1. Double Acting Cylinder
Pneumatics – Module 5

2. Objectives Explain 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.

3. Double Acting Cylinder
Double 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.

4. Applications of DAC Opening and closing doors
Taking things off conveyor belts and putting things on conveyor belts.
Lifting and moving packages around
Presses and punches.

5. Comparison between Single & Double Acting Cylinders
Serial
Single acting cylinder
Double acting cylinder 1
It has one port.
It has two ports. 2
It has a spring.
It has no spring. 3
It 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.

6. Function
Double acting cylinder is an output device that converts the pressure energy to a mechanical energy (linear motion).

7. Way of Operation
Double acting cylinder as mentioned has two ports and the air is applied in both directions (forward and backward)

8. Forward (Advance) Stroke
The air is supplied to port (1) and the exhaust air is forced out through port (2)

9. Backward (Return) Stroke
The air is supplied to port (2) and the exhaust air is forced out through port (1)

10. 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

11. 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.

13. Types of Control of a Pneumatic Cylinder
Direct
Indirect

14. 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 mm
Valves with connection sizes smaller than 1/4"

15. 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

16. NOTE
The 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.

17. Practical Task
A filling system fills bottles with milk. The bottles are fed to the system on a conveyor belt and are stopped underneath the filler using pneumatic cylinders. The double acting cylinder 1A1 (due to its large size) has to be controlled indirectly.

18. Task Requirements
Draw pneumatic circuit that controls the double acting cylinder (1A1) indirectly. You may use the provided space below.
Simulate the circuit using FluidSIM software.
Assemble the circuit practically and check its operation.
Write down your observation below

20. Solution Description
In the initial position, the double-acting cylinder 1A1 is retracted.
A 5/2-way single pilot valve is used to actuate the cylinder. Connection 2 & 4 of the valve 1V1 is connected to the cylinder; connection 4 is exhausted to atmosphere via connection 5.
The valve 1S1 is actuated when the push button is activated and pressure is applied to the control port 14 of the control valve 1V1.
The control valve 1V1 is actuated against spring force and is thus switched to flow.
The pressure building up at the cylinder piston causes the cylinder piston rod of the double-acting cylinder to extend.
The signal at the control port 14 remains as long as the push button is operated. Once the piston rod has reached end position, it returns only after the push button has been released.
 When the push button is released, the valve 1S1 returns to its initial position. Control port 14 of the control valve 1V1 exhausts to atmosphere and the signal is reset. The control valve also returns to initial position. The return spring causes the cylinder to retract. The air from the cylinder chamber is exhausted to atmosphere via the control valve.

21. Review Exc.