Centrifugal Compressor Valve Actuation Comparison

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Compressor Control Valves

Centrifugal compressors usually include the major valves in the original equipment manufacturer’s scope of supply, such as inlet valve or guide vane, unloading control valve, discharge check valve, and sometimes the shut-off valve when needed. The inlet and unloading valves are automatic control valves regulated by the control panel or control system actuators and are essential for safety and energy efficiency during the compressor operation.

Valves need actuation systems to provide the necessary force to open or close them. Two standard actuation systems are pneumatic and electric valve actuators, with different pros and cons. Understanding more actuator features will help make the right decision on a compressor valve.

Valve Actuation

Pneumatic Valve Actuators
Compressed air powers pneumatic valve actuators, which consist of a piston or diaphragm to convert compressed air into mechanical force. It is a simple, reliable option for operating valves, ideal for applications requiring compressed air, and popular among many industries. Pneumatic Valve Actuators receive a signal from a current-to-pneumatic (I/P) transducer. This transducer receives an electrical current signal from the compressor control system to ensure the proper valve position.

Electric Valve Actuators
Electric valve actuators use an electric motor to operate the valve. They are becoming increasingly popular due to their precision and don’t require an air supply. Electric actuators consist of a motor, a gearbox, and a set of controls. They are ideal for applications requiring precise control and complex automation compatibility. Due to the intricate design of electric valve actuators, the reliability is less stable than pneumatic valves and requires additional maintenance. Electric valve actuators receive an electrical current signal directly from the compressor control system to ensure the proper valve position.

Valve Comparison

Below lists a table of detailed analyses of the comparisons.

Comparison	Electric	Pneumatic	Comment
Force Availability	Extremely High but smaller size	High larger size	No impact
Explosion Proof	Need to build per safety code compliance	Does not generate sparks or heat	Pneumatic is a safer option
Overload Ability	High risk of overload shutdown from motor heat protection; Risk of gearing wearing out	Normally designed with larger margin for overloading	Pneumatic will be a better option for instantaneous overloading
Lifespan	Relatively shorter but adequate	Excellent especially for frequently varying loads	Not a big difference
Fail Safe	Feasible but cost is higher	Common and low cost (Spring return option)	Pneumatic is a better option
Responding Time	Relatively slower; Could be faster but with an impact on cost	Excellent response with low cost	Pneumatic is a better option and more economic
Hazardous Conditions	Delicate electronic components. Requires certifications for specific environments.	Rugged, can withstand higher pressures and temperatures.	Pneumatic offers more options in hazardous environments.
Control Efficiency	Operation is approximately 80% efficiency	Greater than 80% when coupled with PID control efficiency.	Both offer excellent efficiency during operation.
Reliability	More complex design; Good for design conditions	Simple and mature design; Robust and better reliability	Pneumatic is more mature and reliable
Lead Time	Around 12 weeks	Around 12 weeks	No impact
Maintenance	Complex for service; usually need replacement	Simple and easy service for the actuator, but not for electrical accessories	Pneumatic is more convenient for service
Control Integration	Direct Signal	I/P Transducer	Not big impact
Utility Requirement	Electricity only	Electricity and air	Not big impact for most industries
Noise Level	Good	Slightly higher noise	No impact
Dimensions	Compact	Slightly Bigger	No impact
Weight	Slightly heavier	Good	Not big impact
Price	Less expensive	More expensive	Electric may cost less initially, but have higher maintenance costs

Conclusion

The choice between pneumatic and electric valve actuators depends on the specific requirements and constraints of the application. When selecting a valve actuator, it is crucial to consider the application requirements, such as torque, speed, and control options, and any environmental factors, such as temperature or hazardous environments. FS-Elliott’s compressors come with a standard pneumatic actuator due to its reliability and fast response time to protect the compressor. Optional electric actuators can also be provided if required.

For more information, download our inlet upgrade guide or contact your authorized FS-Elliott channel partner. Let us help you improve your plant efficiency!

Operating Centrifugal Compressors