Fixed end hydrualic cylinder with a pulley on top

[gjshafer]

I am using a hydraulic cylinder with a pulley on top. The bottom of the cylinder is fixed and the top has the pulley mounted on it free to rotate. I am trying to double the lifing height of the cylinder. The cylinder stroke is 24inches and I need to make if lift something from the ground up to 48inches. I am using a chain that one end is connected to the base of the cylinder, the chain is draped over the pulley and back down to the ground where it is attached to the object I am lifting up 48 inches. I am trying to figure out how to determine what diameter pulley to use to double the lifting height of the cylinder. Any help at all would be greatly appreciated.

Thanks,
Glen

 

[DickL]

Such an arrangement has been used in a number of hoist and jacks. I also think it has been used in some hydraulic elevators, but probably no longer.

The pulley needs to have a diameter greater than the width of the cylinder plus any chain guides, load rails, etc. Then the teeth need to be sized to carry the load and of course fit a chain that can handle the load. Typically speed is not an issue. Non-axial loads, due to asymmetries in the load support and guidance also would play a factor, although probably more in the pulley's attachment and the cylinder's guide bushing.

 

[gjshafer]

Ok, thanks for the information, but doesn't the pulley diameter have an effect on the ratio in which it doubles the cylinder? I guess that's what I'm truly asking is how can I size the pulley? Like you said it obviously has to be bigger than the width of the cylinder but how can I find the diamter to achieve the ratio lifting height of 2:1?

 

[Averagesupernova]

It only needs to be as large as required for clearance. Diameter means nothing as far as ratio goes.

 

[gjshafer]

Ok, so what is giving the cylinder a 2:1 lifting height? We already use this application else where so I know it works. The initial cylinder stroke is 24 inches and the object that is lifted, is lifted from the ground to the its stopping point of 48 inches from the ground. How is the cylinder doubling its lifting height if the pulley diameter has nothing to do with it? The engineer that designed this application is no longer here so I am just trying to understand how it works for future applications. Any help on this is greatly appreciated

 

[Averagesupernova]

Look up pulleys in simple machines.

 

[russ_watters]

Here's 3:1: http://en.wikipedia.org/wiki/File:Pulley2.svg