Every valve needs a means by which it can be operated (e.g., cycled or actuated). There are a variety of options to achieve this including: handwheels, levers, gears, and actuators.
Actuators are a means by which a valve can be automated so that no human interaction with the valve package is necessary to cycle the valve. Actuators can be remotely operated and can act as shutdown mechanisms in case of an emergency situation, wherein human interaction can be dangerous.
“At a basic level, an actuator is a control mechanism that is operated by an energy source. This energy can be hydraulic pressure, pneumatic pressure, or electric current which moves the internal mechanical parts of the actuator.” said Russ Robertson, actuation product manager, “They can be designed to fail-open (in the case of actuator failure, the valve will stay open) or fail-close (in the case of actuator failure, the valve will stay closed). They also are distinguished by whether they are for quarter-turn (e.g., ball valves, plug valves) or linear (e.g., gate valves) valve operation.”
Pneumatic – Pneumatic actuators utilize compressed air to generate the operating energy. These actuators are quick to respond, but are not ideal for environments under high pressures, as gas is compressible. Pneumatic actuators can be either spring return or double acting.
Double Acting – Actuators in a double acting configuration have air/liquid supplied to both sides of the piston, with one side being higher pressure which achieves the movement required to actuate the valve. This configuration uses the air/liquid as energy to both open and close the valve.
Single Acting– Actuators in a spring return configuration have air/liquid supplied to only one side of the piston, and the energy to move the mechanisms comes from a spring on the opposite side. This configuration uses the air/liquid as energy to open or close the valve, while the spring acts to affect the opposite motion.