PneumaticsDouble Acting Cylinder

ObjectivesExplain the function of double

acting cylinder.Describe the main types of

controlling double acting cylinder.Explain the difference between

direct control and indirect control of single acting cylinder.

Explain the differences between single and double acting cylinder.

Draw the required circuit diagram.Simulate the pneumatic circuit

using FluidSIM software.

Double Acting CylinderDouble acting cylinder is considered to be as a

main actuator in any pneumatic systems. Double acting cylinders are more expensive than

single acting cylinders, but double acting cylinders are superior to single acting cylinders by any other important measure.

Double action cylinders are faster and stronger.

In industrial applications, single action cylinders are used in few applications, but when speed and force are important double acting cylinders are employed.

Applications of DAC1. Opening and closing doors 2. Taking things off conveyor

belts and putting things on conveyor belts.

3. Lifting and moving packages around

4. Presses and punches.

Comparison between Single & Double Acting Cylinders

SerialSingle acting

cylinderDouble acting cylinder

1 It has one port. It has two ports.2 It has a spring. It has no spring.

3It exerts force in one direction only.

It exerts force in two directions (forward and backward).

4

It uses compressed air in the forward stroke while the return stroke is achieved by the spring.

It uses compressed air in both strokes forward and backward.

FunctionDouble acting cylinder is

an output device that converts the pressure energy to a mechanical energy (linear motion).

Way of OperationDouble acting cylinder as

mentioned has two ports and the air is applied in both directions (forward and backward)

Forward (Advance) StrokeThe air is supplied to port

(1) and the exhaust air is forced out through port (2)

Backward (Return) StrokeThe air is supplied to port

(2) and the exhaust air is forced out through port (1)

Which Force is larger; The Forward or Backward Stroke?

The force produced by the piston during the advance stroke is greater than the force produced during the return stroke due to the area difference between the two sides of the piston

Control circuit of the double acting cylinder

The piston rod of a double-acting cylinder is to advance when a push button is operated and to return to the initial position when the push button is released. The double-acting cylinder can carry out work in both directions of motion, due to the full air supply pressure being available for extension and retraction.

Types of Control of a Pneumatic Cylinder

Direct Indirect

DIRECT CONTROL

The simplest level of control for the single or double-acting cylinder involves direct control signals.

With this, the cylinder is actuated directly via a manually or mechanically actuated valve, without any intermediate switching of additional directional control valves.

If the port sizes and the flow values of the valve are too large, the operating forces required may be too great for direct manual operation.

Reference values for limits of direct cylinder control:Cylinder with piston diameter smaller than 40 mmValves with connection sizes smaller than 1/4"

INDIRECT CONTROL

Cylinders with a large piston diameter have a high air requirement.

A control element with high nominal flow rate must be used to actuate these.

If the force should prove too high for a manual actuation of the valve, then an indirect actuation should be constructed, whereby a signal is generated via a second smaller valve, which will provide the force necessary to switch the control element.

To achieve the indirect control, a single and/or double pilot valves will be required

NOTEThe actuation of a cylinder is effected via a directional control valve. The choice of such a directional control valve (number of connections, number of switching positions, and type of actuation) is dependent on the respective application. The advancing speed and the retracting speed are different in the single acting cylinder because the piston reset spring creates a counteracting force when advancing. When retracting, the displaced air escapes via the valve. A flow resistance must therefore be overcome. Normally, single-acting cylinders are designed in such a way that the advancing speed is greater than the retracting speed.