Double-acting telescopic cylinder: flexible & universally applicable

Telescopic cylinders are, in themselves, particularly flexible hydraulic linear actuators. Double-acting telescopic cylinders are also universally applicable.

What is a double-acting cylinder?

Simple linear actuators can only perform one movement automatically. As a rule, this is extension. For retraction, they require an external force. This is typical, for example, of hydraulic jacks. After the check valve is opened, the applied load pushes the piston back again.

In a double-acting cylinder, two check valves are installed. One is used to supply the volumetric flow for extending the piston. The second is located at the front side of the cylinder. When the hydraulic flow is switched, the piston is retracted again. No external force is required. Switching is not only used to retract the piston; it also enables the linear actuator to perform a similarly large amount of work as during extension.

A disadvantage when installing double-acting cylinders is the greater design effort required. At this point, hydraulic systems require at least two valves and several additional lines. In addition to the second check valve, at least one directional control valve is also required to redirect the flow direction of the volumetric flow.

What is a telescopic cylinder?

Telescopic cylinders are particularly compact hydraulic actuators. They consist of several pistons nested inside one another like a telescope. Under load, these extend step by step. The advantage of telescopic cylinders is their low-profile design. They are particularly suitable where, due to space constraints, a long linear actuator cannot be installed. A common application is their use in tipper bodies. Under load, they extend continuously to tip the load. The weight force of the empty body is then sufficient to retract the telescopic cylinder again.

What is a double-acting telescopic cylinder?

Double-acting telescopic cylinders offer the flexibility of a double-acting cylinder with the compactness of a telescopic cylinder. They require the same setup with an additional check valve and a directional control valve as conventional retractable linear actuators.

Their key advantage is that they are no longer dependent on an external retraction force. This makes them suitable for varying loads or even operation without any load. Double-acting telescopic cylinders give designers greater freedom. In the case of tipper trucks, this enables bodies made from alternative materials such as GRP, CFRP, or aluminium. The body’s own weight is no longer required to retract the cylinder.

What disadvantages do double-acting telescopic cylinders have?

As complexity increases, so does the effort required for maintenance and inspection. A telescopic cylinder has as many seals as it has telescoping stages. These must be checked regularly for leaks. In addition, these components require a high level of cleanliness, as ingress of dirt can quickly damage them.