Valve actuators are automated mechanical devices capable of adjusting the position of various types of valves. The actuator itself is a mechanism driven by an external power source to produce a particular motion, which controls the valve position. The motion generated by the actuator can be either linear (straight horizontal or vertical motion) or rotary (revolving around a fixed axis).
There are several different types of valve actuators available. However, most actuators fall under two classifications: electric actuators or pneumatic actuators. The main difference between these two types of actuators is the primary driving force used in their operation.
Pneumatic actuators use air (or another gas) pressure as the primary power source to produce motion, which, in turn, controls the valve. In the most common type of pneumatic actuator, the diaphragm actuator, air is pumped into a hollow casing where the resulting pressure acts on a flexible rubber diaphragm to deflect it from its original position.
The diaphragm, which is connected to a valve stem, moves up or down to adjust the valve disc and control fluid flow. Pneumatic actuators typically produce linear motion but can also be used to generate rotary movement.
Electric actuators, on the other hand, use electricity as the main power source to drive the actuator motion. Electric actuators are further subdivided into two classifications: solenoid or motor-driven actuators. In solenoid driven actuators, an electrical current is passed through a coil to generate a magnetic field that moves the metal stem to adjust the position of the valve disc.
Motor-driven actuators use an AC- or DC-powered servo motor to move the valve to the desired position. Electric actuators are capable of producing linear or rotary motion.
Benefits and Uses of Pneumatic Actuators
Pneumatic actuators are capable of producing some of the highest closing forces of all actuator types. Some pneumatic actuators can have a maximum pressure rating of 250 psi and can generate forces of up to 40,000 lb. Relatively fast closing speeds of up to 2m/s are also possible with this type of actuator. Both the speed and the force of the actuator can be easily fine-tuned by adjusting a system of pressure relief valves or flow regulators.
Another key advantage of pneumatic actuators is the comparatively low per unit cost. Pneumatic cylinders are inexpensive and can be easily upgraded to larger diameters. Large air compressors are also very efficient and economical for powering large groups of pneumatic devices.
These actuators are well-known for their clean operation, lack of ignition source, and high reliability making them ideal for use in internal combustion engines, pumps, ventilation systems, and service in flammable or ignitable environments.
Benefits and Uses of Electric Actuators
One of the main advantages of electrical actuators is their precise and accurate positioning control. Intermediate and stop positions can be preprogrammed, allowing the actuators to be positioned at any location based on a specific input. Electric actuators also offer some of the fastest movement among all types of actuators, with speeds up to 10m/s.
The separation of the electrical power source from the actuator facilitates easier maintenance of the actuator components and can minimize replacement costs. Also, electric actuators produce less noise than other types, making electric models very useful in noise-sensitive environments.
Electric actuators are typically used in machinery and equipment such as excavators, dump trucks, and forklifts. Lighter-duty electric actuators are commonly found in factory robotics and other manufacturing automation applications.
Choosing the Right Actuator for Your Application
Both pneumatic and electric actuators offer unique features and benefits that lend themselves to specific applications.
Understanding how these actuators work and fully grasping the differences between their modes of operation is crucial for determining the best type of actuator for a specific application.
- What's the Difference Between Pneumatic, Hydraulic, and Electrical Actuators?
- Pneumatic Actuators
- How to Decide Between Electric, Pneumatic and Hydraulic Actuators
- Electric Actuators
- How to Decide Between a Pneumatic and an Electric Actuator
- Control Valve Assemblies
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