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Pneumatic actuators

Pneumatic actuators use pressurized air to generate mechanical force to operate the valves. They are the most widely used actuators in different industries delivering quick response to the process requirements.

Ramén provides its customers with a various range of high quality pneumatic actuators from well-known brands (e.g. AirTorque, Wirematic, & Rotork (Remote Control)) to assure an accurate and stable control, minimum maintenance and maximum service and support to end users.

These actuators are available in single acting for fail-safe requirement or double acting configuration. In single acting, the air load from the valve positioner drives the actuator in one side while the other side is controlled by the spring load. This type of configuration perfectly suit the process safety applications where fail-close (i.e. valve should be closed in loss of signal) or fail-open (i.e. valve should be opened in loss of signal) is a requirement.

In double acting configuration, the actuator is operated by air load on both sides. Double acting actuators can provide smooth and stable control in many applications. For instance, they are the best choice for fail in last position requirement, meaning the valve should be turned to its last position if the control signal is lost.

We deliver pneumatic actuators that follow either Scotch yoke or rack and pinion principles.

Rack and pinion VS. Scotch yoke

In rack & pinion mechanism a circular gear (pinion) rotates by two gear bars (racks) due to the air pressure in the outer/inner chamber of the actuator. This results in a rotary motion of the actuator. While in the Scotch-yoke actuators rotary motion is achieved by linear motion of a slider/piston. The reciprocating part is coupled to the sliding yoke with a slot that engages a pin on a disk-shaped crank. The air pressure in the piston inserts a force to rotate the crank resulting in the actuator rotary motion.

Rack & pinion actuators are normally used for control purposes since they give a constant torque in all positions, as shown in the graph below. However, Scotch yoke actuators gives better performance for On-Off valves/applications (e.g. ball and butterfly valves) due to higher torque output at the start and end of the valve stroke.

Torque output in rack and pinion vs. Scotch yoke

These actuators have housing and inner parts in anodized aluminium and stainless steel and other treatment on request for harsh environment. They offer highly safe operation in numbers of applications with different hazardous area classifications.

To have an improved control resolution, Ramén can offer a set of auxiliary equipment:

  • Positioners for accurate control
  • Solenoid valves for On/Off applications to isolate
  • Airsets to protect the equipment

Do not hesitate to contact us for further information or assistance regarding our control valve packages.