TM 9-2320-272-24-1
1-24. HYDRAULIC SYSTEM OPERATION (Contd)
(4) The major components for swinging the crane left and right for the SWING action are:
Key Item and Function
1 SWING MOTOR - Converts hydraulic power back into mechanical power needed to turn the crane
turntable when hydraulic fluid is forced through its worm gear. This gear turns a large gear at the
base of the turntable to swing the crane.
2 TURNTABLE ASSEMBLY - Driven by the swing motor through a ring gear at the base of the
assembly, permits the crane to swing 360 degrees.
3 SWING CONTROL LEVER - Manual control attached to the control valve that determines
hydraulic oil flow for swinging wrecker boom to the left and to the right. Lever is pushed inward for
left boom movement, and pulled outward for right boom movement.
4 SWING CONTROL VALVE - Two-way hydraulic valve located directly below swing control lever.
Valve directs hydraulic oil from the hydraulic pump to the swing motor assembly and back through
the valve to the hydraulic oil reservoir.
1-25. CENTRAL TIRE INFLATION SYSTEM (CTIS) OPERATION
The M939A2 Central Tire Inflation System (CTIS) uses the vehicle's air compressor system, pneumatic
valves, and a microprocessor to adjust tire pressure according to mission demands. The system needs clean,
dry air to maintain itself. The turbocharger and aftercooler help supply more compressed air when the
vehicle is loaded and operating at high rpm.
Compressed air enters air dryer, which filters dirt and ejects moisture from air. System air then enters
the wet tank and is available to airbrakes and CTIS. The brake system is protected by an 85 psi (138 kPa)
pressure switch in CTIS air line. If wet tank air pressure measures below 85 psi (138 kPa), the CTIS shuts
down until pressure switch measures 120 psi (827 kPa).
Air is then routed to pneumatic controller, which consists of three valves and solenoids working in
conjunction with the Electronic Control Unit (ECU). The ECU is a microprocessor programmed to issue
commands based on information it receives from pressure switch, pressure transducer (which tests tire
pressure), and speed signal generator (which monitors vehicle speed). The commands are electrically
received by the pneumatic controller, which affects inflation or deflation of tires through quick-exhaust
valves.
Six wheel valves isolate tire pressure during normal operation. They also open to allow tire inflation or
tire deflation through three quick-exhaust valves.
The system is automatic. The operator only needs to select the mode that best accomplishes the mission.
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