PISTON 3S0988 - Caterpillar

Illustration 1 g06285934
Fuel system for C32 engines.
(1) Cylinder head
(2) Unit injector
(3) Fuel transfer pump
(4) Secondary fuel filter
(5) Primary fuel filter and water separator
(6) Fuel tank
(7) Fuel pressure regulator/check valveThe fuel supply circuit is a conventional design for unit injector diesel engines. The system consists of the following major components that are used to deliver low-pressure fuel to the unit injectors:Fuel tank - The fuel tank is used to store the fuel.Fuel filters - The primary fuel filter is used to remove abrasive material and contamination from the fuel system large enough to damage the fuel transfer pump. The secondary fuel filter is used to remove abrasive material and contamination as small as two microns that could damage the injectors.Supply lines and return lines - Supply lines and return lines are used to deliver the fuel to the different components.The purpose of the low-pressure fuel supply circuit is to supply fuel that has been filtered to the fuel injectors at a rate and a pressure that is constant. The fuel system is also utilized to cool components such as the fuel injectors.Once the injectors receive the low-pressure fuel, the fuel is pressurized again before the fuel is injected into the cylinder. The unit injector uses mechanical energy that is provided by the camshaft to achieve pressures that can be more than 200000 kPa (30000 psi).Control of the fuel delivery is managed by the engine ECM. Data from several of the engine systems is collected by the ECM and processed to manage these aspects of fuel injection control:
Injection timing
Fuel injection timing advance
Injection duration
Engine cold mode statusThe mechanical electronic fuel system relies on a large amount of data from the other engine systems. The data that is collected by the ECM will be used to provide optimum performance of the engine.Low-Pressure Fuel Supply Circuit
The flow of fuel through the system begins at fuel tank (5). Fuel is drawn through the primary fuel filter and water separator (7) from the fuel tank by fuel transfer pump (3). The fuel transfer pump incorporates a check valve that allows fuel to flow around the gears during priming. The fuel transfer pump also incorporates a pressure relief valve. The pressure relief valve is used to protect the fuel system from extreme pressure.The fuel transfer pump is designed to produce an excess fuel flow throughout the fuel system. The excess fuel flow is used by the system to cool the fuel system components. The excess fuel flow also purges any air from the fuel system during operation. Air that can become trapped in the fuel system can cause cavitation that may damage the components of the unit injector.After leaving the fuel transfer pump, the fuel flows to the ECM (6) to cool the ECM. Next, the fuel flows to the secondary fuel filter (4). The fuel filter base and secondary fuel filter incorporate a siphon break that prevents fuel from draining when the engine is not in operation. The secondary fuel filter is a two micron fuel