The bubble point test is related to the effective diameter of the largest hole on the membrane, which can directly reflect the size of the pore diameter, but can not reflect the thickness and opening rate of the membrane.
The pressure accuracy of "bubble point" will decrease with the increase of filtration area, so it is better to apply it to the membrane filter with smaller area.
Diffusion flow reflects the opening rate and thickness of the whole membrane, which can not only reflect the integrity of the filter, but also show the comprehensive characteristics of the membrane.
The diffusion flow test has established a reliable connection with the bacterial challenge test. Compared with the bubble point test, the diffusion flow test is most suitable for large area membrane filter.
The result of pressure holding method is the pressure change △P, of pressure drop, which is the process value of the diffusion flow test method, so it has been eliminated at present(rarely using now).
At present, diffusion flow method is a recommended method for hydrophilic filter. The result of diffusion flow method is gas flow rate, which can be relatively quantified. Through the size of the result, the opening rate, effective filtration area and porosity can be roughly judged, and it is suitable for multi filters test.