A butterfly valve actuator is a remotely-operated device used to open and close butterfly type valves. These actuators are widely known as quarter-turn actuators since butterfly valves only require a quarter of a full rotation to fully open or close. They are typically rotary types and feature a range of power sources, with electric and hydraulic types being the most common. The actuation range of these devices is typically controlled by a set of limit switches that stop the butterfly valve actuator when the valve is fully cycled. They also generally include a over-torque protection device designed to stop the actuator if the valve is obstructed.
As one of the most commonly encountered fluid control devices in industrial and domestic installations, the butterfly valve belongs to a family of similar devices known as quarter-turn valves, as they only require a quarter turn to fully open or close. These valves are placed in-line with a pipe and feature a central chamber fitted with a flat, rotating plate in the center. When the plate is turned parallel with the fluid flow direction, the valve is open and the flow unimpeded. When the plate is turned at right angles to the flow, it blocks the chamber and the fluid flow effectively closing the valve.
Many butterfly valves are manually operated using a straight handle or geared control wheel. Where the valves require large amounts of torque to operate, are in inaccessible locations, or are in environments hazardous to an operator, a butterfly valve actuator may be used to facilitate remote operation. These devices make use of an electric motor or a source of compressed hydraulic oil to turn an output shaft connected to the valve stem. Generally, hydraulic actuators are used in applications such as high pressure oil and gas lines where the actuation torque is very high. In these applications, the butterfly valve actuator may also utilize a feed of high-pressure gas bled directly from the pipeline for actuation.
The range of motion that the butterfly valve actuator generates at each cycle is usually controlled by a set of limit switches, one each for the valve's open and closed positions. These switches will signal the actuator controller to stop when the valve opens or closes fully. The control loop will typically also feature some sort of protection device designed to stop the actuator should the valve jam or become obstructed. These switches and limits prevent the actuator from over-cycling and damaging itself or the valve.