Thursday, 9 June 2016

PISTON TYPE HYDRAULIC CYLINDER

PISTON TYPE HYDRAULIC CYLINDER


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, ram type of hydraulic cylinder and telescopic hydraulic cylinders in our previous post.

 
Today we will see here the basics of piston type of hydraulic cylinders with the help of this post. Piston type of hydraulic cylinders will be available in two types and they are designated as single acting piston type of hydraulic cylinder and double acting piston type of hydraulic cylinder.

Piston type of hydraulic cylinders

Following figure indicates the basic constructions of piston type of hydraulic cylinder, such type of hydraulic cylinders are used normally when push and pulling functions are required. As shown in figure, there will be a piston attached with piston rod and it will move within cylindrical housing of cylinder.
Piston type of hydraulic cylinder
Single acting piston type hydraulic cylinder will have single port in order to exert the pressure force in single direction. In order to secure the return stroke, there will be spring and spring will provide the required force for retracting the hydraulic cylinder.

Above figure, displayed here, indicates the single acting piston type of hydraulic cylinder. As shown in figure, spring is located at the rod end side for providing the tension force for retracting of cylinder. However, there is few more design of hydraulic cylinders where spring will be located at cap end side and fluid port will be provided at rod end side of the cylinder.

Double acting piston type of hydraulic cylinders will have cap end port and rod end port in order to provide the hydraulic pressure force in both directions. When hydraulic oil will be supplied to its cap end port, hydraulic pressure force will be applied over the piston or plunger and hence piston will be extended and this stroke of cylinder will be termed as forward stroke. During extension of the cylinder piston or plunger, hydraulic oil at rod end side will be pushed out and will be directed towards reservoir.

 
For return stroke or retraction of cylinder, hydraulic fluid direction will be reversed with the help of direction control valve. During return stroke, hydraulic oil will be supplied to its rod end port and therefore hydraulic pressure force will be applied over the piston or plunger from rod end side and hence piston will be retracted and this stroke of cylinder will be termed as return stroke.

As in above figure of hydraulic cylinder, effective working area on the two sides of piston is not equal hence such cylinders will also be termed as unbalanced cylinder. Pressure force exerting over the piston head from head end side will be greater as compared to pressure force acting over piston from cp end side and therefore cylinder will carry higher load during its forward or extension stroke.

 
We will see “Cushioned hydraulic cylinder” in our next post.

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Image Courtesy: Google
Reference: Industrial hydraulic maintenance manual

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