control valve

What is an anti-surge valve and what are their functions?

The anti-surge valve is a surge relief valve which is a kind of valve that can be used to do the surge control. Anti-surge valve can be considered as a dedicated control system which is capable to act as a surge controlled with great response time. The major function of the anti-surge valve is to open very fast when required and this requirement would be to control the surge, so the valve would open very fast and it will recirculate the gas from discharge to the suction and by that there will be only less flow through the compressor when it is running. The anti surge valve will be capable to remove the surge from the compressor, the surge could occur in the compressor very fast so the anti-surge valve must operate very quickly to handle this. So when the anti surge valve acts against the surge it not only has to remove the surge, it also should reverse the process.

What are the requirements of anti-surge valve?

  • The anti-surge valve must have good stroke speed
  • The valve should be of a proper size so that it can control the surge and if it is oversized then it can’t do proper control
  • The close to open time and the open to close time of the anti-surge valve must be very quick
  • The proper air supply is needed to operate the anti-surge valve
  • In order to decrease the lag time the turbine run should be reduced
  • The fail position must be open
  • More than one volume boosters must be needed for the quick response
  • The anti-surge valve must be capable to handle high-pressure drop and also it must reduce noise and vibration
  • It must provide tight shut-off so that it can avoid energy loss in the system
  • The construction must be robust so that it can handle extreme service conditions
  • It should have a stable response
  • It must reduce overshooting at the time of valve adjustment steps

How to select anti surge control valve?   

  • The characteristics of the valve must be considered mostly linear type valves are used, but in certain cases, an equal percentage valve can be used
  • Speed is an important factor of an anti-surge it should have a quick response time
  •  We must consider the capacity while selecting an anti-surge valve, the selected valve must be capable to allow or pass the highest output of the compressor
  • Noise – In the case of the surge event there could be a high-pressure drop and flow rate and this could cause a high level of noise so according to this, we must select the valve.

What are the characteristics of a surge?

  • It could cause the compressor to trip
  • Noise will be created
  • The temperature of the flowing liquid will be increased
  • The compressor vibration will be high
  • The flow reversal would be quick

What are the consequences of surge?

  • It would affect the compressor life
  • Efficiency would decrease
  • Compressor can’t create better output
  • There will be damages to seals, bearings, etc

Why does the compressor have surge?

The compressor surge occurs when the down-stream flow needs to be changed and down stream flow can’t match the compressor’s operating point. In order to adjust to the new flow rate the flow control system would need to vary the motor speed but this can’t be done very easily because of the large rotating mass. So the compressor surge happens if the compressor speed and the design flow rate doesn’t match the system requirements, this could cause flow reversal and this could badly affect the compressor.

What is the difference between an anti-surge control valve and general control valve?

Mostly these valves are the same the major difference is that the anti-surge valve has a quick opening time so that it can avoid the surge.

How to install anti-surge valve?

  • The anti-surge valve should be kept at a minimum distance from the discharge line
  • The straight pipe lengths upstream and down streams of the anti-surge valve must be provided as required so that we can reduce the noise and pipe vibrations
  • These valves must be located in the higher part of the piping and because of this the upstream and downstream can easily drain into the suction.

How does an anti surge valve work

The anti-surge valve is a fail open solenoid valve, so because of this it needs a high signal to close the valve, so 20mA is needed, and to open the valve a low signal will be used which will be 4ma. So in case of any surge, the valve will receive a low signal and it will open the valve. Initially, the compressor will be with the valve at 100% open and after that, the valve characteristics of 100% open must be removed from the compressor operational region, while the startup of the compressor. The valve must be sized almost 2 times the maximum surge point flow rate and an oversized valve won’t operate properly.

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