SkyTrak 6036 Service Manual - Manual (Page 152)

Section 9 Hydraulic System
9-2 Model 6036/6036T S/N 9B0500 thru 14833
9.1 SYSTEM OPERATION
There are two different types of operator control
systems available on this machine for actuating
main boom functions. The systems are Cable
Control and Electronic Control. Each use a
different main control valve and joystick to actuate
the raise/lower and extend/retract boom functions.
NOTE: Refer to the 6036B Hydraulic Schematics
in Troubleshooting, paragraph 9.8, for overall
diagrams.
9.2 MAIN CONTROL VALVE
OPERATION
CABLE CONTROL
9.2.1 Control Valve
The control valve has four sections – inlet, outlet
and two parallel working sections, one for raise/
lower and one for extend/retract, Fig. 9.3. The
working sections are mounted between the inlet
and outlet sections to form a valve stack. The
supply pressure passages are common in the
stack as are the return to reservoir and pilot
pressure passages.
a. Inlet Section
The inlet section of the control valve contains:
• An inlet port for the hydraulic oil to enter
the control valve from the 30 gpm section
(rear half) of the tandem pump.
• A pilot-operated main relief valve, set at
2700 -100/+150 psi (186 -6,9/+10,3 bar).
b. Relief Valve Operation
Fluid at supply pressure is admitted to the relief
area, Fig. 9.1, of the valve through a hole in the
piston. Initially, the pilot poppet, relief valve
poppet and check valve poppet are seated.
The relief valve setting is determined by the
compression of the pilot spring as set by the
adjustment screw. When the pressure exceeds
the relief setting, the pilot poppet acts against the
poppet spring to unseat. The fluid then flows
around the pilot poppet through cross-drilled holes
in the plug to the reservoir; some pressure is
relieved.
Due to the reduced pressure, the piston seats
against the pilot poppet. This shuts off fluid flow
through the valve and causes a low pressure area
internally. The differential pressure between the
supply pressure and the internal pressure causes
the relief valve poppet to unseat and fluid flows to
the reservoir thus relieving the pressure.
If low supply pressure should occur due to pump
cavitation, the check valve poppet will unseat and
allow fluid to flow back to the supply from the
reservoir.
Refer to each circuit for information on each relief
valve function and testing.
Fig. 9.1 Relief Valve (Sectional View)
RELIEF VALVE
POPPET
PISTON
CHECK VALVE
POPPET
TO RESERVOIR
RELIEF AREA PLUG
PILOT
POPPET
PILOT
SPRING
MA0652
ADJUSTMENT
SCREW