SkyTrak 6036 Service Manual - Manual (Page 157)

Section 9 Hydraulic System
Model 6036/6036T S/N 9B0500 thru 14833 9-7
Wait for the hydraulic fluid to cool before serv-
icing any hydraulic component. Hot hydraulic
fluid can cause severe burns.
2. Check for signs of leakage of hydraulic oil
from circuit hoses and other components.
Correct any leakage problem before testing.
3. Raise and lower the boom fully several times
to purge the system of air if necessary.
4. Starting with the boom fully retracted and at its
lowest position, raise the boom at full engine
speed. The time required for full raise should
be less than 15 seconds (no load).
5. Starting at the fully raised position, lower the
boom at full engine speed. The time required
to lower the boom to its lowest position should
be less than 10 seconds (no load).
6. Repeat steps 4 and 5 to recheck performance.
7. If the boom raise/lower circuit test does not
meet performance requirements, locate the
cause of the problem (refer to Troubleshoot-
ing, paragraph 9.8) and correct before putting
the vehicle into service.
Warning
4. Install a tee and pressure gauge capable of
measuring 0 - 4000 psi (275,6 bar) in the
tandem pump outlet of the 30 gpm section,
Fig. 9.4.
Before starting the engine be sure all hydraulic
connections are tight and all tools are removed
from the forklift.
Warning
5. Start the engine. Raise and lower the boom
fully several times to purge the system of air.
6. Depress the accelerator to full throttle. Place
the joystick in the “raise” position and hold
until the hoist cylinders have fully extended.
Continue holding the joystick in the “raise”
position until the pressure readings are taken.
7. Check the pressure gauge reading. It should
read 2850 ± 50 psi
(196,4 ± 3,4 bar). If not,
adjust the boom hoist port relief valve, Fig.
9.3, by turning the adjustment screw clockwise
to increase pressure or counterclockwise to
decrease pressure. Torque nuts on relief
valve to 10 ± 1.5 lb-ft (13 ± 2 Nm) after
adjustment.
8. Stop the engine. Operate the hydraulic
controls after the engine has stopped to
relieve any trapped pressure.
9. Remove the pressure gauge and tee from the
tandem pump and reconnect the hydraulic
line.
10. Start the engine. Raise and lower the boom
fully several times to purge the system of air.
11. Install the transmission cover after adjustment.
c. Testing
The boom raise/lower circuit should be tested
whenever repairs or adjustments are made to
components of the circuit.
1. Start the engine, park the forklift on level
ground and level the frame.
9.2.3 Boom Extend/Retract Circuit
a. Description
Hydraulic pressure is applied in the boom extend/
retract circuit by the 30 gpm section (rear half) of
the tandem pump, which draws its fluid through a
suction stainer in the reservoir, Fig. 9.5. Supply
pressure is directed to either side of the extend/
retract cylinder piston by the shifting of a spool in a
directional control valve found in the main control
valve assembly. The spool is shifted by the
operator joystick and its associated control
cable. The joystick positions for extending or
retracting the boom are as follows:
Center Position
When the joystick is placed in the center or neutral
position, the directional control valve spool is
positioned so that supply pressure is directed
through ports F to C, Fig. 9.5, 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
(0,69 to 1,03
bar).
Extend Position
When the joystick is placed in the extend position,
the directional control valve spool is shifted so that
supply pressure is directed through ports E to A,
Fig. 9.5, to the base end of the boom extend
cylinder piston. If supply pressure reaches 2850 ±
50 psi
(196,4 ± 3,4 bar), the boom extend port