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clarkspc

PTO belt driven hydraulic pump?

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clarkspc
Has anyone tried (or thought about) mounting a hydraulic pump on the back of a 7117 and running it off of a PTO belt? I'm thinking of using it to run a log splitter and will need more psi and gpm than the built in hydro can provide.

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HubbardRA
Yes, I have thought about that method, when I was working on a design for a homemade front-end loader. You can probably use a power steering pump from an older (60s or 70s) Ford or Chevy, as the hydraulic pump. The usually have a bypass set from the factory to about 1500 psi, and pump around 2 gallon per minute. You can change the bypass pressure. I have a friend who has built hydraulic setups for a couple of tractors with power steering pumps. He eliminates the bypass (I wouldn't recommend this). If he deadheads a cylinder, it will kill his engine instantly, even before the driver can react. If it were me, I would set the bypass to lug the engine heavily, but not kill it. Before you look at high flow rate pumps, make sure to do the horsepower calculation, or you may be getting a pump that your engine can't handle. Also remember that you will need to add an additional fluid reservoir along with the pump. If I can help you in any way, let me know.

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D-17_Dave
To have the power to split a piece of wood it would reqiure a large diam. cyl. To larger you go in dia. the more flow is reqiured to maintain a desired speed, Bottom line is it takes a minimum of 10 GPM to run a large cyl. If you use a single stage pump you'll use better than 25/30HP to biuld decent pressure and maintain any flow. A belt drive isn;t much good for that no matter how big the engine is. You can get a more exspensive 2-stage pump like they use on most premade wood splitters but I wwould still recommend a dirrect drive for the shock loads you'll have as you load the cyl. By the time you over biuld it enough to work decent you could have bought a pump/motor combo set up for what you need.

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clarkspc
I was thinking of using a dual-stage 11gpm pump that runs up to 3500 psi. I see they use these in self-powered log splitters with 5 or 7hp motors so I figured the 17hp in my tractor should do it although I'm sure some of that power is lost through transfering power back to the PTO. I'm also wondering if I have to worry about belt slippage at high load - is that what you mean by the shock loads affecting it D17? My inboard hydro trannie is belt driven and it doesn't slip so I was thinking with proper tensioning this setup should be OK too. HubbardRA - what horsepower calculations are you referring to? I've done the hydraulic calculations and see that at 2gpm it would take about 40 seconds to move a 4 inch cylinder back from full stroke (best case) which is why I'm looking for something with more gpm than a steering pump. I also did the math and see that a 4 inch cylinder running at 3000 psi would give almost 19 tons of pressure max - not sure if I need that much to split a piece of wood but with big pieces of oak I suppose you can never have enough power. ;-)

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D-17_Dave
It takes little HP to build pressure and it takes little hp to flow oil, if you add the two it takes tremendous hp to maintain a decent flow, say 5 gpm at high pressure. You want to set the relief valve at around 2400/2500 psi to keep the safty factor in the system. While the pump may be rated at 3500 your hoses, cyl. packing and other unknowns may not handle this excesive load. Going w/ a 2-stage pump is however the way to go on this. You can use a large pulley so the belt has plenty of surface contact and a spring tentioner to prevent slippage and possibly run about a 2/1 ratio frm the pto driveing the pump. This willkeep your pump rpm up and allow you to put you throttle at half or just above hafl way to keep from haveing the engine screaming in your ears so bad. When it's all said and done, make sure to set the relief valve and leave it there. At exccesive pressures you can make a bomb out of the pump or burst a hose and really hurt someone. If you have the resource I'd suggest a 15GPM 2-stage pump. This gives you decent speed with plenty of reserve. It'll make the cyl. realy move when your in a low pressure cyl stroking mode and still allow good speed at high pressure.

