Textron JACOBSEN R-311 69166, Technical/Repair Manual

Page: 253 / 402

6-22 4203781 First Edition
HYDRAULICS
6
Mow Circuit (OFF) Schematic and
Theory of Operation
System Conditions:
• Engine running
• Cutting units lowered
• Mow switches in the OFF position
• Park brake released
NOTE
See “Mow Circuit—Theory of Operation” on page 4-37
for the electrical operation of this circuit.
Oil Supply to Deck Valves
Oil is drawn from the hydraulic tank through a 100-mesh
screen, and enters the gear pump, supplying oil to all four
pump sections. Sections 2 (right wing deck), 3 (front
deck), and 4 (left wing deck) supply operating pressure
oil to port “P” of the corresponding cutting unit deck
valves.
Motor Shutdown/Blade Braking
Operating pressure oil flows to the 3000 psi (207 bar)
relief valve and the solenoid valve. With the mow
switch(es) in the OFF position, the solenoid valves are
de-engerized, opening the valves. Oil can then flow
through the valves, returning to the hydraulic tank. With
the oil pressure/flow diverted to the hydraulic tank, the
630 psi (43 bar) blade brake check valves close,
preventing oil flow through the motors.
The blade brake check valves have a second pilot line on
the motor side. As oil flow is stopped to the motors, the
motors will act a pumps as they rotate during shutdown.
This pilot line allows the valve to close slowly, acting as a
cutting unit motor brake. This prevents a sudden
shutdown of the motors.
Circuit Relief
The mow circuit is protected by a pilot-operated relief
valve. The relief valve will open if the oil pressure in the
circuit reaches 3000 psi (207 bar), allowing oil to bypass
the circuit and return to the hydraulic tank.