Should a membrane be supported on one side or on both?

A question that has been asked a lot is when using a membrane as a filter to stop moisture passing, should the membrane be supported on one side or on both? The first thing to look at is the membrane itself.

What is a membrane filter?

The membrane is a very thin film of hydrophobic PTFE which means the water molecules gather together into droplets on the surface and cannot easily pas through. If these droplets rest on the surface for too long, i.e. they cannot drop off, eventually the integrity of the membrane could be breached and water will pass through the membrane.

In the housing construction the membrane has to be mounted so that the membrane has support behind it which means that it doesn’t get damaged by the fluid pressure on its surface. Because the support is behind the membrane it never comes in contact with the droplets of water. This leaves the surface directly in contact with the fluid stream free to gather the aerosols droplets and to let them fall back into the liquid drainage area.

If a second support is added any gathering droplets get trapped in the second support, this causes liquid to be continually in contact with the membrane which could cause some problems.

So our membrane housings are supplied as standard with just the one support disc and a second support disc can be fitted on request (but this is not recommended). It could be that there is a reverse flow due to the application and in this case a second support could have some benefit.

Do you have a preference or an experience of using two supports successfully? We really want to get some comments going on the blog so let us know below.

Need some assistance to select the correct PTFE membrane for your application? Contact us by calling +44 (0)1634 724224, use the form on the right or send us an email to [email protected]