Pressure Decay Testing. Why, When, and How?
A simpler integrity test for less critical applications is a Pressure Decay Test. This requires the same air (or nitrogen) source and an accurate pressure gauge but does not require a mass flow meter. This type of test can be performed before and after use and is sensitive enough to detect very small leaks.
All test procedures outlined below should be followed when performing pressure decay testing of cartridge filters. The schematic below represents a cartridge integrity test set up with all of the piping, valves, gauges, and regulators needed to properly integrity test filters in place.
NOTE: This blog and the schematics in it show a filter housing with a single 10” cartridge installed. Different length cartridges can be accommodated using the appropriately sized housing that will also match the end configuration on the cartridge. Contact CPF Customer Service for additional details on multi-filter housing installation.
integrity test parameters
|Pore Size (µm)||Bubble point (psi)||Pressure Decay1 / Diffusion2 Test Pressure (psi)|
* Bubble Point exceeds maximum operating parameters
1Pressure Decay Test Formula
DP = D * T * Pa / V
DP = Maximum allowable Pressure Drop; (starting pressure – final pressure at end of test interval)
D = Diffusion Rate limit; (from cartridge data sheet)
T = Time (minutes); typically, 10 minutes
Pa = Atmospheric Pressure (14.7 psi)
V = Upstream Volume of test apparatus (cc); Can be calculated by filling the upstream side with water, then draining through V2 and measuring water volume
2Diffusion specification values are shown on the Data Sheet for the cartridge being tested
- ALL connections must be airtight. Any leaks in the plumbing can cause inaccurate readings. It is recommended to leak-check the system on a regular basis.
- Marginal integrity failures can often be the result of inadequate cartridge wetting. As indicated in the instructions below, re-wet the module and retest.
- Gross failures could be the result of an improperly installed cartridge in the housing or a plumbing leak. Make sure the cartridge is properly installed with any O-Rings undamaged and properly seated. Check the system for air leaks.
Cartridge Installation & Wetting
- Make sure all parts required to install the cartridge in the housing are available
- Install the cartridge in the housing, ensuring all fittings and connections are tight
- If a pre-wetted cartridge is being tested, skip to the appropriate integrity test section
- To wet out a cartridge:
- Make sure all valves are closed
- Connect feed water to the “Water In” line
- Open valves V3 (Vent) and V4 (outlet)
- Slowly open V1 to allow wetting fluid to enter the housing
- Once the fluid is observed coming out of the vent with no bubbles, close V3
- Adjust V1 as necessary to feed ~2 liters per minute per 10” length
- Allow fluid to flow for ten (10) minutes
- Slowly close V4 until inlet pressure (P2) reads 15 – 20 psi
- Allow fluid to flow for an additional five (5) minutes
- Close V1
- Open V2 and V3 to allow housing to drain
Pressure decay procedure
- Install the cartridge into the housing
- Follow wetting instructions if necessary
- Start with all valves closed
- Connect regulated air or nitrogen line to V6
- Open valves V2 (Drain), V3 (Vent), and V4 (outlet)
- Set pressure regulator to 2 psi
- Open V6, then V5
- Allow the system to purge any upstream fluid
- When the flow from Vent and Drain is mostly air, close V2 and V3
- Slowly increase the air pressure (pressure reading on P3) to the value specified in the table
- Close valve V5
- Allow the system to stabilize for 2 minutes
- Re-pressurize if necessary by opening V5
- Read pressure on P3 at end of test time (typically 10 minutes)
- Cartridge passes the integrity test when the pressure drop is less than the calculated amount
- Relieve pressure at the regulator
- Close valves V6 and V5
- Open valve V3 to completely relieve upstream pressure
- Remove the cartridge from the housing
If the cartridge appears to fail the initial test, repeat the Cartridge Wetting procedure and increase the rinse time to twice the initial amount to assure that the media has been properly wetted. Then, retest. If necessary, check the cartridge seal in the housing.
Critical Process Filtration, Inc., an ISO 9001 certified manufacturer of process filters has been helping customers for over 20 years to build and improve process filtration systems. Proven products, technical services and support, fast shipping, and very competitive pricing assure companies of getting the best value and expertise. Our comprehensive testing & analysis and validation services support your team whenever they need it. Partnering with your process team is how we deliver your company’s solution right the first time. For more information on Integrity Testing in your process, contact us here.