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Telescopic cylinders are a special design of a hydraulic cylinder or pneumatic cylinder which provide an exceptionally long output travel from a very compact retracted length. Typically the collapsed length of a telescopic cylinder is 20 to 40% of the fully extended length depending on the number of stages.〔( Hyco Ultrametal, Telescopic Hydraulic Cylinders )〕 Some pneumatic telescoping units are manufactured with retracted lengths of under 15% of overall extended unit length.〔( Ergo-Help Pneumatics, EHTC Telescoping Cylinders )〕 This feature is very attractive to machine design engineers when a conventional single stage rod style actuator will not fit in an application to produce the required output stroke.〔 Heavy duty telescopic cylinders are usually powered by hydraulics, whereas some lighter duty units could also be powered by compressed air.〔(Bimba TRD Pneumatic Telescoping Cylinder )〕 Telescopic cylinders are also referred to as telescoping cylinders and multi-stage telescopic cylinders. An application for telescopic cylinders commonly seen is that of the dump body on a dump truck used in a construction site. In order to empty the load of gravel completely, the dump body must be raised to an angle of about 60 degrees. To accomplish this long travel with a conventional hydraulic cylinder is very difficult considering that the collapsed length of a single stage rod cylinder is approximately 110% of its output stroke.〔 It would be very challenging for the design engineer to fit the single stage cylinder into the chassis of the dump truck with the dump body in the horizontal rest position. This task is easily accomplished, however, using a telescopic style multi-stage cylinder. ==Design and technical terminology== Telescopic cylinders are designed with a series of steel or aluminum〔 tubes of progressively smaller diameters nested within each other. The largest diameter sleeve is called the main or barrel. The smaller inner sleeves are called the stages. The smallest stage is often called the plunger〔 or piston rod. The cylinders are usually mounted in machinery by pivot mounts welded to the end or outer body of the barrel as well as on the end of the plunger. 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. There are exceptions however, with one pneumatic cylinder manufacturer successfully incorporating up to 9 stages in their cylinder designs.〔 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.〔(Hyco Canada, Telescoping Cylinders )〕 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.〔(Hyco Canada, Tutorial on Cylinders )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Telescopic cylinder」の詳細全文を読む スポンサード リンク
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