TM 5-3805-291-23-1
THEORY OF OPERATION - CONTINUED
0003 00
ELECTRO-HYDRAULIC SYSTEM - CONTINUED
a.
General. Oil from implement piston pump flows to lift control valve (88) at pump port (B). Pump oil flows from
pump port (B) through lift control valve to ride control valve (89) and auxiliary control valve (90). Lift valve stem
(109) is controlled by pilot proportioning solenoids (95). Lift valve stem is spring centered with a closed center.
Lift valve stem has four positions: RAISE, HOLD, LOWER, and FLOAT.
b.
HOLD Position.
(1)
Springs keep lift valve stem (109) in HOLD position when solenoid valves (95) have not been actuated.
Lift valve stem in HOLD position blocks oil in both ends of lift cylinders, which keeps them from moving.
(2)
Drift reduction solenoid valve (93) in lift control valve (88) further limits lift cylinder drift toward
LOWER position if leakage occurs between lift valve stem (109) and valve body.
(3)
Stem movement is controlled by actuation of pilot proportioning solenoids (95) that allow oil to flow to
either end of lift valve stem (109).
c.
RAISE Operation.
(1)
When joystick control is moved to RAISE position, pilot oil is sent to right end of lift valve stem (109),
moving it left. Implement pump oil is sent from pump port (B) around lift valve stem to bottom of com-
pensation 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 raise lift cylinder head end work port.
(2)
Oil is allowed to flow to head end of lift cylinders. This causes bucket to rise. Solenoid valves (95) and lift
valve stem (109) respond in proportion to movement of operator controls.
(3)
Oil from rod end of lift cylinders enters through lower lift cylinder rod end work port and exits through
tank port (D) to hydraulic tank.
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