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Filter Cartridge Integrity Test Methods

Source: tianshan Author: tianshan Release time:2015-11-27

1.Bubble Point Test:
       When the filter membrane is wetted completely by the liquid, liquid will be reserved within a membrane under the effect of surface tension. If you want to squeeze the liquid out from the membrane holes, more external pressure will be needed, the minimum required gas pressure is the so-called bubble point pressure. Bubble point test is one of the most widely used integrity test method.

Bubble point value calculation formula:

P=4×K×ϒ×Cosθ/D

       PS: P is the pressure differential across the membrane, K is the membrane pore shape factor, Υ is medium surface tension, θ is the contact angle of wetting, D is pore diameter.


2.Diffusion flow test:
       When the membrane is fully wetted by the test media, pressure differential on both sides of the membrane is less than the bubble point pressure value (usually 80% of the membrane bubble point value), macroscopic gas will be blocked by the
capillary surface tension, but under the effect of pressure gradient, the high voltage side of the gas will released in the low voltage side in the form of diffusion through the pores of the liquid. The gas flow in the low-pressure side is called diffusion flow. Diffusion flow can evaluate the effectiveness of the membrane pore intercept, and also an important method to assess the integrity of the filter element.

Diffusion flow calculation formula:

DF=K×A×(P1 – P2)×ρ/H

       PS: K is the diffusion constant, A is the effective porosity of the micro membrane, H is the wet membrane thickness, ρ is the gas solubility in the liquid, P1 is the high voltage side pressure, P2 is the low voltage side pressure

       Diffusion flow test methods:

       1. Pressure attenuation: exerting high pressure gas in fully wetted filter cartridge,cutting off gas source after stable pressure, according to ideal gas state equation PV = NRT , the diffusion flow of gas in this pressure range can be calculated

2.Flow test: applying completely wet filter upstream pressure gas, keeping the pressure in constant state ,the traffic of diffusion flow will be directly tested in downstream of the filter cartridge.

       2.Water intrusion method: water intrusion method is developed based on the phenomenon of surface tension and capillary water presented in the hydrophobic membrane surface. Requirement of the minimum pressure which press the water into the biggest membrane pore of the hydrophobic membrane is called water intrusion pressure.Less than water intrusion pressure, the water will not enter the membrane pores.
Pressure difference when water is pressed into the membrane pores and capillary function formula is:

△P=-4×K×ϒ×Cosθ/D

       PS: △P is the pressure differential across the membrane, K is the membrane pore shape factor, Υ is medium surface tension, θ is the contact angle of wetting, D is pore diameter.
       Water immersion method is a highly sensitive ,without alcohol hydrophobic membrane integrity test method based on water flow. Since the filter is not wet, almost dry, it can be put into used immediately at the end of the integrity test with least amount dry work.