How do I stop blowing oil seals?

[wdchyd]

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]

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]

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]

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]

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]

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]

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]

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]

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.

 

[J_J]

I am thinking this hyd motor will serve you better.

Has case drain and 1 in shaft.

Surplus Center - 2.5 cu in WHITE 255040F3DD22AAAA HYDRAULIC MOTOR

 

[oldnslo]

I am thinking this hyd motor will serve you better.

Has case drain and 1 in shaft.

Surplus Center - 2.5 cu in WHITE 255040F3DD22AAAA HYDRAULIC MOTOR

This motor would work if it provides the operating RPM he needs to run the cutter head.

 

[J_J]

He is using a belt/pulley setup, so whatever ratio from pulley to pulley will provide the best rpm for the cutter.

ns_in_tex ,

Have you figured the blade tip speed for the cutter for a good cut.

Are your blades sharp or flat faced? A lot of hyd powered tree cutters are carbide tipped and almost flat face with a small cut back angle.

 

[PILOON]

I noticed that the motor is a flange mount and when normally mounted the surface to which it would be bolted to would tend to hold the seal firmly in its place.
I had a similar situation with blowing seals that I cured by simply adding a 'backer plate' to keep the seal firmly in place. Maybe even add a shim or 2 and keep the backer shaft hole just a tad larger than the shaft.
Serious leaking or bypass might suggest that the shaft or bushing is somewhat worn out allowing pressure to exit between shaft and sleeve.

 

[ns_in_tex]

He is using a belt/pulley setup, so whatever ratio from pulley to pulley will provide the best rpm for the cutter.

ns_in_tex ,

Have you figured the blade tip speed for the cutter for a good cut.

Are your blades sharp or flat faced? A lot of hyd powered tree cutters are carbide tipped and almost flat face with a small cut back angle.

I think most rotary cutters have blade tip speeds near 15,000 feet per minute. I think we originally were trying for that, but don't remember the exact outcome.

We have a 30" blade with the last 8" swinging like brush cutters, and it is sharp. We do mow grass & weeds, as well as trim hanging branches that might hit the cab of the tractor.

 

[ns_in_tex]

I am thinking this hyd motor will serve you better.

Has case drain and 1 in shaft.

Surplus Center - 2.5 cu in WHITE 255040F3DD22AAAA HYDRAULIC MOTOR

I see it is a 2.5 cu in motor, where mine is .517 cu in.

Do you know what speed this motor would turn with 4 gpm flow?

 

[J_J]

370 rpm and torque of 995 in lbs using a pressure of 2500 psi.

You get more speed with more GPM, lower displacement or large pulley to a smaller puller.

 

[ns_in_tex]

370 rpm and torque of 995 in lbs using a pressure of 2500 psi.

You get more speed with more GPM, lower displacement or large pulley to a smaller puller.

Am I correct in thinking, GPM will remain semi relational to tractor RPM, regardless of pressure, just less torque?
So, if I can gear up to get desired blade speed and no load other than turning the blade, maybe the pressure might be only 800 or 1000 PSI, then pressure would jump up when cutting load applied?

Looks to me like with a 30" blade, 370 RPM motor, we would need about 5 times the size pulley on the motor, as the blade shaft, to get close to 15,000 FPM?

 

[oldnslo]

Am I correct in thinking, GPM will remain semi relational to tractor RPM, regardless of pressure, just less torque?
So, if I can gear up to get desired blade speed and no load other than turning the blade, maybe the pressure might be only 800 or 1000 PSI, then pressure would jump up when cutting load applied?

Looks to me like with a 30" blade, 370 RPM motor, we would need about 5 times the size pulley on the motor, as the blade shaft, to get close to 15,000 FPM?

Yes pressure is dependent on the load and you will get some motor speed change with tractor engine RPM change.

My two cents worth. I am not a big fan of using a LSHT Low Speed High Torque motor for this type of application. I believe you would be better off to invest in a good gear motor with the case drain. Gear motors have less moving parts and are typically more efficient than the LSHT geroler or geroter style motors. Do you have a local hydraulic component distributor in your area Vs using what hydraulic supply or Northern tool, etc have to offer. Companies like Sauer Danfoss, Cassappa, Eaton-Vickers all offer pressure side laoded gear motors with the case drain option.

 

[J_J]

Yes sir, the GPM's are directly related to engine speed.

Although the pump is capable of pumping fluid at say 3000 psi, it is the load that develops the pressure up to the stall load.

So when the hyd motor is powered up, and running at max, very little pressure is developed.

As you start cutting, the amount of resistance to the blade will cause the hyd motor to develop pressure.

If you have a hyd gage in the motor circuit, you can see the pressure at any time.

The torque is dictated by the cu in of the motor and psi.

As far as blade tip speed, I am not so sure your tree limb cutter needs 15,000 fps.

It would probably do well at 8,000, depending one the type of blade and the weight of the blade.

Some of the tree limb cutters use what looks like large saw blades.

 

[ns_in_tex]

Yes pressure is dependent on the load and you will get some motor speed change with tractor engine RPM change.

My two cents worth. I am not a big fan of using a LSHT Low Speed High Torque motor for this type of application. I believe you would be better off to invest in a good gear motor with the case drain. Gear motors have less moving parts and are typically more efficient than the LSHT geroler or geroter style motors. Do you have a local hydraulic component distributor in your area Vs using what hydraulic supply or Northern tool, etc have to offer. Companies like Sauer Danfoss, Cassappa, Eaton-Vickers all offer pressure side laoded gear motors with the case drain option.

We do not have a distributor in our county. Adjoining county's have a Northern Tool & a private company which is very expensive.

Another question. Our present gear motor has check valves so it can be reversible. Since we rerouted the return line, we gave up the reverse option. Might it be possible to remove one check valve to make a case drain?