September 19, 2015

Tutorial 3: Cylinders

In this tutorial we will learn everything about pneumatic cylinders. Pneumatic cylinders uses the power of pressurized gas to produce reciprocating linear motion in the piston. On actuation, compressed air enters into the cylindrical column through the inlet port (at one end of the piston) and imparts force on the piston. Piston extends in this process in response to the pressure difference on its two sides. The animation shows the cross section of the cylinder and the movement of piston inside the cylinder.Pneumatic cylinders vary in size, appearance and function. There are various types of pneumatic cylinder available, many of which are designed to fulfil specific and specialized functions. Basically all the pneumatic cylinders can be broadly classified into two main

Pneumatic Cylinders
Pneumatic Cylinders

  1. Single Acting Cylinder (SAC):

    A Single acting cylinder has an entry for compressed air on one side and a spring on the other side. As shown when air is forced into the inner chamber it compresses the spring and makes the piston move forward. Upon removing the air supply it immediately retracts back because of the force due to spring.

    Single Acting Cylinder

    Single Acting Cylinder

  2. Double Acting Cylinder (DAC):

    A Double acting cylinder has two air inlets for compressed air at both the ends of the chambers. On passing compressed air from one end, piston moves forward and pushes the air out from the other end and vice versa. So each end of the cylinder acts as both inlet and outlet for the compressed air.The force which the piston rod can deliver is not the same for forward and backward strokes when both are powered pneumatically by equal pressure of compressed air.

Double Acting Cylinder

Double Acting Cylinder

The reason is that for forward stroke, the effective area where the pressure is applied is equal to the area of the piston, but for backward stroke the effective area is the area of piston minus the area of piston rod.

Forward Stroke:


Reverse Stroke:

F=P(πR^2 – πr^2))
These two types of pneumatic cylinders are very common and are mostly used. There are many other types of pneumatic cylinders as well. Some of those are discussed here.

  1. Multistage/Telescopic Cylinders:

    Telescopic cylinders incorporate a piston which is nested with a number of hollow segments of increasing diameter to provide an exceptionally long output stroke from a very compact retracted length. This kind of piston allows for a longer stroke than the normal single acting cylinder but its piston can be easily flexed due to its segmented design. Therefore it is used in areas which have low side load.
    Multistage Telescopic Cylinders

  2. Through-Rod Cylinders:

    Here piston rod extends on both the sides of the cylinder, allowing for equal force and speed on either side. This type of actuators are used where we require actuation in both the directions one after the other.
    Through-Rod Cylinders

  3. Cushion End Cylinders:

    These cylinders are equipped with regulated air exhaust to avoid impact between the piston and the cylinder end cover. This kind of cylinders are used where sudden jerks need to be avoided.
    Cushion End Cylinders

  4. Rotary Cylinders:

    Here a linear piston and cylinder mechanism are geared to produce rotation. This type of actuators are used to operate pipeline and process valves in the petrochemical industry.

    Rotary Cylinders

    Rotary Cylinders

  5. Rodless Cylinders:

    It does not have a piston rod. It contains actuator that uses a magnetic coupling to impart force, to a body that translates along the length of the cylinder body, but cannot extend beyond it.
    Rodless Cylinders

  6. Tandem Cylinder:

    It is a combination of two cylinders in series to increase the force output. They can provide constant speed at low velocities.

  7. Impact air cylinder:

    These are high velocity pistons to withstand the impact of the retracting piston rod force. Used in applications where piston need to work at high velocity.

    Tandem Cylinder

    Tandem Cylinder

That is almost everything about pneumatic cylinders. In the next tutorial, we will talk about different kinds of pneumatic valves and their functioning. Just click the continue button to go the next tutorial.

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Tutorial 3: Cylinders

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