Lull 944E-42 Service Manual Download

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8.155

Model 644E-42/944E-42

Rev. 6/04

Hydraulic System

8.8.58

Transfer Carriage Circuit Description
(Dual Joystick)

Hydraulic flow is applied in the transfer carriage circuit
(see page 8.106 a nd page 8.110) by the secondary
section of the Hydraulic Gear Pump to the “Inlet” Port of
the Main Control Valve. The primary section of the pump
provides hydraulic flow to the “P” Port the Accumulator
Charge/Secondary Function Valve out the “EF” Port to
the “Inlet” Port of 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 “PIL”
Port, to the Front Joystick “P” Port, to the Pilot Select
Valve “P2” Port, controlled by the button on top of the
joystick handle and regulated by the position of the
joystick.

Return oil from the joystick “T” Port and Accumulator
Charge/Secondary Function Valve “Drain” Port return to
the Hydraulic Reservoir unfiltered.

a. Transfer Carriage Cylinder Extend Circuit

(Carriage Back) (See page 8.106)

With the joystick moved LEFT, the transfer
carriage is RETRACTED (moved backward) by
the EXTENSION of the Transfer Carriage
Cylinder. As the joystick is moved LEFT, the pilot

pressure from Port “1” is directed to Port “P2” on the Pilot
Select Valve and passes out the “A1” Port to the Transfer
Carriage spool on the Main Control Valve. The shifted
spool directs system pressure to the “E” Port on the
Transfer Carriage Cylinder and to the Base End of the
cylinder.

Return oil from the Rod End of the cylinder exits the “R”
Port and passes through the transfer carriage spool
exiting the “Outlet” Port. 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
Transfer Carriage Cylinder Relief Valve on the Main
Valve will open and allow hydraulic oil to return to the
Return Filter and to the Hydraulic 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

(Carriage Forward) (See page 8.110)

With the joystick moved RIGHT, the transfer
carriage is EXTENDED (moved forward) by the
RETRACTION of the Transfer Carriage
Cylinder. As the joystick is moved RIGHT he

pilot pressure from Port “2” is directed to Port “P1” on the
Pilot Select Valve and passes out the “B1” Port to the
Transfer Carriage spool on the Main Control Valve. The
shifted spool directs system pressure to the “R” Port on
the Transfer Carriage Cylinder and to the 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
exiting the “Outlet” Port. 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
Transfer Carriage Cylinder Relief Valve on the Main
Valve will open and allow hydraulic oil to return to the
Return Filter and to the Hydraulic 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.

Lull 944E-42, Service Manual

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