Lull 944E-42, Service Manual

Page: 403 / 844

8.153 Model 644E-42/944E-42 Rev. 6/04
Hydraulic System
8.8.56 Attachment Tilt and Slave Circuit
Description (Dual Joystick)
System pressure is applied in the Attachment Tilt and
Slave Cylinder circuit (see page 8.98 and page 8.102) by
the secondary section of the Hydraulic Gear Pump
through the “Inlet” Port on the Main Control Valve. The
primary section of the pump provides hydraulic flow to the
“P” Port through the Accumulator Charge/Secondary
Function Valve out the “EF” Port to the Main Control
Valve. System pressure is directed to the “E” and “R”
Ports of the Attachment Tilt and Slave Cylinders by the
shifting of the spool in the Main Control Valve. The spool
is shifted by pilot pressure provided from the Accumulator
Charge/Secondary Function Valve out of the “PIL” Port,
to the Front Joystick “P” Port. The pressure is 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. Attachment Tilt Down Circuit (See page 8.98)
With the joystick moved FORWARD, pilot
pressure from Port “4” on the Joystick moves the
Attachment Tilt spool in the Main Control Valve
so System Pressure, from the Pump is directed
to the “R” Ports on the rod ends of the Attachment Tilt
Cylinder and the Slave Cylinders. The oil will open the
Counterbalance Valve in the Attachment Tilt Cylinder and
the forks will tilt DOWN. Return oil flows from the “E”
Ports on the Attachment Tilt Cylinder and the Slave
Cylinders back to the Main Control Valve and out the
“Outlet” port to the Hydraulic Oil Cooler through the
Return Filter to the Hydraulic Reservoir.
If circuit pressure reaches 4000 psi (276 bar) the relief
valve, in the tilt cylinder will open and allow hydraulic oil
to return to the oil cooler, 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 Hydraulic Reservoir
unfiltered.
b. Attachment Tilt Up Circuit (See page 8.102)
With the joystick moved BACKWARD, pilot
pressure from Port “3” on the Joystick moves the
Attachment Tilt spool in the Main Control Valve
so System Pressure, from the Pump is directed
to the “E” Ports on the base ends of the Attachment Tilt
Cylinder and the Slave Cylinders.
The oil will open the Counterbalance Valve in the
Attachment Tilt Cylinder and the forks will tilt UP. Return
oil flows from the “R” Ports on the Attachment Tilt
Cylinder and the Slave Cylinders back to the Main
Control Valve and out the “Outlet” to the Hydraulic Oil
Cooler through the Return Filter to the Hydraulic
Reservoir.
If circuit pressure reaches 4000 psi (276 bar) the relief
valve in the tilt cylinder will open and allow hydraulic oil to
return to the oil cooler, 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 Hydraulic Reservoir
unfiltered.
MT3780
MT3790