Textron JACOBSEN GP400, Technical/Repair Manual

Page: 218 / 354

6-26 4252490-Rev A
HYDRAULICS
6
Backlap Circuit Schematic and
Theory of Operation
System Conditions:
• Engine running
• Cutting units lowered
• Park brake engaged
• Traction lever in the mow position
• Mow switch in the on position
• Reel valve in the backlap position
• Seat switch in the on position (operator in seat)
NOTE
See “Mow Circuit—Theory of Operation” on page 4-26
for the electrical operation of this circuit.
Oil Supply to Reel Valve Unit
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.
Backlap Circuit
Operating pressure oil supplied by the gear pump enters
the reel valve unit body at port “P.” It flows through the
145 micron filter and is routed against the relief valve and
through the reel speed control valve. Oil is then routed to
the 0.020 in. (0.5 mm) orifice and the reel valve. Oil from
the 0.020 in. (0.5 mm) orifice is routed to the pilot of the
reel valve and against the check valve. With the reel
valve in the backlap position, operating pressure oil is
routed through port “B” to the reel motors in series,
driving the reel motors in the reverse direction.
The oil flow to the reel motors is adjustable, with the reel
speed control valve controlling the speed of the reels.
The adjusted rate of oil flow regulates rotational speed
and maintains motor speed as load is applied to the reel
motors during backlapping.
Oil returning from the motors enters the reel valve unit at
port “A” and flows through the reel valve, exiting the valve
at port “T.” Oil exiting port “B” of the reel valve unit is
routed through the lift valve and back to the oil cooler,
then to the hydraulic tank.
Hydraulic oil is used to lubricate the internal components
of the reel motors. This oil is returned to the hydraulic
tank via the case drain lines.
Circuit Relief
The backlap circuit is protected by the 3020 psi (207 bar)
relief valve. The relief valve will open if the oil pressure in
the circuit reaches 3020 psi (207 bar), routing oil through
port “T” of the reel valve unit, through the lift valve, back
to the oil cooler, and then to the hydraulic tank.