How do I stop blowing oil seals?

wdchyd · Sep 4, 2013

wdchyd said:
maybe getting too much back pressure on your return line.....those connections and qc's need to be larger than the inlet side to reduce pressure drop at high flow/rpm

do you have a motor spool in the control valve (free spin when disengaging)

you may need a piston motor w/case drain which can withstand higher pressure/flow and speed

Don't forget this......when you disengage the valve, the inertia and weight of the blade becomes a flywheel and makes the gear motor momentarily a pump......thus the pressure spike on the return port (pop goes the seal)

oldnslo · Sep 5, 2013

ns_in_tex said:
Thanks to all for the good info & thanks to JJ & others for the heads up on galv piping. We knew that was not according to hoyle, but, we had that and **** I am sure I am the only one that has cut corners. The picture of the hand drives the point home.

Made me think of something else we learned the other day. Cutting steel plate with water. They tell me it looks like it had been drilled or machined. Much better than plazma cutter.

When we get a new seal, will look into what we will try next, from all your suggestions.

Does anyone know the best way to get line direct into the tank? and surely it would not be bypassing the filter?

NS,
Can you find any information on the rated shaft seal pressure for this motor. I know Delta Power offers a high pressure shaft seal on some of their motors. Don't know if Haldex does or not.

For return line. I would not bypass the filter but I would certainly try and remove as many fittings, Quick disconnects, etc. as possible. Like farmerford also stated. Use one size larger hose for the return will also greatly reduce the back pressure / line loss.
Also look at your run down or stopping sequence. With out knowing what spool types you have you maybe pressurizing both ports while trying to slow the cutter head down with the valve. Your valve maybe machined so that you are metering flow out of the motor as well as metering flow into the motor. If both ports are pressurized for a short period of time the shaft seal will blow. I noticed two plugs on the side of this motor. Are they possibly optional case drain ports? If yes running one of these directly to tank would solve your problem.

ns_in_tex · Sep 7, 2013

Oldnslo,
I do not know the seal pressure rating. We were told by someone, it is not a high pressure seal, just an oil seal.

OK, ALL, HERE IS MY GAME PLAN, until the next blowout.

We have connected the return line to the tank. Installed a another new seal. Lowered the high pressure bypass some more. Don't plan on running the engine above 1300 RPM. The blade now coast, what seems like 5 minutes, when disengaged. THIS WAS THE EASIEST THING WE COULD DO & SAY WE TRIED SOMETHING.

We ran it for 3 hours today & everything is great so far. Not by any means a complete test, since it ran longer than that previously.

Will try to let you know results after more run time. THANKS TO ALL FOR THE HELP.

ns_in_tex · Sep 14, 2013

Well, I am sorry to say, it didn't last. This seal blew after about 15 hours operation. We need to figure out our next step.

First let me ask, is it possible to operate a hydraulic motor in the fashion we have been doing, where it may get an instant stall out, once or more a minute? Then sometimes we might run several minutes without stalling. Depends on the size of limbs we are cutting.

When it does stall out, & we back up (normally takes maybe 1 to 2 seconds), it may take a few seconds to get full RPM regained. Presumably, the high pressure bypass is working during this interval.

oldnslo · Sep 14, 2013

ns_in_tex said:
Well, I am sorry to say, it didn't last. This seal blew after about 15 hours operation. We need to figure out our next step.

First let me ask, is it possible to operate a hydraulic motor in the fashion we have been doing, where it may get an instant stall out, once or more a minute? Then sometimes we might run several minutes without stalling. Depends on the size of limbs we are cutting.

