Hydraulic Motor Question

[rScotty]

A small update. I'm trying to relax a bit today but, couldn't resist the attraction of getting out in the hot & humid sun to swap the reliefs.

Yesterday, when I cut (three foot tall grass/weeds) it cut and at times, got overloaded and blades essentially slowed down and nothing happened.

Today, swapped the reliefs on both outer wings (same circuit) and cut a swath where I left off yesterday.

Did a poor job cutting BUT, one of the reliefs was screaming like a banshee..... so, without gauges, loosened the locknut and tightened the allen screw down about two turns.

Still squeels but cutting 'better'. I raised the cutting height and did better again however, still squeeled when I got into non-cut stuff.

Vague memory....I seem to recall what drove me to get the reliefs replaced. If I recall correctly, it was the LEFT wing that was cutting poorly and now, it's the right one.

Question since I don't know anything about the reliefs... Do they need to be (pardon my word) a bit 'in balance'? Meaning, if one squeals at say 3 turns out but does NOT squeal at say, six turns out, that is telling me the six turns out is acting more like a bypass.

So if three turns makes it squeal.....would the OTHER side need to be at the same number of turns?

To be fair, I am at times, cutting pretty thick stuff and it's not been cut anywhere from end of last summer to a full year PRIOR. So I have some that's three feet high, some that is six feet high and all between.

I was in some of the very tall, thick stuff, was pulling up a hill and tractor started bogging down to the point I had to clutch it as I was fearing it would stall. (I think it's rated at 100-125 PTO)

No, if they squeal they overheating the hydraulic oil. That can ruin the hydraulic fluid. It may have done so. Smell it.
Sounds to me like you need to slow down & lighten the load.
And get the reliefs set right. If you don't know, set them at 2850 psi. Any tractor shop will have a pop gauge and can set them in 5 minutes.

 

[Richard]

What I wish we had was a schematic of the hydraulic system. Without it, we don't actually know how it is plumbed. Maybe it isn't in series. Any chance you have a few more diagrams to share? We have almost enough info to pin it down.

This strikes me as series, no?

Uh-oh.. the first motor is the only one with a case drain? We do need to see some plumbing details.

This is the only one that has a small diameter hose, going to the "cooling channel" (mower uses part of the frame as secondary resovior and I think they call them cooling chambers.

How sure are you of the direction of flow and cutter geometry?

I'd say yes. As I recall, hose goes from pump to this right hand motor, then left motor, then to the cooling chamber.

Does your hydraulic power source have adjustable flow?

Not that I'm aware of. Speed increaser (4x) hangs on the PTO and takes the 540 up 4x in speed. Pump hangs off increaser. Increaser is brand new (literally, only been used for about 3-4 hours)

On mine the output is adjustable in 3 gpm steps but pressure is constant. Selecting too high of a flow can possibly put more pressure into the return line.
There again, a pressure gauge is valuable. Price some kits on Amazon.
rScotty

Sorry late.... been helping wife rehang a solid core door.... (and she's disappeared on me!)


Schematic like this work?

I've got a friend (machinest, works on Porches, engines, to include evidently, a large Rolls Royce engine that was once in his shop) I'll ask if he's got means of testing these.

If not, surely someone around would have something like that but that's going to be another job finding them!! (I'm very busy at work during the week, getting up at 4:00 A.M. and some days, not getting home until 7:00 or 8:30 P.M.)

 

[rScotty]

Yes, the two outrigger motors seem to be in series. The downstream motor is the one that goes to the cooling chamber in the frame. Better get a new hose for that one. Glad you have a buddy who can help. Maybe he has gauges and adapters. If not, Amazon.

No, what you attached is a "hose diagram". Everything helps. A schematic is a picture that shows a fluid power or hydraulics guy HOW a system operates istead of WHAT the components look like. Most shop manuals have schematics included, but operators manuals usually do not. I'll attach an general example of a schematic - it is NOT for your Alamo mower. I grabbed it online and have no idea what it is for. But still I bet you'll see things that you recognize....valves, motors, spring-loaded levers...that sort of thing.

You're just going to have to break down and check pressures to get the reliefs set right. When you do that, the problem will probably reveal itself. There are TWO reliefs for each motor. I'll attach the picture showing them and their settings. I have no idea why there are two each.... but a schematic would make it clear.
Luck, rScotty

 

[dcarman]

I've got a 15' hydraulically powered flex-wing mower. 4-5 years ago, rebuilt all the motors that operate the blades (and the pump which hangs off the PTO on a speed increaser). Note that the outer two sets of blades are on the same hydraulic circuit. Fluid goes from the pump to the right side motor (call it passenger side). Fluid exits that motor and goes over to the left side motor. Center motor is on its own circuit from the pump.

