PTO gear pump question

Jims1025R · Sep 14, 2022

I've been doing lots of reading here, while I consider my design for a loader mounted brush cutter. Someone wisely mentions that running a hydraulic cutter on the third function valve of the tractor hydraulics could result in power/speed variations with loader operation - good point! Thanks!

So... If I use a separate PTO gear pump, the 540 PTO runs the pump, and my cutter constantly, and the loader operates independently so I can thrash it about for cutting. My question is; if I set up PTO gear pump to cutter hydraulic motor, with only a reservoir, over pressure relief valve, and filter in the circuit, do I need a valve at all? Could I simply start and stop the cutter with the PTO run/stop? (dash switch in the case of my JD 1025R).

I make up a frame to hold the torque of the pump body to the three point hitch, with a reservoir and filter, and just run the two lines up to my cutter hydraulic motor? With no valve, I save cost, and flow restriction, neither of which benefit the design, if the PTO on/off is good enough for cutter run/don't run...

Thoughts?

CalG · Sep 15, 2022

Should work, but what is the cost difference between a control valve and an over pressure valve?

Might not be much savings.

rScotty · Sep 15, 2022

Jims1025R said:
I've been doing lots of reading here, while I consider my design for a loader mounted brush cutter. Someone wisely mentions that running a hydraulic cutter on the third function valve of the tractor hydraulics could result in power/speed variations with loader operation - good point! Thanks!

So... If I use a separate PTO gear pump, the 540 PTO runs the pump, and my cutter constantly, and the loader operates independently so I can thrash it about for cutting. My question is; if I set up PTO gear pump to cutter hydraulic motor, with only a reservoir, over pressure relief valve, and filter in the circuit, do I need a valve at all? Could I simply start and stop the cutter with the PTO run/stop? (dash switch in the case of my JD 1025R).

I make up a frame to hold the torque of the pump body to the three point hitch, with a reservoir and filter, and just run the two lines up to my cutter hydraulic motor? With no valve, I save cost, and flow restriction, neither of which benefit the design, if the PTO on/off is good enough for cutter run/don't run...

Thoughts?

Only a problem if you run the loader and the cutter at the same time and both of them at full speed. Is that likely?

Tractors with simple PTO switches without a PTO clutch are cheap to make, but abrupt. That's hard on any system.

You will probably find a valve useful. It frees you from being next to the PTO switch. A valve controls cutter speed and power plus it reverses the cutter rotation to free it from a bind. Safer too. Most control valves include a relief valve. To avoid having to hold the valve open all the time, consider getting a valve with a detent.
luck,
rScotty

LouNY · Sep 15, 2022

It'll work, I think a motoring valve would be much more desirableness.
This would allow the drive motor to coast down, some hydraulic motors can not take being stopped suddenly
especially with a heavy load on them the back pressure will blow the motor seals.
A hydraulic motor valve will allow the motor to free spool till it stops.
Also you may need a cooling circuit in your system.

rScotty · Sep 15, 2022

LouNY said:
It'll work, I think a motoring valve would be much more desirableness.
This would allow the drive motor to coast down, some hydraulic motors can not take being stopped suddenly
especially with a heavy load on them the back pressure will blow the motor seals.
A hydraulic motor valve will allow the motor to free spool till it stops.
Also you may need a cooling circuit in your system.

Good point. All of those control features can be done with a regular control valve and normally are by any experienced operator. So using a control valve is doable just as using a PTO switch is too. BTW, you will want a over-running clutch on the PTO. Always. Otherwise you may break something.

And ultimately a valve built specifially for motoring would no doubt be better.

Third functions on loaders are usually just added to tractors for occasional cylinder use, not for continuous use. Think grapples; not motors. The difference is cooling. But there again there is a difference between quickly setting up a project using common parts to prove if an idea is feasible or worth pursuing.... Versus refining it into an everyday product.

When designing anything, don't get hung up on the final steps before taking the first one. Just get in there and get something done. Change as needed. If it were me, I'd skip the PTO and run it off the 3rd function until I saw if it would even work and keep an eye on not letting it get too hot. Hydraulic return line radiators are cheap.

rScotty

ptsg · Sep 15, 2022

Jims1025R said:
I've been doing lots of reading here, while I consider my design for a loader mounted brush cutter. Someone wisely mentions that running a hydraulic cutter on the third function valve of the tractor hydraulics could result in power/speed variations with loader operation - good point! Thanks!

So... If I use a separate PTO gear pump, the 540 PTO runs the pump, and my cutter constantly, and the loader operates independently so I can thrash it about for cutting. My question is; if I set up PTO gear pump to cutter hydraulic motor, with only a reservoir, over pressure relief valve, and filter in the circuit, do I need a valve at all? Could I simply start and stop the cutter with the PTO run/stop? (dash switch in the case of my JD 1025R).

I make up a frame to hold the torque of the pump body to the three point hitch, with a reservoir and filter, and just run the two lines up to my cutter hydraulic motor? With no valve, I save cost, and flow restriction, neither of which benefit the design, if the PTO on/off is good enough for cutter run/don't run...

Thoughts?

Yes, it will work perfectly fine without a spool valve, just the pump, relief valve and filter. Turn the PTO on to get the mower running and turning it back off to stop and motor will just slow down on its own. A nice and simple PTO power pack.

Cooling may or may not be needed. I would run it, monitor the temps and decide later on on that.

oldnslo · Sep 15, 2022

What size brush cutter you putting on the tractor. A 1025R is pretty small and would have very low flow rate on standard tractor hydraulics.

Jims1025R · Sep 15, 2022

Thanks for the thoughts... My plan is going to need refinement. I notice that there's a safety shroud around the PTO shaft, which is going to entirely prevent installing the PTO gear pump I'm thinking of. It folds up, but not enough to clear the pump. And, I like safety shrouds, so it'll stay. So... still thinking....

thewalnutguy · Sep 18, 2022

oldnslo said:
What size brush cutter you putting on the tractor. A 1025R is pretty small and would have very low flow rate on standard tractor hydraulics.

If you're thinking of running the cutter off of tractor hydraulics, make sure the tractor hydraulics can be used without damage. I recently bought a JD 5075e thinking I'd be using it at times for running my wood chipper which has hydraulic orbital motors to drive the feed rollers. Only after buying the tractor did I read through the owner's manual and discovered that it clearly states NOT to use the hydraulic port connections on the tractor to power orbital motors. So now I've got a new tractor that can't be used for one of the intended uses for which I bought it. Obviously I didn't do my homework before purchases the JD.