These cylinders consist of a succession of aluminum or steel tubes of progressively smaller diameters set within one another, which allows for significant extension. The collapsed length of the cylinder is usually 20% to 40% of the completely extended length. Of course, this depends on how many stages are included in the design.
Though telescopic hydraulic cylinders may be custom designed for optimum extension and other features, the maximum number of stages is usually restricted to six. The largest, outermost sleeve is referred to as the barrel or the main while the inner sleeves are called the stages, and the smallest is often referred to as the plunger or piston rod.
Telescopic hydraulic cylinders are used in a variety of applications, including construction equipment like dump trucks, large capacity marine cranes, and oil field drilling rigs. In these demanding settings, the cylinders are usually used to raise and lower pieces of equipment as with the dumping action of the dump truck or to erect the mast of a mobile drilling rig. Generally, the cylinders are anchored in machinery by pivot mounts welded to the body of the barrel as well as the end of the piston rod, and can tolerate hydraulic pressure at a maximum of 2000-3000 psi.
No matter the application, it is very important that telescopic hydraulic cylinders be used in a way that avoids side loads from pushing on the actuator as this can cause excessive wear and sometimes very serious damage. At full extension, they are even more susceptible to side forces. Telescopic hydraulic cylinders should always be viewed as force generating devices, never as stabilizing devices.
There are many manufacturers of telescopic hydraulic cylinders to choose from and many offer custom design options to suit specific applications. Double acting cylinders as well as single acting cylinders are also an option when it comes to these cylinders. Double acting cylinders are extended and retracted by use hydraulic pressure in both directions. Some even use a combination of both single and double acting technology, where the piston is double acting and the rest of the stages are single acting.
Telescopic cylinders are often used in and considered in regards to heavy machinery, but there are smaller bore designs used in lighter applications as well. There are a range of specific designs, features, and capabilities that can be considered and employed when it comes to telescopic hydraulic cylinders.