Air Dryers that Don’t Remove Water

We get a number of questions about the dehydration membrane separators and how they work. One of the confusing aspects of membrane dryers is that they do not process liquid water.

Sounds confusing – right? A dryer removes moisture. So why would a membrane dryer not remove water?

Gas separation membranes work at the molecular level. When a compressed air stream is being “dehydrated” the water vapor is actually being separated from the compressed air stream. This separation is the result of the very fast water molecule being able to diffuse into the membrane material and permeate out much faster than other air molecules like oxygen or nitrogen. This is not the same as a “filter” which blocks particulates and holds onto them. The smallest water droplets have a diameter of 0.01 to 1 micron, which is very tiny.  But, water molecules are incredibly small with a typical diameter of 2.75 Angstroms (0.000275 microns). This makes the tiniest liquid phase water droplet 3600x larger than its vapor phase cousin. The droplets don’t have a chance of diffusing and permeating simply because they are too large.

Standard pretreatment is to ensure that all liquid water and entrained mists are removed. This also includes all traces of compressor oil, which will also cause damage. In properly designed systems, PRISM Membrane dryers will deliver consistently dehydrated compressed air (or gas) streams for years without the need to replace parts or consumable media.