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Tuesday, 31 May 2016


We were discussing hydraulic actuators and its various types in our previous post. We have also seen the fundamentals of single acting hydraulic cylinders, double acting hydraulic cylinders, differential and non-differential hydraulic cylinders and ram type of hydraulic cylinder in our previous post. 

Today we will see here the fundamentals of telescopic hydraulic cylinders with the help of this post. Telescopic hydraulic cylinder is also one type of ram type of cylinder and will be available in two types and they are designated as single acting telescopic hydraulic cylinder and double acting telescopic hydraulic cylinder.

Telescopic hydraulic cylinders

Following figure indicates the basic constructions of telescopic hydraulic cylinder, such type of hydraulic cylinders are used when long forward stroke is needed from a compact package. Compact package means space restrictions in the mounting of a cylinder.

As shown in figure, there are series of rams and these rams are installed in an assembly of telescopic design and that is why we designated such type of hydraulic cylinders are telescopic hydraulic cylinders.
Telescopic hydraulic cylinder
Each ram will be hollow except the last and smallest ram. Each ram will act as cylindrical housing for adjacent smaller ram and complete ram assembly will be contained in a cylindrical housing as shown in figure. Largest diameter section will be termed as barrel or main of the telescopic cylinder and smallest diameter section will be termed as plunger or smallest stage of the telescopic cylinder and rest diameter section will be termed as stage of the telescopic cylinder.

Figure shows the cap end port and rod end port. Hydraulic fluid will enter through cap end port for exerting the pressure force over the piston and extending the ram. Largest stage will be extended first and once it will be completed then adjacent stage will start to extend. Smallest stage i.e. plunger of the telescopic hydraulic cylinder will move at last.

Telescopic hydraulic cylinders design and construction are quite complex as compared to one standard conventional hydraulic cylinder and therefore such hydraulic cylinders will be costly as compared to conventional hydraulic cylinder. 

We must note it here that for a specific flow rate of fluid, speed of actuation will be increased for each successive section and similarly for specific pressure value, load handling capability will be decreased for each successive section.

Applications of telescopic hydraulic cylinder

Let us see the application areas of hydraulic telescopic cylinder. We may see the application of such type of hydraulic cylinder in dump body on a dump truck. We need to lift the dump body at an angle of 60 degree in order to empty the truck completely. 
It will be quite difficult to do this task with the help of single stage conventional hydraulic cylinder because dump body could not return to complete horizontal rest position due to length of the cylinder. Application of telescopic hydraulic cylinder in such an application has resolved the above problem of design engineer easily.

Let us see the hydraulic symbol of telescopic hydraulic cylinder, following figure displayed here indicates the single acting hydraulic telescopic cylinder and double acting telescopic hydraulic cylinder.
We will see “Piston type hydraulic cylinder” in our next post.

Do you have suggestions? Please write in comment box
Image Courtesy: Google
Reference: Industrial hydraulic maintenance manual

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