Telescopic cylinder
[2] 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.
In order to empty the load of gravel completely, the dump body must be raised to an angle of about 60 degrees.
[3] Telescopic cylinders are designed with a series of steel or aluminum[2] tubes of progressively smaller diameters nested within each other.
[2] 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.
Sufficient bearing surfaces must therefore be incorporated in the design of the actuator to prevent failure in service due to side forces.
This is because the outward forces produced by internal hydraulic pressure tends to expand the steel sleeve sections.
The danger exists that a permanent deformation of the outer diameter of a sleeve could occur, thus ruining a telescopic actuator.
This can, in some applications, prove to be very difficult to connect with hydraulic hoses due to the distance between these ports at full extension.
An internal passageway must be fitted, however, so that the retracting fluid is supplied to the plunger section at full extension.
The cylinder could thus be rendered unable to retract because of failed seals or jam in position due to binding.
When the piston face catches up again and strikes the oil column a pressure spike occurs which can damage the actuator.
Thus, the plunger stage only of the telescopic actuator is equipped as a double acting cylinder to provide the initial force to pull the mast back from vertical.
Once the tilt back has been initiated, then gravity takes over and supplies the force to complete the full cylinder retraction.
This can also be accomplished in a double acting design by matching the extension and retraction areas of the pistons on all the stages.
