SDSB 79-22
Technical Report
July 1979
Particulate Measurement -
Efficiency of Pallflex T60A20 Filter Media
by
Kevin D. Stulp
NOTICE
Technical Reports do not necessarily represent final EPA decisions
or positions. They are intended to present technical analysis of
issues using data which are currently available. The purpose in
the release of such reports is to facilitate the exchange of
technical information and to inform the public of technical devel-
opments which may form the basis for a final EPA decision, position
or regulatory action.
Standards Development and Support Branch
Emission Control Technology Division
Office of Mobile Source Air Pollution Control
Office of Air, Noise and Radiation
U.S. Environmental Protection Agency
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Abstract
An experiment designed to measure the efficiencies of dif-
ferent lots of Pallflex T60A20 teflon-coated glass fiber filters
has been completed. Results of these tests indicated that: (1)
batch-to-batch variation of filters is generally less than 2
percent, and (2) this media will not satisfy the 98 percent filter
efficiency requirement on all vehicles.
Introduction
The test procedure specified in the light-duty diesel particu-
late NPRM (Federal Register. Vol. 44, No. 23, February 1, 1979)
requires: (1) a filter efficiency of 98 percent, or greater
efficiency and (2) that fluorocarbon-coated glass fiber filters
must be used for testing. Currently, Pallflex Corporation is the
only manufacturer of the required filter media, with the best
candidate being type T60A20. Some manufacturers have expressed
concern that the 98 percent filter efficiency requirement will be
difficult to meet, and that there is significant batch-to-batch
variability with this media. Hence, a brief test program was
conducted to evaluate the significance of these concerns. Two
different production vehicles were used to evaluate batch-to-batch
variation of the above filters, and also to investigate diffi-
culties in meeting the 98 percent filter efficiency requirement.
Objective
This study was conducted in order to evaluate batch-to-batch
variation of Pallflex T60A20 filter media and to evaluate diffi-
culties in satisfying the 98 percent filter efficiency requirement.
Test Procedure
In this investigation, the procedure specified for filter
efficiency evaluation in the light-duty diesel NPRM (Federal
Register, Vol. 44, No. 23, February 1, 1979) was followed. There-
fore, only highlights will be noted.
This procedure requires that efficiency be determined by
collecting particulate on a back-up filter while the vehicle is
operated over a cold start LA-4 cycle. Filter efficiency corre-
sponding to each bag must be determined. The back-up filter must
be three to four inches behind the sample filter as shown below:
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3-4"
Flow
7
7
Sample Filter
Back-Up Filter
For this study, two diesel production vehicles were used to
evaluate vehicle-to-vehicle effects on filter efficiency as well as
the batch-to-batch variabilty.
Results
The results of this study (summarized in Table 1) indicate
that filter efficiency is vehicle dependent, with generally small
batch-to-batch variation.
Specifically, none of the batches of Pallflex T60A20 media
satisfied the filter efficiency requirement when the Peugeot 504D
was tested. The means of filter efficiency ranged from a low of
90.7 percent to a high of 93.7 percent with an overall mean and
standard deviation of 92.1 and 0.9 percent respectively for all
batches combined.
For the 1978 Oldsmobile Delta 88 350D, the Pallflex media met
the 98 percent filter efficiency standard with each bag and batch
combination, the low mean being 98.0 percent, the high mean being
99.2 percent, and the overall mean of 98.8 percent (with a standard
deviation of 0.4 percent).
These results indicate relatively consistent batch-to-batch
efficiency with Pallflex filters on multiple tests on a given
vehicle.
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Table 1
T60A20 Pallflex Filter Test Media
Peugeot 504D
Batches
3991E2
1092B
4009E2
Filter
^*
Bag 1
91.99
91.42
90.71
Efficiency
%
Bag 2
91.70
93.74
93.49
Standard
~ %
Bag 1
1.26
3.22
0.73
Oldsmobile
Batches
3991E2
1092B
4009E2
Note: Filter
Filter
***
Bag 1
98.01
99.06
98.96
Efficiency
%
Baj> 2
98.44
99.13
99.16
efficiencies calculated according
Standard
~ %
Bag 1
0.12
0.15
0.12
Deviation
Bag 2
2.55
2.32
0.45
350D
Deviation
Bag 2
0.49
0.09
0.49
to Section 86. 110-81 (c) (iv)
Number
Bag 1
5
2
2
Number
Bag 1
2
2
2
Federal
of Tests
Bag 2
5
2
2
of Tests
Bag 2
2
2
2
Register
Vol. 44, No. 23, February 1," 1979.
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Discussion and Conclusion
The results indicate that while batch-to-batch variability is
not expected to be a problem, some manufacturers may have diffi-
culty in achieving a 98 percent filter efficiency using the Pall-
flex T60A20 media. This means that it is possible that the filter
requirements, as specified in the NPRM, may be inequitable for
those manufacturers that can achieve 98 percent efficiency.
Therefore, some modifications to the test procedure may be re-
quired.
Possible options are:
1. Allow each manufacturer to select a filter of their
choice and require a demonstration of minimum performance. How-
ever, there is a major difficulty with this modification. EPA
would have to either use several different filter media types in
order to maintain lab-to-lab correlation, or choose one filter type
and let lab-to-lab correlation suffer. Neither are satisfactory.
2. Require a test-by-test efficiency correction based on one
or more back-up filters. There may be inherent difficulties with
this modification, also, as some researchers feel efficiency is
load dependent, and hence the back-up filter may be far less
efficient than the sample filter. There is then some uncertainty
associated with the efficiency of the back-up filter which would
have to be reconciled since its measurement cannot be ascertained
precisely in day-to-day certification testing.
3. Lower the minimum acceptable filter efficiency. However,
even with a reduction to as low as 95 percent, the Peugeot would
still have trouble when Pallflex T60A20 filter media is used.
While helpful, further modification would still have to be made.
4. Require a back-up filter during the certification test.
The combined weight of both filters would be used in determining
particulate emissions for those tests in which the calculated
efficiency is below the specified minimum. This modification has
the advantage of being relatively easy to use in day-to-day test-
ing.
Recommendation
On the basis of the above discussion, it is recommended that
the test procedure be modified in accordance with options 3 and 4
above. That is, the following changes to the test procedure are
recommended:
1. Require a back-up filter during actual certification
testing.
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2. Calculate the ratio of filter weights as indicated in the
light-duty diesel NPRM.
3. If the ratio is greater than 0.95, calculate particulate
emissions on the basis of the first filter net weight.
4. If the ratio is less than 0.95, calculate particulate
emissions on the basis of combined net weights of the first filter
and the back-up filter.
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