6-24 4181384 First Edition
HYDRAULICS
6
Mow Circuit Schematic and Theory of
Operation
See Figure 6-15.
System Conditions:
• Engine running
• Cutting units lowered
• Mow switch in the on position
• Park brake released
NOTE
See “Mow Circuit—Theory of Operation” on page 4-38
for the electrical operation of this circuit.
Hydraulic oil is drawn from the hydraulic oil tank by the
cutting unit pump and is protected by a relief valve set to
a maximum pressure of 3046 psi (210 bar) on early
models and 3626 psi (250 bar) on later models.
Operating pressure oil flows to the pilot line of the cutting
circuit relief valve, against the check valve in the mow
valve, and to the pilot line end of the load control valve,
opening the load valve.
Operating pressure oil then exits the mow and brake
valve at port M1, and is routed to the cutting unit motors.
Oil flows through the cutting unit motors will vary as
follows:
AR-3 (Early [Aluminum-Colored]) Motors and TR-3:
Oil flows from mow and brake valve port M1 to the left
front motor to the right front motor, and then to the rear
(center) motor before returning to the mow and brake
valve at port M2.
Each AR-3 cutting unit motor also has a check valve that
is forced closed by the incoming oil from the mow and
brake valve port M1. These valves will open, bypassing
the cutting unit motors, when the cutting units are shut off
to allow the blades to slow down before stopping.
TR-3 cutting unit motors do not include check valves.
This allows the motors to be driven in the reverse
direction when the oil flow is reversed for backlapping.
AR-3 (Late [Black-Colored]) Motors: Oil flows from
mow and brake valve port M1 to the right front motor, to
the left front motor, and then to the rear (center) motor
before returning to the mow and brake valve at port M2.
After driving the cutting unit motors, oil returns to the
mow and brake valve. Oil then flows through the load
control valve to supply charge-pressure oil to the traction
drive circuit and then through the energized brake valve
to supply charge-pressure oil to the park brake release
valve. (See “Theory of Operation and Sub-Circuit
Schematics” on page 5-4 or “Traction Circuit Reverse
Schematic and Theory of Operation” on page 5-6 for
further information.)
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