Does anyone know about hydraulic drive systems?

[strum456]

We recently bought a John Deere 1600 mower conditioner. It is a center pull hydrostatic drive machine. After about 30 minutes of use, the hydrostatic drive gives out intermittently.


Symptoms:

1. It always seems to stop working when the load is low. If I lift the mower at the end of a pass, it will quit just as I start to mow again. It has never stopped under a hard pull in heavy hay.

2. Sometimes all I need to do is stop the PTO and restart it and it will work again. It seems to be all or nothing. When it stops working it will barely even turn over the machine if it out of the hay, then suddenly it kicks in hard and I can mow for a while.

Checked Already:

Fluid level is correct according to manual

Cracked drain plug, no water in reservoir

Changed filter and dissected old one. Old filter looks fine.

Checked for leaks, there isn't a damp hose, fitting or seal on the system.

Checked for kinks in hoses



The system has a pressure relief valve, as a safety I assume. I am wondering if these symptoms are typical of a malfunctioning pressure relief and if so, how would I tell if the valve is bad upon inspection. I pulled it out, all the o-rings, seats, etc. seem to be normal looking.

 

[Blade Breaker]

Strange. Could it be an electrical issue?

 

[strum456]

Strange. Could it be an electrical issue?

I doubt it....I don't think there is a single wire on the whole machine. I have seen intermittent problems like this stemming from electrically actuated hydraulic solenoids. This machine doesn't have any though.

 

[Blade Breaker]

Is the ground you are working on level? Any chance it could be caused when the machine is on a slope? Possibly an oil pick up line inside that fell off or low oil level. Not sure if that is possible with that machine. The pressure relief may be a possibility.
If it happens right after you use the lifting cylinders to raise or lower the machine could it be that the oil level dropped temporarily to a level where it will not work. Then after a second it will pick up oil again? Try overfilling the hydro oil some and see if that cures it. If the vent is not plugged I would not think it could hurt anything?

 

[strum456]

Yes, the ground is pretty level. There does not seem to be any correlation between the slope of the machine and it shutting down. The tongue is the reservoir and the pickup is a 2" pipe that is welded to the lowest point (much lower than anywhere else). You would have to pull the machine up a VERY steep incline to get the oil away from the pickup.

The hydro was overfull when we got the machine. At first, I thought that was the problem, so I drained it to the correct level. The problem continues...

 

[Xfaxman]

Does the lift cylinder work when the mower doesn't spin?

Tee in a pressure gauge on the output of the pump. Hold the valve open to lift the mower, it will reach maximum pressure and you should hear the relief valve open.

Check the pressure when it fails.

Does it have more than one hydraulic motor?

A bad suction line that collapses intermittently could also do it.

 

[strum456]

The lift and swing cylinders work when the mower doesn't spin because they are a separate system powered by the tractor's hydraulics.

What we're dealing with is a pump on the PTO that turns a single motor that runs the whole machine. I suppose the only time the relief valve should open is when you wrap the rollers or some other overload situation (which hasn't happened yet).

I was looking at the suction line the last time it happened to make sure it wasn't kinked. I don't think it is collapsing unless this can happen internally without it showing on the outside???

Checking the pressure - I was thinking about this. The first problem is that I don't have the tools to do it. But let's say I get the tools, hook it up and sure enough, the pressure drops when the problem occurs. How would I determine the cause of the drop? Wouldn't the failure of one component cause the pressure to fall in the entire system?

 

[jenkinsph]

If the system works well under load when it is working then I suspect you are sucking in air between the tank and pump inlet. The tank pick up screen, filter canister and all lines leading to the pump inlet need to be checked for leaks. Any of these lines that are above the tank fluid level can be sucking in air during operation without showing any signs of leaking oil. I would give this a more thorough examination. Just because they appear good doesn't mean the lines aren't sucking air.

The second thing to check would be the PR valve, if it is dumping the fluid to the tank when the problem occurs you won't have the flow to drive the hydraulic motor.

Installing a test gauge in the outlet of the pump would be a good idea so that you can determine whether the pump is or is not building up pressure when the problem occurs.

 

[Xfaxman]

-------------------------
I was looking at the suction line the last time it happened to make sure it wasn't kinked. I don't think it is collapsing unless this can happen internally without it showing on the outside??? Yes, many instances reported here in the past.

Checking the pressure - I was thinking about this. The first problem is that I don't have the tools to do it. But let's say I get the tools, hook it up and sure enough, the pressure drops when the problem occurs. How would I determine the cause of the drop? Wouldn't the failure of one component cause the pressure to fall in the entire system? No, pressure is highest with little or no flow.

If the pressure drops, it is the probably the pump or suction line. If the pressure goes up something may be keeping the motor from rotating.

:thumbsup:

 

[strum456]

I have to say that you might be on to something about air in the system. The symptoms seem like air to me. I just have no idea where it would be getting in. The picture shows a machine like mine. The pickup is at the lowest point of the tongue. There is a 3 foot long 2" hose that feeds the pump. As far as I know, that is the only place it could suck in air without blowing high pressure fluid out all over the place. BUT, that hose does have gravity pushing 25 gallons of fluid against when the machine is sitting idle. Surely it would leak.... The weather is supposed to clear up Thursday. I'm going to be paying a lot more attention to that pickup hose.

 

[oldnslo]

The inner tube or liner on suction hoses can collapse and the outer shell of the hose won't show any deformation at all. Does the pump sound change when the machine stops? Typically pump cavitation sounds like you are rock grinding Vs pumping oil and is very noticeable.

 

[strum456]

UPDATE:

The problem was the pressure relief valve. The valve is not even available from Deere, so we machined a bolt so it had a sealing surface like the pressure valve and threaded it in the hole, eliminating the valve. The mower has worked great ever since.

Thanks for all the ideas. I'm going to remember the possibility of a suction hose collapsing on the inside only - I never knew that was possible.

 

[oldnslo]

With no relief valve you are running on borrowed time the the pump is a dumb device it just wants to keep moving fluid until the weak link breaks which could be a hose, pump, motor, etc..

Was there any part numbers or brand names on the relief valve. I suspect it was made by a valve OEM and there is a replacement available, Deere just doesn't want to sell the valve, they want to sell a complete manifold.

Any pictures of the valve, thread size, etc.

 

[kuboman]

I concur about no relief. That is a very dangerous situation. I would not want to be anywhere around that machine when operation. If you encountered a situation where the relief would go and you don't have one you can explode a hydraulic motor or hose and have a lethal situation.

 

[beenthere]

UPDATE:

The problem was the pressure relief valve. The valve is not even available from Deere, so we machined a bolt so it had a sealing surface like the pressure valve and threaded it in the hole, eliminating the valve. The mower has worked great ever since.
.................

The relief (the older AE42656 or newer AE48929 depending on s/n) valve appears to be available through Deere. Price of the assembly is $300 for older to $400 for newer, but is available.