical or horizontal
line changes. Concrete thrust blocking genera!! ly is not
necessary, however, compaction in this zone is vi tal.
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2.
! Like line changes, grade changes should not. be made
without a thorough evaluation of how that, change will
i *-.
i affect overall system performance. The abili ty to make
,' ' ' grade changes to avoid unforeseen, underground obstacles is
a huge advantage; however, the abuse of this freedom can
i
1 result in major problems. This very issue has been the
cause of conflicts between the contractor and the engineer
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'. in past projects. J he engineer's inspector instinctively
i desires to eliminate lifts to improve the system
i
hydraulics. This results in a deeper installation. The
r '
I contractor, on the other hand, is constantly wanting to add
lifts to result in a shallower installation. As long as
r~
I nei ther party loses sight of the system' s hydraulic 1imits
r-- and the effect on operational costs, a conflict does not
1 . have to take place.
j Vacuum sewers must be laid with a slope toward the
vacuum station. The only exception to this is where
( vertical profile changes (lifts) are made. The pipe must
slope toward the vacuum station between lifts.
A minimum of 0. 2% slope must be maintained at all
[ times. To ensure this, a laser typically is required. The
L.
use of automatic levels also is acceptable when an
r
j experienced instrument man is on site. In areas where an
obvious downhill slope exists, the pipeline follows the
"- contour of the ground- Grade should routinely be checked
j~ by the engineer" s inspector.
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3.
Most contractors have a crew installsng main 1ines
and a second crew installing the services (vacuum valve
pit). It is common for the line crew to install « wye
fitting on the main to accept later piping from the pit
crew. Typically, the pit crew installs the pit and then
must connect the pit to the main. Connecting these two
fixed points, which have different elevations, with rigid
piping sometimes can be difficult. Many times the result
is the excessive use of fittings. This situation can be
avoided by proper planning and coordination between crews.
L
Each service setting, in- terms of depth, typical ly is
custom designed. The relationship between the ground
elevation where the pit will be situated and.the elevation
of the customers basement/building sewer dictates the depth
of service required. In addition, the length of connecting
lateral required must be considered to allow for sufficient
slope on the building sewer. Prefabricated valve pits with
fixed dimensions can sometimes make pit location critical.
Moving the pit to a lower elevation, while allowing
additional fall for the building sewer, may result i.n lift
being necessary to connect to the main (elevation of main
is generally independent of elevation of the pit). Movi.ng
the pit to a higher elevation may resul t i.n i.nsuf f i cient
fall available for the building se,wer. Each valve pit-
location should be evaluated for adequacy and vwri.fi>-»d to
the contractor prior shipment of the valve pits.
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Substitutions
j ' Equipment sutamittals should be approved by the
engineer prior to the contractor ordering the sspraei fie
I equi.pment. Virtually all of the components in a vacuum
|~~ ' system are available from more than one manufacturer. Even
'I
though much research and development currently is taking
j place, the vacuum sewer industry has grown and improved
largely by the trial and error method. For this reason,
r
|_ substitutions of specified equipment are discouraged- This
r- is not to say that new or alternative brands should
automatically be ignored; it simply means that care «°md
judgement should he exercised prior to any major deviation.
Should a substitution be desired, .the contractor
[ should submit the following information to the engineer to
,-- allow for a complete evaluation of the situation:
'- * Identify the product by stating the manufacturer*«
name and address, trade name of product, and the
[ catalog or model number.
* Include product data such as shop drawings, samples,
r etc.
* Give itemized comparison cif substitution with
( specified equipment, listing variations.
l~- , * Give quality and performance ^comparison of
substitution with specified equipment.
[_ * Give cost data comparing substitution with specified
equipment.
* List availability of maintenance servicws an wr»11 an
replacement parts.
L
* Show the effect of substitution on the project
schedule.
* Show the effect of substitution on other related
equipment.
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5.
a.
The engineer should be present during the
entire testing period. This holds true for both the
vacuum station test and the collection system test.
Any leak not discovered due to flawed testing
procedures, either intentional or unintentional, will
Quickly become evident once the system is
operational. An operator can simply check the vacuum
charts daily to see if any leaks are present.
During testing, temperature and/or climatic
conditions may vary.. The following conditions may
affect the vacuum readings in the pipe being tested:
* A drop in temperature may occur. The-; effect.
will he cooling of the pipe and the air in
it thus causing contraction of both. The
contracting of the air within the pipe will
cause an increase in vacuum (Figure 3O).
* Climatic conditions may cause a change in
the barometric pressure. - Before a rainfall
the barometric pressure may drop by
approximately one—half inch of mercury. A
vacuum gauge measures the di fference i n
pressure br-'tween the volume being tested and
the atmospheric pressure. Therefore, any
change in barometric pressure will cause an
equivalent change* in pressure on the gauge
being used i n the vacuum test.
Where climati c changes may occur duri ng a
vacuum test, it is recommended that pipe temperature
and atmospheric pressure he recorded at the beginning
and end of the test.
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PIPE
TAKE
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9
TEMPER
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To correct the test results, first use Figure
30 to determine the effect of any change in
temperature (T effect),. Then apply the following
formula:
I .
T ef feet- (API. -AP2 )-V2 = actual loss in line vacuum
FXAMPLE
S1ART
Temperature of pipe ( F ) 96
Atmospheric Pressure (Tn. Hg) AP1=HO. 0
Line Vacuum (In. Hg) V11 =24. 0
" 65
AP2=29. 5
V2=23. 4
OHANGF
30
0,6
T effect from Figure 30 for a 3O F
drop in temperature is 24.3-in. Hg.
Vacuum Loss
= T effect - (API - AP2)-V2
= 24.3 - (30. 0-29. 5) -23. 4
24. 3 - 0. R - 23. 4
= 0. 4 in/ Hg
a
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All vacuum piping, and connected appurtenances,
in the vacuum station should be tested for
tightness. A final test of the station pi ping should
be done. In . this test, the station piping is
subjected tn 24-inohes of Hg. There should be no
loss of vacuum in the 4--hour test period.
Al] of the controls should be tented at startup
to see that the system is functioning as designed.
This includes the vacuum pump controls, the sewage
pump controls, and the telephone dialer.
Testing of the collection system is usually
carried out dai.ly prior to backfilling by plugging
1 all connections and subjecting the system to 24-
. inches of Hg vacuum. This daily testing usually if
not a strict requirement, rather it is recommended as
j a means of quality control to the contractor.
The collection system also is subjected to a
^ final acceptance test. The engineer should check to
|~ see that all. di.visi on val vess are opened prior to and
at the end of the test- The system should be
r
vacuum of IX per hour over 4 hours is acceptable.
I- Line sections that were successfully tested on an
P individual basis during the daily testing, may fail
i
the final test when considered collecti.vely-
(7
subjected to 24-inohes of Hg vacuum. 'A drop in
i— t
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6.
r<
The above sections provided insight, into some of the
inherent problems associated with vacuum sewer
construction. These problems can be avoided by sound
design, proper inspection, and preconstruction
planning/coordination between the engineer and the
contractor.
Based on a 1989 study of six (6) systems, three
problems appear to be prevalent during construetlan. They
are discussed below:
Solvent welding PVG pi pie in temperatures
approaching or exceedi ng -freezing. 1 ed to vacuum
leaks. Some contractors made the mistake of
the glue warm, only to apply it to a pipe that was
much colder. This 3.ed to leaking joints, and
difficulty in passing the final leakage test.
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Poor workmanship by the contractor led to valv«
pit settlement. This resulted in alignment problems
for the owner at the time of the valve installation
(vacuum line entering the pit moved from its level
position).
Two .fixed pointR, at varying inverts and
varying locations, but requiring rigid connection
piping, resulted in the excessive use' of fittings.
These fittings? many times were located within the pit
excavation. This i:iverexcavat.F«d 7one was one where
lack of compaction could easily lead to settlement-
Later settlement, in fact, Ted to fitting failures.
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The first problem can he avoided by not solvent;
welding joints during -temperatures of 40 F and colder.
However, since this may not practi oa]l for some contractors,
a better solution would be to minimize the number of
*•*.
solvent welded joints in the system. Along these lines,
there has been a significant move in the vacuum industry
toward gasketed pipe and fittings.
Valve pit settlement problems can be avoi ded by
better quality control on both the contractor* s and
inspector's part during construction. Taking time to
assure proper alignment and proper compaction around the
pit will greatly reduce the likelihood of this problem
occurring. Design improvements, specifically t.he t.apered
pit, have a]lowed contractors to improve their compaction
effort.
The use of fittings in the servi.ce lines can be
minimised by proper planning and coordination between line
and pit crews. To mini mi re the di.fficulti.es, some
contractors install the valve' pi ts first. The use of
gasketed fittings, which adds a certain degree of
flexibility, will also alleviate some of these problems.
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, i "i ,L.;.^. ,F,: OPERATION AND MAINTENANCE COHSJOERATJONS.;^^";"V:e-',/'-
- -. .•:•-:.;.: -:;--Ov%:^v^O-..^
^^^g*/*£F.««JS.- ;'
g^£££?s£r£r
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0 P E R. A.T 10 N AND ..M A I N T E N A -W C -E
1.
& Mg3:ntenance_Manual
To operate a vacuum sewer system requires proper
training. Operation and Maintenance Manuals'(O&M Manuals)
are a vital part of this training process. Problems arose
in some of the early vacuum systems due to the .lack of such
aids. Manufacturers and engineers are now recognizing this
\
fact and are reacting accordingly with improved technical
assistance and O&M Manuals.
A well written O&M Manual should contain the
information necessary to achieve the following goals;
To provide an accessible reference for the
Mastewater collection system-operators_in ..v .
developing standard operating and maintenance
procedures and schedules. . • . •
To provide a readily available source of data,
including permits, design data, and equipment
shop drawings which are pertinent to the
particular system.- ...... "
To provide the system operators assistance and
guidance in analyzing and predicting the system
efficiency.
To provide the system operators assistance and
guidance in troubleshooting the system. .
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While -an Q&M Manual is a valuable tool, it should not
be viewed as the source of the ultimate solution to every
problem. The degree of efficiency of the system depends on
the initiative, ingenuity, and sense of responsibility of
the system operator. Also, the manual, should be constantly
updated to reflect actual operational experience, equipment
data, problems, and implemented solutions.
\.
The O&M Manual should contain the following
information as a minimum:
All design data should be given. Included
would be information relating to the system make-up.
such as the number of valves, line footage and line
sizes. Also included would be component sizing
information, anticipated operating ranges, and other
important design considerations. As-built drawings
showing all system components should be included.
MANUALS
Installation and maintenance manuals from the
manufacturers of the major equipment should be.. .
included. A list showing the manufacturer and
supplier as well as contact persons, addresses, and
phone numbers should be compiled.
_WARRA.N.!y. INFORMATION
All warranties, including effective dates,
should be listed. • • * -
_§HQP QB6WIN.es
A list of all approval drawings should be made
which identifies the manufacturer, model number, and
a general description of .the equipment. A copy of
each approval drawing should be included with the O&M
Manual.
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All applicable permit.s. such as the National
Pollution Discharge Elimination System (NPOES)
permit, should be included in the manual. Mater.
Quality standards should also be included.
-OPERATION A.NQ QQNIRQL INFQRMAHQN
r ~ •
j
j This section should include a description of
the overall system. The major components should be
r~ identified. The following information should be
I given for each major component:
i.
ir - * Relationship to adjacent units
! * Operation
* Controls
f * Problems and -troubleshooting guides
* Maintenance
* Preventative maintenance schedule
* Equipment data sheet
[ -EERSQNNEL INEQRM.A.HQN.
r A description of the manpower requirements,
1 including qualifications and responsibilities should
be listed.
