Textron JACOBSEN GP400, Technical/Repair Manual

Page: 212 / 354

6-20 4252490-Rev A
HYDRAULICS
6
Raise Circuit Schematic and Theory
of Operation
System Conditions:
• Engine running at fast idle
• Mower raise/lower switch in the raise position
NOTE
The cutting unit motors will automatically shut off as the
cutting units are raised.
Oil Supply to Lift Valve
Hydraulic oil is drawn from the hydraulic oil tank by the
gear pump. Before entering the gear pump, the inlet oil is
filtered by a 125 micron suction strainer to remove any
debris. Operating pressure oil from the gear pump is
routed to port “P” of the reel valve unit, through the 3020
psi (207 bar) mowing relief valve, through port “T” of the
reel valve unit, and to port “P” of the lift valve.
Raise Circuit
Operating pressure oil supplied from port “T” of the reel
valve unit enters the lift valve at port “P.” The oil flows
against the 1250 psi (80 bar) relief valve, through the
solenoid valve, through the check valve, and then exits
the lift valve at port “A.”
Oil from port “A” of the lift valve is routed to port “B” of the
top sequence delay valve and to the piston side of the
right and left lift cylinders. Oil flow to the piston side of the
right and left lift cylinders raises the right and left cutting
units.
Oil entering port “B” of the top sequence delay valve
flows unrestricted through the check valve, exits port “A”
of the top sequence delay valve, and flows to the piston
side of the center lift cylinder. Oil flow to the piston side of
the center lift cylinder raises the center cutting unit.
Oil from the rod end of the right and left lift cylinders flows
through port “B” of the soft drop valve, flows unrestricted
through the check valve, exits port “A” of the soft drop
valve, and is then routed through the lift valve, back to
the oil cooler, and then to the hydraulic tank.
Oil from the rod end of the center lift cylinder flows
through port “A” of the bottom sequence delay valve,
against the check valve, through the orifice, and exits
port “B” of the bottom sequence delay valve. The orifice
restricts the flow of oil, dampening the reaction of the
center cylinder extension. Oil exiting port “B” of the
bottom sequence delay valve is routed through the lift
valve, back to the oil cooler, and then to the hydraulic
tank.
When the solenoid valve is returned to the center
position, oil flow from the piston side of the cylinders is
blocked by the check valve, ensuring the cutting units
stay in the raised position.
Circuit Relief
The lift system is protected by the 1250 psi (86 bar) relief
valve in the lift valve. If the pressure on the pilot line of
the relief valve reaches 1250 ± 10% psi (86 ± 10% bar),
the valve will open, dumping operating pressure oil
through port “T” of the lift valve, to the oil cooler, and then
to the hydraulic tank.