How do I stop blowing oil seals?

[ns_in_tex]

We built a 30" mower for our FEL so we could trim trees up high, ETC.
It is powered by a hydraulic motor. Belt drive. 6" v-belt pulley on motor & 5" v-belt pulley on mower.
We are running 5 to 6 GPM & tractor bypass is set at 2500 psi.
After blowing first seal, we put an adjustable bypass adjacent to the motor & set it at 1800 psi.
Next seal, we backed off on adjustable bypass a little more, but did not set with a gauge.
It does a great job, & may cut things we don't expect it to, for a good while, then it will blow the seal on something, we wouldn't expect it to.
Where am I going wrong. We really don't want to give the mower up.
Motor Specs:
Concentric/ Haldex Barnes 4F657A, Product# G2368956,
Hydraulic Gear Pump/Motor, Birotational.
Displacement: 0.517 Cu In.
Max contiuous PSI 2500
Max intermittent PSI 2750

Do you think we need to set adjustable bypass down more or do we need some kind of heavy duty motor?
Thanks in advance

 

[ishiboo]

Don't most hydraulic motors need a case drain? I would make sure there is a case drain with zero restriction on it.

 

[J_J]

I would highly suggest you replace the water pipe fittings with hyd fittings.

Read post 28 below, and look at picture.

http://www.tractorbynet.com/forums/showthread.php?t=285577&page=3&p=3451870#post3451870

6 GPM is turning the motor at 2681 rpm, and you have about 206 in lbs, or 17 lbs of torque.

I believe you are asking that motor to way to much.

The spike pressure may go much higher than your relief.

 

[oldnslo]

Like Ishiboo stated, what type of seals does your motor have?
Do you have any "run down" protection for when you are stopping the motor?

Since the shaft seal is usually connected to the return flow side of a motor I would suspect that you either have to much back pressure in the return line or no run down protection in your circuit.

As JJ states: Get rid of the pipe fittings especially the galvanized ones. Oil flowing past the galvanizing will cause the galvanizing to flake off destroying everything in your system.

 

[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

 

[J_J]

You should have a motor spool valve in the hyd circuit so the motor can wind down.

I can see why you blew the seals if you suddenly stopped the motor.

Use a motor spool valve like this.

Surplus Center - 1 SPOOL 8 GPM PRINCE MB11C5C1 MOTOR SPOOL VALVE

I would think your blade would be turning at about 800 to 1000 rpm, and about 1/2 in thick

At 6 GPM, you are turning that blade at 2681 rpm. I would also be wary about using thin blades above your head, and the bits and parts of tree limbs going everywhere.

How about a picture of the cutter?

 

[Barry 1]

Hey J_J , are those little pumps strong enough to handle belt drive? Seems like alot of stress on that little shaft and bearing? Always thought you had to use a Love-Joy on those??

 

[J_J]

Even with a 1/2 in shaft, the side load is only about 70 lbs.

http://www.grainger.com/Grainger/HALDEX-BARNES-Birotational-Fluid-Motor-4F657

However, I am using a similar one off my gas engine belt drive.

 

[ns_in_tex]

I can see I have lots to learn about hydraulics.
Many of your replys, we do not know enough to answer intelligently.
1. We are running it off one of our rear Kubota remote valves. We don't know what kind of valve this is, and have no idea if it may be case drain.
2. I think I remember, some times it free wheels down & some times it loads down. We normally try to engage slowly & do same on disengage. Many times it will stall instantly when hits dirt or other solid material.
I will admit to cutting 3" cedar tree on purpose, and steel fence post accidently, but it did not blow at this time.
3. Seal is just normal low pressure oil seal.
4. Spike pressure. Would setting my bypass to maybe 1000 psi lower the spike pressure?
5. Our deck is 1/4" steel, open on front side & protecting tractor side.
6. Blade is 1/2x3 with swing ends, some kind of hard steel we had on hand, but holds cutting edge well.
7. It has always blown seal when it strikes something, not when turning on or off.

Picture attached with motor & shields removed.

 

[ns_in_tex]

We cut with blade rotating counter clockwise, viewing from top.
Deck skirt is also 1/4" steel.