INTRODUCTION 777 SERVICE MANUAL
1-16 Published 10-01-2012, Control # 045-08
Supercharge Manifold
The front section of tandem accessory pump (1) delivers up
to 58 gpm of supercharge oil to supercharge manifold (16).
The oil is filtered as it enters manifold through filter 1 (12).
Pressure in manifold is controlled by relief valve (19), which
is preset for 75 psi (5.25 bar). Manifold distributes oil to the
charge pumps of the boom, swing, and travel systems.
Oil Return Manifolds and Cooling System
The hydraulic system oil temperature is controlled by routing
the return oil from all pump and motor case drain lines and
the supercharge relief valve discharge line to return-to-
cooler manifold (20). If thermal control valve (21) detects that
the temperature of the return oil in manifold is below 140°F
(60°C), it directs the flow into return-to-tank manifold (22).
Here, it combines with return oil from all hydraulic system
brake valves, 2-speed travel valve (23), boom cylinders
counterbalance valves (24), load drum band brake valves
(28), load drum loop flush valve drain (29, Figure 1-5), lower
accessory valve (3, Figure 1-7), and cooler bypass safety
valve (26) which is preset at 25 psi (1.7 bar). The combined
flow from return-to-tank manifold (22) is then routed to tank.
If thermal control valve (21) detects that the temperature of
the return oil in manifold (20) is above 140°F (60°C), it directs
the flow into cooler (27) before returning to tank.
EPIC Programmable Controller (PC)
See Figures 1-10 and 1-11 for following procedures.
Most of the crane’s solenoid valves, pumps, and motors are
directly controlled by electronic components on the PC’s
printed circuit boards. This simplifies the crane’s electrical
control system by avoiding mechanical control switches and
relays; reliability and service convenience is increased, while
service down-time is decreased.
The EPIC (Electric Proportional Independent Control)
programmable controller system is a control process
operating in a closed loop. The programmable controller
operates within the loop by collecting information from the
system’s monitoring sensors, such as pressure senders,
speed senders, and limit switches. It accepts desired
reference commands given by the crane operator, through
voltage inputs from hand controllers, selectors, and
switches. This closes the loop as per PC program directives
by establishing commands to the pumps, motors, cylinders,
etc., that cause the direct movements the crane encounters
during normal working cycles. This is an ongoing process
operating continuously in 12 millisecond cycles.
The PC’s standard or custom programming enhances
operation convenience and precision control of the crane.
The programming allows the PC to automatically adjust each
operational mode’s acceleration rate and speed, as well as
apply brakes and release clutches.
The PC provides solenoid valves, pump EDCs, and motor
PCPs with the appropriate voltages to obtain the selected
functions, operation speed rates and direction. The PC
varies the voltage levels and polarity outputs to correspond
with the voltage inputs to the PC from the control handles.
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