SkyTrak 6036 Service Manual - Manual (Page 269)

8.53 Model 6036 Legacy
Hydraulic System
a. Boom Lift Circuit (Fig. 8-7)
With the joystick in the boom lift position,
pressure shifts the lift/lower spool valve in the
main control valve to direct system pressure
through the counterbalance valve to the base
end of both the left and right lift/lower cylinders.
Return oil from the rod end of the cylinder flows through
the pilot-operated check valve to the spool valve, to the
unloader valve, to the oil cooler, to the return filter and
then to the reservoir.
If system pressure exceeds 3250 psi (224 bar), the main
relief will open, allowing oil to return to the reservoir. If the
return filter becomes plugged, return hydraulic oil will
bypass the filter when pressure reaches 25 psi (1,7 bar)
and return to the reservoir unfiltered.
b. Boom Lower Circuit (Fig. 8-8)
When the joystick is in the boom lowering
position, pressure shifts the lift/lower spool valve
in the main control valve. Oil is then directed to
the pilot-operated check valve to the rod end of
the left and right lift/lower cylinders. System pressure also
pilots open the counterbalance valve in the base end of
the lift/lower cylinders.
The open counterbalance valve allows oil from the base
of the cylinders to flow to the main control valve, to the
unloader valve, to the oil cooler, to the return filter and
then to the reservoir.
If system pressure exceeds 3250 psi (224 bar), the main
relief will open allowing oil to return to the reservoir. If the
return filter becomes plugged, return hydraulic oil will
bypass the filter when pressure reaches 25 psi (1,7 bar)
and return to the reservoir unfiltered.
The counterbalance and pilot-operated check valves
serve another main function for safety purposes. This
function can be described as follows:
• Should any of the hydraulic lines routed to the lift/
lower cylinder fail, there will be a loss of hydraulic
system pressure to the cylinder. For example, if a
hydraulic line failure occurred in the pressurized
lowering line during lowering, the counterbalance
valve would lose pilot pressure, closing off flow
returning to the reservoir. The oil in the base end
of the cylinder would then be trapped, which
would immediately stop boom lowering and
prevent an elevated load from falling to the
ground uncontrolled. The load can be lowered
safely to the ground by following the procedures
in Model 6036 Legacy Owners/Operators
Manual.
IMPORTANT: DO NOT attempt to reset the
counterbalance valve cartridge. In the event that the
counterbalance valve cartridge was disabled for
emergency boom lowering, or if any unauthorized
adjustments are ever made to the cartridge, remove and
replace the cartridge with a new part. Failure to replace
the cartridge with a new part may alter the holding
characteristics of the counterbalance valve, creating an
unsafe condition for vehicle operation.
8.8.22 Frame Sway Circuit Description
Hydraulic flow is applied in the frame sway circuit
(Fig. 8 -9 and Fig. 8-10) by the hydraulic gear pump
through the unloader valve. System pressure is directed
to either side of the frame sway cylinder by the shifting of
the spool valve in the main control valve. The spool valve
is shifted by the operator joystick and its associated
control cable.
a. Frame Sway LEFT (Fig. 8-9)
With the joystick moved to the left, the spool
valve in the frame sway section of the main
control valve assembly is shifted.
System pressure is directed to the spool valve
(in the main control valve), and to the base end of the
frame sway cylinder. Oil from the rod end of the frame
sway cylinder flows through a check valve, unseated by
system pressure, back to the spool valve, to the unloader
valve, to the oil cooler, to the return filter and then to the
reservoir.
b. Frame Sway RIGHT (Fig. 8 -10)
With the joystick moved to the right, the spool
valve in the frame sway section of the main
control valve assembly is shifted.
System pressure is directed to the spool valve,
back to the frame sway cylinder, where it flows to the rod
end of the cylinder. Oil from the base end of the cylinder
flows through the check valve, which was unseated by
system pressure, then to the spool valve, to the unloader
valve, to the oil cooler, to the return filter and then to the
reservoir.
MA7200
MA7210
MA7160
MA7170