Passive and Active States of a Closed Check Valve

Check valve operation happens in eight defined stages.  This SmartNews will explore the first stage where the valve remains shut and prohibits flow in either direction.  If you just envisioned a dormant valve, think again.  There’s a lot of action going on behind the scenes because the laws of physics continue to rule over the valve in what we call passive and active states.

Passive

All valves begin in a passive state.  They are not yet in contact with any liquids or gasses, but the makeup of a valve – body material, O-rings, poppet, cartridge, and springs – remain in contact with each other.  The laws of physics win again if certain body materials and O-rings remain together for long periods of time, and two factors should be considered in any application: 1) leak rate and 2) sticking. 

Leak rate can be compared to air in a bicycle tire. If a tire sits unused over a period of time, it will eventually lose some air.  Because of this, we have tested our valves to allow a standard maximum leak rate (in the non-flow direction and at a test pressure of 2 PSI) of 0.32 SCCM (Standard Cubic Centimeter per Minute).  To ensure maximum performance, we perform a leak test on 100% of our valves.    

Our next potential issue is sticking.  Again, if a valve is inactive and sits for a long period of time, the O-ring can stick to the O-ring seat and cause an elevated opening pressure.  This issue can also arise if you use soft O-rings.  Awareness of these two issues is the first step to ensure a valve’s optimal performance when evolving from the passive to the active state. 

Active

Once the valve makes contact with a liquid/gas, it becomes active and will never return to the passive state. While the valve is still closed, the O-rings play a key role when they first come into contact with the liquid/gas for the following reasons: 

-Certain chemical components can make the O-ring expand
-Certain liquids (such as water) can contain debris that will not allow the O-ring to seat correctly 

Smart Products offers seven O-ring materials to choose from, as well as samples for testing in order to create the right valve for a specific application’s design.    

Application Environment

A final consideration is an application’s environment because it can also affect the passive and active states of a closed check valve.  Will the valve reside in tubing? Or, will be outside exposed to elements such as temperature, humidity, sunlight, etc.?  The answers to these questions could affect a valve’s performance based on the selected body material and O-rings. 

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To ensure optimal valve performance every time, it is important to communicate the following when ordering: 

-shelf life of a valve
-liquids/gasses used
-application environment  

Smart Products has over 3 million customizable valve solutions to fit your current and future applications – give us a call today at (800) 338-0404 or visit www.smartproducts.com. 

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About Smart Products, Inc.

Smart Products, Inc., located in Morgan Hill, California, designs and manufactures an extensive family of plastic valves, pumps, and related components. Designed to allow a virtually limitless number of possible combinations to fit specific needs, products are used in a wide range of applications, including medical diagnostic and treatment, gas analysis, filtration, beverage dispensing, printing, and many others. The company also offers custom design capabilities, special testing, and custom assemblies.