THEORY OF OPERATION Continued
HYDRAULIC POWER UNIT
The ramp is raised or lowered by an hydraulic system which consists of a pump, a dual-acting cylinder, a solenoid valve, and
a fluid reservoir. This system is controlled by a three position switch located near the driver. Moving the valve to either
RAISE or LOWER position directs fluid to the appropriate port on the hydraulic cylinder.
FIRE EXTINGUISHER SYSTEM
The fire extinguisher system will detect and put out fires in the carrier. It consists of two CO2 (Carbon Dioxide) cylinders.
Carbon Dioxide can put out fires quickly and effectively. The cylinders are operated manually by pulling cables located on
There is a fire extinguisher located in the drivers compartment that is manually discharged. This cylinder discharges into the
engine compartment. The other is located in the personnel department.
The suspension system supports the carrier and delivers engine power to the road. It allows the carrier to maneuver and be
stable. Suspension system parts are the drive sprockets, tracks, idler wheels, track adjuster, road wheels, and road wheel
support arms. Also, there are torsion bars and shock absorbers.
The drive sprockets drive the tracks. They are powered by left and right final drives from the transmission. The tracks consist
of two flexible chains of track shoes. The tracks ride on the drive sprockets and are guided by idler wheels. The idler wheels
can be adjusted to maintain correct track tension.
There are five pairs of road wheels per side. Track centerguides fit between each pair of road wheels. All road wheels are
connected to support arms.
The electrical system provides power for the carrier. The system operates on wet cell batteries and includes charging,
regulating and monitoring equipment. The batteries provide a normal operating 24 volts with an amperage capability of 200
amps per hour.
The batteries supply the carrier with electricity when the engine is off. All electrical power is delivered through the
distribution box except for the engine coolant heater and personnel heater which are directly powered from the batteries.
Electrical power flows from the batteries through the distribution box, cables, and wiring assemblies to the hull. The hull is a
ground for the electrical system.
The dc generator recharges the batteries and supplies electricity while the engine is running. The dc generator has 200 amps
per hour capability.
There are several electrical subsystems within the hull. Each subsystem contains at least one wiring assembly. Major
electrical subsystems and assemblies include the interior and exterior lights, fuel supply, starting and charging systems,
ventilation, heating, and bilge pumps.
Personnel heaters are standard equipment on M577A3, M901A3, M981A3, M1068A3, and M58 carriers, but are kit items on
M113A3, M1059A3, and M1064A3 carriers. Since maintenance of heater components is the same for both standard heaters
and kit heaters, they are only covered in one place in this manual. See Table of Contents for maintenance of heater
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