Actuation Methods of Butterfly Valves

Jun. 01, 2022

Plastic Lined Butterfly Valve

 

The actuation of butterfly valves speeds up the opening and closing characteristics. Valve actuation enhances the steady, incremental flow of fluids in a piping system. An actuator provides the torque required to maximize valve operation. The following types of actuators are available for industrial butterfly valves:

 

1) Electric valve actuator

The actuator uses a bi-directional motor to facilitate the remote operation of valves. The versatile actuation system incorporates a gearbox that lowers the motor speed, increasing the torque. Electric actuators are majorly maintenance-free, simple to install devices commonly used for process control in non-critical and light-duty modulation activities.. The actual position of the valve replicates as a voltage or current signal. They consume less energy and operate quietly.

Some electric actuators contain limit switches that initiate motor stoppage when the valve is fully closed or fully open. Application areas are limited to processes with a stable power supply.

 

2) Manual valve operation

These are rudimentary, hand-operated actuators that use a wheel, crank, or lever to control the position of the stem and the disc. They are simple, inexpensive valve operating systems that are suitable for remote pipe systems without access to power. Some large valves contain a geared system for increased torque. Advanced, gear-operated actuators have analog indicators that correspond to the approximate positions of the disc.

This category of valve operation is limited for use with small-sized valves. Their operational speed is low, making them unsuitable for critical pipe systems.

 

3) Hydraulic valve actuator

Heavy-duty valves, such as main steam valves, require large turning forces to operate. Such valves require hydraulic actuators, which are available as single-acting (spring return) or double-acting actuators that use fluid pressure to open or close valves. For single-acting actuators, the absence of fluid pressure keeps the valve at a closed position. As upstream pressure builds up, the hydraulic force supplied by a fluid (hydraulic oil or sometimes water) pushes the piston upwards to open the valve. A reversal of these conditions expels the hydraulic fluid in the opposite direction, closing the valve. Double acting hydraulic actuators use an inbuilt hydraulic pump that changes the direction of the hydraulic fluid to match pipeline flow conditions.

Smaller butterfly valves use hydraulic actuators with solenoids that control the linear motion of the plunger. Hydraulic actuators provide an economical means for the automatic or semi-automatic operation of very large valves.

 

4) Pneumatic valve actuators

Pneumatic actuators can be single-acting or double-acting. Their designs accommodate multiple ports for the entry and expulsion of compressed air. When the air enters the chamber of the actuator, it causes linear or rotary motion of the piston/plunger. It results in a rotational or lifting torque on the stem, causing the disc to open or close and control the flow of fluids. The actuators may contain solenoids that respond to electrical signals to control the position of the actuator.

These actuators have a compact design, are lightweight and economical. Their quick reaction time makes them suitable for repeatedly throttled pipelines, such as industrial gas service, conveying slurry, and steam service. They only work when there's an external supply of compressed air.

 

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