Textron Jacobsen SLF530, Repair Manual

Page: 215 / 352

HYDRAULICS
673831-Rev A 6-21
6
Backlap Circuit Schematic and
Theory of Operation
System Conditions:
• Engine running
• Cutting units lowered
• Traction pedal in the neutral position
• Backlap active on the LDU
• Parking brake switch in the ON position (parking
brake engaged)
NOTES
• See “Mow/Backlap Circuit—Theory of Operation” on
page 4-29 for the electrical operation of this circuit.
• The function of each reel valve is the same, except
where noted.
Oil Supply to Reel Valves
Oil is drawn from the hydraulic tank through a 100-mesh
screen, and enters the gear pump, supplying oil to all
three pump sections. Sections 2 (rear reel) and 3 (front
reel) supply operating pressure oil to port “P” of the
corresponding reel valves.
Backlap Circuit
Operating pressure oil supplied by sections 2 and 3 of the
gear pump enters the reel valve bodies at port “P” and is
routed to the pilot lines of the 2200 psi (152 bar) relief
valves, against the relief valves, and to the solenoid
valves. When the backlap switch is in the on position, the
solenoid valves shift, routing operating pressure oil
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
backlap valve controlling the speed of the reels for the
backlap process. The adjusted rate of oil flow will
regulate reverse rotational speed and maintain reverse
motor speed as load is applied to the reel motors. Speed
adjustment settings can be maintained and will not affect
mowing operation when motors are shifted to mow
rotation.
Circuit Relief
The backlap circuit is protected by the 2200 psi (152 bar)
pilot-operated relief valves. The relief valve for the front
and center reel motors will open if the oil pressure in the
circuit reaches 2200 psi (152 bar), routing oil through the
front reel valve to the return filter, oil cooler, and then the
hydraulic tank. The relief valve for the rear reel motors
will open if the oil pressure in the circuit reaches 2200 psi
(152 bar), routing oil through the rear reel valve to the
charge filter.
Oil Return
Oil returning from the motors enters the reel valves at
port “B” and flows through the solenoid valves, exiting the
valves at port “T.”
Front Reels: The oil from the front reel motors is routed
through the oil cooler to the hydraulic tank.
Rear Reels: The oil from the rear reel motors is routed to
the brake valve port “CHG” and the charge filter.
When the parking brake switch is in the ON position, the
brake valve solenoid coil is not energized. The charge
pressure flow is blocked at the solenoid valve. Oil from
left and right front motors Port X are allowed to flow
through the needle valve, solenoid valve and to the tank.
The brake spring in the wheel motors puts pressure on
the friction discs, preventing the wheel motors to rotate.
The charge filter is used to remove debris from the oil. If
the charge filter becomes plugged, the 25 psi (1.7 bar)
crack bypass will open, allowing oil to bypass the charge
filter.
Oil from the charge filter is routed to the traction pump to
fill the closed-loop traction circuit. Once filled, the
200 psi (14 bar) charge pressure relief valve will open,
allowing oil to return to the hydraulic tank.
Hydraulic oil is used to lubricate the internal components
of the reel motors.