ASTM F778-88(2007)
(Test Method)Standard Methods for Gas Flow Resistance Testing of Filtration Media
Standard Methods for Gas Flow Resistance Testing of Filtration Media
SIGNIFICANCE AND USE
The air-flow resistance (pressure drop) of a filter is an important parameter that can assist in characterizing the physical make-up as well as the utility of a filter.
Therefore, flow characteristics of clean filter media can be used for quality control, product development, and basic research. It may be used by the producer of filter media to illustrate media type or to meet product specification and can be used by the consumer as a criterion for media selection.
These methods may also be used for acceptance testing.
For purposes of quality control, meeting product specification, or acceptance testing, a single-point flow regime on multiple samples is adequate. However, for design, development, and research, a multiple-point flow regime may be necessary.
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.
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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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:F778 −88(Reapproved 2007)
Standard Methods for
Gas Flow Resistance Testing of Filtration Media
ThisstandardisissuedunderthefixeddesignationF778;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal
adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope D3574 Test Methods for Flexible Cellular Materials—Slab,
Bonded, and Molded Urethane Foams
1.1 The flow resistance of any fabricated filter device will
E105 Practice for Probability Sampling of Materials
depend on the flow resistance of the media used.
E122 Practice for Calculating Sample Size to Estimate,With
1.2 This standard offers procedures sufficient to determine
Specified Precision, the Average for a Characteristic of a
the gas flow characteristics of flat specimens of media used in
Lot or Process
the filtration process. The methods are extended to include
2.2 ASME Document:
pleated specimens and bulk media as well.
“Fluid Meters,” Sixth Edition, 1971
1.3 In all cases, flow rates through the specimen are
3. Terminology
determined in accordance with procedures outlined in ASME
3.1 Definitions of Terms Specific to This Standard:
“Fluid Meters.” The test fluid is air.
3.1.1 air density, ρ—mass per unit volume.
1.4 This standard may involve hazardous materials,
3.1.2 air flow resistance, ∆P—pressure drop or pressure
operations, and equipment. This standard does not purport to
differential across a test specimen of filter medium at a
address all of the safety problems associated with its use. It is
specified air face velocity or mass flow rate.
the responsibility of the user of this standard to establish
appropriate safety and health practices and determine the
3.1.3 constituted bulk media—those types of filter media
applicability of regulatory limitations prior to use.
formed from bonded aggregates or discrete solid materials.
3.1.4 edge leakage—airflowthatpassesintoorbypassesthe
2. Referenced Documents
test specimen in geometric planes other than those intended for
2.1 ASTM Standards:
resistance measurement.
D461 Test Methods for Felt (Withdrawn 2003)
3.1.5 face area, A—cross-sectionalareaperpendiculartoair
D585 Practice for Sampling and Accepting a Single Lot of
flow at the specimen test boundary.
Paper, Paperboard, Fiberboard, and Related Product
(Withdrawn 2010) NOTE 1—If specimen inlet and exit face areas are different, “Inlet” or
“Exit” shall be used to describe the face area in question.
D645/D645M Test Method for Thickness of Paper and
Paperboard (Withdrawn 2010) 3.1.6 face velocity, V— volumetric flow rate per unit face
D685 Practice for Conditioning Paper and Paper Products area.
for Testing (Withdrawn 2010)
NOTE 2—If specimen inlet and exit face areas are different, “Inlet” or
D737 Test Method for Air Permeability of Textile Fabrics
“Exit” shall be used to describe the face velocity in question.
D1776 Practice for Conditioning and Testing Textiles
3.1.7 mass rate of flow, m˙—mass transport of air per unit
D1777 Test Method for Thickness of Textile Materials
time through the test specimen.
D2905 Practice for Statements on Number of Specimens for
3.1.8 medium area, A —total area of filtration media ex-
m
Textiles (Withdrawn 2008)
posed to air flow.
1 NOTE 3—Medium area may be greater than face area due to pleating,
These methods are under the jurisdiction of ASTM Committee D22 on Air
folding, etc.
Quality and are the direct responsibility of Subcommittee D22.03 on Ambient
Atmospheres and Source Emissions.
3.1.9 medium velocity, V —volumetric flow rate per unit
m
Current edition approved April 1, 2007. Published June 2007. Originally
medium area.
approved in 1982. Last previous edition approved in 2001 as F778 - 88(2001). DOI:
10.1520/F0778-88R07.
