Telescopic cylinders

Telescopic or multi-stage cylinders are a special design of a hydraulic cylinder or pneumatic cylinder, able to reach very long strokes from a compact retracted length.

HOW IT WORKS

A telescopic cylinder is made of several concentric stages nested inside each other. On extension the stages extend in sequence, usually from the largest diameter to the smallest; when closed they all retract into the outer barrel.

• Single-acting: retraction relies on an external force: the weight of the load, gravity or a return spring.
• Double-acting: retraction is driven by pressure.

Single action is the leaner design: the return stroke needs no hydraulic or pneumatic supply, so the version saves components, cost and energy, because the fluid works in one direction only; it makes sense when the useful work is the outward thrust and the return can rely on the load's weight or gravity.

The thrust is generated by the stage that is extending, which has a smaller diameter than a single-stage cylinder of the same closed length: at the same pressure the available force is therefore lower and must be checked on the active stage. Each extra stage adds stroke but increases the retracted diameter and the number of guides and seals, so the number of stages is a compromise between stroke, envelope and stability of the movement.

CONSTRUCTION FEATURES

The number of stages, diameters and strokes are set by the required stroke and the space available when the cylinder is closed.

Each stage has its own guides and seals: the seals work in series between the nested tubes, a mechanical stop limits the stroke of each stage, and the internal and external diameters require machining to tight tolerances. Fossa telescopic cylinders are available in hydraulic or pneumatic versions and are designed and tested in-house.

ADVANTAGES

• Very long stroke from a compact closed length
• Installation where a conventional cylinder would not fit
• Single or double-acting versions
• Custom design for the customer's application

APPLICATIONS

Lifting, tilting and moving structures, in any installation where the closed-length space is limited but a long stroke is needed. See all sectors and markets.

A typical example is the three-way tipper of bulk-material trucks: the bed tilts to the sides or to the rear almost to vertical to discharge the load completely, and it does so thanks to the telescopic cylinder, which extends in any direction from a limited space in the chassis. The same principle serves agricultural machines, mobile equipment and fixed plants where the retracted cylinder must take up little room.

Information for a custom telescopic cylinder

To assess a telescopic cylinder, send an installation drawing and describe the required movement. The following information helps define the project:

• Required total stroke and available space with the cylinder retracted.
• Load to be moved and mounting orientation.
• Available pressure, fluid and operating conditions.
• Required speed and cycle frequency.
• Mountings and required return operation: single or double acting.

To replace an existing cylinder, also provide any available drawings, nameplate details and photographs. Configuration and performance must be defined for each project.

Cylinder selection guide and information for a quotation