I've noticed recently that if I get into tall/dense growth, the right side will tend to bog down while the center and left side will still cut much, much better. Given the right side motor is first in line and the left blades, cut like a bandit I deduce the motor itself might be weak and/or, there is a drain that goes from the motor into the fluid tank.... Not being a hydraulic expert, I suppose this could be leaking some pressure off (but why then does the left side still cut like a bandit!)

Here's the schematic of the right side motor. If I yank it off again, where might I focus my attention, presuming that I don't find broken vanes or O-rings laying about in there. This strikes me as such a simple design, AND the unit down stream works MUCH stronger, it seems this HAS to be getting the pressure yet, why is it bogging down when the second isn't.

I might add, when bogging down, it will still cut, say half of what's under it but some of it just gets laid down, run over and stands back up.

Also.... blades are sharp enough so I can't blame the blades.

When it comes to hydraulics there is pressure and flow. In a static system all points within the system have the same pressure but when fluid is moving pressures may vary with volume and restrictions within the system such as load or. . . . If there is a restriction in the flow you would see such results. Check your hoses. I'd bet you have a bad hose restricting flow to that motor. If you can switch the hoses with the ones on the other side. The restriction could be on either the pump side or the return.

 

[NYlumberman]

A small update. I'm trying to relax a bit today but, couldn't resist the attraction of getting out in the hot & humid sun to swap the reliefs.

Yesterday, when I cut (three foot tall grass/weeds) it cut and at times, got overloaded and blades essentially slowed down and nothing happened.

Today, swapped the reliefs on both outer wings (same circuit) and cut a swath where I left off yesterday.

Did a poor job cutting BUT, one of the reliefs was screaming like a banshee..... so, without gauges, loosened the locknut and tightened the allen screw down about two turns.

Still squeels but cutting 'better'. I raised the cutting height and did better again however, still squeeled when I got into non-cut stuff.

Vague memory....I seem to recall what drove me to get the reliefs replaced. If I recall correctly, it was the LEFT wing that was cutting poorly and now, it's the right one.

Question since I don't know anything about the reliefs... Do they need to be (pardon my word) a bit 'in balance'? Meaning, if one squeals at say 3 turns out but does NOT squeal at say, six turns out, that is telling me the six turns out is acting more like a bypass.

So if three turns makes it squeal.....would the OTHER side need to be at the same number of turns?

To be fair, I am at times, cutting pretty thick stuff and it's not been cut anywhere from end of last summer to a full year PRIOR. So I have some that's three feet high, some that is six feet high and all between.

I was in some of the very tall, thick stuff, was pulling up a hill and tractor started bogging down to the point I had to clutch it as I was fearing it would stall. (I think it's rated at 100-125 PTO)

Setting hydraulic relief valves without a pressure gauge is a real iffy proposition. In my years as a millwright a working relief valve seldom requires even a full turn to bring the pressure up 500 lbs. When a squeal is persistent, check the seat.

 

[NYlumberman]

Setting hydraulic relief valves without a pressure gauge is a real iffy proposition. In my years as a millwright a working relief valve seldom requires even a full turn to bring the pressure up 500 lbs. When a squeal is persistent, check the seat.

After reading your post again, do you have a hydraulic schematic? I’m trying visualize what happens to oil when it goes over relief. I am thinking the pressure just diverts to the return line. If that is correct, then the case drain would only carry internal leakage. And I’m wondering if your pump is a single or a double. A single would require a flow divider, not ideal. Is this a batwing that folds up and is that function fed by same pressure line that powers the center section? Zen and the art of tractor maintenance, be the oil.

 

[rScotty]

Setting hydraulic relief valves without a pressure gauge is a real iffy proposition. In my years as a millwright a working relief valve seldom requires even a full turn to bring the pressure up 500 lbs. When a squeal is persistent, check the seat.

They need to be in balance - i.e. the same setting, because you want your two outrigger motors to be in balance.
Look back on post #13. There are two darn near identical relief valves on each motor. One on each motor is set at 800 and the other at 2000 psi. Other than the setting, they sure look the same. Any chance they got swapped?

 

[Lavender Valley]

Focus on item #32, the relief valve. Although the plumbing to the relief valve is not shown, if it was mine, before tearing the motor apart I'd first want to make sure that the pressures were equa - or at least that they made sense with the symptomsl.

An easy way to learn something useful is just swap the relief valves.

Or you could test pressure by interrupting the pressure input to each motor with a hydraulic "Tee" and mounting a inexpensive 5000 psi gauge on both motors. The gauges can stay there. Since relief valves are adjustable, the gauges would allow you to adjust as necessary.

