Pneumatic actuators

Pneumatic actuators utilize an air signal from an external control device to create a control action via a solenoid. These are commonly available in two main forms

• Piston actuators
• Diaphragm actuators

Piston actuators

Piston actuators are generally used where the stroke of a diaphragm actuator would be too short or the thrust is too small. The compressed air is applied to a solid piston contained within a solid cylinder. Piston actuators can be single acting or double acting, can withstand higher input pressures, and can offer smaller cylinder volumes which can act at high speed.

Diaphragm actuators

Diaphragm actuators have compressed air applied to a flexible membrane called the diaphragm. These types of actuators are single acting, in that air is only supplied to one side of the diaphragm, and they can be either direct acting (spring-to-retract) or reverse acting (spring-to-extend). 

Advantages of Pneumatic Actuators

• The biggest advantage of the pneumatic actuators is their failsafe action. By design of the compressed spring, the engineer can determine if the valve will fail closed or open, depending on the safety of the process. 
• Provide high force and speed, which are easily adjustable and are independent of each other 
• Have a delayed response which makes them ideal for being resilient against small upsets in pressure changes of the source.
• Most economical when the scale of deployment matches the capacity of the compressor. 
• Provide inherent safety and are ideal for hazardous and explosive environment. 
• Low component cost and smaller footprint. Prices for non-repairable, rod-type cylinders range from $15 to $250 depending on body diameter, stroke and options. 

Limitations of Pneumatic Actuators

Maintenance and operating costs can be high, especially if a serious effort has not been made to quantify and minimize the costs. Maintenance costs include replacement cylinder costs and plugging air-line leakages whereas the operating costs include the cost of compressed air, i.e. electricity for the compressor.