Lull 944E-42, Service Manual

Page: 406 / 844

Hydraulic System
8.156 Model 644E-42/944E-42 Rev. 6/04
8.8.59 Transfer Carriage Circuit Description
(Single Joystick)
Hydraulic flow is applied in the transfer carriage circuit
(see page 8.108 and page 8.112) by the secondary
section of the Hydraulic Gear Pump through the Main
Control Valve. The primary section of the pump provides
hydraulic flow through the Accumulator Charge/
Secondary Function Valve to the Main Control Valve.
System pressure is directed to either side of the transfer
carriage cylinder by the shifting of the spool in the Main
Control Valve. The spool is shifted by pilot pressure from
the Accumulator Charge/Secondary Function Valve, to
the Joystick, to the Single Joystick Pilot Select Valve,
controlled by the trigger button on the joystick handle and
regulated by the position of the joystick.
Fluid flow is directed to either side of the transfer carriage
cylinder piston by shifting of the spool the transfer
carriage section of the main control valve assembly. The
spool is shifted by pilot pressure provided from the
joystick to the selector valve, controlled by electrical
solenoids and regulated by the position of the joystick.
a. Transfer Carriage Cylinder Extend Circuit
(See page 8.108)
With the joystick trigger button PRESSED and
the sick moved BACKWARDS, the transfer
carriage is RETRACTED (moved back) by the
EXTENSION of the transfer carriage cylinder.
The trigger button shifts the transfer carriage solenoids to
their active position and with the Joystick also moved
BACKWARD pilot pressure from Single Joystick Port “1”
flows to Port “P1” on the Single Joystick Pilot Select
Valve. Pilot pressure exits the control valve at the “TB”
Port and shifts the spool at the transfer carriage section
of the Main Control Valve. The shifted spool directs
system pressure to the “E” Port on the Transfer Carriage
Cylinder and rod end of the cylinder.
Return oil from the base end of the cylinder exits the “R”
Port and passes through the transfer carriage spool. Oil
then passes through the oil cooler, to the return filter and
to the Hydraulic Reservoir.
If system pressure reaches 2400 psi (165 bar) the port
relief will open and allow hydraulic oil to return to the
return filter and to the reservoir. In any case, if the return
filter becomes plugged the indicator light will come ON,
indicating that return hydraulic oil will bypass the filter
when pressure reaches 25 psi (1,7 bar) and return to the
reservoir unfiltered.
b. Transfer Carriage Cylinder Retract Circuit
(See page 8.112)
With the joystick trigger button PRESSED and
the sick moved FOREWARD, the transfer
carriage is EXTENDED (moved ahead) by the
COMPRESSION of the transfer carriage
cylinder. The trigger button shifts the transfer carriage
solenoids to their active position and with the Joystick
also moved FOREWARD pilot pressure from Single
Joystick Port “2” flows to Port “P2” on the Single Joystick
Pilot Select Valve. Pilot pressure exits the control valve at
the “TA” Port and shifts the spool at the transfer carriage
section of the Main Control Valve. The shifted spool
directs system pressure to the “R” Port on the Transfer
Carriage Cylinder and rod end of the cylinder.
Return oil from the base end of the cylinder exits the “E”
Port and passes through the transfer carriage spool. Oil
then passes through the oil cooler, to the return filter and
to the Hydraulic Reservoir.
If system pressure reaches 3400 psi (234 bar) the main
relief will open and allow hydraulic oil to return to the
return filter and to the reservoir. In any case, if the return
filter becomes plugged the indicator light will come ON,
indicating that return hydraulic oil will bypass the filter
when pressure reaches 25 psi (1,7 bar) and return to the
reservoir unfiltered.
MU0050
MU0040