How do I stop blowing oil seals?

[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?