_REQQRDS
A list of the type of records, as well as a
list of reference materials that are important.
should be included.
MAINTENANCE.
All equipment should be listed and nross-
referenced to equipment catalogs. Maintenance
schedules should be established. ••
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_E[iEBiEfc!CY ''QEEBAIIfcls' AND RESPONSE £8088^1^''"5^
This section should include a description of
actions and responses to be, followed during emergency
situations. Included should be a list of contact
persons, including addresses and phone numbers^ for
those responsible for various community services
.
_SAEE1Y lyFORfaAHQN
A safety plan should be developed which
includes practices, precautions, and reference
materials.
IY LISTING
A list of all utilities in the system area
should be given, .including contact persons.
addresses, and phone numbers.
,<.-- ..-•,.*•
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2. Sfeaffiag Bgayicsffleofes'^.i
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Information gathered from operating systems
,_. . . suggests that the effort to operate and maintain
vacuum systems has been overstated in past
i" publications. The generalization of vacuum systems
as being mechanized, and therefore, Q&M intensive,
f *•
I along with the conservative nature some engineers in
'recommending staffing requirements, many .times
L resulted in an over—staffing situation.
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The system operator is responsible far the
following activities:
^
[
*
*
Analyzes and evaluates operation and
maintenance functions and initiates new
procedures to insure continued system
efficiency.
Reviews and coordinates all data and records
for the preparation of reports and purchase
requests.
Recommends all major equipment purchases and
system improvements.
Maintains effective communication with other
employees, municipal and government officials,
and the general public.
Has a working knowledge of all .phases of
wastewater collection systems and has a
mechanical background.
Supervises daily operation and maintenance of
the system.
Inspects the system daily to determine the
efficiency of operation, cleanliness, and
maintenance requirements.
Prepares work schedules.
Prepares operational, reports and maintenance
reports. '
Determines remedial action necessary during
emergencies.
Maintains communication with higher management.
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-— F—»i ^~ -•—, «"." **• rr •-r.-^-_»«.--„«» '*^^^yt^f4^'^^»^ri'CTFt^Jgyii'^jr'* v^M- •'"*T5 ,• y^-*'*^;'-^""^*-^- * .* "" ^vi»r
• " • ". T^ ' " wf "' -• 'n.~T' ff • J " ' •»-.*". f; •• »_|_-i. •'. t* - . ./ t • " ' • , »-'' * ":• . ' * "
'' "' '• i' ;-.-•'-: ' «X.-...r*wV .- •*».*"~:??*' *-,',; :- ^.-. — - ,- ••-/- "V" . - " ^1*;-:-i"*f,- •• "
r~
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r ...-.., ......
L. ...
It is desirable for the operating entity to hire the
, system operator while the system is under construction.
f . - This allows the operator to become familiar with the
1 ' system, including the locations of all lines, valve pits.
division valves, and other key components.
To add further training. AIRVAC offers a two—week
r™
training program at their facility in Indiana. A general
L.
knowledge of vacuum sewers is obtained by viewing the .
testing setup at this facility. This setup includes clear
f PVC pipe with various lift arrangements where one can watch
i
the flow inside the pipe during a wide variety of vacuum
1 conditions. Faults are simulated so that that the trainee
can gain troubleshooting experience. The operator is
[ taught the valve operation and its overhaul. Finally.
vacuum station maintenance is taught.
The best training is gained by actual operating
f experience. Many times, however, the knowledge gained is
done so at -the expense of costly mistakes. This is
especially true at startup time. During this time the
P engineer, who.provided day to day inspection services
*- during construction, is gradually spending less time on the
[~~ system. The operator is busy setting vacuum, valves and
inspecting customer hookups. Complicating the situation is
the fact that the operating characteristics of the system
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r
,**--: -^^-v-.-^-.^i-"- - ••-*
r.VT*' /• .: >,-.*- :.--.-'. •„& "'.' 'W-f-Ji* <..>:-.-': ^--.V-- = - V •
.- ", . •)'•.-. 1,-,"--;.-.vT*'*>T-is: -v«i..- „ - •• .;^--.^- -/• .
confcinualH.y change until all of the customers are connected
and all of the valves finetuned. However, with the
operator being preoccupied with other tasks, this
finetuning sometimes is not done; problems develop; and
system credibility is lost. This "training gap", is
present at the startup of virtually every vacuum system.
This is an area of the technology that needs improvement.
One solution is for the engineer to budget a 3 to 6 month
on— site training service to aid the system operator in the
finetuning and troubleshooting of the early problems. The
operator will benefit from the engineer* s systematic
approach to problem solving. This most likely will instill
a certain degree of confidence in the operator concerning
the system. Operator attitude is vital to the efficient
operation of a vacuum system.
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L.
;,^.{^.;^|JS:^^ ,.ri.:.l. . :--•_.'.
4.
^ !*,.*.-. 'iVfXi*8 >*••••'• I'*'-.- •£"*•• •=-" .".J-**. -" -.--,-• f •-.*»-»>•• j!'-1'^'•*.*•:/••;, ;«-.- '•' ••- -; •*,*•*;?: -'. *>*.?
"; * *• - ' .-•,"' - . " * •"• " .'•*;- T,--ii ^'*fc-M;jj5L-iH--- -J;,'"-'..- „ ; .-,>?!-- - "'••'.
sOc Bficfes XQ^SQ&SCX*^X* ^•"r^:;1^^^>^''V^^v***" '" *." .'•:?•• ": '•"u *V:ri-"
For optimum operating efficiency, it is necessary
that a sufficient inventory of spare parts be kept. Some
of the spare parts, such as fittings and pipe, can be
purchased through local builder~s supply companies.
However, there are parts that are unique to vacuum systems
that can not be purchased locally. Typically, these spare
parts are included as part of the construction contract.
Following is a recommended list of spare parts that should
be supplied to the owner during .the construction phase.
I?
L,
TABLE IS
SPARE PARTS LIST
2 ea.
4 ea.
2 ea.
2 ea.
5 ea.
4 ea.
2 ea.
2 ea.
1 ea.
1 ea.
2 ea.
5 ft.
10 ft. .
Vacuum valves
Cantr-allere/seneors
Sensor/cleanout tubes
Controller /sensor rebuilding kit
Valve cycle counters
Three-inch "no hub" couplings
Valve pits
Valve pit bottom plates
Standard collection sump
Deep collection sump
Valve pit covers
Clear valve tubing: 3/8-inch
Breather, tubing: 5/8- inch
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In addition to these spare parts, there are certain
specialty maintenance tools and equipment that are needed.
TABLE IB
SPECIALTY TOOLS AND EQUIPMENT
1
2
100
3
2
2
1
15
2
2
1
1
1
ea.
ea.
ea.
ea.
ea.
ft.
ea.
ea.
ea.
ea. -
ea
Portable vacuum pump
Portable vacuum chart recorders
Vacuum charts
Chart pens
0-20" W. G. magnehelic gauges
0-50" W. G. magnehelic gauges
12 VOLT OC submersible pump
Pump discharge hose
No—hub torque wrenches
Vacuum gauges
Flexible mercury manometer
Controller test box
Pipe locator
The vacuum station also requires spare parts. These
_. ,•" r:.-A.!»!ir5fe..
range from spare pump seals to fuses. Specialty items that
should be considered are:
TABLE 1.7
SPECIALTY EQUIPMENT
FQR_yACIJL)M_SIAIJQN
D
E
r.
X «a.
1 ea.-
1 ea.
2 ea.
2 ea.
1 ea.
Inductance -prob* • . . ... .
Probe transmitter
Prnbe microprocessor card
Vacuum swi tch ..
Vacuum gauge
Auto dialer microprocessor card
10
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when "i nt"i I trahi i in ami iri1*'low was ririt occur i (•«••}. wil.h 1.1 >*••
Karnt-.' none l.urji on. It, is «afe t;n assume the ?-;anie
correlation wxipst.fi; with va<:uur« sewer KyKternr:..
At thi :.; Li me, thousands of flow tneawuremwnts have
been made on pr esr-jure sewer f-iys twine:: w:i hh a w t rJc?
l.t-'d 1"inddngr-s of the earil.n er" si.u«ii w:-; ; hh.ii.
f.!«iwK l.yp'i r:« I .'I y r«'inge fn>m 40 l.n BO <3pnd, w i l.h I i tt. I !-*
wi->c-?k^l y rir ;-;<•• i'-rraon.!il va (•-••! at. j.on,
I'l'ip avfl i 1 .-I|MT I :.i t".y and pual i.hy crl wal'.er .:i t t'V-ntf-;
wa tisr use <=ind r:onst"rc|u«anfr,.'J.y soweK 1 Lows, ass d«'ti-->!3 w«t.^*i-'
pK'rtKKu*'!?, r:c'iininun i ty af:1'1 uen< :^, nature nf nr:r:up«"mcy. anci
at'l'.'i t.udws nf upserr: rw!-iat--d:.i n;:? water conrs^rvati nn.
B«=fi':«'iuse of" thp-jse vari.ab.l P?:> and i.o proyn de a r-,a1'elr,y
factor, tl'ip- flow ratr- norrna 1 "l.y af^fsum^-d 1:nr dfjKi.jgn If; !>0
tn '*'O gpod.
Whll.t=f va«':iiijm s«wers arft snmet:;i meK thought to hf
frt^w of inf 'i 1 trt-il..i on and inflow, TAT can ocrrrur -i.ri thf-
non- vacuum porti.oris of ' t.hr-> syKtetn, e.g.. th«> bu"ildi.ng)
sewer. In some casefs IX I hap. been extreme, rfuw l.o
.leaking hui.l dd ng Fsewers or house roof drain0, bvi.ng
oonner:hed to th»* building SRwer. It .is. prudent to makf->
an allowance for I&l whien adopting a deRi SJn 1" Low, bar.r?d
on the extent of T4.T control given to the projot'-.t,.
An for daily variations in flows, pwri orlr. of po.il.-
moment flow which may exceed design v<1» I ue:~ mriy occur '*
OK 'A timer; per day. However, these are of 1 ittlr-
importance due to their r:hort time of dur.'it.-ion> There
are a I. so peri.ods i»f ?»ero 1" I riw.
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PFAK Fl. t'IW:"i
Besides average daily flow rates and the'IK
variabi liti es, it. it-; important ti i cortsi der other
f actors, such at? the rate of' 'Mow from the individual.
home tri the vacuum valve pit.. T h:i K i'lnw r ai.ft r:ari 'he?
ciu i V,e hiij^h til. t.i tn<•>£>.
Th*=- AmeK:ic:an So<.:let.y < if I..! i v i I Fnginr-er:; (ASIT)
repofV-ed pf'-ak fjjiws l-h;:it. may or:r:uK" about, t-.wi r:i-- per yr-«.=iK
a?5 being 2t"i g;=il'tnris in a 4 ininut.r,' per'i od, nr "I OH
«3«-'i'J horiK j.n nne hnur. I hi-^y ci< > on t.o de.scr-j be t
simu!Lt.«in«aus dlr-:< .-hargp' frnrn .=i h»HUhtub and r:
washer resulting in a 46 ci.iLlrin discharge nver a twn
rni.nul.e period, .ind havd rig a high prnhabi lit.y n1"
rmcuranne.
