TM-9-2320-272-10
TRUCK, 5-TON, 6X6, M939, M939A1, AND M939A2 SERIES TRUCKS (DIESEL)
TECHNICAL MANUAL; OPERATOR'S MANUAL
SEPTEMBER 2004
CHANGE 2
TM-9-2320-272-10 - Page 96 of 481
TM 9-2320-272-10
1-79
1-21. CONTROL SYSTEM OPERATION (Contd)
TRANSFER CASE POWER TAKEOFF (PTO) CONTROL
- A manually
operated control lever located inside the cab that engages and disengages the
transfer case power takeoff.
TRANSFER CASE POWER TAKEOFF (PTO) LINKAGE
- Connects
transfer case power takeoff control to transfer case Power Takeoff (PTO).
TRANSFER CASE POWER TAKEOFF (PTO)
- Receives driving power
from vehicle’s engine through the transfer case to provide mechanical driving
power for the hydraulic pump.
POWER TAKEOFF (PTO) DRIVE SHAFT
- Transmits mechanical driving
power from the power takeoff to the hydraulic pump.
HYDRAULIC PUMP
- Draws oil from hydraulic oil reservoir and directs it
to valves inside the crane control console.
OIL FILTER
- Filters used or bypassed oil from the control valve before it
returns to the hydraulic oil reservoir.
HYDRAULIC OIL RESERVOIR
- Storage tank for hydraulic oil.
SWIVEL VALVE
- Permits oil to channel through pivot post while crane is
swinging and eliminates twisting of the hydraulic lines connecting reservoir
to the stationary pump.
BOOM LIFT CYLINDER
- A hydraulically-driven piston that extends
upward when boom control lever is pulled back to UP position, raising the
boom. A check valve located near hydraulic oil inlet hose prevents piston
from lowering when control lever is in neutral. Oil returns through boom
control valve back to hydraulic oil reservoir allowing piston to lower when
control lever is pushed forward to DOWN position.
BOOM HYDRAULIC LINES
- Carry the hydraulic oil to and from boom lift
cylinder. Oil pumped through the bottom lines pushes the lift cylinder piston
upward. Oil pumped through the top lines pushes the lift cylinder piston
downward. When this downward action occurs, the oil that originally pushes
the cylinder upwards is returned to the hydraulic oil reservoir.
BOOM CONTROL LEVER
- Manual control attached to the control valve
that determines hydraulic oil flow for raising and lowering action of the
boom. Lever is pulled back to raise the boom and pushed forward to lower
boom.
CRANE CONTROL CONSOLE
- Houses BOOM, HOIST, CROWD, and
SWING levers and their control valves.
BOOM CONTROL VALVE
- Located directly below boom control lever.
Valve directs hydraulic oil from the hydraulic pump to the boom lift cylinder
for lifting, or out of the lift cylinder and back to the hydraulic oil reservoir for
lowering.
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