TM 5-3805-291-23-1
THEORY OF OPERATION - CONTINUED
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ELECTRO-HYDRAULIC SYSTEM - CONTINUED
d.
LOWER Operation.
(1)
When joystick control is moved to LOWER position, pilot oil is sent to left end of lift valve stem (109),
moves partially right. Implement pump oil is sent from pump port (B) around lift valve stem to bottom of
compensation and load check valve (102). Compensation and load check valve is pushed up and flow goes
through openings in load check valve to bridge passage. Oil flows around lift valve stem and through drift
reduction solenoid valve (93) to lower lift cylinder rod end work port.
(2)
Oil is allowed to flow to rod end of lift cylinders. This causes bucket to lower. Solenoid valves (95) and lift
valve stem (109) respond in proportion to movement of operator controls.
(3)
Oil from head end of lift cylinders enters through raise lift cylinder head end work port, flows through
energized drift reduction solenoid valve (93), and exits at tank port (C) to hydraulic tank.
e.
FLOAT Operation.
(1)
When joystick control is moved to FLOAT position, pilot oil is sent to left end of lift valve stem (109),
moving it fully right. Joystick is held in FLOAT position by a soft detent. Lift valve stem remains in
FLOAT position until bucket reaches preset kickout position. Lift control valve will then return to HOLD
position.
(2)
When an operator moves pilot valve to FLOAT position, lower lift cylinder rod end work port is connected
to tank at tank port (D) through completely shifted lift valve stem (109). Complete movement of lift valve
stem right closes off implement pump oil flow from pump port (B) to bridge passage. Raise lift cylinder
head end work port continues to be connected to tank through energized drift reduction solenoid valve (93)
and lift valve stem at tank port (C).
(3)
Oil from both rod and head end of lift cylinder drains to tank. This allows weight of lift arm assembly to
lower lift arm assembly to ground. Lift arm assembly will follow ground contour. Neither rod nor head end
of lift cylinder is under hydraulic pressure. Lift cylinders can move freely in either direction according to
force on bucket.
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