Pneumatic Valve Actuators

Actuated valve with pneumatic
scotch yoke actuator (Metso Neles)

Pneumatic valve actuators are used in extreme conditions in many industries such as oil and gas, chemical, water and wastewater, bulk storage, pulp & paper, and power generation. These devices are used in a multitude of valve control processes for regulation (or cessation) of flow, and / or controlling pressure and level.  Due to their reliability and simplicity, pneumatic actuators are one of the most popular types of actuators used in industry today.

Pneumatic valve actuators work by conversion of air pressure into motion. The device applies a force of air to a diaphragm, rotary vane, or piston that is attached to the actuator shaft, which is then mechanically connected to the stem of the valve or damper. Depending on the type, pneumatic actuators produce either linear or rotary motion. 

ACTUATOR ACTION - SPRING RETURN OR DOUBLE ACTING

Spring Return — Pneumatic actuators with spring return design have air supplied from one side. The spring on the opposite side is responsible for the motion. With this design, air compression moves the opens or shuts the valves while the spring is responsible for the opposite motion. 

Diaphragm actuator
(Metso Neles)

Double Acting  — Double acting actuators have air fed on both sides of a piston. The pressure on one side is higher as compared to the other that results in the required in movement. Air is used to open and close the valves.  

PNEUMATIC ACTUATOR DESIGNS

Diaphragm Actuators — Diaphragm actuators work by applying pressure to a thin membrane or diaphragm.  

Piston Actuators — Piston actuators apply compress air to a piston that is within a cylinder. Air is fed into a chamber that moves the piston in one direction. The piston moves in the opposite direction when air pressure is removed (spring assisted) or directed to the other side (double acting). 

Rack and Pinion — Rack and pinion actuators produce rotation by applying pressure to pistons with gears that turn a pinion gear. Rack and pinion actuators can be spring return or double acting. They are valued because of their compact size and versatility.

Rack and pinion actuator
(Metso Jamesbury)

Scotch Yoke — A scotch-yoke actuator contains a piston, yoke, connecting shaft, and rotary pin. They can be direct acting or spring return. They are capable of providing very high torque outputs and are generally used on larger valves. Scotch yoke actuators can be powered by air or process gas.

Rotary Vane —Vane actuators use a mechanical vane, connected to a shaft, that separates a circular shaped body in two "clamshell" halves. The vane moves in response to the differential pressure inside the actuator body, turning the shaft clockwise or counter-clockwise in response to the pressure differential. External springs units are available for spring return models.

Scotch yoke actuator (Metso Neles)

BENEFITS OF PNEUMATIC ACTUATORS

The use of compressed air (typically found in all industrial facilities) as the power source is the prime advantage for the use of pneumatic actuators. Additionally, pneumatic actuators have an advantage in suitability for different environments and can be used in extremes temperatures. They are preferred over electrical actuators in explosive, flammable and other hazardous areas because they do not require electricity (a possible ignition source) to operate. They do not create electrical fields or electrical noise since there is no electrical motor. Pneumatic valve actuators are faster opening and closing compared to their electric counterparts. Finally, they are low cost, lightweight, durable, require little maintenance (depending on quality) and there are a myriad of positioning controls, speed controls, and communications devices available for tailoring the actuator to the application.

DRAWBACKS OF PNEUMATIC ACTUATORS

While compressed air is the main reason for using pneumatic actuators, it can also be considered a drawback. For instance, pneumatic actuators can perform poorly when the air supply source is located at a distance, resulting in lag and slow response. Another drawback of pneumatic actuators is the additional cost for the compressed air system due to the requirement of dust filters and moisture removing dryers. These are required to ensure clean air is fed into the system.

APPLYING PNEUMATIC ACTUATORS

There are many aspects to the proper, safe, and efficient application of pneumatic actuators to valves and dampers. The sizing the power (torque) output being paramount. All valves and dampers have unique torque requirements. You must consider a threshold force for opening (breakaway), as the valve continues to move to its open or closed position, and then for seating. Matching the actuators to the valve type, and operating conditions is critical. Published torque curves must be reviewed and understood. Too little torque and the valve will not respond. Too much torque increases cost and can damage the valve. Spring return adds to this complexity. Considering all this, it is strongly suggested you always discuss any valve actuation requirement with an experience applications expert. They will ensure the proper, safe, and cost effective mating of pneumatic actuator to valve or damper.

Understanding Industrial Valve Actuators

Automated Pneumatic
Ball Valve (Jamesbury)

Valves are essential to industries which constitute the backbone of the modern world. The prevalence of valves in engineering, mechanics, and science demands that each individual valve performs to a certain standard. Just as the valve itself is a key component of a larger system, the valve actuator is as important to the valve as the valve is to the industry in which it functions. Actuators are powered mechanisms that position valves between open and closed states; the actuators are controllable either by manual control or as part of an automated control loop, where the actuator responds to a remote control signal. Depending on the valve and actuator combination, valves of different types can be closed, fully open, or somewhere in-between. Current actuation technology allows for remote indication of valve position, as well as other diagnostic and operational information. Regardless of its source of power, be it electric, hydraulic, pneumatic, or another, all actuators produce either linear or rotary motion under the command of a control source.

Thanks to actuators, multiple valves can be controlled in a process system in a coordinated fashion; imagine if, in a large industrial environment, engineers had to physically adjust every valve via a hand wheel or lever! While that manual arrangement may create jobs, it is, unfortunately, completely impractical from a logistical and economic perspective. Actuators enable automation to be applied to valve operation.

Pneumatic actuator
(Jamesbury Quadra-Powr) 

Pneumatic actuators utilize air pressure as the motive force which changes the position of a valve. Pressurized-liquid reliant devices are known as hydraulic actuators. Electric actuators, either motor driven or solenoid operated, rely on electric power to drive the valve trim into position. With controllers constantly monitoring a process, evaluating inputs, changes in valve position can be remotely controlled to provide the needed response to maintain the desired process condition.

Manual operation and regulation of valves is becoming less prevalent as automation continues to gain traction throughout every industry. Valve actuators serve as the interface between the control intelligence and the physical movement of the valve. The timeliness and automation advantages of the valve actuators also serve as an immense help in risk mitigation, where, as long as the system is functioning correctly, critical calamities in either environmental conditions or to a facility can be pre-empted and quickly prevented. Generally speaking, manual actuators rely on hand operation of levers, gears, or wheels, but valves which are frequently changed (or which exist in remote areas) benefit from an automatic actuator with an external power source for a myriad of practical reasons, most pressingly being located in an area mostly impractical for manual operation or complicated by hazardous conditions.

Electric Actuator
(Limitorque)

Thanks to their versatility and stratified uses, actuators serve as industrial keystones to, arguably, one of the most important control elements of industries around the world. Just as industries are the backbones of societies, valves are key building blocks to industrial processes, with actuators as an invaluable device ensuring both safe and precise operation.