ASTM F778-88(1993)
(Test Method)Standard Methods for Gas Flow Resistance Testing of Filtration Media
Standard Methods for Gas Flow Resistance Testing of Filtration Media
SCOPE
1.1 The flow resistance of any fabricated filter device will depend on the flow resistance of the media used.
1.2 This standard offers procedures sufficient to determine the gas flow characteristics of flat specimens of media used in the filtration process. The methods are extended to include pleated specimens and bulk media as well.
1.3 In all cases, flow rates through the specimen are determined in accordance with procedures outlined in ASME "Fluid Meters." The test fluid is air.
1.4 This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety problems associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: F 778 – 88 (Reapproved 1993)
Standard Methods for
Gas Flow Resistance Testing of Filtration Media
This standard is issued under the fixed designation F 778; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 2.2 ASME Document:
“Fluid Meters,” Sixth Edition, 1971
1.1 The flow resistance of any fabricated filter device will
depend on the flow resistance of the media used.
3. Terminology
1.2 This standard offers procedures sufficient to determine
3.1 Definitions—Those definitions appropriate for this stan-
the gas flow characteristics of flat specimens of media used in
dard will be adopted from the F-21 committee approved
the filtration process. The methods are extended to include
submission from Subcommittee F21.92 on Definitions.
pleated specimens and bulk media as well.
3.2 Definitions of Terms Specific to This Standard:
1.3 In all cases, flow rates through the specimen are
3.2.1 air density, r—mass per unit volume.
determined in accordance with procedures outlined in ASME
3.2.2 air flow resistance, DP—pressure drop or pressure
“Fluid Meters.” The test fluid is air.
differential across a test specimen of filter medium at a
1.4 This standard may involve hazardous materials, opera-
specified air face velocity or mass flow rate.
tions, and equipment. This standard does not purport to
3.2.3 constituted bulk media—those types of filter media
address all of the safety problems associated with its use. It is
formed from bonded aggregates or discrete solid materials.
the responsibility of the user of this standard to establish
3.2.4 edge leakage—air flow that passes into or bypasses
appropriate safety and health practices and determine the
the test specimen in geometric planes other than those intended
applicability of regulatory limitations prior to use.
for resistance measurement.
2. Referenced Documents 3.2.5 face area, A— cross-sectional area perpendicular to
air flow at the specimen test boundary.
2.1 ASTM Standards:
D 461 Method of Testing Felt
NOTE 1—If specimen inlet and exit face areas are different, “Inlet” or
D 585 Methods for Sampling and Accepting a Single Lot of
“Exit” shall be used to describe the face area in question.
Paper, Paperboard, Fiberboard, or Related Product
3.2.6 face velocity, V— volumetric flow rate per unit face
D 645 Test for Thickness of Paper and Paperboard
area.
D 685 Method for Conditioning Paper and Paper Products
NOTE 2—If specimen inlet and exit face areas are different, “Inlet” or
for Testing
2 “Exit” shall be used to describe the face velocity in question.
D 737 Test Method for Air Permeability of Textile Fabrics
D 1776 Practice for Conditioning Textiles For Testing 3.2.7 mass rate of flow, m˙ —mass transport of air per unit
time through the test specimen.
D 1777 Method for Measuring Thickness of Textile Mate-
rials 3.2.8 medium area, A —total area of filtration media ex-
m
D 2905 Practice for Statements on Number of Specimens posed to air flow.
for Textiles
NOTE 3—Medium area may be greater than face area due to pleating,
D 3574 Methods of Testing Flexible Cellular Materials—
folding, etc.
Slab, Bonded, and Molded Urethane Foam
3.2.9 medium velocity, V —volumetric flow rate per unit
m
E 105 Practice for Probability Sampling of Materials
medium area.
E 122 Practice for Choice of Sample Size to Estimate the
3.2.10 normalized resistance, sDP—product of sigma and
Average Quality of a Lot or Process
measured air flow resistance.
3.2.11 sigma, s—ratio of air density existing at test condi-
tions to standard air density. Density at standard conditions is
These methods are under the jurisdiction of ASTM Committee D22 on
3 3
Sampling and Analysis of Atmospheres and are the direct responsibility of Subcom-
taken to be 0.075 lb/ft (1.201 kg/m ).
mittee D22.09 on ISO TAG for ISO/TC 146.
3.2.12 unconstituted bulk media—those types of filter me-
Current edition approved Jan. 29, 1988. Published March 1988. Originally
dia formed from unbonded aggregates or discrete solid mate-
published as F 788 – 82. Last previous edition F 788 – 82.