3.1.10 normalized resistance, σ∆P—product of sigma and
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
measured air flow resistance.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. Available from American Society of Mechanical Engineers (ASME), ASME
The last approved version of this historical standard is referenced on International Headquarters, Three Park Ave., New York, NY 10016-5990, http://
www.astm.org. www.asme.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F778−88 (2007)
3.1.11 sigma, σ—ratio of air density existing at test condi- ordered pairs of (normalized resistance, mass flow) are re-
tions to standard air density. Density at standard conditions is ported rather than ordered pairs of (resistance, face velocity).
3 3
taken to be 0.075 lb/ft (1.201 kg/m ).
4.3 To provide for quality control application, statistical
3.1.12 unconstituted bulk media—thosetypesoffiltermedia
procedures are outlined to guide in the selection of a multiple
formed from unbonded aggregates or discrete solid materials.
number of specimens.
3.1.13 volumetric rate of flow, Q—air volume transport per
4.4 Two test methods involving substantially different test
unit time through the test specimen.
techniques are presented.
4.4.1 Method A—A general method applicable to all filtra-
4. Summary of Methods
tion media and forms of media: flat, pleated, constituted, and
4.1 The testing outlined in this standard consists of measur-
unconstituted bulk media; small cartridge-type specimens. The
ing air-flow resistance (pressure drop) across a specimen of
test technique consists simply of mounting a specimen in a
known geometry at one or more air-flow rates. Alternatively,
holder and applying air flow.
the flow rate may be measured at one or more values of
4.4.2 Method B—A limited method applying particularly to
air-flow resistance across the specimen. In either case, test
nondestructive testing of sheets of material that either edge
results are reported as single or multiple data point ordered
leak or substantially deform when using the simple clamping
pairs of (resistance, face velocity).
approaches of MethodA.The technique for Method B is based
4.2 Formanyspecimens,theair-flowresistanceatflowrates on the “guarded cylinder” principle and requires a concentric
of interest is of sufficient magnitude that changes in air density cylinder specimen holder, plus provision for two individually
across the specimen may not be ignored, or the airflow adjustable air flows (See Section 15 and Fig. 1.) In the
resistance is not linear with face velocity. In these cases, implementation of Method B, a parallel, evenly distributed air
FIG. 1 System for Measuring Air-flow Resistance of Specimens with Moderate Pressure Drops
F778−88 (2007)
flowisperpendicularlydirectedthroughaspecimensubdivided 6.2.3 Humidity—TheASHRAE Handbook of Fundamentals
into concentric guard and measuring area sections. The two in the chapter on Psychrometrics reveals that even for the
areas have separate downstream air chambers. To obtain a extreme case of saturated air at 100°F there is not a significant
(resistance, face velocity) data point, the appropriate volumet- viscosity difference from that of dry air. No precaution is
ric flow rate is established through the measuring area. The necessary. However, humidity control is required in specimen
guard area volumetric flow rate is then established so that the preparation. See Section 10.
differential pressure between guard and measuring area cham-
7. Sampling
bers is zero on the downstream side of the specimen. Pressure
drop is then read for flow through the specimen measuring
7.1 The sample to be tested as a flat media, pleated media,
area. Guard area flow rate need not be determined.
or bulk media should be obtained under the guidance of the
particular standard or specification covering the generic mate-
5. Significance and Use
rial or as agreed upon between the purchaser and seller.
5.1 The air-flow resistance (pressure drop) of a filter is an
8. Number of Specimens
important parameter that can assist in characterizing the
8.1 Practice D2905 covers six recommendations for deter-
physical make-up as well as the utility of a filter.
mining the number of specimens necessary to elucidate the
5.2 Therefore, flow characteristics of clean filter media can
average quality of a material under various conditions. The
be used for quality control, product development, and basic
choice of the six recommendations to be used in a specific
research. It may be used by the producer of filter media to
method will depend on the purpose of the test and the available
illustrate media type or to meet product specification and can
information.
be used by the consumer as a criterion for media selection.
8.2 The recommendations in Practice D2905 describe two
5.3 These methods may also be used for acceptance testing.
conditions:
8.2.1 The procedure to follow when the user has a reliable
5.4 For purposes of quality control, meeting product
estimate of the variability of the method in his own laboratory;
specification, or acceptance testing, a single-point flow regime
and,
on multiple samples is adequate. However, for design,
8.2.2 When the user does not have a reliable estimate of the
development, and research, a multiple-point flow regime may
variability of the method in his own laboratory.
be necessary.
