What powers them?
The pneumatic actuator is powered by compressed air from an external source, most often dry, clean air. An air compressor can usually drive several pneumatic actuators at once. Giving them an advantage over other types of actuators. Especially if the system has a large number of valves.
As an example, an electric valve actuator requires a power source (motor).
Why consider a Pneumatic Actuator?
There are several factors to consider when deciding which actuator is best suited for a particular application, including the environment, required accuracy, and closure/opening speed. The main difference between actuators is the amount of thrust or torque they can produce. These are some general applications for actuators:
Hydraulic Actuators: As this type of actuator is powered by compressing oil, it is the most powerful and reliable type and is recommended for heavy-duty and high-load environments since the oil used to power it is non-elastic.
Pneumatic Actuators: Compressed gas powers this type of actuator. It’s ideal for medium-duty, average-load environments and recommended for high-speed, high-accuracy applications. The low operating pressures of pneumatic actuators limit the amount of thrust or torque they can produce. For this reason, they are often used to automate smaller valves. When large actuators are required, thrust or torque requirements are high.
Electrical Actuators: Actuators of this type are powered by electric current. Suitable for medium-duty and light load work environments, it is recommended for accurate control. You can find them in industries like food & beverage, pharmaceuticals, and heavy industries like mining and power generation.
How Do Pneumatic Valve Actuators Work?
Pneumatic actuators typically consist of a piston or pistons inside a hollow cylinder. One side of the piston inside the cylinder is subjected to pressure. As a result of the pressure and the area of the piston, a force is generated that moves the piston along the axis of the cylinder, transferring the energy to the valve to be automated.
The piston is then returned to its original position by a spring, also known as a spring-return actuator. In double-acting actuators, compressed air is applied to the other side of the piston.
What Valve Types Does A Pneumatic Actuator Work With?
There are two types of motion that can provide by a pneumatic actuator.
- Linear motion is suitable for linearly moving valves such as gate valves and globe valves. They are usually spring-return actuators. When air pressure is relieve, the actuator moves back to its original position. This valve is either normally close or normally open. Double-acting actuators are use for continuous control applications. Both sides of the piston are compressing.
- The rotary motion is suitable for quarter-turn valves such as ball valves and butterfly valves. They can be spring-return actuators. Once air pressure is release, the actuator returns to its original position. The valve can either normally close or normally open. Double-acting actuators are use in continuous control applications. Compress air is applied on both sides of the piston.
How should a pneumatic actuator select? What size should it be for a particular valve?
The selection and sizing of a pneumatic actuator depend on three main factors
- Type of motion required
- Required control
- Torque or thrust required
|Type of Motion||Gate valve / Globe valve||Linear Motion Actuator|
|Ball valve / Butterfly valve||Rotary Motion Actuator|
|Required control||Close/open valve positions, isolation valves, or shutoff valves||Actuators for shutoff valves that require a failsafe action or double acting actuators for non-critical valves|
|Variable valve position, control or modulation on a continuous basis||Commonly, dual port double acting actuators, or single acting if a failsafe position is require. They have high duty cycles.|
|Torque||Liner along with opening/closing movement||Rack and Pinion Actuator|
|High torque at the start and end of motion||Scotch-Yoke Actuator|
Torque values required for sizing
Operating torque alone is not sufficient for sizing actuators correctly; the following table shows require torque values.
|Break Torque (BTO)||Torque required to open a completely closed valve|
|Running Torque (RTO or RTC)||Keeping the valve moving at a constant speed between closed and open positions requires a constant torque|
|Seating Torque (ETC)||The torque needed to completely seal the valve (sealed position)|
|Maximum Shaft Torque (MAST)||Torque maximum allowed on valve stem ( for safety reasons )|
Due to different sealing types and materials, even valves with the same PN and DN values may have different torque values.
Industry applications of pneumatic valve actuators:
- Oil & Gas: Drive valves for isolating and regulating the flow
- Mining: valves for isolating and regulating pressure in rock shearing lines
- Water and wastewater: Control valves for isolating and regulating drinking water feed lines and sand filters and tanks
Usually, pneumatic actuator malfunctions are cause by two main factors:
- Power loss due to pressure loss
- Wearing due to lack of lubrication
Aira Euro Automation is a leading manufacturer of pneumatic actuator in India. Also, offer many types of an actuator for different valve as per the size and customer requirement. We have low to high torque actuators.