Annual Book of ASTM Standards, Vol 07.01.
rials.
Annual Book of ASTM Standards, Vol 15.09.
Discontinued, see 1981 Annual Book of ASTM Standards, Part 20.
5 7
Annual Book of ASTM Standards, Vol 09.02. Available from American Society of Mechanical Engineers, 345 E. 47th St.,
Annual Book of ASTM Standards, Vol 14.02. New York, NY 10017.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
F 778
3.2.13 volumetric rate of flow, Q—air volume transport per ment, and research, a multiple-point flow regime may be
unit time through the test specimen. necessary.
4. Summary of Methods 6. General Requirements
4.1 The testing outlined in this standard consists of measur- 6.1 Instrument Accuracy:
ing air-flow resistance (pressure drop) across a specimen of 6.1.1 The procedures of these methods require measurement
known geometry at one or more air-flow rates. Alternatively, of pressure drop and either volumetric or mass flow rate.
the flow rate may be measured at one or more values of 6.1.2 Pressure drop is a direct measurement. Unless stated
air-flow resistance across the specimen. In either case, test
otherwise in the data report, instrumentation such as manom-
results are reported as single or multiple data point ordered eters shall be selected so as to measure pressure within 63%
pairs of (resistance, face velocity).
of the indicated value. Instruments shall be checked against a
4.2 For many specimens, the air-flow resistance at flow rates traceable standard.
of interest is of sufficient magnitude that changes in air density
6.1.3 Flow rate is generally a derived quantity obtained
across the specimen may not be ignored, or the airflow from computations involving a differential pressure type ele-
resistance is not linear with face velocity. In these cases,
ment and flowmeter air density. In other cases, flow rate may
ordered pairs of (normalized resistance, mass flow) are re- be obtained from some kind of direct-reading instrument such
ported rather than ordered pairs of (resistance, face velocity).
as a turbine-type flow meter. Whether read directly or com-
4.3 To provide for quality control application, statistical puted, flow rate shall be determined to within 63 %, unless
procedures are outlined to guide in the selection of a multiple
stated otherwise in the data report. This value shall be checked
number of specimens. using a flow prover with traceable accuracy.
4.4 Two test methods involving substantially different test 6.2 Test Apparatus Environment—Effects of environmental
techniques are presented. conditions on the test air viscosity need to be examined to
4.4.1 Method A—A general method applicable to all filtra- ensure duplication of test results.
tion media and forms of media: flat, pleated, constituted, and 6.2.1 Temperature—Air viscosity increases as temperature
unconstituted bulk media; small cartridge-type specimens. The increases at a rate which, at 20°C, is approximately 0.15 %/°C.
test technique consists simply of mounting a specimen in a Seasonal changes could reflect a temperature differential of
holder and applying air flow. 30°C and result in the apparent flow resistance error of 4.5 %.
4.4.2 Method B—A limited method applying particularly to
Temperature control must be provided.
nondestructive testing of sheets of material that either edge 6.2.2 Pressure—The American Institute of Physics Hand-
leak or substantially deform when using the simple clamping
book, 2nd Edition, gives the pressure increment of air viscosity
approaches of Method A. The technique for Method B is based at 20°C and 1 atm as 0.1224 μp or a possible 0.67 % error per
on the “guarded cylinder” principle and requires a concentric
atmosphere. No precaution is necessary.
cylinder specimen holder, plus provision for two individually 6.2.3 Humidity—The ASHRAE Handbook of Fundamentals
adjustable air flows (See Section 15 and Fig. 1.) In the
in the chapter on Psychrometrics reveals that even for the
implementation of Method B, a parallel, evenly distributed air extreme case of saturated air at 100°F there is not a significant
flow is perpendicularly directed through a specimen subdivided
viscosity difference from that of dry air. No precaution is
into concentric guard and measuring area sections. The two necessary. However, humidity control is required in specimen
areas have separate downstream air chambers. To obtain a
preparation. See Section 10.
(resistance, face velocity) data point, the appropriate volumet-
7. Sampling
ric flow rate is established through the measuring area. The
7.1 The sample to be tested as a flat media, pleated media,
guard area volumetric flow rate is then established so that the
differential pressure between guard and measuring area cham- or bulk media should be obtained under the guidance of the
particular standard or specification covering the generic mate-
bers is zero on the downstream side of the specimen. Pressure
drop is then read for flow through the specimen measuring rial or as agreed upon between the purchaser and seller.
area. Guard area flow rate need not be determined.
