Every valve requires a mechanism (actuated or cycled) for it to operate. This can be achieved through a multitude of choices including actuators, handwheels, motors, and pulleys.
Actuators are mechanical or electro-mechanical devices that are meant to automate a valve. This is so that there is no need for human contact with the valve to be able to operate it. They can be operated remotely to shut down machinery during emergency situations in which human contact can be hazardous. They enable a controlled, mostly limited movements, to valves by utilizing an energy source. This energy source is either from a pneumatic/hydraulic pressure or an electric current that moves the internal parts of an actuator.
Actuators are classified according to the power applied and the motion of movement. To know more about these types of actuators, read on this article.
4 Common Types of Actuators
There are two basic motions in which actuators are operated: linear and rotary.
In linear operated actuators, mechanical energy is converted into linear motions and is usually pushed or pulled. Some of these actuators do not use any source of power and are operated manually using a knob or handwheel.
Rotary actuators, on the other hand, converts energy from a power source to produce rotary motion.
Discussed below are the common types of linear and rotary actuators.
#1 Manual Valve Actuators
A manual actuator either uses a gear, lever or wheel to provide movement. But manually operated actuators are not preferred for most valves. Because the majority of the valves, especially in large industries, are located in remote pipelines and sometimes require great force to operate.
Moreover, manual actuators are not ideal in hazardous environments wherein the safety of the workers is not ensured.
Manual Linear Actuators
Manual linear actuators have manually operated knob/wheels and gearboxes which guides the linear motion produced. This means that they do not require external power sources. They provide linear displacements by converting the energy produced when screws and gears are rotated.
They are generally used in commercial applications that require accurate positioning like equipment manipulation.
Manual Rotary Actuators
Manual rotary actuators provide rotary motions instead of a linear one. They translate energy from levers of gears which are rotated manually through the use of knobs or handwheels. These types of actuators are usually used in valve operations. That is why they are also called valve operators or actuators. They can be used in butterfly, globe, ball and check valves.
#2 Pneumatic Actuators
Pneumatic actuators use compressed gas for operation. The energy produced from the compressed gas is transformed into either a linear or rotary motion. Pneumatic energy is much more preferred for the control of various engines because they respond more quickly. This is because the source of power is not needed to be stored and reserved for operation.
Moreover, if the application requires cleanliness, pneumatic actuators are used rather than hydraulic actuators which will be discussed later. This is because there is a possibility of leakage and contamination of the surroundings when hydraulic actuators are used.
But, leakage in pneumatic actuators is still possible. This makes them less efficient than mechanical actuators. Other than that, they come in big sizes which take up a lot of space. Making them very difficult to transport after assembly.
Pneumatic Linear Actuators
In a pneumatic linear actuator, a piston located inside a hollow cylinder is used. The piston is moved by an external force (compressor) or a manual pump. When the pressure is increased, the cylinder is moved towards the axis of the piston which creates a linear force. The piston goes back to its initial position when fluid is supplied to its other side.
Pneumatic Rotary Actuators
Pneumatic rotary actuators are generally used in air pressure conversion, especially compressed ones, in a cylinder. The energy produced in this conversion is transformed into an oscillating rotary motion. They are durable and offer high forces which makes them operable in hazardous environments.
Pneumatic rotary actuators are classified into two categories: rack and pinion, and vane.
#3 Hydraulic Actuators
A hydraulic actuator consists of a fluid motor that uses hydraulic power to drive mechanical components. Since incompressible liquids are used in the process, it takes a longer time to acquire a certain velocity and power. And thus, they are slower but they can produce greater forces.
Hydraulic actuators also give more precise control of produced movements. They can be manually operated using a hydraulic car jack or a hydraulic pump.
You can go here for some sample applications of hydraulic rotary actuators.
Hydraulic Linear Actuators
These actuators are similar to pneumatic actuators but rather than a pressurized air, an incompressible liquid is used. They consist of a hollow cylinder containing a liquid and a piston inserted inside it.
Hydraulic Rotary Actuators
In order to make valves rotate, a hydraulic rotary actuator utilizes an incompressible and pressurized fluid. Compared to pneumatic actuators, they operate faster and are more powerful. This is because a greater force is produced by the high pressures utilized in the hydraulic systems.
Hydraulic rotary actuators either use a circular shaft or table to create rotational motions. Circular shafts are made with keyways while tables are designed to include a bolt pattern where other components can be mounted.
Moreover, they are used in various industries such as in marine, military and mining applications.
#4 Electric Actuators
This type of actuator is more common than the pneumatic and hydraulic actuators. To be able to use these actuators, they need to be powered by a motor that converts the energy produced to mechanical torque. The electrical energy drives types of equipment that need multi-turns such as ball, butterfly, gate and globe valves.
Electric actuators are the cleanest type of actuators as they do not need oil to be operated.
If you want to learn more about electric actuators, check this link out.
Electric Linear Actuators
In electric linear actuators, mechanical energy is converted into torque. A lead screw connected to an electric motor in the actuator is turned. And when the threads of a ball nut match that of the screw, it is blocked from being rotated. Upon rotating the screw, the nut is controlled through the threads. The directional movement of the ball nut depends on the direction on which the lead screw is rotated.
Electric linear actuators are used with valves that had a sliding stem to open or close the valve. Among these are gate valves which are the most widely used valves. So it’s highly likely that a top gate valves manufacturer always has an actuated globe valve.
Electric Rotary Actuators
Electric rotary actuators are usually made of a gearbox and an electric motor. They control valve components in a rotational manner using the power from the electric motor. These are used to reduce the velocity of the engine and increase the torque.
They generally offer additional control and processing capabilities allowing several stroke stops.
The key component for rotational movements in an electric rotary actuator is either a circular shaft or a table.
Electric rotary actuators are usually used in valves that are rotated like a ball or butterfly valve.
To wrap it all up, the four common types of valve actuators (manual, pneumatic, hydraulic and electric) are discussed in this article. Along with how each type of actuator works, whether through linear or rotary motion and some of the advantages and disadvantages of each.
But in selecting the appropriate type of actuator you’re going to get, you should consider the usage factors depending on your application. Because all of these actuators are designed for certain kinds of valves and do not work for all.