Technical Studies – Study 22
Pneumatic cylinders are the linear actuators that convert the pneumatic energy into mechanical energy. They are of two types –
- Single acting cylinder
- Double acting cylinder
Single acting cylinder (SAC):
A Single acting cylinder takes the compressed air as input for only the forward movement of the piston rod and for the return movement of the piston rod it uses the force of an inbuilt spring. This type of cylinder can deliver the work in one direction only. One operating cycle of a single acting cylinder requires only half volume of air consumed by a double acting cylinder.
The stroke length of the single acting cylinder is 100 mm, because the inbuilt spring takes the space inside the cylinder. Single acting cylinder is used in braking systems, clamping works, lifting etc.
Different types of single acting cylinders:
Diaphragm cylinder is a single acting cylinder that uses a rubber or plastic diaphragm instead of the piston. Such cylinders are used in short stroke applications, because their maximum stroke length is 50 mm. Diaphragm cylinders are particularly used in opening and closing of large size valves.
Rolling diaphragm cylinder:
Like diaphragm cylinder this single acting cylinder also has a diaphragm instead of the piston. In this cylinder, the diaphragm rolls through the inner walls of the cylinder when the compressed air is applied. The maximum stroke length of this cylinder is 50 mm to 80 mm.
Double acting cylinder (DAC):
A Double acting cylinder takes the compressed air as input for the movement of the piston rod in both forward and reverse direction. This type of cylinder can deliver the work in both directions. Double acting cylinder is controlled by the air supply in both the directions.
There is no specified stroke length limit for double acting cylinder. Double acting cylinder is more useful and expensive than single acting cylinder. Double acting cylinders are used in automobile industries, elevators, fork lifts, door opening and closing etc.
Cushioned double acting cylinder:
To prevent the cylinder from damage and the shock, cushioning is used at the end position of the cylinder. The cushioning helps the cylinder to reach the end position slowly by reducing the speed of the cylinder.
Special purpose cylinders:
Special purpose cylinders are designed for specific applications. For different applications there are different designs of pneumatic cylinders available. Those are –
Impact cylinder is designed to perform the function of a press. Such pneumatic cylinder is used for punching, riveting and metal forming operations. It is also called high velocity cylinder, because it can accelerate to a high velocity of 7.5 m/s to 10 m/s.
Tandem pneumatic cylinder is designed by combining two double acting cylinders in series. In such configuration the power of both the cylinders gets added and the piston output gets doubled. Tandem cylinders are used in large force applications.
Rotary cylinder can produce rotary motion. The piston rod of rotary cylinder is machined into a rack shape and attached to a gear wheel to produce rotary motion. The maximum angle this cylinder can produce is 360 degrees. Rotary cylinder is used for bending metal tubes, actuating stop slide valves etc.
The torque of this cylinder is depends upon the pressure applied. Rotary cylinders are designed to deliver high starting torque.
Rotary vane cylinder:
Rotary vane cylinders are similar to rotary cylinders. These cylinders can produce small torque and have limited rotary angle i.e. 300 degree. The rotary angle increases hardly above 300 degrees. The rotary vane cylinder is not frequently used in pneumatic system.
Multi position cylinder:
Multi position cylinder is the combination of two double acting cylinders in reverse arrangement. This cylinder has 4 positions because of the reverse arrangement. Such cylinders also designed for 6, 8 and 12 positions. Multi position cylinders are used for actuating the lever.
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