8. Number of Specimens
5. Significance and Use
8.1 Practice D 2905 covers six recommendations for deter-
5.1 The air-flow resistance (pressure drop) of a filter is an mining the number of specimens necessary to elucidate the
important parameter that can assist in characterizing the average quality of a material under various conditions. The
physical make-up as well as the utility of a filter. choice of the six recommendations to be used in a specific
5.2 Therefore, flow characteristics of clean filter media can method will depend on the purpose of the test and the available
be used for quality control, product development, and basic information.
research. It may be used by the producer of filter media to 8.2 The recommendations in Practice D 2905 describe two
illustrate media type or to meet product specification and can conditions:
be used by the consumer as a criterion for media selection. 8.2.1 The procedure to follow when the user has a reliable
5.3 These methods may also be used for acceptance testing. estimate of the variability of the method in his own laboratory;
5.4 For purposes of quality control, meeting product speci- and,
fication, or acceptance testing, a single-point flow regime on 8.2.2 When the user does not have a reliable estimate of the
multiple samples is adequate. However, for design, develop- variability of the method in his own laboratory.
F 778
FIG. 1 System for Measuring Air-flow Resistance of Specimens with Moderate Pressure Drops
8.3 If the laboratory has a reliable estimate of variation
99 2.326 5.410 2.576 6.636
expressed either as a standard deviation or as a coefficient of
variation, then the number of specimens could be determined
E = the allowable variation of the test results expressed in
by the following equations:
the same units as s, and
2 2 2
n 5 ~t 3 s !/E
A = the allowable variation of the test results expressed as
2 2 2
a percent of the average.
n 5 ~t 3 v !/A
8.4 Criterion for the selection of the appropriate procedure
where:
hinges on: (1) choosing between s or n as the measure of
n = number of test specimens required, rounded to the next
variability; (2) choosing a one-sided or two-sided limit for the
higher whole number,
property being measured; and, (3) if no variation data are
s = standard deviation of individual observations expressed
available, arbitrarily decide on the number of specimens
in the appropriate units,
dictated by the type and character of the material. For more
n = coefficient of variation of individual observations ex-
details, refer to Section 5 of Practice D 2905.
pressed as percent of the average,
n = 100 s/ x¯, and
9. Conditioning of Test Specimens
x¯ = average of all the observations for a specific material
9.1 Because many of the materials used in filter media
t = a constant depending upon the desired probability level
undergo physical changes with changes in temperature and
and equal to Student’s t for infinite degrees of freedom,
moisture, it is usually desirable to expose the test specimen to
for example:
a standard conditioned atmosphere for a period of time before
Probability Level, % One-sided Limits Two-Sided Limits
2 2 testing is initiated.
tt tt
90 1.282 1.644 1.645 2.706 9.2 Those materials which are considered to be textiles or
95 1.645 2.706 1.960 3.842
textile-like (woven, knitted, or nonwoven fabrics; fiber batts or
F 778
mats; or coated fabrics) should be conditioned as specified by 11.1.3 Pleated Specimens—Positive end sealing of pleats is
Practice D 1776. The standard atmosphere for this Practice is a required. Three suggested mounting schemes are delineated in
relative humidity of 65 6 2 % and a temperature of 21 6 1°C Annex A2.
(70 6 2°F). When international testing is involved, a relative
11.1.4 Bulk Media—Air-flow resistance of bulk media is
humidity of 65 6 2 % and a temperature of 20 6 2°C may be
materially affected by the packing method used. It is a
used.
requirement that the packing procedure be fully documented in
9.3 Those materials which are considered to be paper or
any test of these materials (see Section 18).
paper-like should be conditioned as specified by Method
11.2 Specimen Area—Specimen size shall be dictated by the
D 685. The standard atmosphere for this Practice is a relative
prevailing practice for the class of materials under test.
2 2
humidity of 50 6 2 % and a temperature of 23 6 1°C (73.4 6
Examples are 5.94 in. (38.32 cm ) for papers and paperlike
2 2
1.8°F).
materials and 15.5 in. (100 cm ) for blanket-like materials. In
9.4 The time duration required for conditioning should be
no case shall test specimen size for flat media be less than 5.94
2 2
that necessary for the test specimen to attain equilibrium with
in. (38.32 cm ). Specimens may be rectangular or round;
the conditioning atmosphere. This is considered to have
however, rectangular specimens with length to width ratios
occurred when the change in the mass of the specimen in
different by more than 2:1 are to be avoided.
successive weighings made at intervals of not less than 2 h,
11.3 Measurement of Pressure and Pressure Drop:
does not exceed 0.2 % of the mass of the specimen.
11.3.1 Pressure tap location can materially affect test values
9.5 At times, it may be judged inappropriate to condition the
for some kinds
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