When is a 0.2 micon filter not a 0.2 micron filter?
It is important to understand that a membrane filter is not the same as a pleated Polypropylene filter even though the rating may be the same. To take a membane filter rated at 0.2 micron and replace it with a pleated polypropylene filter rated at 0.2 micron may seem fine until you investigate how they are rated and tested. 0.2 micron is the rating designed to remove bacteria but a 0.2 micron pleated polypropylene filter will not stop bacteria, fact! Please beware of the unscrupulous suppliers who will sell a filter at 0.2, 0.45 or even 0.1 micron as a replacement for a membrane filter because it really is asking for trouble. Why you ask? Ok let me explain.
When is a 0.2 micron filter not a 0.2 micron filter?
In filtration it is important to understand how a filter is rated and how it is tested, if in fact it is tested at all. It is important to understand why it is not advisable to replace a 0.2 micron membrane filter with a pleated polypropylene filter rated at 0.2 micron. This could literally risk life and is undertaken by those with poor knowledge or less scrupulous filter sales companies. Let me explain the science here
A membrane filter falls into two categories, "validated" and non validated" or tested and non tested. A membrane filter presents a physical barrier to particles and bacteria and the membrane itself is a cast sheet with small micro porous holes to stop the contaminant. A membrane filter has to be integral and the better filters are integrity tested. This ensures there are no manufacturing defects using pure water and compressed gas for the test. A membrane filter is normally "microbially" rated, a 0.2 micron usually used to stop brevundimonus diminuta a 0.3 micron bacteria, and full validation being an independent test to stop ALL bacteria at a level of dictated by the Health industry Manufacturing Association. This test is done in a dedicated laboratory and the filter provides protection to health. Please note not all membrane filters are tested from competitors and a filter is as good as the largest pore.