Design and technical terminology of telescopic hydraulic cylinders
Telescoping cylinder, 8-stages, single-acting, retracted and extended
Telescopic cylinders are commonly restricted to a maximum of 6 stages. 6 stages are commonly thought to be the practical design limit as stability problems become more difficult with larger numbers of stages.
Telescopic cylinders require careful design as they are subjected to large side forces especially at full extension. The weight of the steel bodies and the hydraulic oil contained within the actuator create moment loads on the bearing surfaces between stages. These forces, combined with the load being pushed, threaten to bind or even buckle the telescopic assembly. Sufficient bearing surfaces must therefore be incorporated in the design of the actuator to prevent failure in service due to side forces. Telescopic cylinders must only be used in machinery as a device for providing force and travel. Side forces and moment loads must be minimized. Telescopic cylinders should not be used to stabilize a structural component.
Hydraulic telescopic cylinders are often limited to a maximum hydraulic pressure of 2000-3000 psi. This is because the outward forces produced by internal hydraulic pressure tends to expand the steel sleeve sections. Too much pressure will cause the nested sleeves to balloon outward, bind the mechanism and stop moving. The danger exists that a permanent deformation of the outer diameter of a sleeve could occur, thus ruining a telescopic actuator. For this reason, care must be taken to avoid shock pressures in a hydraulic system using telescopic cylinders. Often such hydraulic systems are equipped with shock suppressing components, such as hydraulic accumulators, to absorb pressure spikes.