Joystick Circuit Description; Pump, Unloader Valve And Cooling Circuit Description - JLG sky trak mmv Service Manual

Hydraulic System
b. Mode 2B
When the bottom of the attachment tilt
mode switch is depressed (Mode 2B)
(1), press and hold the right button (2) on
the joystick (3). As the mode is activated
the corresponding lights will illuminate
on the logic panel (4).
Boom Lift ................... move handle BACKWARD
Boom Lower ................ move handle FORWARD
Attachment Tilt Down ....move handle to the right
Attachment Tilt Up........... move handle to the left
OS0610
3
1. DOWN Position (Mode 2B) (See page 9.44)
With the attachment tilt switch in Mode 2B (bot-
tom depressed) (1), the right button (2) on the
joystick (3) pressed and held and the joystick
MT3780
moved RIGHT, the attachment tilts DOWN. The
spool valve in the main control valve is shifted so system
pressure is directed to the rod end of the attachment tilt
cylinder and the slave cylinders.
The extension of the slave cylinders is fixed by the posi-
tion of the boom so that only the attachment tilt cylinder is
retracted to tilt the attachment downward. The pilot pres-
sure opens the counterbalance valve. The open counter-
balance valve allows return oil from the base of the
attachment tilt cylinder to flow to ports of the attachment
tilt section of the main control valve, to the return filter and
ultimately to the reservoir.
If system pressure reaches 3500 ±100 psi (241 ±7 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
9.80
return filter becomes restricted, hydraulic oil will bypass
the filter when the pressure reaches 25 psi (1,7 bar).
2. UP Position (Mode 2B) (See page 9.46)
1
MT3790
the main control valve is shifted so system pressure is di-
OM0690
rected to the base end of the attachment tilt cylinder and
the slave cylinders.
If system pressure reaches 3500 ±100 psi (241 ±7 bar)
the main relief will open, allowing hydraulic oil to flow to
the return filter and to the reservoir. If the return filter be-
comes restricted, hydraulic oil will bypass the filter when
the pressure reaches 25 psi (1,7 bar).
Return oil from the rod side of the attachment tilt cylinder
is directed back to the attachment tilt section of the main
control valve through the spool valve, to the return filter
and to the reservoir. If the return filter becomes restricted,
hydraulic oil will bypass the filter when the pressure
reaches 25 psi (1,7 bar).
4
9.8.29
Joystick hydraulic circuit (see page 9.48) commands are
achieved through electric and hydraulic signals via a set
of cartridge-type, solenoid-operated control valves
mounted in an array at the pilot select manifold.
The cartridge valves shift to allow hydraulic oil to flow to
2 the proper circuit as commanded by joystick position. Hy-
draulic fluid flows from the joystick valve to the pilot select
manifold, then to the appropriate working section of the
OM0700
main control valve.
9.8.30
In the pump/unloader valve/cooling circuit (see
page 9.52), the pump draws oil from the hydraulic reser-
voir and sends pressurized oil from the front section to the
unloader valve. The rear section of the pump sends pres-
surized oil to the accumulator charge valve which pro-
vides pressure to the secondary function manifold which
provides pilot pressure to the joystick. Excess accumula-
tor charge valve flow is routed to the unloader valve.
The unloader valve regulates maximum system operating
pressure for various vehicle functions and sends oil to the
main control valve. When oil from the unloader valve is
returned to the reservoir, it 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 reservoir un-
cooled if pressure on the check valve exceeds 85 psi (5,9
bar).
With the attachment tilt switch in Mode 2B (bot-
tom depressed) (1), the right button on the joy-
stick pressed and held and the joystick moved
LEFT, the attachment tilts UP. The spool valve in

Joystick Circuit Description

Pump, Unloader Valve and Cooling
Circuit Description
Model MMV Rev. 12/04