6-20 4181384 First Edition
HYDRAULICS
6
Lower Circuit Schematic and Theory
of Operation
See Figure 6-13.
System Conditions:
• Engine running
• Weight transfer switch in the off position
• Raise/lower joystick in the lower position
NOTE
See “Raise/Lower Circuit—Theory of Operation” on
page 4-36 for the electrical operation of this circuit.
Operating pressure oil is supplied to the lift valve by the
steering circuit, and oil flows to the primary weight
transfer valve in the lift valve. With the primary weight
transfer valve de-energized, and the lower valve
energized, oil flows through the primary weight transfer
valve and is directed to the raise/lower valve. With the
raise/lower valve in the lower position, the pressurized oil
unseats the check valve once oil pressure is built against
the 0.052 inch (1.3 mm) orifice located in the raise/lower
valve drain hose at the return manifold.
Gravity pulls the mower decks down, pulling against the
lift cylinders. The rear deck has an orifice located in the
rod end hose, which lowers the rear deck at a slower rate
then the front decks. Oil from the rod side of the lift
cylinders flows through the open check valve and through
the raise/lower valve, returning to the hydraulic tank.
Some of the pressurized oil used to unseat the check
valve is used as “make-up” oil to the piston end of the lift
cylinders. Any extra oil is returned to the hydraulic tank.
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