INTRODUCTION 777 SERVICE MANUAL
1-12 Published 10-01-2012, Control # 045-08
Hydraulic Tank
Hydraulic tank (7) is mounted on the right side of the rotating
bed. It has a vented fill cap, high and low level sight gauge,
temperature and level sensors. The digital display indicates
if the hydraulic oil temperature exceeds 180°F (82°C), and a
low oil level in the hydraulic reservoir.
Filtration
See Figures 1-8 and 1-9 for following procedures.
Hydraulic circuit filters remove contaminants introduced by
replacement oil or parts, dust particles acquired from the
surrounding work area, and impurities generated from
normal wear during system operation. To protect the crane’s
hydraulic circuit from harmful concentrations of these
contaminants, filter elements should be periodically changed
in accordance with an established maintenance schedule.
The hydraulic system provides various filtration circuits for
maintaining the manufacturer’s standards for hydraulic oil
purity. The methods of filtration include inline, charge
pressure, supercharge pressure, and suction filtration.
All oil exiting hydraulic tank is suctioned through a 200 mesh
strainer with a 3 psi (0.21 bar) bypass valve. The bypass
valve opens to permit oil flow to the various crane systems
when the strainer is dirty or the oil temperature is too cold for
direct operating conditions. At this time, hydraulic vacuum
switch closes to complete a circuit to the PC. The PC
responds by sending a diagnostic message HYDRAULIC
FILTER 5 to the operator display, indicating the strainer
requires servicing. In addition, the PC activates fault system
light and fault system alarm. If activation of the fault system
continues after the oil has warmed to normal operating
temperatures, the tank strainer must be cleaned and/or the
hydraulic oil changed as soon as possible to meet the
operational viscosity requirements. Oil may exit the hydraulic
tank through safety check valve.
The inline filter or filter 4 has a 50 psi (3.4 bar) bypass valve
and a filter element with a rating of 13 micron absolute. As
the element becomes soiled, the pressure differential
between the inlet and discharge flow ports of the filter
increases, causing the element to lift, permitting oil to bypass
the filter element. Prior to the oil bypassing the filter, the filter
4 hydraulic sensing switch on the filter head closes to
complete the circuit to the PC. The PC responds by sending
a diagnostic message HYDRAULIC FILTER 4 to the operator
display, indicating filter 4 requires servicing, and activating
fault system light and fault system alarm. The filter must be
replaced at this time.
The pressure limiting feature of the multifunction valves in
the travel pumps is not disabled. Should the pressure reach
6,090 psi (420 bar), the multifunction valves will destroke the
pumps as needed.
Table 1-2
System Pressure Settings
System Load Drums Boom Swing Travel
Function
Hoist
PORT A
Lower
PORT B
Up
PORT A
Down
PORT B
Left/Right
PORT A / PORT B
Fwd / Rev
PORT A / PORT B
Pressure
psi (bar)
6,090
(420)
2,900
(200)
6,090
(420)
2,900
(200)
6,090
(420)
6,090
(420)
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