Filter Information

Nominal Filtration

Expressed as an average micron pore size and designed to retain some particles of that size. In theory you could have a 1 micron nominal cartridge from one supplier that operated at 20% efficiency whilst another was 50% efficient. Neither supplier would be breaking any rules. Here at Alchemy we are happy to confirm that our AlcaFil N cartridges operate at around 65% efficiency.

Absolute Filtration

Expressed as the maximum sized particle that the filter will pass. Should provide consistent retention at stated pore size.

Here we must start to be careful and consider the differences between microbiological and particulate retention absolutes.

With regard to Particulate Retention absolutes we should consider this to mean a “filter tested to the modified OSU-F2 test protocol(single pass)” which is shown to perform at 99.98% at the stated micron challenge. This is the basis for a filter rated at Beta 5000. Filter cartridges of this type will generally, but not exclusively be manufactured from Pleated Polypropylene(Alca Pleat) or Melt Blown Polypropylene(AlcaFil B).

Be aware, that a filter advertised at 99% efficiency and rated as “absolute” is far from absolute and would allow many thousands of particles that would have been captured on a 99.98% rated filter to pass through.

When we now consider Microbiological Retention absolutes the rules of the game will change slightly. We must consider that an Absolute Particulate rated cartridge(Beta 5000)will not perform in a satisfactory manner and is not simply interchangeable with a true absolute rated cartridge. We must therefore move to the application of a “Membrane Filter”. Membrane filters will typically utilise a cast membrane with micro porous holes and be manufactured either from POLYETHERSULFONE or NYLON and which have been validated and rated according to the micron rating at which they are tested.

There is as you can see a big difference in “absolute” and it is important to apply the correct cartridge attributes according to application.

Beta Ratio

A mathematical expression that isolates the number of particles of a given size upstream of a filter relative to the number of particles of the same size downstream of the filter. Beta Ratio may be said to provide both the filter manufacturer and the user an accurate and representative view on filter cartridge performance.

Rated Efficiency

The percentage of contaminants removed. Determined by comparing contaminant before and after filter.

Surface Filtration

In surface filtration all particles retained are on the upstream surface of the filter media.

Depth Filtration

In depth filtration all particles are held within the voids within the filter media.