Bennett reported starve l"'l owr; of BO «:jal.lonF5 in a 7
minute period. .loners reported findings f?i.mi "I ar t-o
those of ASCF nnd Bennett and appl led the d;=ita tn
rK-gi-es&J.on aria l.yses. The results of the various
studies are shown in the Prossure Sewer ««?r:tlon of t-.hia
manu'al ( Figure A--A, page ^~
ATRVAl": 3" vaTves havn .•=* maximum capacity of :"IO
gpm when connected t;o a 6" or "J arger main.. This
assumes that the vacuum ner:r>ssary (B in. Hy) to
the va.lve is present at that part:i<':ular 'l.oc:r<1.e. ! o
acheive this capacity, with the normal 111 ga'l Ion valve
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c
5. ftsrBuilfe -Qcatticias
It. is common in the industry for changes to be made
("""
[ during construction. The changes should be reflected on
f- the as— built drawings. As the name implies, these drawings
i
' depict, exactly how the system was built. This is a vital.
f tool tri the operating entity for maintenance.
;
I —
troubleshooting, and future improvements or extensions to
J the system.
r.. An index map showing the entire system should be
included in the as-built drawings. Shown on this map will
be all key components, line sizes, line identifications,
I.
valve pit numbering and locations, and division valve
f
I locations. Detailed plan sheets of each line of the
collection system should be included, with dimensions
necessary to allow the operator to locate the line as well
as all related appurtenances.
Unique to a vacuum system is the need for an as-hui] t
hydraulic map. This is similar to an index map but also
includes special hydraulic information:
* the locations of every lift
* the amount of vacuum loss at key locations,
such as the end of a line or the intersection
of a main and branch line.
number of main branches, number -.of valves in
each branch, and total footage (or volume ) of
pipe in each branch-
This simple, but vital information al 1 owr; t.he
operator to make intelligent decisions when finetuning or
troubleshooting the system.
E 12
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,
Another tpbX^, that.; is helpfulL.to the .operator, is an .as-
built drawing of each valve pit setting. This drawing will
show the location of the setting relative to some permanent
markers (house, power pole. etc. ), the orientation of the
gravity stub-outs, the depth of the stub-outs, and any
other pertinent site specific information.' These records
are used by the operator as new customers connect to the
system.
The" vacuum station drawings should be» altered to
reflect changes made during construction. Especially
important in these drawings are? dimensions, since any
future modification will depend on available space.
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L - 6. Maintenance •t^';»: ^;?v'"^%J%^?|^^>%.:,,::;--; c/ ••. _. /•'.- ^
*•*„.- .*.; ,-J "*.- • •••„••*" ' .-. -. • •*> __ operation
of both the vacuum station and the collection
f
I system. The operator is notified of low vacuum, high
levels of sewage in the collection tank, and power
r -
I. , outages.
r Normal operation includes visiting each vacuum
station daily. Some maintenance procedures include
the daily recording of pump running hours and a
+ . .
^^ checking of all oil levels. Once an operator is
L familiar with the operating characteristj.es of his
r system, a simple visual check of the gauges and the
charts in the station will alert him of any
j problems. This visual check along with recording
operating data generally takes about 3O minutes.
[ Weekly procedures include checking battery terminals
r- and battery conditions of the standby generator,
cleaning of the collection tank sight glass, a check
I of th«= mechanical seal pressurizers of sewage
discharge pumps, and a test of the telephone alarm
system.
c
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•/;-..' On '« .normal day. the operator, will not be
required to visit the collection system. Normal
station gauge and chart readings are an indication
that the collection system is "Pine. Depending on a
system" s history of breakdown maintenance, some
periodic inspection may be required. This would
include the inspection and manual operation of each
valve on some regular interval. The breather lines
should b»? inspected for the accumulation of
moisture. An experienced operator will quickly learn
the sounds of a properly functioning valve.
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L
areas.
r
fcj.
Wastewater co] lection systems: operate and must-
be maintained 365 days a year. Variations in flow
and maintenance workload© occur, making it imperative?
that preventive maintenance he planned and
scheduled. This will ensure that there is no idle
time during nnn— peak workload periods. Inspection
and maintenance planning and scheduling involves
time, personnel, equipment, costs, work orders, and
pri orities.
A preventive maintenance schedule for all major
equipment should he developed. To initiate the
preventive maintenance tasks, a work- order aypitwm
must be established. This system identifies the
required work, priori. ty of task, and any special
information, such as the tools or parts required for
the job. These work orders provide a record of work
completed.
Scheduled maintenance on the collection pT_pi ng
should be minimal. Areas where difficult or unusual
" '*.
conditions were encountered during construction
should be visited periodical! y. flther areas to he
visited include steep slopes and potential slip
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At. least once a year, the division valves ;.." ...
should he checked. This is done by moving the valve
through the entire opening and closing cycle* at least
once. This procedure will keep va3.ves in operating
condition. In addition, it will, familiarise the
operating personnel with the location of all valves.
All vacuum valves should be inspected once a
year. They should be manually cycled to see that
they are operating properly. The controller timing
cycle should be recorded and compared to the original
setting. If necessary, the timing should be reset.
This entire procedure can be done by one man,
requiring about 10—15- minutes per valve.
Every five or six years, the vacuum valves
should be removed, a spare put in its place, and the
old valve returned to the workshop. The valve should
be taken apart and inspected for wear. If needed,
the seat, should be replaced. When the valve is
reassembled, a new shaft seal and bearing should be
fitted. The seals and diaphragms of the
controller/sensor should be checked and replaced if
necessary. This procedure can be done by one* man,
requiring 2O—30 minutes per valve.
Preventive maintenance for the major equipment
at the vacuum station should be done in accordance
with manufacturers' recommendations. Yearly
maintenance might include inspection of check valves,
plug valves, vacuum pumps, sewage pumps, generator,
and the telephone dialer.
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Although very little effort is required on a
day to day basis, there will be times that emergency
maintenance is necessary. This effort usually
requires more than one person, particularly when i.t
involves searching for a.malfunctioning valve. Many
times problems develop after normal working hours,
requiring men to be called out on an overtime basis.
Emergency or breakdown maintenance can occur in the
piping system, at the vacuum station, or at the
vacuum valve.
Assuming proper design and construction, there
is very little that can go wrong in the piping
system. Occasionally, a line break will occur, due
to excavation for other utilities or landslides,
f causing a loss of system vacuum. Using the division
valves, the operator can easily Isolate the defective
section.
"Malfunctions at the vacuum station are
i generally caused by pump, motor, or electri ca3
r; control breakdowns. Duplicity of most component**
~ allows for the continued operation of the system when
i this occurs. -.
r
iJ
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Most emergency maintenance is related to ;;v~j^,.
malfunctioning vacuum valves, caused by either low
system vacuum or extraneous water. Failure of the
valve is possible in either the closed or open
position. A valve failing in the closed position
will give the same symptoms as a blocked gravi ty
line, that is, the customer will experience problems
with toilet flushing. A phone call from the effected
party makes identification of this problem academic.
Fortunately, this rarely happens. Virtually all
valve failures occur in the open position. When this
happens, a loss of system vacuum occurs as the system
is open to atmosphere. The fault monitoring system
will recognise this low vacuum condition and alert
the operator of the problem. A common cause of
failure in this position is the entrance of
extraneous water into the controller.
Valve failures, if not located and corrected in
a reasonable amount of time, may cause failures in
other parts of the system. A valve that is hung open
or that continuously cycles will cause system vacuum
to drop. If the vacuum pumps oan not keep up with
this vacuum loss, the result is insufficient vacuum
to open oth«r valves. This, in turn, -.may lead to
backups. When vacuum is "finally restored, a large
amount of sewage, in relation to the amount of air,
will, be introduced into the? system -possi b I y resulting
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L
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L
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in "waterlogging";:. " When this occurs, the system -;
must be manually operated, allowing the vacuum pump«
to run longer than usual. Repetitively cycling the
vacuum and sewage pumps in effect 3 ncreases the
capacity of the vacuum station. This repetitive
cycling is continued until the system "catches up".
At that point the system is returned to its automatic
mode.
••'A
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7.
Good records are important for the efficient.
orderly operation of the system. Pertinent, and
complete records provide a necessary aid to control
procedures as they are used as a 'basis of the system
operation. The very first step of any
troubleshooting procedure is an analysis of the
records. This is especially true of the collection
system. A wealth of information its contained in the
basic records kept on a daily basis.
The following types of records should be kept:
* Normal maintenance records
* Preventive maintenance records
* Emergency maintenance? records
* Operating costs records
* Personnel record
These records should be carefully preserved
filed where they are readily available to operating
personnel. A31 records should be neat and accurate
and made at the time the data is obtained.
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The following records should be kept, on a daily
basis:
* Date
* Personnel cm duty
* Weather conditions
* Routine duties performed
* Operating range of vacuum pumps
* Run times of vacuum pumps
* Run times of sewage discharge pumps
* Run time of standby generator
* Flow data
* Complaints receri ved and the remedy
* Facilities visitors
* Accidents or injuries
* Unusual conditions
* Alterations to the system
In addition to this daily information, an
annual report should be prepared to summarise the
operational characteristics of the system.
L
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"22
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Adequate records provide information which tel 1
operational personnel when service was last performed
and indicate approaching service requirements.
Necessary scheduling of maintenance can then be made
without overlooking important aspects of system
operation.
Results of periodic inspections should be
kept. This would include a list of all problems, the
cause of the problem, the repairs, and
recommendations for future improvements.
Records should be kept concerning all emergency
maintenance. This includes the following:
* Date and time of occurrence
* Person(R) responding to problem
* Description of problem
* Remedy of problem
* Parts and equdpment used
* Total time to correct problem
* .Recommendations for future improvements
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QP£BATING_CGSI__RECQRnS
To insure budget, adequacy. It- i s very important
to keep accurate information concerning the casts of
all operation and maintenance items. Costs include:
* Wages and fringe benefits
* Power and fuel consumption
* Utility charges
* Equipment purchases
* Repair and replacement expenses
* Chemicals
* Misoel laneous costs
I PERSONNEL RECORDS
* ™™——..—*. _. „...»-«. «.
u
|_ Personnel records; should be kept on all empl
r- Each file should include information about employment
i
1 application, change of status, absences, vacation time, and
j an evaluation of performance by the immediate supervisor.
t..
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I.
8.
A procedure for locating the source of a vacuum
•failure has been developed by AIRVAC as follows:
r
L.
When a low vacuum condition occurs in the
system, isolate each incoming line tn the
collection tank to identify the problem line.
Close off the problem line. Open the remaining
lines to clear the sewage from them.
Allow vacuum in.the operational lines to reach
the maximum vacuum level possible; then close
these lines off. --. -
Open the line with the problem.
Starting at the collection tank, go to the
first division valve on the problem line.
Connect a vacuum sage to a nearby vacuum valve
(or to a gauge tap. if one exists) downstream
of the division valve. Close the division
valve and'observe' if vacuum builds" up. "'If it -
does not, the problem is between the vacuum, .
station and the division valve. If vacuum
rises, repeat the process on the next division
valve. Before reopening each division valve.
allow vacuum to build up in the non-problem
sections of the sewer to clear that section* s
sewage. '; . •
After isolating the problem section, check each
valve pit to locate the malfunction. Often
this can be accomplished by driving to each pit
and listening for the sound of rushing air in
the auxiliary vent.
After locating the malfunctioning valve, follow
the manufacturer* s valve troubleshooting -
procedures.
•
If no valves are malfunctioning, check for
underground construction that could have caused
a break in the transport piping. Also, walk
the route of the problem sewer and look for
evidence of a break, such as a sunken area.
L..
25
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r. ... . , .The. above procedure is a systematic approach to
! ••"-•'.. .'•-'• ' " • -."l". • "-. . ..I • '. * • • ."<.",•.*.'-... ,' ' '..'•', .-•*«.
