6-26 4181384 First Edition
HYDRAULICS
6
Backlap Circuit Schematic and
Theory of Operation (TR-3 Only)
See Figure 6-16.
System Conditions:
• Engine running
• Cutting units lowered
• Mow switch in the on position
• Park brake set
• Backlap valve in backlap position
• Backlap speed control valve adjusted for the desired
backlapping speed
NOTE
See “Backlap Circuit Operation (Model TR-3)—Theory of
Operation” on page 4-43 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, closing the relief valve and to the pilot line end of
the load control valve, opening the load valve.
Operating pressure oil flows through the backlap valve,
reversing the direction of oil flow to the cutting unit
motors. Before reaching the cutting unit motors, the oil
flows through the backlap speed control valve. This valve
can be adjusted to control the speed of the cutting unit
drive motors.
Oil then flows through the cutting unit motors and flows
through the backlap valve and 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.
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