WHAT IS A PNEUMATIC ACTUATOR?
A pneumatic actuator converts the energy in compressed air into rotary torque used to drive a valve.
Using the principle of force = pressure x area, the compressed air generates a force relative to its pressure and the area upon which the pressure acts, this force is then either used directly in linear applications, or converted to rotary torque in part-turn applications, to drive a valve.
WHAT DIFFERENT TYPES OF PNEUMATIC ACTUATOR ARE AVAILABLE?
Relating to valves, there are initially two main categories of pneumatic actuators, those for part-turn rotary valves and those for linear valves.
There are two styles of part-turn rotary pneumatic valve actuators, rack and pinion and scotch yoke. Both achieve part-turn movement but achieve it in a different way that affects the way the torque is generated. Linear pneumatic actuators either use a piston or a diaphragm to produce thrust.
Within these types and styles, all of the pneumatic actuators are available in a variety of housing materials, varying from plastic to aluminium to forged stainless steel, enabling the pneumatic actuators to be used in widely differing applications.
HOW DOES A DOUBLE ACTING PNEUMATIC ACTUATOR WORK?
Double acting pneumatic actuators have a piston or diaphragm driven by compressed air to both open and close the actuator, the phrase ‘double acting’ using terminology taken from pneumatic cylinders. When compressed air applied to one side of the piston, the air displaced on the opposite side is exhausted to allow the piston or diaphragm to move. Should the compressed air supply fail, the double acting actuator will stay put.
HOW DOES A SINGLE ACTING PNEUMATIC ACTUATOR WORK?
Single acting pneumatic actuators’ piston or diaphragm are driven by compressed air which compresses a spring in one direction, the air displaced on the opposite side is exhausted to allow the piston or diaphragm to move. The compressed air is maintained to prevent releasing the springs. When required to move in the opposite direction, the compressed air is released and the energy stored in the springs drives the piston or diaphragm its full travel. Loss of compressed air will result in the springs releasing and moving the actuator, a feature taken advantage of as a safety feature. Single acting pneumatic actuators are commonly referred to as ‘spring return’ actuators.