RECOVERY VEHICLE, FULL TRACKED: MEDIUM, M88A1
FUEL SUPPLY, AIR INTAKE, AND EXHAUST SYSTEMS THEORY OF OPERATION
Fuel Supply, Air Intake, and Exhaust Systems
Fuel Supply System
Three fuel tanks supply fuel to the engine, the APU, and the refuel system. Two tanks are adjacent to the engine, one on either
side, and the third tank is forward of the bulkhead in the winch compartment. A system of four manually operated control valves
maintains fuel flow through the check valve and directs fuel to the engine and refueling systems. These valves are also used to
drain the fuel tanks.
The fuel from the vehicle fuel tanks is supplied at a minimum pressure of 5 psi (34 kPa) to the primary fuel filter (3), which is
mounted on the engine right front. Fuel flows through the main fuel check valve (5) to the fuel pump assembly (7) mounted on
the front center of the engine. This is an engine-driven, gear-type pump; it boosts fuel pressure to the fuel injector pump. A relief
valve is incorporated in the pump as a pressure-limiting safety valve.
Fuel from the fuel pump assembly (7) is filtered through the fuel/water separator fuel filter (9) and passes into the fuel injector
pump (23). This pump is located in the engine V between the cooling fans. The fuel injector pump delivers accurately metered
quantities of fuel under high pressure to each cylinder. An integral governor, of the mechanical centrifugal type, is used to control
fuel delivery as a function of engine speed. Engine shutoff is accomplished by a normally open solenoid control unit in the fuel
injector pump. The engine fuel shutoff switch on the master control panel actuates the circuit to close the solenoid. Closing of
the solenoid cuts off fuel delivery from the injector pump and stops the engine. The engine is equipped with a manual fuel shutoff
control to stop the engine if the electric fuel shutoff should fail. A bleeder pressure-relief valve in the pump outlet maintains a
constant fuel pressure by allowing any accumulated air and excess fuel to return to the fuel tanks through the engine and fuel
tank fuel return lines, check valve, hose, and selector valve. Excess fuel is used to lubricate and cool the fuel injector pump. The
check valve prevents a backflow of fuel into the injector from the fuel return line and prevents continued engine operation after
the fuel shutoff valve is closed.
Twelve stainless steel fuel lines (13) carry fuel under high pressure from the fuel injector pump (23) to the 12 fuel injector nozzles
(15) on the left and right banks of the engine. The nozzles inject a fine spray of metered fuel under pressure into each cylinder.
Excess fuel is carried from the nozzles through fuel return hose assemblies (2) on each cylinder bank to the fuel return system.
A hand-operated purge pump, next to the driver's seat, provides a means of purging the fuel injector pump (23), fuel filters (3
and 9), and engine fuel lines of air. The air is forced by the fuel pressure from the purge pump through the engine fuel lines and
back to the fuel tanks through the injector pump fuel return line.
Air Intake System
Two dry-type air cleaners, mounted in the right and left rear of the crew compartment, filter intake air for the engine. A damper
control, mounted on each air cleaner, is used to select air intake from either the crew compartment or from outside the vehicle.
Exhaust pipes connect each exhaust manifold to a turbosupercharger. Exhaust gases are ejected from the engine, via exhaust
pipes, through deflector-type louvers at the rear of the vehicle.