Hydraulic trouble shoot question

[Bison]

How do you tell a orbit motor is failing?
Pressure relief valve is set at 3500 PSi.The PTO driven Pump is easely capable of building that pressure till the relief valve opens with the Orbit motor prevented from turning.
Seems like both components are OK,yet the motor loses RPM when load is applied.
The machine can be turned over with 2 fingers with the PTO off

This is on a hydrostatic driven NH 114 haybine

 

[J_J]

Check and see if there is any air/foam in the system, and if it is, check suction hoses and re-tighten everything.

Here is some good reading material/data from.

http://www.sauer-danfoss.dk/stellent/groups/publications/documents/product_literature/520l0232.pdf

Volumetric efficiency
The volumetric efficiency is an expression for the proportion of the applied
quantity of oil [as a percentage] that is
converted to output shaft revolutions
(speed). The remaining quantity of oil
(leakage) is led across clearances and
sealing surfaces to act as a lubricant/
coolant.
When the load (pressure drop) increases,
leakage also increases.
The quantity of oil supplied to the
gearwheel set thus diminishes, and the
number of revolution (speed) falls.

If there is air in the system
• Replenish the oil.
• Connect the system to a separate tank with filter (filter mesh max. 10 µm). The tank
capacity must be twice the max. oil flow. Allow the system to run without load [no
pressure] for around 30 minutes.
• Do not load the system until it has been completely bled and is clean.
• Check for system leakage and make sure it operates satisfactory.
• Replace the oil filter and, if necessary, replenish the oil.

 

[Bison]

I think i found the problem.
There was a busted 0 ring between pressure and return sides in the housing on the relief valve cartridge,result,... lots of oil blowby.

 

[J_J]

You mean you were leaking oil and didn't tell us.

 

[Bison]

It was bypassing oil internally between the relief valve cartridge and the valve housing,ie;pressure to return side.
I had no way of knowing til i removed the cartridge and a O ring piece washed out with the oil.