What is an anti-surge valve?

An anti-surge valve is specifically designed and installed to protect the compressor from reaching its surge point. The valve is in the system, in a by-pass that connects the inlet and the outlet of the compressor. In normal operation, this valve remains closed, however, if the surge is detected, it quickly opens to maintain a minimum flow and directs the backflow to the outlet of the compressor to avoid damages. The valve must be completed with controllers that use the suction and discharge pressure and temperatures to determine the flow at which the condition of surge will occur. It is crucial for such valves to be operated by actuators that can achieve extremely fast stroking times, high frequency of operation minimal dead time and minimal overshoot.

What is compressor surge? 

In simple terms, Surge in a compressor is the phenomenon that occurs when  the flow through the entire compressor is reversed intermittently.

How does surge in a compressor occur?  

In the normal operation of a compressor system, the gas is sucked from a tank or reservoir by the compressor and as it passes through is pressurized and stored in a receiver. If the pressure in the receiver starts building up to a point where it reaches or exceeds the discharge pressure of the compressor, the gas will backflow and the compressor will go into surge.  This means it will reach its surge point –  this is the point where the flow rate is minimum in the compressor operating curve.

Representation of normal operation

Representation of compressor surge

It is critical to avoid this phenomenon from happening since it is catastrophic for the integrity of the compressor as it will severely damage it. To prevent surges from happening, systems normally use anti-surge valves.

Anti-Surge Valve Actuator

For such critical operation, Cowan Dynamics has developed solutions within our product lines of pneumatic and Electro-hydraulic actuators that allows opening times as fast as 0.5 secs, dead time of 0.3 seconds and an overshoot of 0.4 of 1% of the stroke.

The anti-surge valve actuators use standard components from our line of solutions, which increases availability and reduces maintenance or troubleshooting time.

Pneumatic Anti-Surge Valve Actuator

antisurge valve actuator


Electro-hydraulic Anti-surge Actuator

electro-hydraulic actuator control valve


Written by Cowan Dynamics

February 16, 2022

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