Toro Groundsmaster 5900 Series Service Manual page 115

Traction Circuit Operation (continued)
Groundsmaster ® 5900 & 5910
16227SL Rev B
The final gear pump section supplies oil to the steering, cutting deck lift and
traction charge circuits. This gear pump section provides a constant supply of
charge oil to the traction circuit to make up for oil that is lost to internal leakage
in the traction pump and wheel motors. Charge pump flow is directed through
the charge oil filter attached to the steering/deck lift manifold before entering the
piston pump. A bypass valve is located in the manifold to allow charge oil flow to
the closed traction loop if the filter becomes plugged.
Traction charge pressure is limited to 20 bar (290 PSI) by a relief valve located in
the piston pump. Charge pressure going into the pump can be measured at the
pressure test port (CH1) located on the steering/deck lift manifold. Measured
pressure should be approximately 26 bar (380 psi) with 150F oil. Charge
pressure inside the pump can be measured at the pressure port (AM3) located
on the LH side.
The traction manifold includes a shuttle valve (SH) for cooling of the closed
loop traction circuit. The shuttle valve spool is shifted by traction pressure and
allows hydraulic fluid to bleed off for cooling of the closed loop traction circuit.
The charge system replenishes oil that is bled from the traction circuit due to
shuttle valve operation.
The front wheel motors include an internal, multi−disc parking brake system. The
parking brake is automatically applied by internal motor spring pressure when
the engine is not running or charge pressure drops below 12 bar (174 psi). The
brake is released when the engine is running, charge pressure is above 12 bar
(174 psi) and the parking brake rocker switch is in the disengaged position.
Page 5–15 Hydraulic System: Hydraulic Flow Diagrams