Yes some styles of motors will withstand this type of duty. I believe you just need to get a motor with a high pressure shaft seal or one with a case drain. Without knowing what exactly is causing the seal failure it is difficult to prescribe a cure. I would look for a motor with a case drain. This will vent the seal chamber and prevent or significantly reduce seal failures. Some multispindle lawn mowers use this type of gear motor

A more expensive option is a Rexroth bent axis piston motor which are used extensively on mulcher heads and they are seeing duty very similar to yours. Models A2F(M) for fixed displacement in sizes 5 cc/rev (0.3 CIR Cubic Inch Revolution) 10 cc, 12 cc, 16cc, etc. Google RA 91001 for a data sheet. These motors are rated to 5000 PSI. They require a case drain line directly to tank.

good luck

ns_in_tex · Sep 15, 2013

oldnslo said:
Yes some styles of motors will withstand this type of duty. I believe you just need to get a motor with a high pressure shaft seal or one with a case drain. Without knowing what exactly is causing the seal failure it is difficult to prescribe a cure. I would look for a motor with a case drain. This will vent the seal chamber and prevent or significantly reduce seal failures. Some multispindle lawn mowers use this type of gear motor

A more expensive option is a Rexroth bent axis piston motor which are used extensively on mulcher heads and they are seeing duty very similar to yours. Models A2F(M) for fixed displacement in sizes 5 cc/rev (0.3 CIR Cubic Inch Revolution) 10 cc, 12 cc, 16cc, etc. Google RA 91001 for a data sheet. These motors are rated to 5000 PSI. They require a case drain line directly to tank.

good luck

OK, please excuse my very limited knowledge here. You mention might need a motor with a case drain, then a second suggestion of a different motor that requires a case drain line directly to the tank.

On our last improvement trial, we removed the hyd return line from its normal tractor disconnect, removed the tank filler plug & connected the return line here. Are we talking about two different kind of case drains? One (maybe built into the motor) plus another similar to what we have done with the return line?

We have not done all the other suggestions, people have mentioned above, such as remove or enlarge the disconnects. We do not even know the size of our disconnects, but they are the popular ones sold at most tractor dealerships, with 1/2" pipe threads.

We also noticed, we do have 1/2" lines for the last 10' to the motor.

ns_in_tex · Sep 15, 2013

Another question.

I presume it is not possible to get a higher pressure seal for the motor we have.
It is .5" bore x 1.12" OD x .25" thick.

Todd727 · Sep 15, 2013

I'm thinking that belt should slip if the blade comes to a sudden stop when it hits something and comes to a sudden stop. Otherwise, you are transmitting a large shock back to the motor, shaft and seal. In fact, I notice that your idler seems to be fixed with two bolts. I'm more accustomed to seeing that tension provide through a spring which will absorb that shock load.

oldnslo · Sep 16, 2013

ns_in_tex said:
OK, please excuse my very limited knowledge here. You mention might need a motor with a case drain, then a second suggestion of a different motor that requires a case drain line directly to the tank.

On our last improvement trial, we removed the hyd return line from its normal tractor disconnect, removed the tank filler plug & connected the return line here. Are we talking about two different kind of case drains? One (maybe built into the motor) plus another similar to what we have done with the return line?

Sorry for the confusion: Anytime you a case drain line it must go directly to tank. It does not matter if it is a gear or piston style motor. The case drain port on the motor is connected directly to the seal cavity and prevents pressure buildup on the seal.

What may be happening in your current system is: You get the motor running at speed and then stall it. This causes a momentary change in the flow rate in the return line and a pressure spike in the inlet. Depending on the quality of the gear motor this spike may transmit excess leakage flow into the seal chamber. This flow could be leaking past the gears through the bearings to seal chamber. The bi-rotational checks could also possibly be leaking a little. Incoming flow into the seal chamber may be greater than the vent line currently in your motor can handle. This causes a momentary pressure increase in the seal cavity which blows the seal out.

Could also be seeing pressure pulses or spikes in the return line from the flow fluctuations. I.e. Motor stalls causes the hoses to swell slightly and act like an accumulator. Motor spins back up and you potentially get a flow surge in the return line. This also could cause a pressure spike in the seal chamber blowing the seal.

Both of the above situations would require some expensive data acquisition equipment to identify if these are the problem.

Gear style pumps and motors are by far the most common in the fluid power industry. In my opinion you have just unknowingly misapplied your current motor. Get a good quality motor with a high pressure or seal if you don't want to run the case drain line or get a good quality motor with a case drain.

A document you use for reference on showing the internals of a gear motor and explains the case drain well is Rexroth Gear motors ra14025 pages 3 & 4.