Hydraulic Cylinder Stroke Length

[ldeem]

I am working on a project to add hydraulic cylinders to move large steel deflectors in bulk material handling chute. I know the actuator arm length and positions so I can find the required cylinder stroke length, which is around 30". My question is when specifying the cylinder stroke length is it a good practice to add 1 or 2" (or more) to the cylinder doesn't bottom out at the end? We plan to add limit switches to control the stopping points?

 

[Compositepro]

If the piston does not 'bottom out' in the cylinder then you must limit the stoke externally. So, which do you want?

 

[hydtools]

Your choice. Might depend on your confidence in knowing the required stroke.

Ted

 

[TugboatEng]

You may also want cushions which is more difficult to implement outside of the cylinder.

 

[Jboggs]

Is there a possibility that there will be a need to adjust the closed or open positions in the future? When in doubt give yourself more flexibility for future requirements. My father used to tell me, "It is better to have something and not need it than to need it and not have it."

 

[Scuka]

Cylinders have to be stopped one way or another.
It can either "bottom out", i.e. the piston / rod hits the end of the cylinder, or something that's attached to the rod hits a stopper on the outside, or you can stop the fluid flow (which requires sensors and control, and is unnecessary if you require your cylinder only to stop at points A and B)

Unless you've got some special case (crazy speeds or something like that), you don't have to worry about these internal impacts, cylinders are capable of handling them, and that's how most of them are used. Check the cylinder manufacturers datasheet. Pneumatic cylinders are generally less robust so the manufacturers list the maximum impact energy the cylinder can take. I haven't used a hydraulic cylinder in ages so I don't know about those, but definitely refer to the datasheet.

 

[handleman]

Assuming you are controlling them properly, hydraulic cylinders can stop at any point in the stroke at any time without hitting an internal or external stop. As soon as you close the valve, incompressible fluid is trapped on both sides of the piston and the movement stops.

 

[ldeem]

Thank you everyone for your input. In this situation I am refitting several parts and I don't think construction tolerance will be very tight. So I am going to add to go with the added stroke length option.

 

[Jessica Herron]

The stroke is the amount of travel the piston rod can move in and out. It can be found by subtracting the maximum extended length of the hydraulic cylinder from it's minimum compressed length. Generally the compressed length is given along with the stroke.