[AT] MT 1155 hydraulic system was 8.9 liter Perkins

[James Peck]

Cecil,
      Any luck finding the MF 1155 manual You do not need to scan the hydraulic schematic page if you find it. Just snap a shot with your cell phone.

     Any modern bonified tractor mechanic training program is going to include a fair amount of mobile hydraulics content.

[John Maddock] I note that the 1155 was built between 1973 to 78.  As I understand, MF lower horsepower tractors of a similar age (and certainly the 100 series) had three pumps: the Scotch yoke piston pump to drive the 3 pt. lift; an internal  gear pump driven by a gear off the pto shaft to supply external services, a second gear pump piggy-backed on the first gear pump to supply Multi-power and pto clutch packs if fitted. A pressure maintaining valve was fitted on the line to the Multi-power clutch to maintain the pressure for the PTO clutch when Multi-power was set to "low", the oil being dumped in that state.

The medium horsepower tractors had a fourth (gear) pump with its own oil supply, driven from the engine for power steering.

[Dennis] I agree that using relief valves to regulate pressure or flow is not a  good thing, especially with a fixed displacement pump. I have seen it  done before, but agree that it generally just makes heat. It might  work with open center valves where there is no pressure in the circuit  until a valve is actuated. With closed center valves it is just a heat  generator that wears out relief valves and hydraulic fluid. I have trouble believing a tractor manufacturer would design a system  like this. I think a more probable design would be a 3 stage pump or  multiple pumps. If they were pressure compensated pumps it would be a  great circuit