TESTING HYDR PUMP

carrottop

New User
I CHECKED THE PRESSURE ON PUMP AND IT STARTED OUT AROUND 200PSI, BUT THE PRESSURE STARTED DROPPING .IMMEDIATELY,AFTER COMPLETE WARM UP IT STOPPED AT 85PSI.
also CHECKED IMPLEMENT PRESSURE AND COULD ONLY GET 140PSI AT END OF CYLINDER STROKE.
dOES THIS MEAN VALVES BAD OR PUMP NEEDS REBUILT? dOWN LOADED SUNDSTRAND MANUAL AND CLOSET COULD COME UP WITH, IS WARMER OIL GETS WORST SYSTEM GETS, I CAN PUSH TRACTOR WITH UNLOADER VALVE CLOSED
APP. ANY AND ALL HELP EVERYONE CAN GIVE ME
thanks
 
You did not say what machine you are having problems with. That would help us a lot in answering your questions.
 
(quoted from post at 19:19:05 09/12/14) You did not say what machine you are having problems with. That would help us a lot in answering your questions.
it is a 1979 wh tractor c-141
 
I am not a Wheel Horse guru by any means but I do know that on
some models, there was an optional belt driven pump to look
after the implement lift. However, your post seems to imply that
you are talking about the hydrostatic drive on your tractor.

Assuming I am right, then you need to understand that hydro
units are actually made up of TWO pumps, not one. The actual
hydrostatic pump that powers the rear wheels is a variable
displacement pump that supplies oil ONLY to the trans-axle
drive motor when the Operator moves the Travel Lever/Pedal
into Forward or Reverse. It does not supply oil to the implement
lift or any remotes.

The SECOND pump is called the CHARGE PUMP and it is
contained inside the Hydrostatic pump housing. Its primary job
is to circulate oil through the hydrostatic pump to keep it full of
oil and to keep the hydro cool. Manufacturers will often put
"work ports" on the better quality hydrostatic pump units that
allow the oil flow from the Charge Pump to be used to raise
implements or to operate remote cylinders such as a power-
angle plow blade.

If you have downloaded the manual for the hydro unit that is in
your Horse, then it should indicate the rate of flow in GPM for
the Charge Pump along with the MAXIMUM PSI that pump can
put out. This might be as little as 3 GPM and 400 PSI but
knowing the specs is important.

Whenever performing tests on hydraulic pumps, it is a good idea
to drain the system completely and refill it with the exact oil
recommended by Sunstrand. Oil viscosity is important and so is
the ability of that oil to maintain its viscosity as it reaches
operating temperature. However, it does sound to me that you
have a worn out charge pump in your hydro and the only
solution is to have the entire hydro unit rebuilt by a competent
hydraulics shop.

You might want to source out such a shop and have a talk with
them prior to yanking the hydro out of the tractor. If you give
them the Sundstrand pump model number, they may have some
insight to share with you on that model with respect to proper
test procedures and their opinion on what it may cost for the
rebuild.
 

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