8.3 If the laboratory has a reliable estimate of variation
6. General Requirements
expressed either as a standard deviation or as a coefficient of
variation, then the number of specimens could be determined
6.1 Instrument Accuracy:
by the following equations:
6.1.1 Theproceduresofthesemethodsrequiremeasurement
2 2 2
of pressure drop and either volumetric or mass flow rate. n 5 ~t 3s !/E
6.1.2 Pressure drop is a direct measurement. Unless stated 2 2 2
n 5 ~t 3v !/A
otherwise in the data report, instrumentation such as manom-
where:
eters shall be selected so as to measure pressure within 63%
n = number of test specimens required, rounded to the next
of the indicated value. Instruments shall be checked against a
higher whole number,
traceable standard.
s = standard deviation of individual observations expressed
6.1.3 Flow rate is generally a derived quantity obtained
in the appropriate units,
from computations involving a differential pressure type ele-
ν = coefficient of variation of individual observations ex-
ment and flowmeter air density. In other cases, flow rate may
pressed as percent of the average,
be obtained from some kind of direct-reading instrument such
ν = 100 s/x¯, and
as a turbine-type flow meter. Whether read directly or
x¯ = average of all the observations for a specific material
computed, flow rate shall be determined to within 63%,
t = a constant depending upon the desired probability level
unless stated otherwise in the data report. This value shall be
and equal to Student’s t for infinite degrees of freedom,
checked using a flow prover with traceable accuracy.
for example:
6.2 Test Apparatus Environment—Effects of environmental
Probability Level, % One-sided Limits Two-Sided Limits
2 2
conditions on the test air viscosity need to be examined to tt tt
90 1.282 1.644 1.645 2.706
ensure duplication of test results.
95 1.645 2.706 1.960 3.842
6.2.1 Temperature—Air viscosity increases as temperature
99 2.326 5.410 2.576 6.636
increases at a rate which, at 20°C, is approximately 0.15 %/°C.
E = the allowable variation of the test results expressed in
Seasonal changes could reflect a temperature differential of
the same units as s, and
30°C and result in the apparent flow resistance error of 4.5 %.
A = the allowable variation of the test results expressed as a
Temperature control must be provided.
percent of the average.
6.2.2 Pressure—The American Institute of Physics
Handbook, 2nd Edition, gives the pressure increment of air 8.4 Criterion for the selection of the appropriate procedure
viscosity at 20°C and 1 atm as 0.1224 µp or a possible 0.67 % hinges on: (1) choosing between s or ν as the measure of
error per atmosphere. No precaution is necessary. variability; (2) choosing a one-sided or two-sided limit for the
F778−88 (2007)
property being measured; and, (3) if no variation data are that mounting techniques be selected which eliminate edge
available, arbitrarily decide on the number of specimens leakage, yet do not deform the medium to the extent that
dictated by the type and character of the material. For more air-flow resistance is affected.
details, refer to Section 5 of Practice D2905.
11.1.2 Flat Media—For flat filtration media in particular, it
is desirable to use simple clamping techniques such as sug-
9. Conditioning of Test Specimens
gested in Annex A1 instead of more elaborate specimen
9.1 Because many of the materials used in filter media preparation.Absence of edge leakage or clamping deformation
effects for simple clamping or both, shall be demonstrated for
undergo physical changes with changes in temperature and
moisture, it is usually desirable to expose the test specimen to each new combination of material and clamping method used.
To do this, the new combination of material and simple
a standard conditioned atmosphere for a period of time before
clamping method shall be tested; then the same specimen shall
testing is initiated.
be retested with edge sealing and spacer bar of equivalent
9.2 Those materials which are considered to be textiles or
thickness to the test specimen. No change in resistance shall be
textile-like (woven, knitted, or nonwoven fabrics; fiber batts or
noted.
mats; or coated fabrics) should be conditioned as specified by
11.1.3 Pleated Specimens—Positive end sealing of pleats is
Practice D1776. 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-likeshouldbeconditionedasspecifiedbyMethodD685.
ThestandardatmosphereforthisPracticeisarelativehumidity 11.2 Specimen Area—Specimen size shall be dictated by the
prevailing practice for the class of materials under test.
of 50 6 2 % and a temperature of 23 6 1°C (73.4 6 1.8°F).
2 2
Examples are 5.94 in. (38.32 cm ) for papers and paperlike
...
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