reciprocation of a double-acting cylinder using pressure switches

RECIPROCATION OF A DOUBLE-ACTING CYLINDER USING PRESSURE SWITCHES

1. Circuit and Construction

Fig.14.11 shows how two pressure switches can be used to control the operation of a double-acting hydraulic cylinder. Fig.14.11(a) shows the hydraulic circuit diagram and Fig.14.11(b) shows its ladder diagram. In Fig.14.11(b), as long as switch 1-SW is closed, the cylinder reciprocates continuously.

2. Operation

The sequence of operation is as follows :

Extension stroke

1. When solenoid SOL A is energized, the 4/2 DC valve is shifted to left mode and it forces the oil to flow into the blind end of the cylinder. Thus the cylinder extends.

2. When the cylinder is extended to its maximum stroke, the pressure builds up to actuate pressure switch 1-PS. This energises the solenoid SOL B, as could be seen from Fig.14.11(b).

Retraction stroke

3. When the solenoid SOL B is energised, the 4/2 DC valve is shifted to right mode and it forces the oil to flow into the rod end of the cylinder. Thus the cylinder retracts.

4. When the cylinder is fully retracted to its left, the pressure builds up to actuate pressure switch, 2-PS. During retraction period, pressure switch 1-PS has been de-actuated to de-energise SOL B.

Cycle of operation

5. The closing of the contacts of 2-PS energizes SOL A to once again begin the extending stroke of the cylinder. Thus the cycle of operation can be repeated again and again.