TM-23, Determination of Equivalent Opening Size of Plastic Filter Cloth

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This method determines the equivalent opening size (EOS) of Plastic Filter Fabric. This test method is adapted from the Corps of Engineers Civil Works Construction Guide Specification CW-02215, dated November 1977, for Plastic Filter Fabric. Selection of Specimens

Select five specimens smaller than 10 in. x 10 in. from the sample. Procedure

Obtain 50 grams of each of the following fractions of standard glass beads. Within each size range, 98 percent of the beads shall be within the specified range.

Designated EOS Passing (U.S. Sieve No.) Retained on (U.S. Sieve No.)
40 35 40
50 45 50
70 60 70
100 80 100

Affix the fabric to a standard 8 in. sieve having openings larger than the largest bead to be used in the test. The fabric shall be attached to the sieve in such a manner that no beads can pass between the fabric and the sieve wall.

Starting with a fraction of beads that would permit more than 5 percent by weight to pass through the cloth, dry-sieve for 20 minutes with an automatic shaker. Sieve the successively coarser fractions until it is determined which fraction has 5 percent or less, by weight, passing the fabric.

The equivalent opening size (EOS) of a fabric sample is the "retained on" sieve size of the fraction of glass beads at which 5 percent or less, by weight, passes through the fabric. Reporting

Report the results as a sieve number, except when the EOS is outside the range of the glass bead fractions shown in EPG In such a case, report as "coarser than No. 40" or "finer than No. 100".