I want to get a PTO pump to run my 3pt backhoe. Im guessing its about as large as a 3pt unit would get. The cylinders are fairly large, I would guess they have about a 4" OD and maybe about 2 3/4 rods? Common pumps seem to be 11 or 21 gpm. PTO is rated at 45 hp so I should have plenty of power even at lower rpms. I have a weekend project and I can get the 11 in stock locally but for $20 more I can get the 21 but it will take a week to get.
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skidsteer.ca
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The 21 gpm is at the rated 540 rpm of the pto? Because if it is, the tractor will need to run near full engine speed to produce that flow. I'd think you will be better off with the bigger pump so you can do your backhoe work at a lower engine speed.
Can you get a flow range recomendation from the backhoe manufacturer?
The see what rpm you would have to run each of those pumps to be in the desired flow range.
This is calulated by the displacement (usually in cubic inches) of the pump mutiplied by the rpm the pto turns. Google "hydraulic formulas"
You should also check that the pump is capable of the the pressure (psi) the hoe runs at. But it likely is.
Ken
Can you get a flow range recomendation from the backhoe manufacturer?
The see what rpm you would have to run each of those pumps to be in the desired flow range.
This is calulated by the displacement (usually in cubic inches) of the pump mutiplied by the rpm the pto turns. Google "hydraulic formulas"
You should also check that the pump is capable of the the pressure (psi) the hoe runs at. But it likely is.
Ken
Its an old machine. Looks like the company has been bought and sold a few times. Found what I think may be a distant relative that has manuals on line and their largest model recommends 6-8 gpm. My tractor pto is rated at 40hp so I dont think there is going to be an issue there. Even the 21 GPM at full pressure said it consumes something like 28 HP. Must be the internal gearing that gains some efficiency. I have both 540 and 1100 shafts but the 540's seem to be much more common so I was thinking of sticking with that since all tractors have the 540. Tractor is a diesel so my 540 is at 1800 rpm and that just does not give a very comforting feeling running it that fast. 21 seems like a lot but I will have to look at the charts and do some math to see what I would be getting around 1000 rpm since thats where I tend to run it.
SkidRoe
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73Eldo, only one thing was missing from Ken's explanation:
GPM = Pump displacement (in cubic inches) x RPM / 231 (cubic inches per gallon)
dozer
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I also looked at converting a tractor backhoe to skidsteer. I have yet to find one yet that requires more than 15 GPM. Most are lower. Most 3-point backhoes don't even run at PTO speed to be useful.
I was looking a LONG model B 3-point backhoe last year and that pump only needed 8 GPM @ 1500 PSI. I would have had to buy restrictors just too get my machine down far enough. If its as old as you think I doubt its requirements will be any different even if it is a large backhoe. Honestly if its that big you might have to figure out how your skidder is going to move it.
good luck. I love converting things to skidsteer. Cheap, challenging, and fun.
Dozer
