Variable displacement pumps - winches

[rockcrawler31]

i'm looking at fitting a hydraulic pump and motor to the PTO winch on my truck. Can anyone suggest a good supplier here or in the states for hydraulic gear. Also can anyone suggest a good variable displacement pump for this application.

I'm told that a VDP doesn't need a accumulator box and loads of oil, nor does it get hot like a gear pump and spool valve setup. Your thoughts?

[ricky1970]

True that a variable pump may run cooler than a gear type pump. You need to know what speed you want you motor to run, HP (or torque actualy) that is required to do the job, the speed that the pump will be running at. Then you can 'size' a pump for the job.
The good thing about a variable pump is that you can vary the output flow compared to the pump speed, so that if you only need a lower flow, the pump only gives you that flow. Unlike a fixed displacement pump. where excess flow is diverted to the tank, generating heat.
The only consideration is system cleanlyness is very important with a variable piston pump and decent filteration is a must.
Be prepaired for the $$$$$ tho, decent piston pumps are not cheap!

[1MadEngineer]

I'm told that a VDP doesn't need a accumulator box and loads of oil, nor does it get hot like a gear pump and spool valve setup. Your thoughts?

So who told you that????

why would you need an accululator on a whinch??

you do realise that a complete system done properly will cost over the 10k mark.

[rockcrawler31]

Yep, i know about the priceyness, i just have a hard on for pto and hydraulic winches.

i was told that with a normal gear pump, the oil is always circulating and getting hot which is why you need a larger volume of oil and a tank to hold it in. It was explained to me that a swash plate style pump isn't always pumping the oil, so only needs a small reserve and top up tank.

if that's not right can you explain why?
It's only curiosity and research at the moment.

MILO

[ricky1970]

If you use the load sensed (variable) pump to its full advantage, ie decrease pump output flow when its not required, then it will run cooler because you are circulating less total oil in the curcuit. If you use the full volume of oil, ALL the time, then you would see little advantage heat wise.
The load sensed system make better use of input horsepower, ie a system with a max flow of 10GPM, but using only 2gpm @ 3000psi needs a input HP of approx 4hp. A gear pump systen with the same 10gpm, and using only 2 @ 3000psi requires approx 20hp to drive the pump. This lower hp requirement is where you save on heat generation.
If you are worried about heat, size EVERYTHING right. ie hoses and valves of correct size to minimise pressure drop, dont run pumps top fast or slow, same with the motor. Build the tank right and allow air around it to aid cooling and dont think that you need the biggest pump you can fit to get it to work.