The only slight problem in putting on guages is ordering the Tee with the right threads.
All the parts to do this can be gotten online. Googe SurplusCenter or others.
Or there are simple hydraulic test gauge kits on Amazon that will do the same thing and come with several threaded adapters.
luck,
rScotty

check the rotation is correct, I have seen hydraulic motors re-assembled incorrectly.

 

[Richard]

Been out of town all week, sorry so late to comment. Pulling the owners manual out, it says two of the reliefs are 1,500 PSI and the third/center is 2,500 PSI.

Might I presume my local JD dealer might be able to test those? Better to go to a hydraulic shop?

I looked through the manual and didn't see anything that looked like the diagram above (hydraulic diagram) I'll scan through it again (wife is/was sitting here talking to me so I'm a bit distracted)

Would it work to instead, insert a "T" in between each relief and mount a gauge to that (I think someone said something about that already?)

Kind of makes me nervous though as if I envision it correctly, the mower would have to be running while I'd be climbing above adjusting the relief, then what RPM do I use.... (not a comfortable thought)

Intent is to call someone to see if they can do it.

I also saw some numbers on one of them so I'm guessing they are identifiable. If numbers are same, I'd presume they are identical. Numbers different then I want to find two of them the same.

These motors only have ONE relief. I've seen some of those with two but these aren't like that. I appreciate all the thoughts.

 

[rScotty]

Been out of town all week, sorry so late to comment. Pulling the owners manual out, it says two of the reliefs are 1,500 PSI and the third/center is 2,500 PSI.

Might I presume my local JD dealer might be able to test those? Better to go to a hydraulic shop?

I looked through the manual and didn't see anything that looked like the diagram above (hydraulic diagram) I'll scan through it again (wife is/was sitting here talking to me so I'm a bit distracted)

Would it work to instead, insert a "T" in between each relief and mount a gauge to that (I think someone said something about that already?)

Kind of makes me nervous though as if I envision it correctly, the mower would have to be running while I'd be climbing above adjusting the relief, then what RPM do I use.... (not a comfortable thought)

Intent is to call someone to see if they can do it.

I also saw some numbers on one of them so I'm guessing they are identifiable. If numbers are same, I'd presume they are identical. Numbers different then I want to find two of them the same.

These motors only have ONE relief. I've seen some of those with two but these aren't like that. I appreciate all the thoughts.

Best back up a little.
A hydraulic gear pump like you have producing the system pressure, and the hydraulic motor driving your cutter blades - are both positive displacement" types. "Positive displacement" simply means that there isn't any slippage, leakage, or circulation inside the pump or the motor.

Most tractors and implements with a hydraulc pump and motor are made the same way.
BTW, that also means your hydraulic motor is simply a hydraulic gear pump hooked up backwards.

If either one is deadheaded - that is if either the hydraulic pump or the hydraulic motor is deadheaded without a relief valve - it will either stall your diesel or else quickly build enough pressure to blow something up.
You can deadhead a pump by blocking the flow, and you can deadhead a hydraulic motor by preventing it from rotating....Like when it slugs on too much of a load. It can't cut that grass so the motor stalls. All that keeps it from blowing up when the motor stalls is that the relief valve opens and relieves the pressure.

The relief valve is a spring loaded poppet valve that opens up when spring pressure is exceeded and cures the deadhead by dumping hydraulic flow directly back to the sump through the return line. It also is built so that it will make a lot of whistling chattering noise when it goes into relief. You said you have heard that.

Hydraulic pressure is high enough that it will kill you. Don't ever mess with a relief valve when the engine is running. Shut it off and remove all pressure.

There are two problems with relief valves. One is that they can get crud or rust caught in the poppet valve and so they hold themselves slightly open which makes that circuit weak, and the other is that when you take it apart to clean problem number one, you can end up with it adjusted wrong so that we don't have any idea where they are set for safe operation.

I'd say to take those reliefs and go get them set right somewhere, A hydraulc shop would be my best guess. The relief valve settings may or may not be your original problem, but you still need them working right. You've already done the hard work by taking them apart and cleaning them up.

You asked about a pressure gauge. I like them, and don't know why they aren't standard on all tractors.
The best place for a pressure gauge is on a "T" fitting right at the output of the hydraulic pump. It mostly tells you if you have enough pressure to do work or if the system is losing pressure somewhere. If you happen to be watching the gauge right when a relief valve goes off, it will also tell you the relief pressure.

Hope this helps. Sorry about the confusion on the number of reliefs on yours. Apparently the ALAMO cutter is made in a number of different versions.

rScotty