Sundstrand 90 series

[Alex]

need some help have 2 90 series pumps working in tandem on a T755 VERMEER TRENCHER.I have not flow thus no pressure from both pumps.
These unit a directly controlled by the solenoid mounted on the pumps ie not CV( Control valve).We tried moving the manual over ride located on the solenoid to no avail.
Similar movement on the track drive pumps gave us the anticipated results track movement.is it possible that both pumps are defective or would the problem be something common to bothpumps.
Please note we have no technical manual for the Trencher or these pumps

[Sergiy]

Sauer -Sunstarnd merged with Danfoss in 2000, forming Sauer-Danfoss. You can find lots of information on series 90 on
thier site - www.sauer-danfoss.com. Alternatively you can look online for Sauer Danfoss series 90 closed loop pumps technical information.
You'll find tons of it, this is a very common pump. However, I wouldn't advise you to venture troubleshooting a closed loop
without COMPLETE understanding of how it works - you may end up with your transmissions damaged even more than they already are...
I've seen lots of those end in our shop this way...
If your problem is a proportional displacement control issue - check for the clogged screen mounted under the
torque motor part of the displacement control - it is not uncommon to clog, however if it cloggs so bad that the control stops working -
your circuit is too dirty, cleaning the screen will solve the "function" problem but will not solve the "dirty" problem...

[Doug Hanson]

Check the direction of rotation for the pumps to start with, then check that there are no restrictions in the suctions lines for the charge pumps or a closed ball valve or clogged strainers. Then check for charge pump pressure. Maybe a little more information will be helpful. Was this machine working fine then suddenly stop, or were the pumps replaced recently, or is this a machine that you just got?

http://www.sauer-danfoss.com/stellent/g ... 0l0603.pdf

http://www.sauer-danfoss.com/stellent/g ... 0l0818.pdf

Oh hey Sergiy, I just got the above typed out and seen you posted. Thanks for posting.