Just as there are many forms of valves, there are several specific types of valve actuators. Most, however, fall to a few common types, based on the type of power applied and the Kind of movement required:
Pneumatic and hydraulic actuators (fluid power) -- quarter-turn -- These types of actuators are flexible and can be used where electric power isn't readily available or from applications where simplicity and dependability are prioritized. They also possess a wide assortment of abilities, from smaller actuators providing a few inch lbs of torque into the largest actuators, which could deliver a million inch pounds of torque or longer. Most pneumatic and hydraulic actuators use a cylinder coupled with some mechanism that turns the linear motion generated from the cylinder to the quarter-turn motion necessary for valve operation. Adding an opposing spring permits for positive shut-down in crises.
While electrical actuators are usually used for these kinds of valves, hydraulic and pneumatic actuators are workable options for applications where power isn't readily offered.
Electric actuators -- multi-turn -- These kinds of valves are among the most frequent and the most reliable. They're capable of quickly operating a number of the biggest valves, and they are powered by one or three-phased electric motor that drives a mixture of level gears along with spurs. Subsequently, these gears and spurs drive a stem nut, which ends up the stem of the valve to open or shut it. They frequently incorporate a declutching mechanism and a hand wheel which permits manual operation in the event of a power failure.
Electric actuators -- quarter-turn -- Similar in layout to multi-turn electric actuators, the primary difference is that the last element is positioned in a single quadrant supplying 90 degrees of rotation. These types of actuators are streamlined and frequently utilized in smaller valves, and because they have reduced power requirements, they may be configured using an emergency power supply (for instance, a battery) for fail-safe operation.
Manual actuators -- Manual actuators utilize levers, wheels, and/or gears to facilitate movement. Manual actuators vary from automatic actuators, as automatic actuators have an outside power supply providing the force and movement required to operate a valve remotely or automatically. For several valves, manual operation is not an option, possibly because the program comprises valves in distant pipelines or on account of the sheer pressure needed for operation. Furthermore, manual actuators aren't a practical alternative for valves located in toxic or aggressive surroundings, and they are much less helpful in programs requiring the safety precaution of allowing for immediate shutdown.
Pneumatic and hydraulic actuators are described together and function similarly; however, they differ slightly in how the cylinder is transferred. Hydraulic actuators move the cylinder with an incompressible liquid out of a pump, even whereas pneumatic actuators move the cylinder using pressurized atmosphere. Pneumatic actuators are not as practical for big equipment which requires large bore cylinders because of compressed air consumption.
They also tend to leak fluid, and they need a number of companion components including pumps, motors, discharge valves, fluid reservoirs, heat exchangers, and noise-reduction gear.
Valve actuators may also be categorized as diaphragm actuators, direct-acting along with reverse-acting actuators, direct-acting diaphragm actuators, field-reversible multi-spring actuators, and piston actuators, even though there are different forms also.
All valve actuators should perform several roles such as:
Transferring the valve closure member to the proper site. A close member is usually a plug, disc, or ball, along with an actuator should have sufficient force to maneuver even in difficult or undesirable ailments. Furthermore, it has to be paired with the necessary controls to direct it.
Maintaining the valve closure member in position. Once in the desired position, a valve actuator should have the ability to hold it in place. In certain programs, like throttling programs, this requires a robust spring or liquid electricity or mechanical stimulation to maintain the closure member securely in place.
Seating the valve with sufficient torque to fulfill desired shutoff specifications. Some kinds of valves may call for exceptional accessories for actuator pruning to maintain enough torque to maintain closed positions.
Having a failure mode. A failure mode needs to occur in the event of a system failure. Depending on the application, failure mode may be as-is, entirely shut, or totally open.
Having the correct rotational value. Some valves need a certain amount of rotation, often 90 or even 180 degrees. Multi-ported valves often demand more than 90 degrees of rotation, and electrical actuators are usually preferred for programs requiring rotation of greater than 180 degrees, as they are not limited in rotation mechanically.
Supplying the perfect operating speed. The cycle rate of an actuator could be regulated with controller circuit components, but bicycle speeds less than half of their typical actuator cycle time require careful valve choice. Specially trained pneumatic valves might be required for high cycle speeds without risking damage to valve components.