" ' -'..•••• ,-.,iV:.' -.,;.: '.•.'. -•• ., .„ - >•• - _ •"'—":• . .- • -•••:.'.-' '?-•;:<'. ' .". "'"
^^ locating the source of vacuum loss. Sometimes a shortcut
I.. can be taken. In a recent study of operating systems, it
r was found that many times the same valve(s) fail. This is
usually due to some particular hydraulic condi tion at that
*
r~ • "
! specific locale. In these systems, the operators check
these valves before any other isolation is done. In
r
| another situation, a skilled operator can usually tell how
c far from the vacuum station the' problem is simply by
I
1 analyzing the vacuum charts. This allows for the
[ . simplification of the isolating procedure.
There have been attempts made to determine the time
c~
I necessary to locate a failed valve. At AIRVAC* s
' Plainville. Ind. location, a valve was caused to fail at a
location unknown to the maintenance personnel. This valve
.... ..?. •-; ..;• • ':_;,., ,*!: -..-„;. .••*•;? --.••-•» . L '-- - -•: ..;-?tt?t>1f:tiHA>.*4l/tH(&*t\*i:^'-\,'-' •••• .•-v-.-; -••. • ;:;. -
was located and the problem corrected in 21 minutes.
System operators report that the typical valve failure is
located within 30 to 45 minutes. Most also cite driving
time from their house to the system as being the critical
factor in this response time. A key component in continual
operation is an effective alarm system, coupled with
available maintenance personnel.
[
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9.
"' 2f
Qa Systems"'
a.
Early vacuum systems were often plagued with
consistent operational problems. These systems were
installed without sufficient field testing of system
components. In addition, operation and maintenance
guidelines were not yet available. As a Vesult,
several operational problems were encountered. •'
Early systems, particularly those by Vac—Q-Tec.
experienced problems because of the lack of knowledge
of the two-phase transport' concept. Small vacuum
mains, improperly planned vacuum main profiles, too
large liquid slug volumes, and insufficient air all
resulted in transport problems. - < • . •
Vac-Q-Tec* s systems also located sensitive
electronic valve control equipment in 55 gallon drums
near to the sewage holding tanks. Corrosion of these
drums and the control, boxes caused numerous
problems. The complex electronic control system
proved to be a major drawback as highly skilled
technicians were required to operate the system.
Valves on Vac-Q-Tec systems are presently being
retrofitted with AIRVAC valves.
-------
. Early. Colt "and AIRVAC systems lacked components ••'•&»*•.
that are now generally accepted as minimum design
standards. The lack of standby power and fault
j monitoring devices are examples. The lack of standby
power 3 ndirectly caused the Colt valve boot to
! rupture. During power outages, liquid"built up
behind these valves. When power was restored and the
i
valves cycled, the higher than normal column of water
I resulted in the timed valve operation sequence
i -
closing on the column of water instead of on air. " '
r ' . _•'".:
L This "water hammer" of sorts resulted in unusually
'," high forces which ruptured the valve boots. These
problems were alleviated to a large degree when
r *
standby power was added to the system. .
^^ • .-....- AIRVAC* s jearly valve pi-ts were made of a tar—- -••"£><«•-
i -.•-..;". '
impregnated paper which deformed when placed in
r unstable soil or in areas subjected to vehicle
i . . . . • _
traffic. This deformation eventually led to damaged
I valves. Additional problems resulted from the use of
t.
valve pits without bottoms in areas of high
j groundwater. Tn this case, water entered the
r— sensitive sensor-controller causing the valves to
L" continually cycle and eventually deplete system
I vacuum. Corrective measures included-.replacement of
L...
the early valve pits with fiberglass pits capable of
-------
withstanding traffic loadings. Breather, tubiif;j-*'^-' „-•'. -"i^;;,.:
extensions above ground and controller modifications
have minimized these past problems.
Simply stated, the early,vacuum systems
suffered from growing pains. A better understanding
of vacuum sewer hydraulics, improved' system
components, and established operation and maintenance
guidelines have led to significant operational
improvements.
*.' • •'•-
-------
b.
r
L
Although operational reliability has improved
with each successive generation of systems, some
problems still exist. Six operating systems were
visited in 1989 so that meaningful operation and
maintenance data could be generated. An attempt was
made to visit systems that would give a good cross
section of the technology. Topography, geographical
location, size, and -varying design concepts were '' -
considered in the selection process. One early
system was visited to see if improvements through the
years has resulted in increased reliability.
TABLE
L
PRQJECI_NAME 1
Ocean Pines
Westmoreland
Ohio Co-Phase I
Lake Chautauo.ua
Central Boaz PSD
White House
.UQQAIIQN _ f
Berlin, Md.
Westmoreland. Tenn
Wheeling, WVa
Celeron, N. Y.
Parkersburg, WVa
White House, Tenn
DATE
DPERATIONA
1970
1979
3.984
198B
1988
1988
SYSTEM
L TYPE
VAC-Q-TEC
AIRVAC
ATRVAC
AIRVAC
AIRVAC
AIRVAC
30
-------
•- "•" ' ' :" -"»-~s •:•-f*-***:. •—-if..4'f».'-'»" I'^CC^'-^R-iS^Jii^i^-i^r''viv.V •-* .'=.
Table 19 gives general information on each
the systems visited.
TABLE 19
GENERAL INFORMATION
ON_QPERATING SYSTEMS
L. F. of Pipe
# Vac. Stations
H Valves
# Homes served
Topography -7* - ••".
Soils
Community Age
Seasonal Pop. ?
Mean Income
Ocean .
285. 000
12
1500
,3500
^ Flat-
Sandy
New
No
High
"testae
83. 000
4
490
540
Rolling-
Rock
Old/New
No
Middle
Ohio
Qoynt*
43. 000
1
. 20O
250
Hilly -
Clay
Old
No
Middle
Lake
Central
121. 000 39, 000
4 1
900 180
2500 350
Flat Flat
Sandy Sandy
Old Old/New
Yes No
Middle Middle
White
_Housg
85. 000
260
360
Rolling
Rock
Old/new
No
Middle
31
-------
QiSIGN/QQNSIBUCIIQN.DAIA
Table 20 shows design and construction data as
it relates to the collection systems of each of the
systems visited.
TABLE 20
DESIGN/CONSTRUCTION DATA
r -
.
Valve Type
Pipe material
Diameters (in. )
Min Cover (ft. }
Win. Slope
Div. Valve
Thrust Blocking
Multi—branches
Longest line (ft)
Design Concept
Pit/House Ratio
Type Sumps
Ocean
PiQes
Vac-0-Tec
solvent
Melded
all 4 :
3
none
Plug
No
Yes
Unknown
none
.43
concrete
7OO gal
We§ferno.r_
AIRVAC
Model-0
solvent
Melded
3. -4." 6 {'.:*'•••
4
0.2%
Plug
Yes
Yes
Lin known
reformer
pocket*
.91
2 pit
fbgls
Ohio .
GQynty._
AIRVAC
Model-S
solvent
Melded
3.4.6 .if
3
0.2%
Plug
No
Yes
8. OOO
early
AIRVAC
.80
fbgls
Lake
AIRVAC
Model-S
rubber
gasket
3. 4. 6. 8
4
0.2%
Plug
Yes
Yes
8.500
early
AIRVAC
.36
fbgls
Central
fioag :
AIRVAC
Model-D
rubber
gasket
3.4.6
3
0.2%
Gate
No
Yes
6.500
early
AIRVAC
.51
fbgls/
concrete
White
House
AIRVAC
Model-D
solvent
Melded
3. 4, 6. 8
4
0.2%
Plug
No
Yes
8.200
current
AIRVAC
.72
fbgls
* Converted over the years to meet "early AIRVAC" design standards
32
-------
Table 21 shows design and construction data a«
it relates to the vacuum stations of each of the
"}"'-:"••-•"' '"•" -" ' ' .•''-?-' -..;" . ;,.'.. ' :',.:*•'"•--•*-""".," -ttj'"'^- ". ' ' "
systems visited.' ' ''"'.'•'.'".* ***""'
TABLE 21
DESIGN/CONSTRUCTION DATA
.VACUUM.SIATIQN
Ocean
# Probes Multi
Equalizing Lines No
Odor Filters Yes
Multi
Yes
No
Ohio
Lake
Single Single
Yes Yes
No No
Central
toss
Single
No
Yes
White
House
Multi
Yes
No
33
-------
Significant improvements have been made to the
f- components in the last ten (10) years, particularly
to the valve controller unit. This has been
. attributed to a combination of research and testing
1 ....
and an increased quality control effort. It is
I estimated that this alone has reduced the problems
that plagued the early systems by 50%. Continuing to
[- educate the designers, builders, and operators of
I . proper techniques will .result in a further reduction
of the problems. Evidence of this is starting to
r
j • surface in some of the more recently constructed
I,
systems.
(.^^ Operation and maintenance data was gathered on
W •--• -• •- - •• • -|- •'•- • •.*. iLyj*. •- '"•::- -> - - • ••• .-,•..'-.- -.: f- •-,• -• -.
[' each of the systems visited. This data is presented
in'Tables 22 through 25.
TABLE 22
OPERATION & MAINTENANCE DATA
_SENERAL_!N£QRMA!!QN
# Operating personnel
Other duties ?
# Men needed for
vacuum part of system
SYSTEM
8
No
8
SYSTEM
6
Yes
1
SYSTEM
C
5
Yes
1
SYSTEM
0
7
Yes
2
SYSTEM
E
1
Yes
1
SYSTEM
_F
3
Yes
1
P
u
-------
TABLE 23
OPERATION & MAINTENANCE DATA
MANHQURS^XEAR
Normal Maint. (hrs/yr)
Prev. Maint. (hrs/yr )
Emerg. Maint. (hrs/yr )
Total manhours/yr.
# of valves
Manhours/yr/ valve
# of customers
Manhours/yr /cust.
SYSTEM
A
16. 640
2,500
1 660
20, 800
1,500
13.9
3,500
5. 9
SYSTEM
_B
1,915
245
192
2,352
490
4.8
540
4.4
TABLE
SYSTEM
_ Q
260
10O
240
600
20O
3.0
250
2.4
24
OPERATION & MAINTENANCE
_PQWER_QQNSUMP.TIQN^YE/
. • .-
Power cost/yr ($)
41 of valves
Cost/yr/ valve ($)
# of customers
Cost/yr/cust. ($)
SYSTEM
A
120.000
1,500
80. 00
3,500
34.29
,
SYSTEM
B _
15. 000
490
30. 60
540
27.77
TABLF
SYSTEM
•_ C .
2. 400
200
12. 00
250
9.60
25'
OPERATION & MAINTENANCE
of valves
# service calls/yr
Mean Time Between
MEAN TIME
SYSTEM
A
1.500
1,500
1.0
BETWEEN
SYSTEM
B
49O
48
10.2
SYSTEM
D
365
1. O13
48
1.426
900
1. 6
2, 500
0.6
DATA
SYSTEM
_-.£> _
27, 54O
90O
30. 60
2.500
11.30
DATA
SYSTEM
E
315
90
384
789
190
4.4
35O
2.3
SYSTEM
E
4.800
180
26. 51
350
13. 71
SYSTEM
. E
260
200
60
520
260
2.0
360
1. 5
SYSTEM
__£__ i
3,900
260
15.00
360
10. 83
SERVICE CALLS
SYSTEM
C
200
24
8.3
SYSTEM
b
90O
40
22.5
SYSTFM
E
180
30
6.0
SYSTEM
F
260
24
1O. 8
Service Calls (MTBSC)
(years)
35
-------
r
I
'
r
r,
c.
