Pneumatic Actuators

In this case we are talking about rotary 90 degree turn Pneumatic Actuators (you can also get linear as well) which are designed to turn a valve (usually ball, butterfly or plug) through 90 degree rotation (open and close). Pneumatic air pressure is used to operate the actuator. The base of the actuator pinion is attached to the valve stem which turns the valve through 90 degrees. These actuators come in various designs namely; Rack and Pinion, Scotch Yoke and Vane. Rack and Pinion are commonly used for smaller sizes due to their compact design whereas Scotch Yoke are usually used in much larger valve applications. Vane style is now rarely used. Pneumatic actuators are available in Double Acting or Spring Return (also sometimes referred too as single acting) configurations and use compressed air as the medium. Various accessories can be used in conjunction with the actuator such as Namur direct mount solenoid valves, speed controllers, load control and feedback limit switches. Pneumatic actuators come in various sizes and corresponding torque ranges, with the torque increasing as the bore size increases (larger surface area of the piston).

The Rack and Pinion actuator are a pair of gears which convert linear motion into rotational motion. The rack with its piston head and seals engages teeth on the circular gear called the pinion giving rotational motion. The actuator uses two piston-type racks moving in opposite directions (double acting) to give a balanced force on the central pinion. Pneumatic air pressure is used to operate the actuator. The base of the pinion is attached to the valve stem. Air pressure can be applied to open or close the valve usually through a five way 2 position valve (eg. solenoid or manual valve).  As air pressure increases the force on the surface area of the piston is increased resulting in higher torque from the actuator. Preloaded springs give a single action option when required. Scotch Yoke actuators use a piston to operate a cam that is fixed to the pinion arm for rotation. They have an over-centre function at the end of stroke. If required a spring pack attached to the other end gives a single action function.

The actuator sizing is based on the torque requirement for the valve to be actuated. From the valve data sheet obtain the working torque Nm (torque required to turn the valve at the required pressure, temperature and media viscosity) and add a minimum 30% safety factor. Always check breakaway- torque for the valve. Especially on butterfly valves this can be higher than the working torque because of the unseating of the valve disc off the seats. Using this find the corresponding actuator with this figure (or greater) and select. Also check the valve mounting pad configuration against the valve hole pattern. It may be necessary to step up an actuator size to accommodate ease of mounting.

Like any valve this depends upon the usage case of your actuator, its environment, media and how many times it is cycled. These are available as spare parts. The actuators life will depend upon how clean and dry the supply air is (the air that makes the actuator operate) however we regularly test these to over 800,000 cycles. Install a basic air filter if you are not sure about the quality of your air, we have pneumatic actuators that have been in operation for decades. The most common failure we see is due to dirty wet air used in the actuator. An Air Service Unit in the air supply will help with contaminated air. We have had these actuators operating for decades without any maintenance.

The Pneumatic Actuator can be installed either by direct mounting or via an adaptor to any ball, butterfly or plug valve that requires a 90 degree rotation. The actuator can be mounted in any position and tolerate most environments. If the valve does not have the ISO 5211 mounting pad an adaptor can be customized to fit. Drive adaptors can also be supplied to accommodate various stems. Namur valves directly interface onto the actuator for control and feedback can be achieved by mounting a suitable limit switch box directly onto the ISO indicator area. Speed of rotation can be controlled with precision using inline or exhaust controllers. Force (torque) can be regulated by pressure control of the air supply vai the Air Service Unit.

Applying rotational control through 90 degrees the pneumatic actuator can operate ball, butterfly and plug valves in many sizes. There are many uses outside actuating a valve and we have even seen our actuators used on sheep gates. Pneumatic actuators use compressed air giving reliability in difficult environments, explosive atmospheres and where electrically cannot be supplied.

This depends upon where you are based and the freight method chosen. If the express freight option is selected it is usually next day delivery to metropolitan areas in Australia for under 5kg. If free freight has been selected it will go by road freight which can be anywhere from 1 to 10 days depending upon your location. It usually averages 3 days.

All of our products come standard with a 12 month warranty. The good news is we have very strict quality controls and all actuators leave our warehouse tested (full material and testing certificates to API598 are available) and inspected so there are rarely any issues. Also once your valve is in and operating it will most likely continue to do so for a very long time barring any debris getting caught in the valve or power spikes causing the coil to fail..