Lull 944E-42, Service Manual

Page: 396 / 844

Hydraulic System
8.146 Model 644E-42/944E-42 Rev. 6/04
8.8.46 Pump and Cooling Circuit Description
(Dual Joystick)
In the Pump and Cooling Circuit (pages 8.56 and 8.58),
the Pump draws oil from the Hydraulic Reservoir and
sends pressurized oil from the secondary section of the
Hydraulic Gear Pump to the “Inlet” Port on the Main
Control Valve.
The primary section of the pump sends pressurized oil to
the “P” Port on the Accumulator Charge/Secondary
Function Valve which also provides pressure to the Main
Control Valve from the “EF” Port.
The Main Control Valve regulates main system pressure.
When oil from the Main Control Valve is returned to the
reservoir, it exits the “Outlet” Port and is sent through the
Hydraulic Oil Cooler. A Check Valve, located in the line,
will allow oil to bypass the cooler, if the cooler is plugged
or restricted, and return to the Hydraulic Reservoir
uncooled if pressure on the check valve exceeds 85 psi
(5,9 bar).
Return pilot pressure, from the Joystick “T” Ports and
“Drain” Port on the Accumulator Charge/Secondary
Function Valve and “Bridge Drain” Port from the Main
Control Valve, is returned to the Hydraulic Reservoir
unfiltered.
8.8.47 Pump and Cooling Circuit Description
(Single Joystick)
In the Pump and Cooling Circuit (see page 8.60), the
Pump draws oil from the Hydraulic Reservoir and sends
pressurized oil from the Secondary section of the
Hydraulic Gear Pump to the Main Control Valve “Inlet”
Port.
The Primary section of the Pump sends pressurized oil to
the Accumulator Charge/Secondary Function Valve “P”
Port and exits the “EF” Port. Flow provides pressure to
the Main Control Valve and provides Pilot Pressure to the
Joystick from the “PIL” Port and Single Joystick Pilot
Select Valve from the “P1” Port. Excess Accumulator
Charge/Secondary Function Valve flow is routed to the
“Inlet” Port on the Main Control Valve.
The Main Control Valve regulates main system pressure.
When oil from the Main Control Valve is returned to the
reservoir, it exits the “Outlet” Port and is sent through the
Hydraulic Oil Cooler first. A Check Valve located in the
line will allow oil to bypass the cooler and return to the
Hydraulic Reservoir uncooled if pressure on the check
valve exceeds 85 psi (5,9 bar). Return pilot pressure from
the Joystick “T” ports and “Drain” Port on the Accumulator
Charge/Secondary Function Valve is returned to the
Hydraulic Reservoir unfiltered.
8.8.48 Joystick Circuit Description
(Dual Joystick)
Hydraulic flow is applied in the Front and Rear Joystick
hydraulic circuit commands (pages 8.62 and 8.64) by the
primary section of the Hydraulic Gear Pump through the
“P” Port of the Accumulator Charge/Secondary Function
Valve. Pilot pressure is supplied by the “PIL” Port to the
individual joysticks “P” port. From the joystick ports “1,”
“2,” “3,” and “4,” flow is directed to the Main Control Valve
by the corresponding movement of the joystick.
Hydraulic fluid (pilot pressure) flows from the joystick
valves to the appropriate working section of the Main
Control Valve or to the Pilot Select Valve. Return oil from
the joystick “T” Port and Accumulator Charge/Secondary
Function Valve “Drain” Port return to the Hydraulic
Reservoir unfiltered.
8.8.49 Joystick Circuit Description
(Single Joystick)
The joystick hydraulic circuit, boom extend/retract, lift/
lower, transfer carriage extend/retract and auxiliary
hydraulic commands (see page 8.66) are achieved by
pilot pressure supplied by the Accumulator Charge/
Secondary Function Valve “PIL” Port to the joystick “P”
Port.
The joystick hydraulic circuit, attachment tilt commands
(see page 8.66) are achieved by pilot pressure supplied
by the Accumulator Charge/Secondary Function Valve
“P1” Port to the Single Joystick Pilot Select Valve “P”
Port.
From the joystick ports “1,” “2,” “3,” and “4,” pilot pressure
flows to the Single Joystick Pilot Select Valve Ports “P1,”
“P2,” “P3,” and “P4,” then oil is directed to the Main
Control Valve by the corresponding movement of the
joystick.
Return oil from the joystick “T” Port, Single Joystick Pilot
Select Valve “T” Port and Accumulator Charge/
Secondary Function Valve “Drain” Port return to the
Hydraulic Reservoir unfiltered.