THEORY OF OPERATION - CONTINUED
ELECTRO-HYDRAULIC SYSTEM - CONTINUED
Supply oil flows to these components: tilt control valve (87), lift control valve (88), ride control valve (89), and
auxiliary valve (90).
Supply oil flows to pressure reducing valve (104), which reduces oil pressure to pilot pressure. Pressure reducing
valve provides oil to pilot system.
Oil flowing to pilot oil accumulator (100) charges pilot oil accumulator. This allows bucket to be lowered if engine
stops. Oil then flows through main control valve as pilot oil. Pilot oil flows through solenoid valves to move spools
to correct positions. Engine start switch must be in ON position for this function to work. Manual valve (101) can
be used to lower bucket if no power can be supplied to solenoids.
Oil flowing to load sensing circuit enters signal duplicating reducing valve (105). Normally, oil flows through sig-
nal duplicating reducing valve.
Signal duplicating reducing valve (105) and load sensing relief valve (106) operate for all control valves in main
control valve. Load sensing relief valve limits maximum signal pressure to pump at point (E) by draining excess
signal oil to tank at point (F). Signal duplicating reducing valve sends signal oil back to implement piston pump at
Control valves are proportional priority and pressure compensated. If a circuit is active, or if more than one circuit
is active, signal duplicating reducing valve (105) duplicates highest signal oil pressure and applies it to all control
Oil flow enters control valve and flows through a parallel feeder passage to all circuits. All four circuits can be
Both tilt control valve (87) and auxiliary control valve (90) have two line relief valves. One relief valve is for each
end of cylinders. Also, tilt, lift, and ride control valves have an identical solenoid valve. Solenoids for tilt and lift
control valves are for drift reduction (93).
Tilt Control Valve.
General. Oil from implement piston pump flows to tilt control valve (87) at port (B). Tilt valve stem (107) is con-
trolled by solenoids (95). Implement pump oil flows through tilt control valve to lift control valve (88) at pump
port (B). Tilt valve stem is spring centered with a closed center. Tilt valve stem has three positions: HOLD, TILT
BACK, and DUMP.
Springs keep tilt valve stem (107) in HOLD position when solenoids (95) have not been actuated. Stem
movement is controlled by actuation of pilot proportioning solenoids that allow oil to flow to either end of
tilt valve stem.
Tilt valve stem (107) in HOLD position blocks oil in both ends of tilt cylinder. This keeps tilt cylinder
from moving. Drift reduction solenoid valve (93) in tilt control valve (87) further limits cylinder move-
ment toward DUMP position if leakage occurs between valve stem and valve body.