SkyTrak 6036 Service Manual - Manual (Page 158)

Section 9 Hydraulic System
9-8 Model 6036/6036T S/N 9B0500 thru 14833
A B C A B C A B C
Fig. 9.5 Boom Extend/Retract Circuit
CENTER
RETRACT EXTEND
MA3010
RESERVOIR
RETURN FILTER
EXTEND
COUNTERBALANCE VALVE
RETRACT
30
GPM
15
GPM
MAIN RELIEF VALVE
2700 -100/+150 PSI
PILOT OPERATED
CHECK VALVE
TO BOOM RAISE/
LOWER CYLINDER
DIRECTIONAL CONTROL VALVE
POSITIONS
MAIN CONTROL
VALVE
0-4000 PSI
PRESSURE
GAUGE
TANDEM
PUMP
STRAINER
BOOM EXTEND/RETRACT PORT RELIEF
VALVES 2850 ± 50 PSI
relief valve, Fig. 9.5, 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. 9.5, 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
(0,7 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. 9.5, to the rod side of the boom extend
cylinder piston. This supply pressure also pilots
open the counterbalance valve, Fig. 9.5. The
open counterbalance valve allows return oil from
the base end of the cylinder to return through ports
A to D, Fig. 9.5, of the directional control valve to
the return filter and reservoir. If supply pressure
reaches 2850 psi
(196,4 bar), the boom retract
port relief valve, Fig. 9.5, 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
(0,69 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 2000 psi
(137,8 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.
D E F D E F D E F