United States
Environmental Protection
Agency
Industrial Environmental Research"
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S7-81-019 May 1981
Project Summary
Comparison of Relative
Emissions from Double
Mechanical Pump Seals to
Other Types of Pump
Shaft Seals
LP. Provost, J.E. Tobias, and S.L Preston
This study compares emissions
from double mechanical pump seals
and other types of pump shaft seals.
Analysis of emissions from the EPA
Fugitive Emissions Data Base does
not show significant differences
between double mechanical pump
seals and other types of pump shaft
seals. Both the percentage of seals
leaking and emission factors for
double mechanical seals were similar
to other types of seals in the data
base.
This Project Summary was devel-
oped by EPA's Industrial Environ-
mental Research Laboratory, Research
Triangle Park, NC, to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
Pump seal data from nine petroleum
refineries were extracted from the
EPA Fugitive Emissions Data Base for
comparison of emissions from double
mechanical pump seals to other types of
pump shaft seals. Separate
comparisons were made for light and
heavy liquid service.
Nonmethane leak rates for single and
double seals were compared using
schematic plots.1 Because the emission
data have been shown to be lognormally.
distributed2, a logarithmic transforma-
tion was performed before the
schematic plots were made. The plots
illustrated that seal type had practically
no effect on leak rate for leaking seals in
light or heavy liquid service.
Centrifugal/mechanical pump,
centrifugal/packed pump, and
reciprocal/packed pump leak rates
were also compared with scheVnatic
plots. The plots illustrated that pump
type had little effect on non-methane
leak rate for both light liquid and heavy
liquid service.
The percentage of seals leaking and
95 percent confidence intervals about
the percentage leaking, were calculated
to evaluate the tendency for pump shaft
seals to leak. Calculation of confidence
intervals is equivalent to performing a
Student's t-test on the groups of data.
Non-overlapping confidence intervals
for two sets of data indicate that a t-test
would show the averages of the two
data sets to differ significantly.
'Tukey, John W, Exploratory Data Analysis.
Volume I, Chapter 5. Reading, Massachusetts:
Addison-Wesley Company, 1977
2Weatherold, R. and Provost, L, Emission Factors
and Frequency of Leak Occurrence for Fitting in
Refinery Process Units, EPA-600/2-79-044,
February 1979.
* US GOVERNMENT PRINTING OFFICE. 1961 -757-012/7118
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Similarly, overlapping confidence
intervals indicate no significant
difference between the averages of the
data sets. The overlapping confidence
intervals illustrated that there was no
significant difference in percentage of
seals leaking between the single and
double seals for either light liquid or
heavy liquid service. There was also no
significant difference in the percentage
of seals leaking among centrifugal/
mechanical pumps, centrifugal/packed
pumps, and reciprocal/packed pumps.
The percentage of seals leaking
among centrifugal/mechanical pumps,
centrifugal/packed pumps, and
reciprocal/packed pumps were
compared separately for single and
double seal pumps and heavy and light
liquid service. In all cases, the
confidence intervals for the three types
of pumps overlapped, indicating no
significant difference among pump
types for either single or double seals
and light or heavy liquid service.
For a comparison ' of both the
percentage of seals leaking and the
amount of leakage per seal, emission
factors and 95 percent confidence limits
about the emission factors were
calculated. No emission factors were
calculated for cases where the number
of pump seals screened was less than
20 because confidence limits for such
small sample sizes would have been
extremely wide. For this reason, there
was little information for comparison of
the effect of pump seals on emission
factors for any particular service and
seal type. Where enough information
for comparisons existed, all emission
factor confidence intervals overlapped.
This indicated that there was no
significant difference in emission
factors between single and double seals
for either light or heavy liquid service,
no significant difference in emission
factors among centrifugal/mechanical,
centrifugal/packed, and reciprocal/
packed pumps for either light or heavy
liquid service, and no significant
difference between centrifugal/
mechanical and centrifugal/packed
pumps for single seal pumps and heavy
liquid service.
Conclusions
Analysis of emissions from the
refinery data base shows no significant
differences between mechanical pump
seals and other types of pump shaft
seals.
Recommendations
Lack of significant differences maybe
due to the small amount of data
available when subcategories of pump
seals were analyzed. Also, the effect of
other variables such as point of
emission measurement,whether or not
the pump was running, and the
particulars of the service for each pump,
may mask differences in performance of
the various seal types. A more complete
study should consider these variables
and be based on a larger sample size.
L P. Provost, J. E. Tobias, and S. L. Preston are with Radian Corporation, Austin,
TX 78766.
S. L. Rakes is the EPA Project Officer (see below).
The complete report, entitled "Comparison of Relative Emissions from Double
Mechanical Pump Seals to Other Types of Pump Shaft Seals," (Order No.
PB 81-162 083; Cost: $5.00, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use $300
PS 0000329
U S ENVTR FPOTt'CXIUN AGFINCX
KEGION 5 LiBrtAKY
230 S DEARBORN STREET
CHICAGO IL 60604
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