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Piping System Safeguards: Air Release Valves & Degassing Valves

In certain circumstances, pockets of compressed air can cause catastrophic failure in a liquid piping system

Air pockets and outgassing in a liquid piping system can result in water hammer, pressure surges, pump damage, and in extreme cases, compressed air will cause catastrophic failure. Strategic use of specialized air release and degassing valves can eliminate the danger and improve system performance. This brief tutorial explains when, how, and where to use these piping system safeguards.

Air Release: High Volume at System Start-Up















An Air Release Valve is open when the system is depressurized. At startup, the liquid process forces most of the air in the pipeline to high points, where the ARV allows it to escape. Once liquid rises, the valve closes and will not allow anything – gas or liquid – to pass in or out. It will not vent gas as it occurs during daily operations. It will reopen only when the system is depressurized and the liquid level drops.

Degassing: Continuous, Trace Amounts During System Operations















A Degassing Valve is also open when the system is depressurized, but due to its small vent orifice is not well suited to expelling a large volume of air at system startup. The DGV’s strength is the fact that it will open automatically – even when the system is pressurized – to periodically allow small amounts of gas to vent. Once the gas vents, the valve automatically closes as long as liquid is present.

The DGV on the suction side improves pump efficiency by eliminating trace amounts of gas that are commonly present in liquids that are prone to outgassing, such as sodium hypochlorite.

Other Considerations:

These issues will determine if an application  requires one or the other…or in many cases, both valves:
  1. If the application requires that a large volume of air be vented at one time, such as when the system is fired up in the morning, it calls for an air release valve.  An air release valve should be installed on virtually every system because sooner or later you have to turn it off. When you start it up again, you want to get all the air out so that the system will run at peak efficiency.
  2. If the application is prone to outgassing or otherwise routinely forming small air pockets that must be vented throughout the day, it calls for a degassing valve. With ozone or sodium hypochlorite applications, a degassing valve on the suction side can significantly improve pump efficiency and longevity.
  3. Because most piping systems will benefit from installation of an air release valve, the designer should consider using both the ARV and DGV in applications prone to outgassing.
Another important thing to note is that both valves need to be located at high points in the system, or wherever air or gas will routinely accumulate. Keep in mind that neither valve will “collect” gas as it passes by.


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Depending on system design, applications requiring both air release and degassing may benefit from using a Combination Valve. This is a new, patent-pending design that incorporates both the air release and the degassing function in one unit, called Series CARD: