How to detect filter filtration precision?
because of this, the filtering precision of the filter and filter products description will appear the following features:
1. Manufacturer for filter nominal units may be different;
2。 Different testing methods can lead to different filter nominal accuracy.
many filter and filter product filtration precision of specific test method has the following kinds:
1, the bubble point filter efficiency
2, 3, bacterial challenge
4, the SEM a, bubble point
assumes that the microporous membrane is made up of many around capillary shape channel, the relationship between the membrane pore size and bubble point pressure can be expressed in the following formula:
P = 4 x K * Cos theta Y/D:
P - Filtration membrane pressure difference on both sides
Y - Wetting liquid surface tension
theta - For wetting contact Angle of
K - Hole shape factor.
this formula further simplified to:
P = Ko/D ( Ko in the same kind of membrane and under the same kind of wetting liquid, for a fixed value)
on the basis of the bubble point pressure to determine filtration precision, this method is widely used in aperture irregular filtering material detection. Filter efficiency
2, filtering efficiency is the most important performance indexes in microporous membrane, it's the largest controlled by membrane pore size and the distribution of the membrane pore size. Filter product filtration precision is different, also determines the filtration efficiency is different. Challenge
3, bacteria for aseptic filter, filtration precision has its special definition: defined as 0. 22 um filter to aseptic filter filtration precision, challenges need defect pseudomonas certification, pseudomonas challenge level is 1 million defects per square centimetre effective filter area, requirement for leaching liquid of sterile.
— — According to ASTM F - 838.
defined as 0. 1 um filter precision filter usually with mycoplasma.
4, the SEM
the SEM is the most intuitive method of testing filtration precision is in electron microscopy (SEM) images from the lens under certain times, we need to know when shooting magnification and the length of the scale, membrane filter can calculate roughly the aperture.
aperture = scale length/magnification
this kind of method of faults: typical microporous screen mesh is a kind of irregular overlapping structure, aperture is not uniform, different sample points, can cause large differences, especially the relative membrane, uncertain aperture size.