6-14 4203780 First Edition
HYDRAULICS
6
Raise Circuit Schematic and Theory
of Operation
System Conditions:
• Engine running at fast idle
• Right, left, and/or front lift/lower lever(s) in RAISE
position
NOTE
The cutting unit motors will automatically shut off as the
cutting units are raised. (See “Mow Circuit (OFF) Theory
of Operation” for more information.)
Oil Supply to the Lift Valve
Hydraulic oil is drawn from the hydraulic oil tank by
section 1 of the gear pump assembly. Before entering the
gear pump assembly, the inlet oil is filtered by a
100-mesh screen to remove any debris.
Operating-pressure oil from section 1 of the gear pump is
routed to port “P” of the control valve and flows through
the 4.5-gpm priority valve. The four-section gear pump
will need to produce a flow rate of 4.5 gpm before the
priority valve opens to supply oil to the lift valve.
The priority valve will supply oil flow to the steering valve
before allowing oil flow to the lift valve, to ensure
maximum steering control at any engine rpm range.
Raise Circuit
Operating-pressure oil supplied by section 1 of the gear
pump enters the lift valve body at the “IN” port, and is
routed to the relief valve (1500 psi) and lift valve spools.
The oil flows through the lift valve, and is routed to the
pilot line of the detent valves, causing the valves to shift.
The oil then flows through the check valve and 0.60 fitting
orifice to the piston side of the lift cylinders, lifting the
cutting units.
Oil from the other end of the lift cylinders flows back to
the hydraulic tank.
Circuit Relief
The lift system is protected by the 1500-psi relief valve. If
the pressure on the pilot line of the relief valve reaches
1500 psi, the valve will open, dumping
operating-pressure oil through the “OUT” port of the lift
valve body, through the weight transfer valve to the
hydraulic tank.
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