TM 5-2420-231-10
OPERATOR LEVEL
THEORY OF OPERATION
PRINCIPLES OF OPERATION
The Backhoe Loader (BHL) is designed for moving earthen materials around a construction site, opening up an
underground utility site, etc. It has a Front End Loader (FEL) to move material a short distance away from the
immediate area or load it into a vehicle for moving to a new, more distant location. It has a backhoe to dig earth
and loosen material so it can be moved or excavated. It can dig openings for basements, trenches for drainage
tubes, and all general construction excavation. Together, the FEL and backhoe can be used to level or prepare a
construction site.
Engine
A diesel engine supplies the power for the drive train to move the BHL. It also drives a large hydraulic pump to
provide the hydraulic power for FEL and backhoe operation. The engine has a fuel system and cooling system
typical of diesel engines.
Fuel System
The fuel system supplies fuel from the fuel tank through a fuel pump, fuel filters, injector pump, and injectors to
the engine. Air is supplied through an air filtration system before entering the engine to be mixed with the fuel.
Cooling System
The cooling system uses a water pump to circulate water through the radiator. A fan behind the radiator pulls air
through the radiator core to cool the coolant solution inside the radiator. The coolant is then circulated through
the engine to cool the engine. Engine temperature is regulated by a thermostat which controls the coolant flow
through the radiator depending on engine temperature.
Transmission
The transmission is mechanically linked to the engine. It is also linked to the front and rear wheels providing Two-
Wheel Drive/Four-Wheel Drive (2WD/4WD). The transmission provides several output speeds to move the BHL
forward and backward. The transmission output speed is controlled by the transmission gear selection control
lever and by engine speed.
Steering System
The steering system allows the operator to turn the front wheels left or right to steer the BHL using the steering
wheel. The steering system is powered by the hydraulic pump.
Electrical Power
The engine drives a 24 Vdc alternator to produce the electrical power used on the BHL. Two 12 Vdc batteries in
series provide 24 Vdc for starting the engine and for powering the blackout lights. All other lights, controls, and
indicators operate on 12 Vdc. The 24 Vdc NATO slave receptacle allows slave starting from or to any other
vehicle with a 24 Vdc NATO slave receptacle.
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