... An EPA Technology Transfer Seminar, Publication^
prepared in 1977, detailed the failure rate (MTBSC)
of some of the early vacuum systems. In general, the
MTBSC of the early systems ranged from 0. 06 to 8. 33-
years. All but one of the systems had a MTBSC of
less than 4-years. 8y contrast. all-of the systems
studied in 1.989, with the exception of the early
system, had a MTBSC of greater than 6-years. with the
average being approximately 10-years. This indicates
that component improvements coupled with design
advancements has had a tremendous impact on the
reliability of vacuum systems.
-------
Each of the systems visited experienced some type, of.'".jj :?,"
problem which predominated' as a demand on Q&M staff time.
However, most were short lived. Tahle 26 describes the
types of problems found.
TABLE 26
_BRQBLEM_QLASSIFIQAIIQN
Responsible
Avoidable/
% of Total
Component defect
Design shortcomings
Operator error
Construction related
Equipment malfunction
Extraneous water related
Manufacturer
Engineer
Operator
Contractor
Manufacturer
Customer
Avoidable
Avoidable
Avoidable
Avoidable
Unavoidable
Unavoidable *
40 %
10 %
5 %
25 *
5 %
15 %
In theory, this should avoidable with proper smoke testing,
I/I analysis and correction prior to•construction.
However, operators report that no matter what the effort,
some amount of extraneous water usually enters the system.
A sophisticated statistical analysis was not
performed to develop the above percentages. The
percentages were determined by a combination of frequency
of occurance and demand on staff time as reported by the
sytem operators that were interviewed. They are presented
only for the purposes of putting the different problems
into perspective.
Assuming the percentages roughly approximate reality,
80% of the problems to date can be categorized as
avoidable. This does not mean that they were not or are
*t
not problems. With good design, construction, inspection.
training, and quality control, however, these problems can
be avoided in future systems. .
-------
c
Shortly after startup of one system, an unusual
amount of valve failures were occurring. It was
determined that these failures were caused by a
broken spring in the valve controller. An
investigation revealed that the springs were made of
defective material. The springs were systematically
replaced with new ones, an effort that two men
accomplished on a part time basis over the span of a
month period. .
This effort did not require the removal of the
. valve itself,; . .Using spare parts, the District put
r -
' new springs in the controller component of the valve
r- at their workshop. After a sufficient amount of
<-- controllers were rebuilt, they were taken to the
f" field where they were simply was put in the place of
i_.
the controller with the defective spring, a procedure
I"
that took 10 minutes per valve. These defective
controllers were then brought back to the shop where
the procedure was repeated until all controllers were
rebuilt with the proper spring. This, problem has not
since returned.
-------
The original valves in one system had a
controller that was different from the ones used
presently. They were found to be very unreliable.
The result was more valve failures, and h«=?noe, more
O&M expense, that originally anticipated.
In the 1970' s, AIRVAC designed and patented their own
controller. After the successful testing of these
controllers at their Indiana facility, they began
mass production. '• . '
Every valve in the system has since been
retrofitted with the AIRVAC controller. The failure
rate has been greatly reduced since the changeover. '
Some valves were found to cycle more than once
after the sump was emptied. A redesigned controller
shaft and seal has solved this problem. Controllers
with the old 'shaft and seal have been retrofitted
with the latest version.'
39
-------
The type of division valve used in most
operating systems is the plug valve. Some systems
have experienced major problems with plug valves
while others have not.
Problems reported in one system included times
when system vacuum pulled the division valve closed
thereby cutting off system vacuum beyond that point.
As workers attempted to re-open these valves.
frequently the valve shaft was twisted off due to the
heavy load applied by system vacuum. When this
happened, the division valve could not he opened
resulting in part of system being out of service.
until corrective measures were taken,
I . . Some system operators reportedI. problems with
I plug valves not holding vacuum when closed. This
renders them useless as troubleshooting tool, which
! is their primary purpose.
f
C
Problems with plug valves have been attributed
to quality differences between manufacturers, in some
cases, and to defective materials in others. Plug
valves without these qualities can and have been used
successfully.
F Some recent systems have used rpsilri ent-wedge
gate valves instead of plug valves with much
| success. With proper care in selection process, both
types of valves can successfully be used.
'—^P
r 40
-------
L,
Some valve •failures that. occurred af'ter startup
of one particualr system Mas caused by de-feotive
tubing in the controller. These tubes were
systematically replaced with new ones. " This problem
has since not re-ocurred.
41
-------
_Qg§IGN_SHQRIQQMIN6S
[
F
*"••",„* LV "*•*/ ^ • • .'..
"\ "I"* * •*:" '..,
Some systems have reported problems with sewage
discharge pump cavitation. This • is due to the antual
characteristics of the pump itself. A vortex plate
installed in the bottom of the collection tank is one
method of correcting this problem, assuming the pump
has already been installed.
The real solution lies in proper design. Net
positive suction head (NPSH) calculations should be
done. Section D of this Chapter discusses these
calculations. A pump having sufficient NPSH
avail-able should be selected. -...•..••;- .»• ..... . ->
r _Lea!
-------
.
One of the newest systems in operation was ., •
designed with the most recent design guidelines.
which are more conservative than in the past. This
resulted in larger vacuum pumps than would be
selected using the old design standards. While this
additional capacity has helped in terms of system
pump—down time, it also has caused a small problem.
The vacuum pumps appear to have sufficient
capacity to keep up with an open valve. This being
the case, low vacuum is not recorded at the station.
even though it is occurring at the location of the
open valve. In addition, the automatic telephone
dialer is not activated. This results in increased
run time of the vacuum pump and increased power _-••
casts. In order for the problem to be noticed, the-
operator must be very observant when analyzing the
daily vacuum charts to notice that the pumps are
cycling more frequently than normal. Otherwise, a
valve that is hung open may go unnoticed for days
resulting in a waste of power.
A simple solution to this problem involves
installing another relay in the control wiring that
causes the dialer to call the operator if both pumps
are running together for a predetermined amount of
time (say 1O minutes), despite the vacuum level.
43
-------
•' -. -. ,--..••• .; - : - . •-•.£..:-X--*-*..v.>.-.,-. -~- *,-•• ..... .
'..-'• . '• :.- '•'."•-' '•'••""•: -'•'* f"^-' ' ;£.' *'f :•*•"'* .'>'•'...- ."-.•--'
_§®as9e_eyllgd_into_yacuym_eym.e§
A high sewage level in the collection tank can
be caused by pump failure (usually control related
rather than actual pump malfunction) or hy more flow
coming in than the sewage pumps are capable of
pumping out. The system design normally calls for an
automatic shut—down of both vacuum and discharge
pumps in the event of this happening. Some systems,
however, do not have provisions to prevent the
automatic mode from being overridden by manual
operation.
The natural, inclination, when faced with a ssero
(0) vacuum situation, is for the operator to manually
operate the vacuum pumps in an attempt to restore
system vacuum. Doing this with a full collection
,-. tank can result in sewage being pulled into the
•-• • vacuum pumps. This can result in damage to the
f vacuum pumps, especially with a sliding-vane type.
The proper procedure, assuming the discharge
J pumps work, is to valve off the incoming lines and
turn the vacuum pumps off. The discharge pumps are
!••-• then used to pump the col lection tank down to th«
f normal, operating level. The line valves can then be
opened and the vacuum pumps returned to their
automatic mode. Good design will include electrical
provisions to prevent overriding the automatic: mnde
' .^^^^
without these steps first being taken.
44
[
-------
Line breaks, caused by a trench settlement,
were most likely the result of inadequate bedding
materials or poor compaction during construction.
There have been cases of loss of system vacuum
due to broken fitti.ngs. In all but « few cases, the
failures have occurred at fittings at or near the .
valve pit. This is most likely due to insufficient
compaction around the valve pit coupled with system
rigidity due to solvent welded fittings.
45
-------
[
[
r
•^
[
c
[•
• •*
Most systems experienced problems shortly after
start-up. Construction debris (stones, small pieces
of pipe, etc) in the homeowner' s building sewer
causes the vacuum valve to hang open until manually
cleared. These problems usually disappear within a
few weeks of startup. Problems of this nature are
easily discovered by the operator simply by listening
to the auxiliary vent. Hearing the constant rushing
of air is a good indication that valve is hung open.
; Opening the valve pit, unscrewing the valve body and
clearing the obstruction is a 10-minute procedure.
i
Temperatures approaching 175 degrees were
I reported in one system shortly after startup. The
hot air from the vacuum pumps was blown directly at
I the motor control center (MCC). The extreme heat
caused relay and starter problems in the MCC which
resulted in pump and telephone di.aler malfunctions.
46
-------
r
r
An analysis of the situation revealed that the
vacuum pumps.were Mired incorrectly. Rather than the
pump fans coming on when the temperature reached ±50
degrees and remaining on until the pumps turned off,
-------
.E9U!PMEN!_MALFyNC!!QN
L.
, At one system, a problem with one of" the level
I probes occurred. The probe failed to send the proper
r signal to the motor control center to turn the vacuum
pumps off during periods when high sewage levels
j existed in the collection tank. This resulted in
sewage being pulled into the vacuum pumps causing
damage. Another time the probe failed to send the
p- proper signal to the motor control center to turn off
'- a discharge pump. This resulted in the pump
f continuing to run until the tank was dry. The
^P problem was traced to a faulty transmitter which was
r-*
|
i replaced.
Since failure of the probe can lead to the
ruining of a vacuum and/or sewage pump, the operator
developed a simple inexpensive backup system. This
involves the use of a magnet strapped to the site
! glass above the highest set point of the probe and
one below the lowest set point of the probe. A
L- third, float mounted magnet, held inside a plastic
f tube, moves with the level of the tank inside the
L_
site glass. Should the probe fail and the level rise
r~
: (or fall) beyond the last set point, the two magnets
will meet causing a circuit to close and the
appropriate pumps to either start or stop.
• • 48
-------
At one system the automatic telephone dialer
malfunctioned by calling the operator only to report
that the system "was all clear". Investigation of
this problem revealed that interference from the
motor control center, caused by electrical spikes,
was sending false signals to the dialer. Shielded
cable added to the dialer Miring did not help. The
dialer was taken out of the MCC and mounted on a
nearby wall. This corrected the problem.
It is now known that the microprocessor based
equipment is very sensitive to power spikes.
Provisions should be made during design to filter the
power supply or to provide a separate "clean" power
supply to this kind of equipment. •. .
A big problem in one of the earlier systems has
been the inability of the telephone dialers to
function properly. Without -a dialer, which provides
24-hour a day coverage, problems go unnoticed until
the next work ..day. While this has reduced the amount
49
-------
r
r
of overtime significantly, it has also resulted in
u increased run times. .The operating personnel . '.
apparently feel that the system is reliable enough
(i.e., oversized vacuum pumps can keep up with a
i valve failure) and valve failures are so infrequent
L
that replacing the dialers cannot be 'economically
r ''
, 1
| Justified.
r The above rationale may be a case of falsw
'" economy. Allowing a low vacuum situation to go
j undetected for hours will result in unnecessary
L
additional run time of the vacuum pumps. This will
r .
j result in increased power costs as well as -increased
r- wear on major equipment. This increased wear leads
t
1 to decreased equipment life. A high sewage level in
[ the collection tank typically results i.n total system
shut-down until the operator corrects whatever is
wrong. With no-dialer to notify the operastor of
this situation, the system may be shut—down for hours
at a time. This will lead to waterlogging, which
will require a significant labor effort to correct.
