Join Date: Dec 2001
Location: Belleville, Illinois
Thanked 22 Times in 17 Posts
Re: What determines a hydraulic pump\'s PSI? RPM\'s?
It's good to see that you're finally getting on with that project. How long have you been planning it now?
The pumps you're looking at are positive displacement. For all practical purposes, they'll discharge a fixed amount of oil with every revolution, regardless of the pressure they're working against. I say 'for practical purposes' because at very low speeds and high pressures, the unavoidable leakage will decrease the output, and of course, at some point the pressure will get so high that something will break.
First you need to decide what input RPM you want to use. Something around 1000 to 2000 is probably what you will want. Then get a pump with a displacement that will give you 3.5 GPM at that speed.
Don't worry about pressure - it will take care of itself as long as all components are rated above 1500 PSI. I'd recommend at least 2000 PSI rating on everything, and then put in a relief valve set at 1500.
The pump output volume will be directly proportional to speed, again, for practical purposes, and in the speed ranges you'll be using. The pressure in the system will be determined by how hard the winch is working. It might be 300 PSI when you're just reeling in the cable, and 1800 PSI just before the cable pops.
I'd also recommend putting a pressure gauge in the system where you can see it while running the winch. It will tell you how hard the winch is working.
I'd also recommend that you find an industrial hydraulics shop in your area. An interested, sympathetic salesman will help you pick the right valves, fittings, pump, hoses, reservoir . . .