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CUSHIONING HYDRAULIC CYLINDER WORKING PRINCIPLE

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

Today we will see here the basics of cushioned type of hydraulic cylinders with the help of this post. Cushioned type of hydraulic cylinders could be seen in those applications where we need to avoid the impact loading or shock at the end of stroke of piston.

Figure, displayed here, indicates the basic construction of cushioned type of hydraulic cylinder. Cushioning device is basically a metering device which restricts the flow of hydraulic fluid through the port and hence it will reduce the speed of motion of cylinder and therefore shock or impact could be avoided at the end of the stroke of piston.
Cushioned type of hydraulic cylinder

Reduction in speed of cylinder as it approaches to end of stroke will reduce the stresses over components of cylinder and also will reduce the vibrations also.


As piston approaches to end of the stroke, cushioning bush will enter in to the chamber and will create additional resistance for the fluid flow leaving the chamber. Profile of cushioning bush will determine the desired resistance in fluid flow leaving the chamber.

Cushioning device could be installed at one or both ends of the hydraulic cylinder depending on the requirement of applications.

Symbol of cushioned type of hydraulic cylinder
Let us see here the hydraulic symbol of adjustable cushioned type of double acting hydraulic cylinder
Symbol of cushioned hydraulic cylinder

Example of an application of cushioned type of hydraulic cylinder
 
Applications of cushioned type of hydraulic cylinders could be seen in cargo handling cranes or harbor mobile cranes. I had one experience of a cargo handling crane. Hydraulically operated grab bucket was attached with this cargo handling crane. We were facing issue of striking of lips of hydraulically operated grab bucket with each other during closing of grab bucket.

We have replaced standard hydraulic cylinders with cushioned type of hydraulic cylinders and we have observed the positive result. Cushioning device restricted the flow of fluid at the end of grab closing stroke and therefore during the closing of grab bucket and at the end of stroke of cylinder, motion of cylinder got reduced due to cushioning device. Reduction of cylinder velocity, as cylinder approaches to the end of stroke, lowers the stresses over components of cylinder and also lowers the vibrations and impact noise. 

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Reference:

Image Courtesy: Google 
Reference: Industrial hydraulic maintenance manual

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