ASTM E908-98

1.1 This practice covers procedures for calibrating leak artifacts of a specified gas, that may be used for determining the response of leak detectors, or in other situations where a known small flow of gas is required. The purpose of this practice is to establish calibration without reference to other calibrated leaks in as straightforward a manner as possible using the likeliest available equipment. While the uncertainties associated with these procedures will most likely be greater than those obtained via traceable calibration chains (on the order of 10%), these procedures allow independent means of establishing or verifying the leakage rate from leak artifacts of questionable history, or when traceable leak artifacts are not available.

1.2 Two types of leaks are considered:

1.2.1 Type I -Pressure to vacuum.

1.2.2 Type II -Pressure to atmosphere.

1.3 Three calibration methods are described under each type of reference leak:

1.3.1 Method A -Accumulation comparison, using a known volume of gas at specified conditions of temperature and pressure as a reference.

1.3.2 Method B -Accumulation comparison, using a leak artifact calibrated using Method A.

1.3.3 Method C -Displacement of a liquid slug, by the leak, in capillary tube of known dimensions.

1.4 The values stated in inch-pound units are to be regarded as the standard. The metric equivalents of inch-pound units may be appropriate.

1.5 This standard does not purport to address 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.