To successfully perform a Water Intrusion Test (WIT), the entire length of the filter has to be covered by (submerged in) water for the duration of the test.
During pressurization of the filter housing assembly to the water intrusion test pressure, the water level drops upstream of the filter. The reason is due to compression of the membrane pleats and elimination of gas bubbles during initial pressurization.
This can leave a portion of the filter exposed to pressurized air, which will freely flow through the exposed area and result in a false test failure.
To troubleshoot the cause of a test failure, Pall recommends:
· To refill the filter housing with water and repeat the test, or
· Before the test, increase the upstream volume, to have more water above the filter, to compensate for the reduced water levels resulting from the compression.
For more information, please see Pall Publication, USD 3033 Application Note: Best Practices for Successful Filter Integrity Testing Using the Water Intrusion Test (WIT) Method