special hydraulic cylinders telescopic cylinder

SPECIAL HYDRAULIC CYLINDERS

TELESCOPIC CYLINDER

1. What is a Telescopic Cylinder?

• Telescopic cylinder is used where there is a space constraint.

• A telescopic cylinder consists of a series of rams nested in a telescopic assembly which provide a long extension.

• Such cylinders are useful for applications requiring a long stroke but with only limited space available for the unextended ram.

• Some of the applications of telescopic cylinders include hydraulic cranes, high-lift fork trucks, dump trucks, dipper wagons, etc.

2. Construction and Operation

Fig.5.4 illustrates the arrangement of a typical telescoping type cylinder having three rams.

Since the diameter A of the ram is relatively large, this ram produces a large force for the beginning of the lift of the load. When ram A reaches the end of the stroke, ram B begins to move. Now ram B provides the required smaller force to continue raising the load. When ram

• In many fluid power applications, the greatest force is required to begin lifting the load. Once the lifting of load has started, then the required force to continue raising the load will be smaller.

B reaches the end of its stroke, then ram C moves outwards to complete the lifting operation. These three rams can be retracted by gravity acting on the load or by pressurized fluid acting on the lip of each ram.

3. Working of a Two-Stage Double-Acting Telescopic Cylinder

Fig.5.5 illustrate the operation of a typical two-stage double-acting telescopic cylinder. 

Retraction stroke: During the retraction stroke, the fluid is fed into the first-stage annulus via retract port A. Therefore the first stage piston is forced to the left until it uncovers the fluid ports connecting this with the second stage annulus. This, in turn, moves the larger piston to the left until both the pistons are fully retracted into the body of the cylinder.

Extension stroke: During the extension stroke, the fluid is fed through the extend port B. Now the fluid forces both pistons to the right until the cylinder is fully extended.

As could be seen from Fig.5.5 that many seals are provided for preventing any possible fluid leakages.