TM 9--2815--247--34 0004 00--8 THEORY OF OPERATION -- CONTINUED 0004 00 FUEL SYSTEM -- CONTINUED Fuel Purge System  A manually operated purge pump is provided in the vehicle operator’s compartment and is used to clear the engine’s main fuel system of air and fill it with fuel. Most of the purged air is removed through bleeder valves, located in the top of the primary fuel filter and the fuel/water separator filter. The rest of the air is forced through the main fuel tubes into the fuel return lines and on to the vehicle fuel tanks. Water is removed from the system by a constant bleed orifice in the primary fuel filter and an automatic water drain in the fuel/water sepa- rator filter. Fuel Filters  (Figures 1--1 and 1--2). The replaceable element type primary fuel filter is mounted on the right front of the engine and is equipped with a constant bleed orifice and drain line which constantly removes a metered amount of fuel, and returns it to the main fuel tank through the fuel injector nozzle drain lines. This continuous drain, from the bottom of the filter, removes water in the free state that has been filtered from the fuel by the prima- ry fuel filter element. The replaceable element fuel/water separator type filter is mounted on the left front of the engine. Fuel from the vehicle fuel tank passes through the primary filter before entering the engine fuel pump. The pump delivers fuel to the fuel/water separator filter and on to the fuel metering pump. Excess fuel provides pump cooling as it flows through the fuel metering pump hydraulic heads and is returned to the fuel tanks (Figure 1--9). The fuel/water separator filter unit has three replaceable elements and contains a chamber for collecting water. The two outer elements are coalescer elements and will remove emulsified water that has passed through the pri- mary filter. The center element is a fuel filter element. The water removed from the fuel is automatically drained from the filter housing. Two water sensing probes are located in the filter housing. When the water level reaches the upper probe an electrical circuit is completed, a solenoid valve opens and allows the water to drain. The valve closes when the water level reaches the lower probe. A drain cock is installed so the fuel/water separator may be drained manually. The unit provides moisture--free and uncontaminated fuel to the injection pump. Both the prima- ry filter and the fuel/water separator filter incorporate top mounted bleeder valves to assist in the removal of air from the fuel system. Fuel Cutoff Solenoid  An electrically operated fuel cutoff solenoid is mounted in the fuel metering pump. The so- lenoid is normally open. A switch in the vehicle driver’s compartment actuates the circuit to close the solenoid. Closing the solenoid cuts off fuel delivery from the fuel metering pump and stops the engine. A manually operated override shutoff is provided to permit stopping the engine in the event of an electrical failure. MANIFOLD AIR INDUCTION AND HEATER SYSTEM Turbosupercharger Assemblies  Exhaust gas--driven turbosupercharger assemblies (Figure 1--4), one for each bank of cylinders, are mounted on each side of the engine, at the rear. The turbosuperchargers increase the pres- sure of the intake air thereby delivering a higher density air to the cylinders as compared with a non--supercharged engine. This higher density air, with a proper fuel flow, increases engine power. Intake Manifold Heater The intake manifold (Figure 1--1), which distributes induction air to each bank of cylinders, is equipped with an elec- trically--operated flame--type intake manifold heater (Figure 1--10). The heater is provided as an aid for cold weath- er starting and cold weather operations. Operation of the heater switch (in the vehicle operator’s compartment) energizes the manifold heater fuel solenoid valve, the heater ignition unit, and spark plug for each heater simulta- neously. Fuel is hand--pumped through the manifold heater fuel filter and fuel solenoid valve and sprayed into the intake manifold. The fuel is ignited by the spark plug and burns in the intake manifold as the engine is cranking, and the flame heats the incoming air. This flame--heated air and the products of combustion are fed directly into the cylinders with little heat loss.  This results in an immediate engine response, and assures complete combustion at low engine rpm and at no--load operating conditions with low ambient temperature.