Textron JACOBSEN R-311 69166, Technical/Repair Manual

Page: 245 / 402

6-14 4203781 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 the 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 (17 lpm) priority valve. The four-section gear pump
will need to produce a flow rate of 4.5 gpm (17 lpm)
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 1500 psi (103 bar) relief valve 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
0.060 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 (103 bar)
relief valve. If the pressure on the pilot line of the relief
valve reaches 1500 psi (103 bar), 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.