Process Description of Dissolved Air Flotation
May 15,2023Read More
Many types of actuators can control the opening and closing characteristics of a butterfly valve. The actuator provides the torque required to properly open and close the valve during service. The following types of actuators are paired with butterfly valves:
Manual valve operation is the simplest form of actuation. It uses a wheel or lever to control the position of the stem and disc. Manual operators are also very inexpensive and typically are used with smaller sized valves that have a lower torque requirement. These are especially suitable in applications where power is not present to operate the valve. The speed of manual operators is somewhat slow, so they would not be used in emergency shut-off applications.
Electric valve actuators contain a gearbox that can adjust motor speed, raising or lowering the torque. The electric actuators are easy to maintain, are relatively simple to install and are fairly quiet during operation. The position of the valve is based on the voltage or current signal input and can contain limit switches that stop the actuator when fully closed or fully open. Electric actuators are used where there is a stable power supply.
Rack and pinion actuators contain springs within a chamber that operate from the entry and exit of compressed air. These types of pneumatic actuators can be single or double acting, are compact in design, relatively inexpensive and lightweight. They have quicker reaction times, allowing for their use in throttling services; they need an external supply of compressed air.
Scotch yoke actuators can be operated with compressed air or with hydraulic fluid. These consist of a crank and piston in a hollow cylinder. Pressure is applied to one side, and the resulting force moves the piston linearly to rotate the stem and disc. These actuators can be designed with modules for ease of maintenance by just removing one section of the actuator instead of the entire assembly. The scotch yoke is larger and more costly than the rack and pinion, but output creates much higher torque for larger sized valves. The scotch yoke also can be paired with control accessories for use in quick acting or soft closing applications.
Hydraulic valve actuators use hydraulic force supplied by a fluid to control the position of the disc and stem. They are available in either single or double acting. Single acting works by the absence of fluid pressure, keeping the valve in the closed position; as pressure builds up, the fluid pushes the piston towards the valve to open. The double-acting type contains a hydraulic pump that changes the direction of the fluid to open and close the valve. These actuators are used for the very large or heavy-duty valves that require a large torque to operate; they also can be used with solenoids to better control position.
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