Using hydraulic cylinder as pump

Hi guys:

I have an application where I need a foot-operated, reciprocating hydraulic pump for a lift cylinder. The load is light (few hundred pounds), but I need to move enough fluid to advance the cylinder as much as possible with each stomp. So I'm looking at low-pressure/high-displacement for each stroke. I've looked at all the ready-made pumps available and they tend to be high-pressure/low-displacement types.

I'm kicking around the idea of using a hydraulic (or perhaps oil-compatible air) cylinder as a pump. I foresee a check valve on the exit line to the lift cylinder and another check valve, in the opposite direction, to an oil reservoir. The pedal mechanism connected to the pump rod would provide a spring-return. A relief valve from the cylinder to the reservoir would lower the load.

Do any of you have experience with doing this, or something similar? What are the caveats? Thanks for all replies.

Reply to
Don A. Gilmore
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Don;

Just make sure you don't cheat on the suction line from tank thru check valve to cylinder. I would size this line for around 2 feet per second velocity. Also the suction check valve needs a very low pressure spring or no spring at all and mounted to close with gravity since all you have is a portion of 1 atmosphere to open it and push the oil to the cylinder.

If the cylinder is double acting you may, in the future, need a line from the rod port to tank to return oil bypass to keep from making a mess. A Ram type cylinder would only leak if the ram seals wore out..

Bud Trinkel

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oil-compatible

Reply to
Bud Trinkel

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