End-position cushioning

Cushioning, or end-position cushioning, is a term that refers to the braking and deceleration of final stroke portion until standstill occurs. End-position Cushioning is required above a certain stroke speed. The kinetic energy released on impact at the stroke end must be absorbed by the stroke limit-stops, which are built into the end caps. Their capacity to absorb this energy depends on the elasticity of the material. Hydraulic braking function or end-position cushioning must therefore be applied where piston speeds (v) exceed 0.1 m/sec. The figure given below, shows a cross-section of the end-position cushioning mechanism of the end cap.

The piston is fitted with a tapered cushioning bush which when enters into the bore of the end cap during the final part of the stroke, the main fluid exit begins to shut until it finally closes off. This is the first stage of exit-flow throttling, which causes an initial speed deceleration. The remaining fluid must now exhaust through the cushioning valve. The degree of cushioning and second stage speed control can be regulated at the cushioning valve (flow control valve).

A check valve is fitted to achieve fast and full force brake-away from the end position. A bleed screw may also be built into the check valve. Some manufacturers have separate bleed screws available as a option. It is essential that the bleed screw are mounted uppermost.