SkyTrak 6036 Service Manual - Manual (Page 122)

Section 9. Hydraulic System
9-9 Model 6036 S/N 9B0499 and Before
When the boom is raised, the slave cylinder is
extended which causes pressure buildup on the
rod end of the piston. This pressure pilots open
the counterbalance valve, Fig. 9.4, and forces
hydraulic oil to flow from the rod end of the slave
cylinder to the rod end of the grille tilt cylinder and
from the base end of the grille tilt cylinder to the
base end of the slave cylinder. The grille tilt
cylinder rod retracts to tilt the grille down and
compensate for upward boom movement. The
amount of grille tilt cylinder rod movement is
proportional to slave cylinder rod movement to
always keep the grille at the same attitude.
When the boom is lowered, the slave cylinder is
retracted which causes pressure buildup on the
base end of the piston. Hydraulic oil flow and
cylinder and grille action are just the reverse of
raising the boom. Oil flows through the counter-
balance valve without piloting.
c. Pressure Checks and Adjustments
Grille Tilt “Up” Relief Valve
1. Engage the park lock, place the travel select
lever in neutral, and stop the engine.
2. Operate the hydraulic controls after the engine
has stopped to relieve any trapped pressure.
3. Remove the transmission cover from the
frame.
4. Install a tee and pressure gauge capable of
measuring 0-4000 psi (275,6 bar) at the 30
gpm section of the tandem pump, Fig. 9.4.
Warning !
Warning !
Warning !
grille tilt “up” relief valve, Fig. 9.2, will open
allowing hydraulic oil to return to the return filter
and reservoir, Fig. 9.4.
Return oil from the rod side of the grille tilt cylinder
piston is directed back to the directional control
valve through ports B to D, Fig. 9.4, to the return
filter and reservoir. If the return filter becomes
clogged, hydraulic oil will bypass the filter when
the pressure reaches 10 to 15 psi
(0,7 to 1,03 bar).
The counterbalance valve, Fig. 9.4, will allow oil
flow to the base end of the grille tilt cylinder but will
not allow reverse oil flow from the base end of the
grille tilt cylinder. This prevents the grille from
tilting down due to the load on the grille which
causes back pressure on the grille tilt cylinder
piston. Without this check valve, the back pressure
would tilt the grille down if the extend line should
fail.
Down Position
When the fork and frame tilt control lever is placed
in the “down” position, the directional control valve
spool is positioned so that pump supply pressure
is directed through ports E to B, Fig. 9.4, to the rod
(retract) end of the grille tilt and slave cylinders.
The extension of the slave cylinder is fixed by the
position of the boom so that only the grille tilt
cylinder is retracted to tilt the grille down. This
supply pressure also pilots open the counterbal-
ance valve, Fig. 9.4. The open check valve
allows return oil from the base end of the cylinder
to return through ports A to D, Fig. 9.4, of the
directional control valve to the return filter and
reservoir, Fig. 9-4. If the supply pressure reaches
2650 psi
(182,6 bar), the grille tilt “down” relief
valve, Fig. 9.2, will open allowing hydraulic oil to
return to the return filter and reservoir. If the
return filter becomes clogged, hydraulic oil will
bypass the filter when the pressure reaches 10 to
15 psi (0,7 to 1,03 bar).
b. Grille Tilt Cylinder, Slave Cylinder and
Hoist Cylinder Interaction
The slave cylinder is mounted to the boom in a
way that is similar to the hoist cylinders, Fig. 9.4.
When the boom is raised or lowered, the move-
ment of the slave cylinder follows the movement of
the hoist cylinders. The slave cylinder shares a
common extend hydraulic line with the grille tilt
cylinder, and also a common retract line. The
movements of the cylinders are interactive.
Wait for the hydraulic fluid to cool before servic-
ing any hydraulic component. Hot hydraulic fluid
can cause severe burns.
Relieve hydraulic pressure before servicing any
hydraulic component. Escaping hydraulic fluid
under pressure can penetrate the skin causing
serious injury.
Before starting the engine be sure all hydraulic
connections are tight and all tools are removed
from the forklift.