cylinder cushioning

CYLINDER CUSHIONING

1. What is Meant by Cylinder Cushion ?

• When the pressurised fluid is allowed to enter inside the cylinder, the piston accelerates and travels in the cylinder barrel. If the piston is allowed to travel at the same speed till the end of the stroke, it will hit the end cap with a great impact. To avoid this impact, the piston needs to decelerate at the end of the travel. The arrangement made at the end caps to achieve the same is called 'cylinder cushion’.

• In other words, the cylinder cushioning slows down and prevents impact at the end of a piston stroke (by gradually decelerating the piston speed from start of stroke to the end of stroke).

2. Construction and Operation

A typical cylinder cushioning arrangement is illustrated in Fig.5.3. Figs.5.3(a) and (b) show the position of the piston at the start and of the cushioning action, respectively.

As the piston approaches the end of its stroke, the plunger enters the end cap port and thus blocks the free flow. Now the fluid is trapped between the piston and the end cap. This fluid, can escape only by passing through the adjustable restrictor, as shown in Fig.5.3(b). This fluid flow through the restricted flow path causes the piston to decelerate. The rate of deceleration of the piston can be controlled by the adjustable needle valve. A non-return or check valve is provided to allow free flow of fluid to the cylinder quickly during the return stroke. Fig.5.3(c) shows the symbolic representation of cylinder cushion.