Comparison of Valve Actuator Features

Spring and diaphragm
Advantages:-

• Lowest cost
• Ability to throttle without positioner Simplicity
• Inherent failure-mode action
• Low supply-pressure requirement
• Adjustability to varying conditions
• Ease of maintenance

Disadvantages:-

• Limited output capability
• Large size and weight

High-pressure spring and diaphragm
Advantages:-

• Compact, light weight 
• No spring adjustment needed 
• Costly cast components not needed 
• Inherent fall-safe action
• No dynamic stem seals or traditional stem connector block needed
• Design can include integral accessories

Disadvantages:-

• Requires high supply pressure 40 psig (2.8 bars) or higher
• Positioner required for throtting

Pneumatic piston
Advantages:-

• High force or torque capability 
• Compact, light weight
• Adaptable to high ambient temperatures 
• Fast stroking speed 
• Relatively high actuator stiffness

Disadvantages:-

• Fall-safe requires accessories or addition of a spring
• Positioner required for throttling
• Higher cost
• High supply-pressure requirement

Electric motor
Advantages:-

• Compact 
• Very high stiffness 
• High output capability 
• Supply pressure piping not required 

Disadvantages:-

• High cost
• Lack of fail-safe action
• Limited duty cycle
• Slow stroking speed

Electrohydraulic
Advantages:-

• High output capability 
• High actuator stiffness 
• Excellent throtting ability 
• Fast stroking speed 

Disadvantages:-

• High cost
• Complexity and maintenance difficulty
• Fail-safe action only with accessories