Service Manual

2 - 8 5xi Series Tractor Hydraulic Service Manual
THEORY OF OPERATION
2
Flow diagrams show hydraulic circuits inside hydrostatic unit and illustrate high and low pressure areas during
operation.
Pressurized oil from the charge pump is maintained between 30 and 90 PSI (2.1 - 6.2 bar) by the charge relief
valve located inside the hydrostatic unit. When the valve opens, excess oil pressure is bled back to the transaxle
sump through a hole in the housing.
The charge pump oil enters the transmission pump section, which is turning at engine speed, and “supercharges”
it.
HYDROSTATIC TRANSMISSION FLOW DIAGRAM, UNITS WITHOUT POWER STEERING
(A) Charge Pressure Relief Valve.
(B) Motion Control Shaft.
(C) Filter.
(D) Cam Ring - Radial ball-piston hydraulic pump.
(variable displacement).
(E) Charge Pump - Transmission charge pressure 30-
90 PSI (2.1 - 6.2 bar). Implement lift system
pressure 700 PSI (48.2 bar).
(F) Charge Pump.
(G) Input Shaft.
(H) Hydraulic Pump.
(I) Hydraulic Lift Control Valve - With 700 PSI (48.2
bar) relief valve.
(J) Acceleration Valves.
(K) Hydraulic Motor.
(L) Output Shaft.
(M) Radial Ball-Piston Hydraulic Motor - Fixed
Displacement.
(N) Forward/Reverse Check Valves.
(O) Transaxle Sump.