A valve actuator comprises the mechanism to open or close a valve. Manually operated valve requires some watching over, to adjust the valves using an assembly attached to the valve stem. Power operated Actuators employing gas pressure, hydraulic pressure or electricity have the flexibility of controlling the valve operation remotely or when you are considering operation of huge valves that have lightning speed.
Power operated valve actuators may engage itself in the final stage of the automatic control loop to regulate the flow of some known process. Actuators may be leveraged either to open or shut a valve or some intermediate positioning. Valve actuators at times accommodate switches to indicate the position of the valves. Thus a valve actuator controls the position of the valves by using an external power source to operate the actuator. The power source can take one of the following means: Electric ( using electricity), Hydraulic (using flow of oil) or Pneumatic (compressed air)
Two Actuators are present to regulate the operation of a valve and they are rotary and linear.
Rotary Valve Actuators:
Rotary Valve Actuator as the name suggests produces a rotary motion to regulate the flow of liquid in ball, plug or butterfly valves.
Linear Valve Actuators:
Valves such as gate, pinch and globe valves use this type of actuator to produce linear motion that runs the operation of the valves.
Manual Valve Actuators are of many types:
A long arm is attached to the valve stem that operates the valve by providing a fast action needed to rotate the valve Small valves need no leverage to operate the valve such as oval, Tee and various other shaped knobs.
Bigger valves that require high torque to work regularly hold equipped hand wheels. These administrators have a huge hand wheel with a gearbox that further levies a mechanical advantage. The span of the wheel and gearing proportion decides the measure of mechanical allotment. These wheels will require various circular motions to turn the valve just 90 degrees. These sort of administrators are normally found on bigger butterfly valves, commonly 8 inches or more.
Manual Valve with Limit Switches:
At times, valves may not require any actuation, but the system still needs to ascertain the exact position they are in. Manual Valves (position indicators)with limit switches find application over here.
Some specific manual operators in consideration include levers, levers with a spring return and knobs.
Types of Pneumatic Valve Actuators:
There are two types of rotary pneumatic actuators for use on ball, plug and butterfly valves, namely Rack-n-Pinion and Scotch Yoke.\The function of both equals transferring load from a linear motion of the piston in the cylinder to a rotary position of the stem. Both are present in dual and single versions.
There is one totally different actuator, rather old and called Vane that takes the place of the piston in the cylinder. This Vane is attached to the stem drive. Air is circulated in the chamber on either side to force the vane to move and attributing rotary motion to the stem drive.
Double Acting Actuators require air to be forced in to move the piston in either direction. A solenoid valve is used to control the air through the inlet and outlet.
Actuators are indispensable to the operation of the valve and are unique to the valve assembly by the act of displacing air in the valve chamber that produces linear or rotary motion of the piston.