An overview article on Actuators
An actuator is a type of motor, typically operated by electric current, hydraulic fluid or air pressure that’s widely used in the Process Industry for moving or controlling a mechanism or system.
How do actuators work?
Actuators take fluid, electric or some other source of power and convert it through a motor, piston or other device to perform work. Basic versions are used to move valves to either fully opened or fully closed positions. While actuators for control or position regulating valves are given a positioning signal to move to any intermediate position with a high degree of accuracy.
There are four main types of actuators that are a combination of the type of power applied and the type of movement required at the valve.
Electric multi-turn actuators are one of the most common and dependable configurations of actuators and are capable of quickly operating very large valves. The main advantage of this type of actuator is that all of the accessories are incorporated in the package and are physically and environmentally protected. It has all the basic and advance functions incorporated in a compact housing which can be water tight, explosion proof and in some circumstances, submersible.
Electric quarter-turn actuators are very similar except that the final drive element is usually in one quadrant that puts out a 90° motion. The newer generation of quarter-turn actuators incorporates many of the features found in most sophisticated multi-turn actuators. They are compact, so can be used on smaller valves, and because of their lower power requirements, they can be fitted with an emergency power source such as a battery to provide failsafe operation.
Fluid power quarter-turn actuators are extremely versatile and can be used where there is no readily available electric power or where simplicity and reliability are essential. They can also withstand considerable mechanical abuse. The smallest can deliver a few inch pounds of torque where the largest are capable of producing in excess of a million inch pounds of torque. Almost all fluid power actuators utilize a cylinder and a mechanism to covert the linear motion generated in the cylinder to a quarter-turn motion.
Fluid Power multi-turn actuators are frequently used when multi-turn output is required to operate a linear type valve (such as a gate or globe valve). Electric actuators are often used for this type of valve but, if there is no electric power supply readily available, pneumatic or hydraulic motors can be used to operate multi-turn actuators.
Selecting a valve actuator
The correct type and size of valve actuator can be determined by checking:
- The Power source
- The type of valve
- The torque required by the valve
One of the great advantages of an automated valve is that it can be remotely controlled without having to physically go to the valve and give it an open or close command. A common method of positioning an actuator is to feed it a proportional signal (such as 4-20 mA), so that the actuator can then position itself in direct portion to the received signal.