SkyTrak 6036 Service Manual - Manual (Page 166)

Section 9 Hydraulic System
9-16 Model 6036/6036T S/N 9B0500 thru 14833
balance valve will have no effect and the
cylinder rod will bend and other damage
may occur.
• Should any of the hydraulic lines going to
the extend cylinder fail, there will be a loss
of hydraulic system pressure to the
cylinder.
Example: If there was a hydrau-
lic line failure in the pressurized retract line
during retracting, 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 retracting and prevent an elevated
load from retracting uncontrolled. The
load can be lowered safely to the ground
by following the “Emergency Boom
Lowering” procedures in your Owners/
Operators Manual.
NOTE: Shifting the extend/retract working section
spool manually by moving the optional valve lever
toward the control valve will also actuate the
extend cylinder to extend the boom.
Retract Position
When the joystick is placed in the retract position,
PWM signals are sent to the retract pulsar sole-
noid. The control valve spool is shifted so that
supply pressure is directed through ports P to C2
to the rod end of the extend cylinder piston. This
supply pressure also pilots open the counterbal-
ance valve. The open counterbalance valve
allows return oil from the base end of the extend
cylinder piston to be directed back to the control
valve through ports C1 to T and the return line to
the filter and reservoir. If supply pressure reaches
2650 psi (182,6 bar), the inlet relief valve will
open allowing hydraulic oil to return to the reser-
voir.
The counterbalance valve in the extend cylinder
serves two other main functions. One prevents
component damage and the other is for safety.
These functions can be described as follows:
• If the machine is traveling and the boom
runs into an immovable object, pressure
will build up on the base end of the
cylinder. If the counterbalance valve was
not installed, the rod of the cylinder would
bend damaging the cylinder. With the
counterbalance valve installed, the
pressure will build up until it reaches 2000
psi
(137,8 bar) and then the counterbal-
ance valve will be internally piloted open,
allowing the pressure to return to reser-
voir. This condition will only exist if the
cylinder has been extended. If the cylin-
der is already fully retracted the counter-
Extend Position
When the joystick is placed in the extend position,
PWM signals are sent to the extend pulsar sole-
noid. The control valve spool is shifted so that
supply pressure is directed through ports P to C1
to the base end of extend cylinder piston. Return
oil from the rod end of the boom extend cylinder
piston is directed back to the control valve through
ports C2 to T and the return line to the filter and
reservoir.
There is an additional relief valve which is set at
2850 psi
(196,4 bar) in the extend line. If the
extend supply pressure reaches this pressure, the
relief valve will open allowing hydraulic oil to return
to the reservoir.
IMPORTANT: DO NOT attempt to reset the
counterbalance valve cartridges. In the event that
the counterbalance valve cartridges were disabled
for emergency boom lowering or any unauthorized
adjustments are ever made to these cartridges,
remove and replace both cartridges with new
parts. Failure to replace these cartridges with new
parts may alter the holding characteristics of the
counterbalance valves creating an unsafe condi-
tion for machine operation.
b. Checks and Adjustments
Refer to paragraph 9.6.2.h for control valve
pressure checks and adjustments.
9.4 SECONDARY CONTROL
VALVE OPERATION
The cable controlled secondary control valve and
its associated joystick actuate the grille tilt and
slave circuit, the frame tilt circuit, and optional
auxiliary circuit.
9.4.1 Control Valve
The control valve has four sections – inlet, outlet
and two or three parallel working sections, one for
grille tilt and slave cylinder functions, one for frame
tilt functions and a optional working section for
auxiliary functions. The working sections are
mounted between the inlet and outlet sections to
form a valve stack. The supply pressure pas-
sages are common in the stack as are the return
to reservoir and pilot pressure passages.