Actuators Used in Pneumatic Systems.

Updated: Feb 10

In previous blog we had seen the components used in pneumatic systems, one of them was actuator which takes action on the basis of command given.

Pneumatic actuators are devices which uses pressure energy of compressed air to give mechanical work. This devices can exert force of required parameter for the given purpose.

Talking about actuators, a pneumatic cylinder is capable of giving all three basic motions i.e., linear, rotary or oscillating by arranging it with particular mechanism.


Types of Actuators used in Pneumatic System.

Basically their are three types of pneumatic cylinder,

Linear Actuator or Pneumatic Cylinder.Rotary Actuator or Air MotorsLimited angle actuator.


Types of Pneumatic Cylinder.

1. Single Acting Cylinder


These cylinder are operated in one direction only, as we know cylinders have two strokes forward and backward, the single acting cylinders are controlled for only one stroke either forward or backward(generally their forward stroke is controlled) and the other is spring controlled it means once the piston reaches to its maximum possible point it is reverted back by spring force, at this point compressed air stops acting.

In these cylinder their is only one inlet port from where compressed air can be supplied, during exhaust stroke air inside the cylinder is released by a exhaust port.

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Fig. : A single acting cylinder.


2. Double Acting Cylinder


These cylinders consists of two ports so that both forward and reverse motion of the cylinder can be controlled. To get forward motion compressed air is inserted from piton side port and to obtain reverse motion air is inserted from rod side.

In double acting cylinder there is no return spring. Benefit of double acting over single acting is magnitude of motion is controllable for both strokes.

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Fig. : Double Acting Cylinder

These cylinders are of two types

i) Double acting cylinder with piston rod on one side.

In these cylinder the rod is on only side of the rod as shown in figure below,


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Fig.:  Double acting cylinder with piston rod on one side.


ii) Double acting cylinder with piston rod on both side.

In these cylinders the rod is on both side of the piston as shown below,


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Fig. : Double acting cylinder with piston rod on both side.


Rotary Actuators


A the name signifies, rotary actuators are used when rotary output is needed. These devices high torque output with limited angular moment of 90, 180 or 270 degrees. 

These actuators are of following types,

Vane type limited rotation motor.Rotary actuator or rack and pinion type 


Vane Type Limited Rotation Actuator


It's name says limited rotation because in this actuator we can not obtain a complete rotation but the torque and motion produced in rotary sense.

These actuators got circular design with two ports, inside the circular housing there is a shaft which is connected to a vane, the vane is in between both ports so when compressed air is inserted from one port the vane moves toward the other port and it rotates the shaft, once the vane is at the end of stroke the second port is feeded with compressed air now vane will move in reverse direction and the first port will act as exhaust port.


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Fig.: vane type limited rotation actuator

Rotary Actuator of Rack and Pinion Type


As we know in rack and pinion mechanism, the rack gives linear motion but it is converted to rotary by help of a pinion, gears of same configurations are used on both rack and pinion to obtain this motion.

In this actuator similar mechanism is used, a geared rack is mounted with piston heads from both ends and in between a pinion is placed. Air is supplied from both sides of the rack to rotate the pinion clockwise and counter-clockwise.

With the figure below it can be understood better,


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Fig.: Rack and pinion type rotary actuator.

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References

1. NPTEL

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