Even more serious is the liability potential that
r
I exist as a -result of damage done by system backups
i .
• * *
into the-customers homes. For these reasons. •
L • telephone dialers are considered to be an absolute
f" must component in the vacuum station..
(j 50
L
-------
ern _water logging
One of the most severe problems that nan
occurred with the collection system is loss of vacuum
due to "waterlogging". This occurs when sewage is
admitted to the system with insufficient atmospheric
air behind it. (See Section F. 6 for a discussion on
waterlogging). The result in ever decreasing vacuum
levels beyond the waterlogged section. This may lead
to insufficent vacuum to open the vacuum valves and
ultimately to sewage backup in the home. In most
cases, waterlogging is caused by too much l.iciuid
(extraneous water) entering the system at one time.
This is a very dif -f icult problem to address since it
typically is related to illegal and difficult to find
storm sewer connections by the customer. An
aggressive I/I program wiJ 1 keep problems such as
these to a minimum..
51
-------
Component defects have been responsible for
many of the valve failures in the pant. With these
failures being drastically reduced by component""
u.
improvements, one of the remaining ways for a valve
f- —
j ' to fail is through water in the controller. Water in
r the controller will prevent it from completing its
cycle and the valve will remain open. This problem
[ is more likely to occur with the A1RVAC Model "S*
i .
valve than the Model "D" valve. (See Section D. 4 -for
a discussion on Model "S* and "D* valves. )
, • In either the Mod«'.l "S" or Model "D* valve,
*- water can enter the controller in two general ways.
f In the first way, water that is present in the upper
LA
^P valve chamber enters directly into the controller as
i a result of the controller not being air and/or
vacuum tight. A tightness test is normally done at
installation, during the annual preventive
f maintenance, and any time emergency maintenance is
j
performed on the valve. The other possibility is
r
: through condensation in the breather tubing. A
r- properly installed breather line, with a drain
•-• leading to the valve, wi.l 1 prevent this second case
f from ocurring.
L<
rr 52
L. " ' . • .
-------
With the Model "S* valve, a third possibility
exists. In this case, water comes directly •From the
lower sump to the controller. The Model "S* valve
requires a watertight seal between the upp€*r and
lower sections of the valve pit so that a bubble nf
air can he trapped for use by the valve controller
during its? cycle. Should the sea] be broken and
water take the place of air, it will be drawn into
the controller by vacuum when the va'l ve cycles.
53
-------
W':':*?£K#^
• ,- -• '."-.-•'.'•>/;•->;;»«•«:.*«
1.. • • • • ...-..-•..• • .*-.*<'.;•*.F
. ' . V - •*','•'•' -r T.:
i'^,\».^/p*-5^.J*i»^r «-^*t» ^J •
^%!^^;;
^^iS*!-1^'^-'-"".'
^."••11 •wVf'i ".r^fe^ -2^r •• •A't^j-*.-
•
- ".• • •--"•v-"-:
f"^^:::^^r/^?^%^^«
^nM:^- tv^vv.---:^^.'..^ -^r-^xir.^
tLJ^i.^"-?': •- "^'-lV>iv??^sS
--
-------
SECTION
_§_X_§_I_E_M C_g_
1-
Certain site conditions make conventional sewer
installation expensive. These include unstable soils,
rock, and a high Mater table. In addition, restricted
construction zones or areas that are flat may also carry.
high construction costs. By using vacuum sewers, the
construction costs for these difficult conditions can be
reduced. Smaller pipe sizes installed at shallower depths
are the prime reasons for this. The uphill transport . C< .
capability, even when used only to a very small degree, may
save many dollars in installation costs. One other major
advantage is the extent to which unforeseen subsurface
obstacles can be avoided. Each of these considered
individually" results in lower"\costslf;' Considered ' '••"..-,
•'.-'• '• -.:>. ~ :A>^./;>,*&-VS-.-VV> : ' ' '••-•• . ..:"•.. ' .'
collectively, they may result ip.substantial cost savaings.
There are three key costs that will materially effect
the price of a vacuum system: the vacuum station, the pipe.
and the valve pits. The price of the vacuum station
depends very much on the equipment selected, the type of
structure it is house in. and the amount of excavation
required. The pipe installation prices depend on pipe
diameter, trench depth, and soil conditions. Valve pit
costs will vary depending on the type of valve, type of
pit, and depth of pit. These three items typically make up
6O-8OX of the total bid. The remaining items include
appurtenances, testing, and restoration.
-------
Many factors affect construction cost bids. Material
•
surpluses or shortages, prevailing wage r.ates^ the" .local..." ,
- ,: •'•:"; :^'a; .: >-. '•&. •-'•? -T •• - :"i;. ^r-'^^^&^;-.?$^&
bidding climate. ' geographic area; ' time of year, -"soundness-^
of the design documents and the design engineer.' s-
reputation are examples of these. As such, it is
i" - ^
i impossible to accurately predict construction costs on a
* ' nationwide basis. Using sound engineering practices.
however, the engineer should be able to make a fairly
accurate estimate of the construction costs. The following
.-.,--.•
steps may be of some value for engineers considering vacuum
[ sewers for the first time: - ....;..
Analyze bid tabulations of other vacuum projects. It
is desirable to use a project that is in the same
geographical area and having similar site conditions.
Request a set of plans and specifications in order to
gain a full understanding of what each bid item . ••
includes. . Ask about any peculiar or unusual bidding
conditions. ' • : '-,..'. -..'-:.
-- ••:. *•**?:.-••-' •-.•-— ":-- t?> • . . ____ - . :., . ..t.v-^-y viii--.^--'.'-u. •- • -, . •
Estimate * the cost of the system by" "applying" modified
unit prices that take into consideration the locale
and site conditions, ' _.'-.'
Correct for inflation by applying cost "indexes.
r • ., . •
Because of the many factors that influence a bid. it
i
is difficult to say if the above procedure will yield
information of quantitative value. ' although qualitative
assistance is possible. Quite simply, the project will
r cost what the low bidder feels it will cost.
•
-------
It is not uncommon -For a wide range of bids to be
received on an engineer's 'first -vacuum projecti",.-..-
.; ,-"4..-" "~ir •?,~i^*^*•&.'»*•-••^'••-•?;'?•''§''• -'•J-..;--: •-••• **.;*-. y ••«;>• Y..."?/..-V" '• '
" •••• •'"• '.';;•>' :"'•-"•'A-"'-:'r •• v" *•"• '•*••?••£•*'?-•>•',?*••'• "•••• ' ••' ">•••>-"' '••'• • •'*. ' .
Contractors -unfamiliar 'withT~vacuum sewers may bid l-iig
simply because of the fear of the unknown (e. g. . bid as if •
the project was a gravity sewer). Equally passible is a
contractor who bids too low because of an underestimation
of the effort required (e. g. , bid as if it was a water
line). Usually the cost is somewhere between these two
extremes. Once the contractors have experience
constructing vacuum sewers, the spread between • low and high
bid diminishes. It then becomes much easier for the
engineer to estimate the construction costs of future • .'••-,
projects.
Most engineers are capable of estimating capital
• • ' ^ . . 'i
costs in their geographic area of practice once major : *'
-^ -;• , •
material component costs are known. . Installation costs can
•->;•". * *- * • .."-***-/•''';•»-"- * v ^4, . rt* .'-\ '•-***•.- *'?£' ^**:.**V;.:, • -s-*; *••";. ' >- . -' • - _ i ;T" • .*.'-.%*,„
be developed by analyzing the effort required to install "
conventional- technology and applying the appropriate
modifications to the unit prices to correct for the local
site conditions. .
— •**.'•."••-
-------
r " -
L 2. Qeerstion an.
.
L
E
' Thi»"'"oh\/;i"r«jR *«rl\/*in'fc.aais fcn uti'l -i SM na'^x/jtr-ijum •"jseweK-s "i «••*'•'•••-*"
r
Therofavxbus ; advantage 'to utilizing"'* vacuum'"sewers -is--a'-
savings of capital costs:' This 'savings, however, may come
at the expense of higher operation and maintenance (O&M)
costs. The question then becomes, "Is the savings of
r capital cost enough to offset the increase in O&M
expenses"? A present worth analysis, where life cycle
costs are converted to present values, will answer this
question. This analysis, however, is only valid if
1 reasonable capital and O&M cost figures are used.
r Very little historical cost data exist 'because of the
relatively new nature of the vacuum sewers. This is
; especially true for operation and maintenance costs. This
lack of data has led'many to the conclusion that vacuum'"
sewers must be O&M intensive. A review of cost records of
operating systems suggests that previously published O&M
figures no longer apply. Reasons for this are twofold.
First, the previous figures were based on very limited data
on a few early systems. Second, component improvements in
the valve have resulted in significantly.fewer service
calls, and hence, lower O&M costs. These factors render
the previously published data obsolete.
-------
Information gathered "from the systems that were -
visited in 1989 is presented in the -following sections. .T,.
;•; •...-, . -''-^ .^ v>?\V;vrwj-- .'
Data -from the Ocean- Pines"" system :"i;e" not included since" this
system is not representative of the current state of vacuum
technology.
r-
Table 27 shows typical Q&M cost components.
TABLE 27
_IYPICAL_Q1,CLCQ§I_CQMPQNENIS
Labor
* Clerical
* Power
* Utilities
* Transportation
* Supplies/maintenance
* Misc. expenses
* Equipment
* Future connections
a-
Normal, preventive. & emergency
Billing
Vacuum & sewage pumps
Water, phone, fuel - s- > .
Vehicle amortization, fuel. ins.
Maintenance contracts
Insurance, professional fees
Renewal and replacement
Set-aside amount (if required)
.. Labor costs are estimated by multiplying the,
number of manhours required by the hourly rate, and
adding fringe benefits. The annual manhour
requirements are made up'of normal, preventive, and
emergency maintenance. "••'.- " "
For normal maintenance, an operator is not
required 24 hours a day to monitor the system, as the
telephone dialer does this for him. However, someone
must be available around the clock in case the
\
telephone dialer calls with a problem. In this
respect, vacuum systems are unique. Very few
problems in a vacuum system can go uncorrected for
any length of time without causing a cumulative
effect.
. 5 ' • •
-------
The operating entity's' overall fesponsi.bi.l3.ti.es
should be considered when estimating the labor
[~
costs. "; For example., the entity may' also be
j
r
responsible for other sewer facilities, or possibly
•_ even water facilities. In these cases, operating
L personnel are usually shared. At the end of the
• ' year, the time charged to the operation of the vacuum
system most likely will relate exactly to the effort
! required (e.g., one (1) hour per day plus some hours
charged to emergency maintenence). If the overall
r~
[ facilities are large enough to warrant different
r shifts, emergency work most likely will be done
i ' ' "' "
without overtime being required.
f An entirely different situation exists for the
entity operating nothing but a similarly sized vacuum
system. Typically a full time operator is hired.
This' man charges 8 hour's a day to the maintenance of
'- the system although most days he will spend much less
f than this. Should a problem develop after normal
1..- '." " ----.. .._
working hours, he most likely will be paid overtime.
Even though both operators will spend the same amount
p of fl£tual_meiQteQfiDEe_ti!!»e, the amount of b.illed._fcime
L- will be entirely different. . The engineer should
f carefully analyze the client* s overall operation,
taking into consideration the possibility of shared
duties, prior to making an estimate o"f the labor
costs.
-------
Preventive maintenance is usually scheduled to
be done by the normal work force during off peak .;.
working hours. •- Because of this, preventive ;'.:;-.'-^isSi?^-,
maintenance is usually reported as normal :
main ten an ce.
