Filters are a media or components fabricated with filter media to remove particles from fluid or gas, after fluid or gas pass through filter media or filter parts, certain-sized particles are filtered or intercepted and stopped onto the surface or filter media or inside filter media (in-depth filters) and clean fluid or gas will pass through filter media or filter part to the downstream. However, It is only known when testing methods or filter standards are known. The two major filter ratings are: Absolute Filter Rating and Nominal Filter Ratings.
Absolute Filtration Rating
When fluid or gas passes through filter media or filter components made with filter media, 100% of designed particles will be retained and captured at the surface of filter media (surface filtration) or inside filter media (depth filtration), and no particles larger than set particle will be able to flow through filter media to the downstream.
Nominal Filtration Rating
Nominal Filtration is to capture and intercept most of particles (60-98%) from fluid or gas, some of particles will be filtered and small portion of particles will go with fluid or gas to the downstream. However, as the particles captured onto the filter media surface or inside filter media, filter rating will be increased (to form a filter cake) and even smaller particles will be retained.
