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 98 of 481
TM 9-2320-272-10
1-81
1-21. CONTROL SYSTEM OPERATION (Contd)
(3) Major components for extending and retracting the boom for the CROWD
action are:
ROLLERS
- Guides inner boom assembly and permits smooth extension and
retraction of boom.
INNER BOOM ASSEMBLY
- Extends when crowd control lever is pushed
forward and retracts when control lever is pulled back.
CROWD CYLINDER
- A hydraulically-driven piston that extends outward
when crowd control lever is pushed forward to EXTEND position. Piston is
hydraulically driven back into the cylinder when crowd control lever is pulled
back to RETRACT position. This cylinder is contained in the inner boom
assembly.
CROWD CONTROL LEVER
- Manual control attached to the control valve
that determines oil flow for extending and retracting the crane boom. Lever
is pushed forward to extend the boom and pulled back to retract the boom.
CROWD CONTROL VALVE
- Two-way hydraulic valve located directly
below crowd control lever. Valve directs hydraulic oil from the hydraulic
pump to the crowd cylinder to extend and retract inner boom assembly.
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