Emergency maintenance many times requires
personnel after normal working hours. The result is
overtime pay. In addition, emergency maintenance
typically requires two men.
Table 28 gives a range of manhoure required per
year as a function of the number of vacuum valves.
This table was based on data from the systems that .
were visited in 1989. As such, the values shown
should be considered as realistic values for new
systems with proper design, construction, and ""''
operation.
TABLE 28
MANHOUR ESTIMATING FACTORS
NORMAL
PREVENTIVE
EMERGENCY
LOW
0.4
0.5
0.2
3.9
1.1
1.2
AVE
1.7
0.7
O. 6
-------
r
L. When a full time operator is to be hired,
r regardless of anticipated work load, the values in
"'••'.: ":~- "••• '." '••!••'••**?••£'•'••':•••': ' '•'"•'-.• ''•'.&••'
Table 28 should not be used?'":" In this casesV; the ""-r' ' •-*-'*£'
I
r
'i ~v:--
estimated annual manhour requirements should include
the full time hours of employment plus an estimate of
the overtime (emergency maintenance) hours, taking
P into consideration overtime work generally requires
I
two people. No allowance is needed for preventive
maintenance since this can be done during normal
working hours.
( The following formula can be used to estimate
r- annual labor hours for these cases. This formula .
t '
assumes a 40 hour work week and that some of the
emergency maintenance will occur during normal
working hours.
. ,. ..,. . %
2080 hrs/yr + (.75 x Emergency factor x 8 valves x 2)
No. of valves : 200
Emergency factor: 0. 5
Annual labor hours = 2080 + (. 75 x 0.5 x 200 x 2)
= 2080 + 150
= 2230
8
-------
b.
Clerical
.-,.-• * jit •r:^•'^^-:^*^:•*^^-'•" '* .-•
"' This ' "xtenis includes wages* for* tihe'clTerical'^.?-?'''.•,
staff. Also included would be the billing costs such
as envelopes and stamps. Like labor costs, the value
of this item most likely Mill depend on whether the
operating entity has an existing, on-going operation
which requires office staff. If so, the costs would
be limited to the direct billing expenses only.
-------
c.
:" Power is required 'for the vacuum pumps, the""""
sewage pumps, and for heating and lighting of the
i.
vacuum station. Once the design is completed, it is
l_ possible to estimate the annual power consumption
f with a high degree of accuracy.
Power costs for the pumps are estimated by
using the following general formula:
[ p = T x H x .746 x C
where P = Annual power cost -
r— T = Time of operation (hrs/yr)
; H = Horsepower
C = Cost of electricity ($/kwhr)
' This formula does not include any surcharge the
[ power company may assess on peak demands. The local
rate. structure of. the power company should be
analyzed and an appropriate surcharge estimated.
The capacity of the vacuum pumps, ' and the
resulting horsepower requirements, can be determined
by using the formulas in the Section 0. Likewise,
the run time of the vacuum pumps can also be
determined. An allowance, typically an additional 1O
to 20 X, should be made in the run time to account
for leaks, breaks, and valve failures.'"
•^
[
10
-------
The capacity of the sewage pumps, and the
resulting horsepower requirements, can be determined
by using -the^formulas in the Section D. JRun time is
estimated by the following formula:
T = 6. 08 x F/0
where T= Time of operation (hrs/yr)
F = Average daily flow (gpd)
O = Pump capacity (gpm)
There are also power costs, for. heating.
ventilation and lighting at the vacuum station.
These generally, amount to less than $50 a month.
For planning purposes, values shown in Table 29
can be used to estimate the annual power consumption
for the entire vacuum station. These factors were
derived from information obtained from the systems
visited in 1989.
TABLE 29
VACUUM STATION POWER CONSUMPTION
... - „_. . ESTIMATING FACTORS... v_ ,v
LQW HIGH AYE
160 460 250
It should be noted that the high factor was for
a early vacuum system that was designed under the
reformer pocket theory. This design concept results
in a sealed pipe bore during*, static conditions, which
is less efficient method of conveyance. The average
figure is a more accurate representation of the power
requirements of recent vacuum systems.
11
-------
d. Utilities
."'»'-• * ' ''
••'' Utilities at the vacuum station generally :.V," .".
include water, phone and fuel. Water may be required
for sinks, hose bibs, or toilets. A telephone is
required for the fault monitoring system. Some
systems make use of cellular phones, while others use
• .
radio communications rather than a,telephone. Fuel
is required for the standby generator. The cost of
these utilities generally is less than $50 a month.
e-
Vehicle expenses to maintain the system will be
incurred. For estimating purposes, a mileage rate
multiplied by the estimated annual miles will
L suffice. This rate should include vehicle
f amortization, depreciation, taxes and similar
expenses. Mileage will be required for the following
I tasks :
L.
t
L * Daily visits to the vacuum station
j" * . Annual visits to valve pits for preventive
i maintenance
i._
r * Periodic emergency maintenance
12
-------
f.
As with a conventional system, certain supplies
will be required. Restocking of spare parts and
inventory is included in this item, as are ail,
fuses, charts and chart pens. Initial purchase of
items on quantity discount should be maximized to
take advantage of the lower unit costs when compared
to subsequent prices for replacement.
Service contracts for emergency generators as
well as fuel for the generators is also included in
this item.
g-
Miscellaneaus_exEenses
Miscellaneous expenses include insurance on the
system structures as well as professional services
(engineering, accounting, legal) that may be required
during the year.
13
-------
h.
An annual set aside account should be .%.-:'
j^^ established to generate sufficient funds for major
i
* equipment renewal and replacement. The annual cost
i
I is estimated by dividing the replacement cost by the
( • • useful life. This amount is generally set aside in
an interest bearing account until needed. Present
t
dollars can used in the estimate since the interest
earnings most likely will offset inflation.
Altenative methods dictated by regulatory agencies
also can be employed.
Table 30 lists the major equipment items, and
their useful life.
r
E-
TABLE 30
.AQEHiN
USEFUL
HEM
Vacuum pumps 10 years
Sewage pumps 1O years
Vacuum valve rebuild 6 years
Misc. station equipment 10 years
14
-------
3..
The costs of future set-vice" connections may'"
have to be included in the O&M budget. Unlike
conventional systems, where a future connection may
be relatively inexpensive, a future vacuum connection
can be quite costly. The costs of a valve, valve
pit/sump, fittings, pipe, and labor may approach
$2, 000.
Most systems that were visited simply charge
the future customer the cost of the connection. This
does not appear to be a problem, since most new
houses would have a similar expense for an on—lot
system. In this case, the annual operating budget
does not have to include a line item for future
service connections.
In West Virginia, however, this is not the
case. Sewer utilities are regulated a Public Service
Commission. This agency will not approve a tap fee
greater than $25O, regardless of the type of system.
For this reason, the operating entity must include
the cost of future connections in their rate package
as an annual set—aside. The total installation cost
is discounted by the $25O tap fee and multiplied by
the number of estimated annual future connections.
Since some future customers may be able to connect to
an existing valve pit, a sharing factor may be
applied. This method, in essence, requires present
customer to subsidize the cost of future connections.
15
-------
r " -
L- A modification of this concept includes
f~~ a set amount of future connections in the
construction capital budget, and adjusting the annual •
set-aside amount accordingly. An example calculation
«_. of this set-aside amount follows:
t.
# vacuum customers 140
T~ # vacuum valves 110
[ Sharing factor 78%'
20 year growth rate 15%
r Cost of new service $2. 000
' Tap fee $ 250
1 U prefinanced connection 8
f
1. 4t of future customers = . 15 x 140 = 21
# of future connections = . 78 x 21 = 16
r # prefinanced connections = _ 8
I - 8
Net cost of connection = 2, 000 - 250 = $ 1, 750
Total Set-aside required = 1, 750 x 8 = $14, 000
f" Annual set-aside required = 14, OOO/20 =• $ 700
[
[
16
-------
3.
Usgr.
To generate sufficient revenues to offset expenses.
the operating entity must develop a user charge system.
Components of the annual budget are:
* O&M expenses
Labor
Clerical . .
Power
Utilities
Transportation
Supplies/maintenance
Miscellaneous expenses
Equipment renewal and replacement
Future service connection
* Debt Service
There are many different methods of developing
rates. A common method includes a charge based on metered
water consumption, with a flat rate for non—metered users.
The rate structure may be the same for all usages, or may
decline as water use increases. Others simply charge a
flat rate for all users. No matter what system is used.
the rates must be sufficient to generate the required
revenue.
Most tariffs include provisions for tap fees. These
generally cover initial users of the system as well as
future users. The initial tap fees are generally used to
cover start—up expenses. Tap fees for future connections
are used to offset all or part of the actual, cost to make
the connection.
17
-------
C
[•
As an example, the projected annual operating budget
of a project in Meet Virginia is presented below. This
project is scheduled -for construction in 1991, with
operation to begin in 1992. The project consists of a
hybrid collection system (vacuum, pressure, and gravity)
and a treatment plant.
GENERAL PROJECT INFORMATION
FOR
r
I
-
Construction costs ( $ )
Number of customers
ANN
VACUUM
PRESSURE/
GRAVITY
1. 000. 000 1. 000. 000
140 160
r
TABLE
UAL.iUDeEI
31
TREATMENT
PLANT
750, 000
300
IQTAL
2. 750. 000
300
PRESSURE/ TREATMENT
Q&M
Labor
Clerical
Power
Utilities
T r an spor ta t ion
Supplies/maintenance
Miscellaneous expenses
Chemicals
Equipment R&R
Future service conn.
TOTAL O&M
Debt Service
TOTAL ANNUAL BUDGET
V.A.QUUM
3. 50O
460
2. 20O
750
1,400
1.500
1.000
0
1.600
_2QQ
13. 130
16.6§5
29. 785
GBAVIJY.
2. OOO
540
2, OOO
500
200
2OO
500
0
3, 100
g§
9. 670
ig^g§5
26, 325
PLANT _
~'~.
14. 300
0
6.900
750
400
1.630
2,OOO
1,200
2,200
Q
29, 380
12^710
41. 090
IQT.AL
19, 800
1,000
11. 1OO
2,000
2,000
3. 330
3, 500
1.200
6.900
-1^350
52.180
45fcQlQ
97, 200
18
-------
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-------
r
S E C T I 0 N
H
. . ..
;£^
- •• - ••
••• ' • "
1-
dgrneowner
Factors such as topography, location of existing
utilities, and construction constraints dictate the routing
of a sewer. Many times this results in main line
construction within private property. For service lines.
the construction.is almost always within, private
propeerty. For this reason easements are required from
property owners for the installation and future maintenance
of the system. ' -.-'...
Generally,"" the user* s responsibility "-begins at the"'" -
vacuum pit stub-out. The length of stub—out is usually 6
to 10 feet. Shorter stub-out lengths are undesirable.
They would require the homeowner to excavate closer to the
valve pit to connect to it, possibly damaging the pit or
disturbing the backfill/compaction around the pit in the
process.
!!!!!!!!!!! M !!!!!!!!!!!! H !! M !!!!!!!! M ! M !! M M !!! M
SOD DISCUSSION ON HISTORICAL EPA ELIGIBILTY
*
-------
Most, operating entities require the homeowner to -. .
.\ /: '£&£'•
' •
replace the building 'sewer -from the house •foundation to the :
stub— out connection. .The reason is simple. Vacuum sewers
are not designed to handle extraneous water. By accepting
old. possibly defective building sewers, the operating
entity is taking a risk on operation and maintenance
problems, particularly "waterlogging". .
The building sewer is temporarily under vacuum during
the valve* s open cycle." For this reason the pipe material
must be able to withstand those forces without collapsing.
