control of a double-acting hydraulic cylinder

CONTROL OF A DOUBLE-ACTING HYDRAULIC CYLINDER

1. Functional and Operational Requirements

A double-acting hydraulic cylinder is to be provided with a forward and return control. A provision of 'inching' or 'hold' of piston in any intermediate position is necessary. Also the speed of piston during forward and return strokes should be the same. The actuation is to be manual.

2. Circuit

Fig.8.3 illustrates a hydraulic circuit meeting the above functional and operational requirements. This circuit uses a three-position, four-way, manually operated directional control valve (tandem position) and a double-acting cylinder.

3. Operation

left Extension: When the 4/3 DC valve is manually shifted to the left mode (i.e., envelope flow path configuration), oil from the pump flows to the blind end of cylinder. As oil flows from port P through port A, the cylinder is extended against the load force Fload At the same time, the oil in the rod side of the cylinder flows back freely to the-fank (via the 4/3 valve from port B through port T).

Retraction: At the end of extension stroke, the 4/3 DC valve is manually shifted to the right envelope. When DCV is shifted to the right mode, the oil from the pump flows to the rod side of the cylinder. As oil flows from port P through port B, the cylinder is retracted. At the same time, oil in the blank end flows back freely to the tank (via the flow path from port A to port T).

Cylinder locking: When the 4/3 DC valve is shifted to the centre position (i.e., spring • centered position in tandem design), the pump flow completely goes to tank and hence the cylinder is hydraulically locked.