Hydraulic Motor Question

[Richard]

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.

 

[rScotty]

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

 

[Richard]

Guess I might have mentioned.... all three relief valves have been replaced with new. I've actually tightened this one up a bit (1, maybe 1 1/2 turns) to see if that might help and it hasn't.

I should have thought to mention that I've tinkered with them. Now, THAT said, I am presuming that screwing them IN raises the breakaway, ostensibly, making the fluid do the work instead of bypassing.

 

[Richard]

Gotta say though, I did NOT think of swapping them nor, adding a gauge into the circuit.

Both, excellent ideas (although I'd expect to smash the gauge over time.....seems to be what I do!)

 

[rScotty]

Gotta say though, I did NOT think of swapping them nor, adding a gauge into the circuit.

Both, excellent ideas (although I'd expect to smash the gauge over time.....seems to be what I do!)

Let us know what you do. But that is where to start. The exploded motor diagram you posted shows that it is a positive displacement motor. So if they are in series, they should run at the same speed.

 

[Richard]

The exploded motor diagram you posted shows that it is a positive displacement motor. So if they are in series, they should run at the same speed.

I will and thank you for above. Although I'm pretty fearless mechanically, I'm not very technical..... but that (being in series) is what wasn't making sense to me.

I suppose it's possible that the reliefs are out of whack or maybe one is defective.

 

[LouNY]

I will and thank you for above. Although I'm pretty fearless mechanically, I'm not very technical..... but that (being in series) is what wasn't making sense to me.

I suppose it's possible that the reliefs are out of whack or maybe one is defective.

When it's warmed up good, you could disconnect the case drain hose and place it in a jug and see how much goes to the jug when worked. Or a piece of clear hose installed to see the flow, the case drain should be non restricted to the tank.

 

[Richard]

If the case drain is the third much smaller hose (this first motor is only one that has this) Frankly, I'd be nervous on removing it.

This mower is probably 39-40'ish years old. The fitting where this drain goes back into the tank gets constant inspection by me..... my fear is one day it's going to simply break loose. It's very deteriorated. at the fitting and the hose itself? Yikes. It's looking very frail but again, I'm nervous on simply removing it from the tank. If this were to break at the fitting, not sure what my options would be to try to fix it.

 

[Richard]

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)

 

[rScotty]

I will and thank you for above. Although I'm pretty fearless mechanically, I'm not very technical..... but that (being in series) is what wasn't making sense to me.

I suppose it's possible that the reliefs are out of whack or maybe one is defective.

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.

When it's warmed up good, you could disconnect the case drain hose and place it in a jug and see how much goes to the jug when worked. Or a piece of clear hose installed to see the flow, the case drain should be non restricted to the tank.

Thank you Lou, Good test. That is another possible way it could run at different speed - and interpreting it also depends on how the motors are plumbed.

If the case drain is the third much smaller hose (this first motor is only one that has this) Frankly, I'd be nervous on removing it.

This mower is probably 39-40'ish years old. The fitting where this drain goes back into the tank gets constant inspection by me..... my fear is one day it's going to simply break loose. It's very deteriorated. at the fitting and the hose itself? Yikes. It's looking very frail but again, I'm nervous on simply removing it from the tank. If this were to break at the fitting, not sure what my options would be to try to fix it.

Uh-oh.. the first motor is the only one with a case drain? We do need to see some plumbing details.
How sure are you of the direction of flow and cutter geometry?
Does your hydraulic power source have adjustable flow?
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