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Filtration technologies


Filtration is a process to remove rigid or gel-like contaminations from liquid or gaseous media. A special form of filtration is coalescing, which seperates different liquids from gasesous media, resp. liquids from liquids (for example, water from fuel)

Filtration is achieved with re-usable (backflush-able) elements or exchangeable elements (Filter cartridges, Filterbags, etc.)
W.A.S. specialises in Microfiltration of gases and liquids between 0.01 - 1000 micron, primarily with exchangeable elements.

There are different Filtrationmethods for various applications:

Surface Filtration

Particles bigger than the micron graduation of the filtermedium cannot pass and stay at the filtersurface. Depending on the construction of the medium, we offer absolute or nominal Filterelements.

Surface (or pleated) elements are usually used for removing rigid particles out of a gas or liquid stream.
Examples for surface filtration are:

Depth filtration

Depth filtration means that the contaminant is hold inside of the filtermedium. The filtered medium itself finds its way through the filter by following the way of least resistance. This allows graded filtration troughout the whole element and also holds back gel-like contaminations. Depending on the construction of the medium, we offer absolute or nominal Filterelements.

Membrane filtration

Membrane filtration is a special form of surface filtration. The filtermedia is designed with a predefined pore-structure and allows a precise absolute filtration.

Examples for membranematerial are: Polyethersulphone (PES), Nylon, PTFE

Membranefilterelements allow a precise filtration down to 0.05 microne and are used for applications with high requirements regarding the quality of the filtered medium (for example filtration of germs)

A special form of membrane filtration is sterile Ventilation filtration with PTFE Cartridges, where the vessel has to be sterile through the whole draining process.


There are various terms for Filterefficiency (= performance to hold back contamination), often specified by the supplier. There is no binding directive, descriptions and values differ, depending on the method of filtration and supplier.

Below the most common definitions for describing filterefficiencies are listed:



= 98%
= 99%
= 99,9%
= 99,98%
= 99,99%

( 1 - 1/ß) x 100 in % filterefficiency