3.  Case study C

Sequencing application  

In process control applications such as sequencing, the Pneumatics systems are generally employed. Electrical components such as relays, programmable logic controllers are used to control the operations of Pneumatic systems. A simple example of a pneumatic sequencing is shown in Figure 6.6.3.

Fig. 6.6.3 Cylinder sequencing- Oscillating cylinder

3.1 Components used

The components used in the circuit are: double acting cylinder, 3/2 roller lever valve, 5/3 pilot operated direction control valve and a 3/2 push button valve. By using this circuit, a continuous to and fro motion of the actuator is obtained.

3.2 Working

When the 3/2 push button is actuated, the air flows from the source through the push button valve to the 3/2 roller valve (S1). The roller valve is already actuated by the cylinder when the piston rod hits the lever of S1. Therefore, there is continuous flow to the 5/3 pilot operated direction control valve (DCV). The flow given to the pilot line 14 actuates the first position of DCV. The air flows from port 1-4 pushes the piston head which causes the extension of the cylinder. As the cylinder fully extends it actuates the 3/2 roller lever valve (S2). The roller valve is actuated and air flows through the valve to the 5/3 DCV. The air enters the DCV through pilot port 12 actuating the second position. Hence the air flows from port 1-2 to the actuator rod end, causing its retraction. The cylinder reciprocates till the supply is stopped. In this way, we can achieve the sequencing operation by controlled actuation of various valves in a pneumatic system.