ASTM E128-99

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Designation:E128–99
Standard Test Method for
Maximum Pore Diameter and Permeability of Rigid Porous
1
Filters for Laboratory Use
This standard is issued under the fixed designation E 128; 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 4. Summary of Test Method
1.1 This test method covers the determination of maximum 4.1 Maximum Pore Diameter, is determined by immersing
pore diameter and permeability of rigid porous filters used in the filter in a suitable test liquid and applying air pressure until
the laboratory for filtration or diffusion. They are applicable to the first bubble of air passes through the filter. The maximum
filters made of sintered glass, ceramic, metal, or plastic. This pore diameter is calculated from the surface tension of the test
test method establishes a uniform designation for maximum liquid and the applied pressure.
pore diameter and also provides a means of detecting and 4.2 Permeability is determined by measuring the flow of
measuring changes which occur through continued use. air through the filter when subjected to a pressure differential.
1.2 This standard does not purport to address all of the
5. Apparatus
safety problems, if any, associated with its use. It is the
5.1 Because of the variety of shapes of apparatus in which
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica- porous filters are incorporated, the apparatus for this test
method is not specified in detail.Apparatus that has been found
bility of regulatory limitations prior to use.
satisfactory is illustrated in Fig. 1 and Fig. 2.
2. Referenced Documents
6. Procedure
2.1 ASTM Standards:
2
D 845 Specifications for Five-Degree Xylene 6.1 Maximum Pore Diameter—Thoroughly wet the clean
filter to be tested by soaking it in the prescribed test liquid (see
3. Terminology
Table 1). Connect the filter to a controllable source of clean,
3.1 Definitions: dry compressed air, and a manometer (Fig. 1). Immerse the
3.1.1 maximum pore diameter—the diameter in microme- filter just below the surface of the test liquid (Note 2) and
tres of a capillary of circular cross section that is equivalent gradually increase the air pressure at a rate of about 5 mm/min
(with respect to characteristics related to surface-tension ef- in the area of the test until the first dynamic bubble passes
fects) to the largest pore in the filter under consideration. through the filter and rises through the liquid. The appearance
of the first true dynamic bubble is readily recognized since it is
NOTE 1—It is recognized that the maximum pore diameter as defined
followed by a succession of additional bubbles. Read the
herein does not necessarily indicate the physical dimensions of the largest
pressure from the manometer. If the test is to be repeated,
pore in the filter, and furthermore, that the pores are highly irregular in
shape. Because of this irregularity in shape and other phenomena thoroughly re-wet the filter by soaking it in the test liquid,
characteristic of filtration, a filter may be expected to retain all particles
before proceeding with the retest. Calculate the maximum pore
larger than the maximum pore diameter as defined and determined by this
diameter from the following equation (see Appendix X1 for
test method, and will generally retain particles which are much smaller
derivation):
than the determined diameter.
D 5 30g/p (1)
3.1.2 permeability—the flow of air, in millimetres per
minute per square centimetre of filter area per 1 cm of water
where:
pressure differential. D 5 maximum pore diameter as defined in 3.1.1,
g5 surface tension of test liquid in dynes/cm at the
temperature of the test, and
1
This test method is under the jurisdiction of ASTM Committee E-41 on
p 5 pressure, mm Hg (Note 3).
Laboratory Apparatus and is the direct responsibility of Subcommittee E 41.05 on
Filtration Materials. The uniformity of distribution of pores approaching the
Current edition approved May 10, 1999. Published August 1999. Originally
maximum pore size may be observed by gradually increasing
published as E 128 – 57 T. Last previous edition E 128 – 94.
the air pressure and noting the uniformity with which streams
2
Discontinued, see 1981 Annual Book of ASTM Standards, Part 29.
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E128
NOTE 1—For tests on filter-type crucibles, use a standard rubber crucible adapter. For test sticks and candles a rubber stopper with a rub
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