It is standard practice for 4-inch, Schedule 40. SDR .21, . or
SDR 26 PVC pipe to be used for this purpose. Fifteen
hundred pound (1500-lb) crush-type pipe is not acceptable.
nor is SDR 35 PVC. '—^: * : '
The homeowner also is responsible for the
installation of th®4"""auxiliary vent. This vent is '•""""
necessary for the proper operation of the valve. It should.
be located no closer than 20-feet to the valve pit. It is
desirable for this vent to be located against a permanent
structure, such as the house itself, a fence, or a wall.
There have been attempts by some engineers in the
past to include this work as part of the construction
project. This was -found to be unworkable, as this required
the complete knowledge of the homeowner1 s plumbing system
prior to the project bid. Many times, the homeowner was
unsure of ,the exact location of his building sewer.
Contractor liability was increased since excavation near
the foundation was required. This led to high unit bid
-------
~ prices. Finally, installing a vent on the building sewer
I - -... ....-..••-... ...... . ......
I •" .,': .-.,•••:• =
before the system was ready for operation did nothing more
than vent the septic tank, which created odor problems.
^ All of the work required by the homeowner is to be
i inspected by the operating entity prior to final
p ' connection. This ensures the proper and efficient
j ....
operation of the system. Compliance with the Sewer Use
I Ordinance is the only remaining user responsibility.
-------
2.
§ewer Authority Re
Easement, acquisition is the responsibility of the
Sewer Authority, either directly, or through contract with
a right-of way agent. In either case, the hydraulic limits
of the system must be understood prior to making any
changes that may be requested by the property owner. For
this reason, some Authorities employ the services of the
design engineer for this task.
The actual vacuum valve is not installed until the
customer is ready to connect to the valve pit setting. It
is common for the the contractor to install the valve
pit/sump, including all of the necessary piping, during
system construction The valve is then supplied to the
Authority for their installation at a later date. In this
manner, the Authority can systematically install the valves
as each customer requests connection. Each valve is "timed-
out" with the time setting being recorded for future
reference. The time setting on the first few valves are
typically changed once or twice after start-up as system
hydraulics continually changes until all customers are
connected. All valves are then finetuned to operate as a
complete system. ....
-------
ADD DISCUSSION ON VIDEO TARING-SEE BOWNES SECTION!!
ff-
I I ] I j I I t I I I I I I I I j I | J I I I I » | ! II MM
................................ '
Once all customers are connected, the Authority is
focused on providing reliable, efficient service to their
customers. To achieve this, the operating personnel must
be capable, dependable, and knowledgeable. Of utmost
importance is attitude. An operator that does not believe
in the system will ultimately cause the system to operate
below its potential, in terms of reliability and costs.
Conversely, one with a good attitude uses creativity to get
more out of the system than was originally planned.
To operate any system at a high level of efficiency
requires a Sewer Use Ordinance. This document sets
consistent rules for all users to follow. Included are
material specifications for the building sewer, minimum
slope requirements, and vent locations. Of extreme
importance to the Authority is to limit use of the vacuum
sewer to sanitary wastes only, as extraneous water will
cause operational problems.
-------
An active program far the identification of
extraneous Mater sources should be developed.' This may
include smoke testing and dye testing. To identify and
quantify sources of extraneous water, the Authority can
w
take advantage of a integral feature of a vacuum system;
the cycle counter. This device, when connected to the
valve, will record the number of times the valve opens in a
given period. Knowing that each cycle is approximately 11
gallons, the Authority can estimate, based on water
consumption records, the number of cycles expected over
that period. A count much in excess of the expected may be
a sign of extraneous water. To quantify the amount, the
number of cycles is multiplied by 11 gallons and compared
to the water consumption. Listening to the auxiliary vent
for sounds of running water when no flushing activity is
taking place may also provj.de clues for sources of
extraneous water.
The Authority also is responsible for future
extensions of the system. This includes proper planning.
design, and construction of such extensions. Finally.
future connections to the existing system are made by the
Authority in accordance with the provisions of the Sewer
Use Ordinance.
-------
r
3.
Qther Entities
F
During the planning, design and construction of sewer
systems, there are many different entities involved. Two
of these are regulatory agencies and the engineer. It is
during these times that many decisions are made and details
finalized- Often, these entities view the start-up of a
system as their final involvement. While this attitude is
understandable, it is not acceptable. Continuing
involvement is needed to help a viable, cost-effective
technology grow.
The engineer should spend a significant amount of
time during the start-up of the system. Tests should be
run, and problems simulated, to eee if the system is
operating as designed. Periodically, the operating records
should be analyzed for budget sufficiency purposes.
Problems and the'ir solutions should be recorded. In short,
the engineer should use the operating experience of the
system to help develop improvements in future designs.
Likewise, regulatory agencies should follow up on the
operation of a new system. Information on problems,
including the cause and the remedies, should be gathered.
Cost data should be obtained. This type of information can
then be used for future projects.
It is this present lack of information that causes
many engineers and regulatory agencies to shy away from a
new technology. It has become easier to be conservative,
and hence' unduly critical, rather than to learn the details
of a new technology, no matter how cost—effective.
"--"-'-. 7
-------
•~ , .• ••-.-.- -',7;>>"-'• .^r-v^r*2"->?'tt¥&$^mss3^&&
, v.:" V. V-'^^|Sg^P^|
'-.- ' •'" " ;'^::'<^-'fe^^^li>^
-------
r
CHAPTER 5
SECTION 2
DESIGN EXAMPLE
VACUUM SEWERS
r
Reprinted from AIRVAC
Design Manual
-------
Chapter 7
Design Example
Consider the vacuum sewer layout shown In figure 28. The location of the collection
station, sewers and A*tJv£fe* valves have been selected in accordance with the
^S-SKJ£7~
requirements oVChapter a which are restated below:
Locate sewers to: Minimize lift
Minimize length
Where possible to equalize flows on each sewer.
Loje£^eAJFW£gx*al»ee4o'sfe^ —
For the design example each 4QFrvMU& valve Is assumed to serve two homes and that the
peak flow per home is 0.64 gpm or 1.28 gpmlfflM&F* valve Installation.
To efficiently serve the area shown inSTgure28l four main sewers will be required. Each of
these main sewers is connected directly to the vacuum tank at the collection station.
Sewers are not joined together into a bus main outside the station.
Division valves have been located to isolate areas of the sewer network for trouble-
shooting purposes.
/^~~~-
Prof lies (F/ff. 29 and sqAtave been prepared for main #1 and Its two branch sewers. The
profiles for mains 2,3, and 4 will be similar.
Profiles for main #1 follow the principals stated In Chapter 5 and
Maximum length of 4" sewer • 2,800 ft.
80% pipe diameter drop or 0.2% fall between lifts; whichever is greater.
Where the ground profile falls greater than 0.2% in the flow direction, the sewer pro-
file follows the ground.
55
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Location otXwV^p* valves and branch sewer connections follow the principals of
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Location of U/tpMKP- valves and branch sewer connections and access points follow the
principals of Qb«f$tg}»*5-aQiL£i — "5
Prepare total line loss calculations from the sewer profiles {Fig. 31).
Procedure. Commence at point A. Calculate losses to point D. Calculate losses and flows
from C to D. Determine the line with the greatest loss and carry forward, i.e. if the total line
loss from A to D is greater than the total line loss from C to D, carry forward A to D. DO
NOT ADD TOTAL LINE LOSSES WHERE BRANCH SEWERS JOIN THE MAIN. If the total
line loss from C to D is greater than A to D then C-D-F becomes the main sewer for total
line loss calculation purposes. Total the sewage flow from A-D and C-D. Calculate the
total line losses from D to F and continue towards the collection station.
See figure 31 for calculation of line losses in main #1. Remember the static loss of profile
A
changes of 12" or under is counted as half the change. (12" change 6" loss, etc.)
Using the same method total line loss, flows and pipe sizes can be calculated for mains 2,
3 and 4. Flows,- pipe sizes and lengths for these mains have been estimated to enable
figures 32 and 33 to be completed.
When all machinery calculations are complete, consult manufacturers literature to
select suitable standard size pumps and tanks. Vacuum and sewage pump sizes should
be selected to allow for additional house connections to be made without overloading.
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Vacuum Sewerage System
PROJECT.
DESIGN EXAMPLE
PROJECT NUMBER.
STATION NUMBER.
DATE.
MARCH 1986
LINE
1
2
3
4
TOTALS
CROSSOVERS
41 *» «r
TOTAL
3" PIPE
3"
PIPE
1640
1640
4"
PIPE
4640
3825
3750
5850
18,265
6"
PIPE
8"
PIPE
PEAK
FLOW
25.6
23.04
21.76
34.56
104.96
NUMBER
CROSS-
OVERS
*
10
9
8
14
41
NUMBER
AIRVAC'
VALVES
20
18
17
27
82
* ASSUME 50% OF VALVES REQUIRE CROSSOVERS.
VOLUME OF PIPEWORK (BASED ON SDR 21 PVC PIPE)
Vp m 7.5 (.0547 x LENGTH 3" + .0904 x LENGTH 4" + .1959 x LENGTH 6" + .3321 x LENGTH 8")
Vp m 7.5 ( 90 + 1651 + - + )
Vp * 7.5 (1741) GALLONS
Vp = 13,057 GALLONS
*A Vp = 8705 GALLONS
FIGURE 32
n
62
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Project
DESIGN EXAMPLE
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Station Number.
(Flow
Average Flow
Minimum Flow
Qmax
Qa =
Qmin
Vacuum Pump Capacity Required
(Insert A in Calculation For Qvp:)
Longest Line Length
0-3000'
3001'- 7000'
7001 '-10,000'
10,001' • 12,000
Over 12,001'
A
5
6
7
B
10
Discharge Pump Capacity
Collection Tank Operating Volume
(for 15 mln. cycle at Qmln)
Vo = 15 QmJnJQdp • Qmin)
Qdp
Total Volume Collection Tank
NOTE: MINIMUM Vet =400 gal.
Vacuum Reservoir/Moisture
Removal Tank
(Recommended Volume Vrt = 400 gal.)
System Pump Down Time for Operating
Range of 16" to 20" Hg Vacuum
t should be less than 6 mins. If over,
increase Qvp to give *t* under 6 mins. If
't' is under 1 mln. Increase Vrt.
Total Dynamic Head On Discharge Pump
® Project Number
Date MARCH 1986
Vacuum Sewerage System
Qmax
Peak Factor
105
.g.p.m.
= Qmax
Qa
2
Qvp = Ax Qmax
7.5 gal/ft»
5x105
30
15
7.5 gal/ft»
.g.p.m.
c.f.m.
c.f.m.
Qvp =
Qdp =
Vo =
Vo =
Vo =
Vet =
Vrt =
70
c.f.m.
Qmax = 105 g.p.m.
1.84 Qmax for 3.5 Peak Factor
1.64 Qmax for 4.0 Peak Factor
3V6
580
400
gal.
t =(0.045 cfm-min.) (2/3 Vo + (Vct-Vo) 4- VrQoai.
gal. Qvp cfm
t m Q.04S t 8705 4. | 580 . 193 \ + 400 \
70
6.10*
.mins.
Tdh
Tdh = Head Due to Vacuum + Static Head + Friction Loss
Tdh = 23 + + ft.
Tdh m ft.
NPSH Calculation
= ha + Vmax = ' +
NPSHA
NPSHA
navt + hs - hf - hvpa
+
ft.
RQURE 83
63
IN THIS EXAMPLE TO GIVE
A T UNDER 6 MINS.
Qvp SHOULD BE INCREAS
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