7 Reasons Why Liquid Might Be Found Downstream of a
Genie Membrane Filter

A question we get asked all the time is, “If a Series 100 Genie® Membrane Separator is designed to remove 100% of entrained liquid from gas samples, then why am I getting liquids downstream of my Genie membrane filter?” The answer to this question is not always easy because it can be caused by one or a combination of the seven reasons listed below.

Wrong Membrane Type

All membranes are NOT created equal. The Type 6 membrane should be used when possible as it rejects ALL types of liquids. The Type 2 and Type 7 membrane will not stop all liquids. Always refer to our Membrane Comparison Chart for more details on each membrane type when ordering for your application.

Overwhelmed Membrane

The membrane available in Genie Membrane Separators™ is primarily for separating liquid occasionally entrained in gas streams. The membrane can be overwhelmed by a slug of liquid that completely fills the membrane filter’s inlet cavity or by particulates or aerosols continuously present in sufficient quantity to coat the entire surface of the membrane.  Once completely coated, liquid can be forced through the membrane if the membrane differential is high enough. The Liquid Block™ option is recommended in a Genie used at locations where there is a known presence of a significant amount of liquid because it prevents liquid from being forced across the membrane.  In addition to the Liquid Block™, additional coalescing and particulate filters upstream of the Genie® may be required.


If the Genie® is separating liquid AND the sample temperature downstream of the Genie® is lower than the temperature at the Genie®, then condensation will occur.

Excessive Flow Rate

An excessive pressure difference between the upstream and downstream sides of the membrane can force liquid through the membrane. An excessive flow rate requires an excessive pressure differential so thereby forcing liquid through the membrane. Each type of liquid has its own breakthrough differential pressure so it will vary from liquid to liquid.

In order to prevent liquid breakthrough as a result of excessive flow rate, the maximum recommended flow rates listed for a given model should be adhered to. If the flow rate through the membrane cannot be reduced, then the membrane area should be increased by using a larger Genie® or adding an additional Genie® or more in parallel, not in series.

Damaged Membrane

Even a very small pin hole can result in liquids or particulate downstream. Carefully inspect  your membrane or change your membrane to be sure it is not damaged.

Loose Cover

The cover of all Supreme Series membrane filters must be properly tightened in order for the membrane o-ring to seal properly. If it does not seal, the membrane can be bypassed thereby resulting in liquids downstream.

Alternate path

Ideally the Genie® outlet is close coupled to the analyzer inlet with no connection to any other part of the sample handling system between the two. If there are any other tubes connected between the outlet of the Genie® and the inlet of the analyzer, then these should be considered as possible sources of liquids.