1-10. LOCATION AND DESCRIPTION OF MAJOR COMPONENTS - Continued
f. Air System.
Refer to Air System Schematics in Appendix G. The air system includes a main engine driven
compressor, an air dryer, six reservoirs, and a variety of valves and hoses. Pressure protection valves
ensure the reservoirs are filled successively.
The three rear service reservoirs supply air to the rear brakes.
The single front service reservoir supplies air to the front brakes and the parking brake release.
The supply reservoir provides air to the air horns and air system gauges located in cab.
The spring brake release reservoir supplies air to the emergency spring brake release system.
Air system pressure gauges are located in the cab. Audiovisual alarm lamps indicate when pressure is
low. Manual draincocks are fitted to each reservoir.
g. Auxiliary Power Unit.
(1) The Auxiliary Power Unit (APU) consists of a vertical four-stroke, overhead-valve diesel engine. The
APU engine is air-cooled and governor-equipped to maintain constant speed and output. The APU is
equipped with an electric starting motor and draws its fuel from the main engine fuel tank.
(2) The APU is located in the hosebed, directly above the curbside pump panel. The APU engine exhaust
is connected to a muffler located under the curbside, front outrigger.
(3) The APU can be started and stopped from any one of three locations. Controls are located on the pump
panel (street side), cab dash panel, and on the APU itself.