Pressure Hold Integrity Testing
Last Updated: 8/2022
Applies to: Beverage producers using membrane filters (cartridge filters) prior to bottling/packaging. This article explains integrity testing and offers a pressure hold testing protocol.
WHAT IS INTEGRITY TESTING?
Integrity testing ensures the accuracy of absolute filtration media (ensures it is operating at its rated porosity/titer reduction rating). In other words, integrity testing validates that filtration media was not compromised before or during filtration. This is especially important if a filter is being used as a final sterile filtration step prior to bottling. Integrity testing is typically done immediately before bottling, and again after bottling to confirm that the membrane remained integral during the process.
There are three common manual tests used to assess the integrity of a membrane (cartridge) filter:
- Pressure Hold Test (best for single round membrane filters)
- Bubble Point Test (only for single round membrane filters)
- Pressure Diffusion Test (best and most accurate for both single and multiple round membrane filters)
WHAT IS A PRESSURE HOLD TEST?
The pressure hold test is a simplified version of the bubble point test and is most appropriate for integrity testing single round membrane filters*. During a pressure hold test:
- Filter media is wetted and water is held by capillary action within the pores of the filter media.
- Gas is applied to the upstream side of the filter at approximately 80% of the bubble point pressure while the outlet valve remains open.
- The filter passes the pressure hold test if the pressure does not drop more than 2 psi over a 10-minute period.
*Can you use the pressure hold test for multiple round filters?:
While pressure hold tests can be conducted on multiple round filters, be advised there is a masking effect that can occur. For example, if one cartridge/membrane has a hole in it, the others in a multiple round setup can compensate. This hides the fact that one might be letting air (and eventually microorganisms) through at a higher rate than the rest of the elements.
We only recommend conducting a pressure hold test on a multiple round filter if you are confident the cartridges underwent proper quality control during the manufacturing process. The only way to confirm integrity of multiple round filters is with a pressure diffusion test.
POTENTIAL PROBLEMS
The filter was improperly wetted
The filter may fail the integrity test if the filter media was not properly wetted prior to the test, ensuring all gas was expelled from filter pores. Repeat the wetting process and try the test again.
O-rings or valves were leaking
If the cartridge fails the pressure hold test, it may not mean the membrane is bad. Pressure may be leaking from O-rings that have been improperly seated or are cracking, or from faulty valves.
To determine if this is the problem, perform a pressure hold test on the housing by bringing the pressure up to 10 psi, closing the outlet valve, and waiting a couple minutes to see if the pressure drops. If so, please inspect all valves and gauges and refer to the housing exploded view drawing (found on the product page) to identify any O-rings that are not visible and may need replacing.
Pressure hold test was conducted at the wrong time
Pressure hold testing should be conducted only after
sterilization, especially when sterilizing with steam. Improper cooling of cartridges after steam sterilization can cause severe warping that affects the integrity of the membrane. Integrity testing after sterilization (and proper cool down) will identify this issue if it has occurred. Conduct a chemical sanitization after opening the housing for the integrity test.
Pressure Hold Testing Protocol
WARNING: Pressurized containers present a safety risk to operators. Ensure proper safety procedure and tools are used and in all cases regulator and approved vessels are utilized per local regulation and common safe practice.
Required materials:
- Filter and filter housing
- Compressed, filtered, oil-free air (nitrogen or argon, NOT CO2)
- Pressure regulator
- The gauge connected to the pressure regulator should have subdivisions of at least 0.5 psi and the capacity to measure up to 60 psi. A digital pressure gauge can also be used
Instructions:
- Record the filter part number(s), lot number, and product information. Also include physical observations.
- Properly wet the filter to be tested expelling all air from the filter membrane. This is simple but critical:
- Run water through the cartridge housing.
- Bring the back pressure up to 5 psi by slowly closing the outlet valve until your outlet pressure gauge reads 3-5 psi while your pump is running and water is flowing.
- Now vent the top to release any trapped air bubbles.
- Close the vent, open the outlet valve all the way. Repeat 2-3 times.
- Finally, stop the pump or switch off water source.
- Drain the water by opening the vents and valves. Close the inlet valve.
- Note: Do not use gas to drain the housing at this stage.
- Connect the gas source to the inlet port of the filter.
- Consult technical data sheet for pressure hold testing value (this is generally approximately 80% of the bubble point value).
- Starting from zero pressure, gradually increase the pressure (2 psi at a time) using the pressure regulator until the pressure hold value is reached.
- Note: The inlet pressure gauge should read the same value as the pressure gauge on the gas tank. If not, one or more of the gauges may be faulty.
- Once the pressure hold value has been reached, close the inlet valve and then turn off the gas source. The only valve open should be the outlet valve.
- If after 10 minutes the pressure holds and did not drop more than 2 psi, the cartridge has passed the integrity test.
- Record the date and pressure hold results in a log.
- If the test was conducted prior to bottling, proceed with a chemical sanitization. If it was conducted after bottling, proceed to standard cleaning steps.