Cylinders, Telescopic

Telescopic hydraulic cylinders are relatively simple devices, but their successful application requires an understanding of this components idiosyncrasies. Knowledge of how telescopic cylinders work and which special application criteria to consider will enable you to design them safely and economically into equipment.

Main stages as the name suggests, telescopic cylinders are constructed like a telescope. Sections of steel tubing with successively smaller diameters nest inside each other. The largest diameter section is called the main or barrel; the smaller-diameter sections that move are called stages; the smallest stage is also called the plunger. The maximum practical number of moving stages seems to be six. Theoretically, cylinders with more stages could be designed, but their stability problem would be daunting. Telescopic cylinders normally extend from the largest stage to the smallest. This means the largest stage - with all the smaller stages nested inside it - will move first, and complete its stroke before the next stage begins to move. This procedure will continue for each stage until the smallest-diameter stage is fully extended. Conversely, when retracting, the smallest-diameter stage will retract fully before the next stage starts to move. This continues until all stages are nested back into the main.

Basic cylinder types conventional cylinders have two basic types of telescopic hydraulic cylinders- single- and double-acting. Single-acting cylinders extend under hydraulic pressure and rely on gravity or some external mechanical force for retraction. Single-acting cylinders are used in applications where some form of load is always on the cylinders. The classic single-acting telescopic applications are dump trucks and dump trailers. Pressurized oil extends the telescopic cylinder to raise one end of the dump body. When pressure is released, the weight the dump body forces oil out of the cylinder, it retracts. Double-acting telescopic cylinders are powered hydraulically in both directions. They can be used in applications where neither gravity nor external force can retract the cylinder. They are well suited to non-critical positioning applications requiring extension and retraction movement of a substantial load. Basic cylinder types- as with conventional cylinders the two basic types of telescopic hydraulic cylinders are single and double-acting. Single-acting cylinders extend under hydraulic pressure and rely on gravity or some external mechanical force for retraction. Single-acting cylinders are used in applications where some form of load is always on the cylinders. The classic single-acting telescopic applications are dump trucks and dump trailers. Pressurized oil extends the telescopic cylinder to raise one end of the dump body. When pressure is released, the weight the dump body forces oil out of the cylinder, it retracts. Double-acting telescopic cylinders are powered hydraulically in both directions. They can be used in applications where neither gravity nor external force can retract the cylinder. They are well suited to non-critical positioning applications requiring extension and retraction movement of a substantial load.