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clarkspc
Thanks Dave - I did a little more reading on the Barnes 2 stage pumps and I couldn't find any info on relief valves. Are you familiar with them and do you know if they come with an integrated relief valve? I dropped their sales folks an email asking. I also asked them about a statement on the Northern Tool website that these pumps are for direct drive only. I wonder if they won't hold up with the stress of a tensioned belt pulling on them or something. I'll keep the safety aspect in mind also - saw pictures of my friend's old air compressor tank that blew up on em and broke his arm in 3 places. no need for that kind of excitement! Thanks again for the info, I'll keep posting if I keep moving forward with this project.

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D-17_Dave
Most pumps made for the indusral setting like the ones we are refering to don't have a relief valve in them. They are just pumps. The relief valves are built into the valve. On a standard single or double spool valve, there is a screw with a cap on it normally comeing out right beside the spool. This is the relief valve. It has a cap nut on it, a jamb nut and the screw is slotted to accept a flat screw driver to turn it when the nuts are loosened. Turn it in increases the pressure. So the standard thing is a pump, then to the valve whitch gives you dirrectional control of what ever you hook up to the circut. This may be a cyl, a motor, or some other hyd. mech. that will convert the energy of the flow into mech. motion of some sorts. Then from the valve back through a low pressure filter, then to the reservior. You will want to use at suction rated hose at least the size of the intake port on he pump from the tank. You don't want to "STARVE" the pump for fluid. From the pump use a size hose matched for the flow AND max pressure you might encounter. Use this type hose from the valve to the motor or cyl. You can drop down in quality of hose from the valve back to the filter and tank as there will be little to no pressure here. As for the pulleys on a pump deal, they make pumps that are equiped for this type service. They normally have feet made on the pump so it can be bolted down to a mounting surface rether than the flange mount arrangement found on the dirrect drive setup like you looked at. These pumps also have a larger diam. input shaft to handle the side load of a belt or chain drive.

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HubbardRA
clarkspc, Input Horsepower(needed to drive the pump) = Pressure (lb/sq-in) x Flow (gallons / minute) x .0007 11 GPM @ 1500 psi = 11.5 Hp 11 GPM @ 3200 psi = 24.6 Hp This comes from the formulas listed in a Grainger Catalog. If you can get hold of one of these catalogs, they have all the formulas necessary to do the hydraulic calculations. I use the bypass pressure in the horsepower calculation. This will guarantee that the engine will neot stall if a cylinder is deadheaded. I agree with Dave that the pressure in the system is always related to the load that is being moved. Very little load, very little pressure. Flow is, however, constant with a specific pump at a constant rpm. If the hydraulics are configured with an open center valving setup, then there is essentially no pressure till the valve is closed and the cylinder energized. As can be seen from the calculation above, a smaller engine can be used if a lower pressure is set on the bypass valve. Remember that Pressure (lb/ sq-in) x Area of Piston (sq-in) = Force Produced (lb) Another good thing that I want to mention. If you have the bypass valve set too high for the engine size, it will only kill the engine if the force needed to split the wood ends up being higher than the engine will produce with that pump. Pressure rises with load. If the wood splits easily, then the pressure in the system will remain relatively low. Remember that pressure only builds up as the load increases, and the highest pressure in the system can be calculated from the highest load needed in splitting the wood.

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clarkspc
OK, its all starting to come together for me now! It seems that the two stage pumps basically allow you to get higher gpm at low pressures (for faster return cycling of a log splitter) and give lower gpm at high pressures (to allow the use of small engines). Since I want to belt drive a pump off my PTO (and the two stage pumps are meant for direct drive) and I have a 17hp motor it looks like a single stage pump will work. Doing the math however it looks like I may have to reduce the pressure a bit to keep the motor from killing. The single stage pump I was looking at on Northern's web site is a .61 cu in pump that says it does 9.44gpm at 3600 rpm. Since my tractor supposedly runs close to that, I used that gpm number in the calculations and figured that at 2500 psi and 9.44 gpm I would need around 16.5 hp. I don't know how much force is required to actually split a piece of wood but if I get into a knot or something and hit max psi it sounds like that might be close to killing a 17hp motor. Maybe 2300 or 2400 psi with that setup would probably be wiser. Thanks for all the great info guys! Is there even more technical wisdom in the "members only" areas of the site?

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