ASTM F797-88(1993)

1.1 This practice guides the investigator into designing, and subsequently employing, a test where a feed stream, flowing at a constant rate, and after emerging from the filter medium as the filtrate is recirculated back to the feed tank while fresh, or make-up, test particles are continuously added to the feed tank.

1.2 The filter medium, held in an appropriate housing, may be a sheet of any sort of "flat stock," such as felt, paper, cloth, membrane, or porous metal. It may be any sort of porous material held in a cartridge, no matter how thick or what shape. But, this practice is not meant for preformed beds of filter aids, because the practice does not address the method of laying down the bed.

1.3 This practice addresses the methods of measuring the permeability of the filter medium, the efficiency with which it separates particles from the feed stream, and life, or capacity (see section on Descriptions of Terms). Expressions of filtration efficiency are derived from any, or all, of three, separate examinations of the liquid streams, that is, turbidity, mass concentration of suspended solids, and particle-size distributions.

1.4 The investigator is here reminded that test results, for a given filter medium, will change with a change in test particles, or a change in test liquid, or both. Indeed, test results can change with changes in the temperature of the liquid; and, if the liquid is water, results can change with a change in pH.

1.5 This practice is written with the view that the investigator has already decided what test liquid and test particles will be used to evaluate a given filter medium (or to compare one medium to others). The practice, then, instructs the investigator how to proceed, what to observe, and how to report results. This practice is presented to form the basis from which specific test methods will emerge, where those specific methods actually identify the test particles, the test liquid, and the test equipment.

1.6 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 whoever uses this standard to consult and establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.