PULLEY 7S8289 - Caterpillar

Illustration 2 g03877599
(1) Secondary fuel filter (2) Common rail in cylinder head (3) Mechanical Electronic Unit Injector (MEUI) (4) Return fuel pressure regulator (5) Electric priming pump (6) Primary fuel filter base (7) Fuel tank (8) Primary fuel filter and water separator (9) Fuel transfer pumpThe low-pressure fuel system supplies fuel from the fuel tank to the injectors. The low-pressure fuel system has four basic functions:
Supply fuel for combustion
Supply fuel in order to cool the injectors.
Remove air from the fuel.
Warm the fuel in the fuel tank.The major parts in a low-pressure fuel system consist of the following components:
Fuel tank
Fuel transfer lines
Primary fuel filter or water separator
Fuel transfer pump
Secondary fuel filter
Fuel priming pump
Return fuel pressure regulatorThe mechanical electronic unit injectors, the fuel transfer pump, the ECM, sensors, and solenoids are part of the low-pressure fuel system.In the low pressure fuel system, the fuel is pulled from the fuel tank to the primary fuel filter or to the water separator. The primary fuel filter (9) removes debris from the fuel that is larger than 10 microns before the fuel flows into the fuel transfer pump (10). The fuel transfer pump is a gear pump that contains a pressure relief valve. The pressure relief valve opens at approximately 60 to 125 PSI. Fuel then flows from the outlet port of the fuel transfer pump to the secondary fuel filters. The 4 micron filters remove small abrasive contaminants from the fuel system, which can damage the unit injectors. The primary fuel filter base (6) contains an electric priming pump (5). The electric priming pump forces the air out of the system through the orifice on the regulator. Priming usually takes place after servicing the fuel system such as the changing of the fuel filter. When air is trapped in the fuel filters, the fuel lines, and other fuel system components, the engine could be difficult to start. This problem can also occur when the engine has not run for a long time. When there is air in the fuel line, the electric priming pump is activated by flipping a switch or by turning the start switch, in order to prime the system. The length of time for priming the fuel system depends on the size of the system, the length of the fuel line, and the size of the filter. The time that is needed in order to prime the fuel system is about 30 seconds. This value varies with different applications.The primary fuel filter base also contains a check valve that prevents reverse flow during priming.The return fuel pressure regulator (4) consists of a check valve that is spring loaded. When the engine is in the off position and the fuel pressure drops below 60 PSI, the check valve closes. The check valve closes in order to prevent the fuel in the cylinder head from draining back into the fuel tank. Retaining the fuel in the head maintains a supply of fuel for the injectors during start-up.The ECM controls major engine functions.