SkyTrak 6036 Service Manual - Manual (Page 119)

Section 9. Hydraulic System
Model 6036 S/N 9B0499 and Before 9-6
• 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 retraction preventing 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.
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 any unauthorized
adjustments are ever made to this cartridge,
remove and replace the cartridge with a new part.
Failure to replace this cartridge with a new part
may alter the holding characteristics of the
counterbalance valve creating an unsafe condition
for machine operation.
b. Pressure Checks and Adjustments
Boom Extend Port Relief Valve
1. Engage the park lock, place the travel select
lever in neutral, level the boom 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) in the
tandem pump outlet of the 30 gpm section,
Fig. 9.3.
Warning !
Warning !
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. 9.3, to the base end of the boom extend
cylinder piston. If supply pressure reaches 2650
psi
(182,6 bar), the boom extend port relief
valve, Fig. 9.2, will open allowing hydraulic oil to
return to the reservoir.
Return oil from the rod side of the extend cylinder
piston is directed back to the directional control
valve through ports B to D, Fig. 9.3, 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).
Retract Position
When the joystick is placed in the retract position,
the directional control valve spool is shifted so that
supply pressure is directed through ports E to B,
Fig. 9.3, to the rod side of the boom extend
cylinder piston. This supply pressure also pilots
open the counterbalance valve, Fig. 9.1. The
open counterbalance valve allows return oil from
the base end of the cylinder to return through ports
A to D, Fig. 9.1, of the directional control valve to
the return filter and reservoir. If supply pressure
reaches 2650 psi
(182,6 bar), the boom retract
port relief valve, Fig. 9.2, will open allowing
hydraulic oil to return to the 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 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 pres-
sure will build up until it reaches 2650 psi
(182,6 bar) and then the counterbalance
valve will be internally piloted open
allowing the pressure to return to the
reservoir. This condition will only exist if
the cylinder has been extended. If the
cylinder is already fully retracted the
counterbalance valve will have no effect
and the cylinder rod will bend.
Relieve hydraulic pressure before servicing any
hydraulic component. Escaping hydraulic fluid
under pressure can penetrate the skin causing
serious injury.
Wait for the hydraulic fluid to cool before servic-
ing any hydraulic component. Hot hydraulic fluid
can cause severe burns.