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Monday, 23 May 2016

WORKING PRINCIPLE OF SINGLE ACTING HYDRAULIC CYLINDER


We were discussing hydraulic actuators and its various types in our previous post, where we have seen the basics of hydraulic actuators and simultaneously we have classified the hydraulic actuators in linear actuators i.e. hydraulic cylinders and rotary actuators i.e. hydraulic motor. We have also seen the various types of hydraulic linear actuators i.e. hydraulic cylinders in our previous post. 

Today we will see here the fundamentals of single acting cylinders

Single acting hydraulic cylinders

Single acting hydraulic cylinders are the simplest form of hydraulic cylinder which is used for pulling, lifting, moving and holding the load. Single acting hydraulic cylinder is displayed here in following figure. Single acting cylinder, as shown in figure, will have one port i.e. cap end port. Single acting cylinder, as name indicates, will be operated hydraulically in one direction only.

Single acting hydraulic cylinder will have one piston within a cylindrical housing. 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.
Single acting hydraulic cylinder
For return stroke or during retraction of cylinder, piston or plunger will be returned due to its own weight or by any mechanical media i.e. spring force. When piston will start its retraction i.e. return stroke due to its self weight or spring force, oil will flow back to reservoir during retraction of cylinder.

Hence piston will be operated hydraulically only in one direction i.e. during extension or forward direction. Retraction of cylinder will not be operated by hydraulic force but also it will be operated by mechanical force such as spring force or piston may also returns due to its self weight on the basis of design of cylinder.

Single acting cylinders are classified in two types on the basis of mechanism of retraction of cylinder.
  1. Single acting cylinder- Gravity return
  2. Single acting cylinder- Spring return

Single acting cylinder- Gravity return

In gravity return type single acting cylinder, hydraulic cylinder will lift the weight once hydraulic oil will be supplied to the cap end port of the cylinder because pressure force will be applied over the piston. Single acting gravity return cylinder is displayed here in following figure.
Single acting cylinder- Gravity return
For retracting the hydraulic cylinder, hydraulic oil supply will be removed from the cylinder by simply connecting the pressure port to reservoir and therefore cylinder will be retracted due its self weight or by gravity and hydraulic oil will be returned back to reservoir from cylinder during retraction of cylinder.

Single acting cylinder- Spring return

Single acting cylinder- Spring return is displayed here in following figure; hydraulic cylinder will be extended when hydraulic oil will be supplied to cylinder cap end port as pressure force will be applied over the piston.
Single acting cylinder- Spring return
 
During retraction of cylinder, mechanical force will be there such as spring force to push back the piston to its complete retracted position. Once hydraulic pressure will be released and hydraulic fluid will be directed to reservoir from cylinder, piston will be retracted by spring force.

Symbol of single acting hydraulic cylinder

Image displayed here indicates the hydraulic symbol of single acting hydraulic cylinder.
Hydraulic symbol of single acting hydraulic cylinder

We will see double acting cylinder in our next post.

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Image Courtesy: Google

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