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metalmagpie
09-29-2013, 11:37 AM
I'm thinking about replacing the hydraulic unit in a small machine I own. The existing unit is powered by a 3hp electric motor. The machine uses a 1250 psi hydraulic system. The pump spins at 1740 rpm so it probably displaces 3 or 4 gallons per minute. My current reservoir holds 8 quarts. It's a steel box with a low-profile pulley-driven pump mounted on its side. The pump basically has a topology sort of like a power steering pump on a car.

I don't see a lot of hydraulic pumps with that kind of form factor, so I'm thinking of going to a more conventional vane-type pump with a foot mount, and use a low-pressure hydraulic hose from the reservoir to the intake of the pump, with a high pressure hose from the pump to the cylinder and a low pressure return hose from the other end of the cylinder back to the reservoir (it's basically a single acting system with a 2-port pump).

My question is how to actually design a hydraulic reservoir? I suppose the easiest thing to do would be to remove the existing side-mounted pump, plug the holes, and add a low-pressure hose port. But if I have to build it from scratch, don't I need baffles and air vents and things?

metalmagpie

1-800miner
09-29-2013, 12:08 PM
nothing fancy...just a tank with a vented fill cap.
Bigger is better,the more surface area equals more cooling capacity.
If you want fancy,weld some cooling fins on the out side.

wierdscience
09-29-2013, 12:30 PM
Surplus center has the fill caps,sight glasses and weld in fittings to build your own.

http://www.surpluscenter.com/Hydraulics/Hydraulic-Reservoirs/Hydraulic-Reservoirs/?page_no=1

A removable top or access hole is a good feature too.

I also had a small power unit that used a heater core from a Ford car for a return oil cooler.The mfg mounted it just behind the motor so it's cooling fan did double duty.

winchman
09-29-2013, 02:03 PM
Seems like it would be pretty easy to fabricate a plate to cover the place on the tank where the existing pump is mounted, and add a fitting for the low pressure hose to the new pump. If the tank was venting through the pump housing, you'll have to add a fitting for that, too. I'd try to use what you've got to the greatest extent possible.

A couple pictures of the unit would really help.

Ohio Mike
09-29-2013, 02:17 PM
If you scratch make it I would recommend not placing the pump intake directly at the bottom of the tank. Leave a place for "gunk" to collect. I would also avoid placing the return line into the tank in such a way that the intake is collecting that oil. A baffle can help but is not required. Proper venting is essential (often done in the cap) along with a little space for the oil to expand when it gets hot.

davidh
09-30-2013, 10:56 AM
many years ago I used a mopar power steering pump with its little built in tank, mouted on the back of a very small farmall tractor, for a log splitter. I found that its tank capacity was too small so I brazed a small propane bottle on and added a vented cap to the top of the propane bottle. worked like a charm albeit quite slow.
I think I still have a spare one of those pumps from my 65 Chrysler.

Dr Stan
09-30-2013, 12:33 PM
nothing fancy...just a tank with a vented fill cap.
Bigger is better,the more surface area equals more cooling capacity.
If you want fancy,weld some cooling fins on the out side.

Ditto. I'd just add a removable top and a drain plug on the bottom or as close as possible to the bottom on a side.

On edit. Add a filter in between the tank and the inlet of the pump.

cameron
09-30-2013, 01:10 PM
Just make sure the suction line to the pump is big enough. Twice the size you think you need is probably just a bit too small. :rolleyes:

Black Forest
09-30-2013, 01:26 PM
On edit. Add a filter in between the tank and the inlet of the pump.

Are you sure you want to tell him to do that? We never put the filter on the suction side of the pump. Always on a return line to the tank. Maybe you do it differently but what you recommend goes against normal filter installations on a hydraulic system.

cameron
09-30-2013, 01:48 PM
A filter on the intake would need to be larger in order to keep intake losses low. Undetected partial clogging of the intake filter could cause cavitation of the pump. It won't only hurt performance, it can destroy the pump.

And, of course, too small a suction line can do the same.

Dr Stan
09-30-2013, 01:57 PM
On edit. Add a filter in between the tank and the inlet of the pump.

Are you sure you want to tell him to do that? We never put the filter on the suction side of the pump. Always on a return line to the tank. Maybe you do it differently but what you recommend goes against normal filter installations on a hydraulic system.

All I can say that is what we were taught in fluid mechanics. The rationale is to keep the garbage out of the system, pump etc., one filters it just before it enters. Granted it requires a larger filter, but will save the components a lot of wear & tear. If you're getting cavitation it would not be caused by the filter, but by a leak where air can enter. If its pseudocavitation it is most likely caused by improper sizing.

davidh
09-30-2013, 02:21 PM
inlet "filters" should be strainers, metal mesh, to keep the chunks out of the pump. but now we're talking bigger and more expensive, than necessary, systems for the hobby guy. . . filter hanging on the tank RETURN lines have always been the main "filters". thinking Barko, Hood, etc. hydraulic machines.

CCWKen
09-30-2013, 03:08 PM
One other item worth mentioning. Watch the overhang on your pulley if you're changing pumps. Many pumps aren't designed for a lot of side load on the shaft and you can smoke the bearing or bushing pretty fast. Power steering type pumps have large bearings and can take the side load from a pulley. If you're changing to a more conventional type pump, you should also consider using an in-line type drive system.