The nature of the membrane material determines to a great extend its filtration characteristics. Generally speaking, materials that give membranes mechanical strength and chemical resistance are of a hydrophobic (water repelling nature). It is the kind of material on which a drop of water stays a drop, instead of being absorbed by the material.

Hydrophobic membranes need wetting agents in order to start the filtration process with aqueous solutions. As the membrane material is not hydrated (chemically bound with water) as is the case with a hydrophilic membrane, feed components easily adsorb onto the membrane surface. This explains why hydrophobic membranes need high pressures for the filtration process, foul much faster and are much more difficult to clean.

By using an unique blend of polymeric and mineral compounds, Prime Water International succeeded in creating micro- and ultra filtration membranes with ideal features for point of use application.

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Capillary membrane with asymmetric micro-porous structure, internally skinned, 1mm OD

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Very high flow rates at low pressure gradients

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Narrow consistent pore size ranges
- micro filtration 0.15 µm (micron max)
- ultra filtration 0.02 µm (micron max)

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High surface porosity and overall porosity 85%

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Permanently hydrophilic with low fouling characteristics.

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Withstand feed- and backwash pressures up to 6 Bar - > 118 PSI

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Chemical resistant to allow for a wide range of cleaning agents, incl. chlorine

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Heat resistant up to 120 ^oC (248 ^oF) if applied in polysulphone cartridge

Cross section capillary membrane (156x)
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Outside wall capillary membrane (5000x)
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Due to the exceptionally high overall porosity of the capillary membranes, in conjunction with the hydrophilic nature of the membrane material, the Ster-O-Tap^® micro- and ultra filtration membranes have outstanding hydrodynamic characteristics as demonstrated by the pressure/flow chart for units  containing 1000 cm² (1.1 sq.ft) capillary membrane.

1 Bar = 14.7 PSI 
1 L = 0.264 US gallon 
1 US gallon = 3.784 Liters

A Ster-O-Tap^® Micro (MF) or Ultra (UF) filtration cartridge is composed of a bundle of many capillary membranes, which are sealed in a housing, with the membranes closed on the feed side.

The feed water follows a path from the large pores on the outside wall to the small pores on the inside wall for high flow rates at low pressure (US Patent: 5.895.573 - European Patent: 97942301.9)