The pressure hold/drop integrity test; its correlation to diffusive flow

A M Trotter, T H Meltzer
PDA Journal of Pharmaceutical Science and Technology 1998, 52 (4): 182-5
The pressure-drop/hold procedure enables the diffusive flow integrity testing of filters to be performed without breaching the system downstream of the filter. It is not necessary to measure volumetrically the diffused gas on the downstream side of the filter. By means of pressure transducers the pressure loss is determined upstream; thus eliminating the threat of sepsis due to down-stream invasions. The pressure decay exercise can be used to characterize the various filter types. A constancy of filter manufacture is required for a given filter type. Unless the pressure drop exceeds the value established as the maximum allowable decay, the filter is judged to be integral. It qualifies as a sterilizing grade filter. Excessive pressure decays will also eventuate from leaks, as from improperly sealed housings. Performed prior to the filtration, the procedure serves to eliminate the wasteful use of an imperfect system, whether caused by faulty sealing, incorrect filter type or flawed filters. Where leaks are detected, the filter can be reexamined for its integrity. To enable the pressure-drop procedure to serve as an integrity test, the measured pressure decays require being correlated with organism retention data. This is made possible by the arithmetic conversion of the pressure decay curve into the conventional diffusive airflow curve established to have such a correlation. The transformation of the pressure-drop curve into the differential airflow plot is automatically performed by certain of the automated integrity test machines. These devices, utilizing pressure transducers, are capable of measuring small pressure drops with requisite sensitivity; gauges commonly are not. Moreover, as previously stated, the measurements are advantageously made on the upside of the filter. The use of automated test machines is, therefore, recommended for the performance of the pressure hold/drop integrity test in furtherance of the practice of filter integrity testing.

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