Tractor Repair: IH 856 Steering, pressure relief valve, broken spring

Question
William attempted to answer this question, but also asked me to follow up with you to make sure.  He thought it might be the pressure relief valve or the orbital valve.  Let me know what you think, and thanks for your help.  

I have an issue with the steering in my IH tractor.  I am able to steer the tractor but it turns slowly and it takes quite a bit of effort.  It is hard to steer if it is moving or stopped and my TA, clutch and brakes all seem fine.  In trying to figure it out I found that if I turn the tractor off I am not able to move steer it at all with the steering wheel (hand pump).  The steering wheel will spin freely for a few turns and then slowly start to build pressure, but never enough to move the wheels.

Answer
Hello,

  It's not unusual to not be able to steer with the engine off.  When the power steering doesn't work on one of these, it's not like the power steering not working on  a car.  A car will at least steer manually, but with more effort.  Trying to steer manually on a tractor with hydrostatic steering rarely works very well.
  It sounds like the steering pressure is low with the engine running.  There is a steering relief valve in the MCV valve on the left side of the transmission.  The pressure can be checked by putting a gauge in one of the hoses at the steering cylinder, running the engine and turning the steering wheel.  You should get a minimum of 1400 to 1500 psi.  Low pressure can be caused by a blown o-ring or broken spring in the steering relief valve.  A bad hand pump is possible, but is not very likely and is the most expensive to fix.  If the pressure is good, then the seals in the steering cylinder could be blown.