Although pneumatic actuators are typically used for valve control processes to get a fast response, it usually doesn’t work efficiently when there is a need for a large amount of motive force. The basic design is hundreds of years old and is suitable for robust applications where high pressure, low friction, high pressure and high torque are desired. In contrast to electric linear actuators, hydraulic actuators can be adapted to almost any weight and are suitable for applications with high power.
The hydraulic actuator is the best alternative that can drive a large amount of motive force. Given the low pressure of a hydraulic pump or a valve or a mechanical valve, it is possible to generate enormous operating forces in a hydraulic actuator, the lubricating effect of the hydraulic oil helps to overcome the frictional properties of piston actuations. The resultant mechanical motion may be in linear, rotary, or oscillatory motion.
As we know, liquids are extremely difficult to compress, which is why a hydraulic actuator is used to apply a great amount of force. If you are able to generate a force that is 25 times that of a compressed air cylinder, then a hydraulic valve actuator should be considered. The compressibility of the oil makes it more suitable for load control applications, as it can provide a cushion that would otherwise have to mechanically replicate.
However, the term ‘single-acting’ uses when the fluid pressure is applied to piston’s one side, while the term ‘double-acting uses when pressure is applied on the two sides of the piston.
Types of Hydraulic Actuators
- Hydraulic Helical Valve Actuator
- Hydraulic Scotch-Yoke Valve Actuators
- Electro-Hydraulic Actuator – Electro-hydraulic actuators (both linear and rotary) can also consist of a mechanical feedback mechanism in which mechanical feedback forces can be provided by generating mechanical “feedback forces” that compensate for the input forces of the load generator in order to create a more precise and reliable control system for the use of electro-hydraulic actuators.
- Gas Hydraulic or High-Pressure Pipeline Pneumatic Valve Actuators
- Hydraulic Wellhead Protection
- Hydraulic Emergency Shutdown System
Mechanism of Hydraulic Actuator
The supply and return line of the hydraulic actuator is attached to the lower chamber; thus, it allows fluid to flow from the lower chamber of the hydraulic actuator. However, the system of actuator transmits the piston’s motion to a valve. At times when fluids enter the lower chamber, the level of pressure gets increased in the chamber.
This results in an increased force applied at the bottom of the piston, which is opposite to the force caused by spring.
Hydraulic actuator operation works on the principle alike of a pneumatic actuator. Both actuators use some force to overcome the spring force to let the valve more. The hydraulic actuators are designed to fail-open or fail-closed to offer a fail-safe feature.
Hydraulic actuators are able to hold a force or torque for as long as they need without sending an additional fluid pressure to the pump. The downside of hydraulic actuators is that they can leak fluid and this can cause them to be inefficient. This also makes it difficult to have them in a position where they have to be some distance away from you without suffering a loss of power.
Advantages of Hydraulic Actuators
- Hydraulic actuators are the best for producing large force. These can easily produce forces 25 times greater as compared to pneumatic cylinders of the same size.
- This can hold force and torque constant without suppling more pressure.