3034 Engine for Caterpillar Built Machines Caterpillar


Fuel System

Usage:

3034 3NW

General Operation of the Fuel System

Refer to Systems Operation, "General Information" for locations of the components for the fuel system.




Illustration 1g00918385

Diagram of the fuel system

(1) Fuel tank

(2) Emergency shutoff valve

(3) Water separator

(4) Fuel transfer pump

(5) Fuel filter

(6) Fuel injection pump

(7) Fuel injection nozzles

(8) Fuel return line from the fuel injection nozzles and the fuel injection pump to the fuel filter.

(9) Fuel return line from the fuel filter to the fuel tank.

When the engine is cranking, the fuel is pulled from fuel tank (1) through emergency shutoff valve (2) and through water separator (3) by fuel transfer pump (4). The fuel flows from fuel transfer pump (4) under low pressure to fuel filter (5). From the fuel filter, the fuel flows at low pressure to fuel injection pump (6). The fuel injection pump sends fuel at high pressure to each of the fuel injection nozzles (7). The fuel injection nozzles spray fuel into the cylinders. Leakage from the fuel injection nozzles and the fuel injection pump flows through fuel return line (8) to the inlet side of fuel filter (5). Excess fuel from the fuel filter flows through fuel return line (9) back to fuel tank (1) .

Note: When the fuel goes through the water separator, any water in the fuel will go to the bottom of the bowl. The water can be drained through a valve which is located at the bottom of the bowl.

The fuel injection pump needs fuel for lubrication. The precision parts of the pump are easily damaged. For this reason, the engine must not be started until the fuel injection pump is full of fuel that is free of air.

The system must be primed when any part of the system is drained of fuel. The following list contains examples of both service and repairs when you must prime the system:

  • The fuel filter is changed.

  • Low pressure fuel line is removed.

  • The fuel injection pump is removed.

  • Fuel injection nozzle is removed.

  • The fuel tank is drained.

  • A leak exists in the low pressure side of the fuel system.

The fuel transfer pump has a lever which is manually operated in order to remove the air from the fuel system. In order to release air from the system, a vent plug is located on the side of the fuel injection pump. The vent plug is loosened when the lever of the fuel transfer pump is operated in order to pump air through the vent plug.

Governor

The fuel rack is connected to the linkage, which controls the fuel injection pump. This linkage is located in the timing case.

These engines have a mechanical governor in order to control engine rpm. The governor operates for all engine rpm. The governor weight assembly is installed on the front of the gear of the camshaft. The other components of the governor are installed in the timing gear case.




Illustration 2g00822233

Governor control mechanism in the timing gear case

(1) Connection for the linkage to the fuel injection pump

(2) Mechanical stop control

(3) Lever return spring

(4) Control lever

(5) Start spring

(6) Arm

(7) Governor adjustment screw

The movement of the governor weight assembly is transferred to the fuel rack on the fuel injection pump by control lever (4), arm (6) and the linkage to the fuel injection pump. A spring connects the arm and the control lever. This spring controls the movement of the governor weight assembly on the camshaft. When the angle of the control lever changes, tension on the spring changes. This action controls the linkage to the fuel rack on the fuel injection pump, which controls the engine rpm.

The bolt for the maximum speed adjustment is mounted in the cylinder block. This adjustment limits the movement of arm (6). This adjustment should only be made by personnel with the correct training.

The bolt for the maximum fuel adjustment is mounted in the cylinder block. This adjustment regulates the fuel injection at high engine rpm. This adjustment should only be made by personnel with the correct training.

A spring connects the linkage to the fuel injection pump and mechanical stop control (2). When the engine is first started, the spring automatically increases the fuel flow to the cylinders.

The fuel injection pump timing, the low idle, and the high idle are preset at the factory. Adjustments to the pump timing and idle rpm should only be made by personnel which have had the correct training. The timing for the fuel injection pump should only change if the camshaft or the cylinder block are replaced. The fuel injection pump timing should not change if the fuel injection pump is reinstalled with a shim that is the same size.

The fuel rack automatically returns to the excess fuel position when the engine is stopped. The excess fuel position aids the cold starting of the engine.

Fuel Injection Pump




Illustration 3g00746909

Fuel injection pump (typical example)

(1) Fuel line to the fuel injection nozzles

(2) Fuel delivery valve

(3) Nuts and bolts for mounting the fuel injection pump to the cylinder block

(4) Shim

(5) Vent screw for the fuel injection pump

(6) Fuel flow from the fuel transfer pump

The fuel injection pump is a cassette type pump. The pump is installed directly into the cylinder block.

The fuel injection pump is a pressurized system that is totally enclosed. The pump sends the correct amount of fuel under high pressure at the correct time through the fuel injection nozzles to the individual cylinders. The fuel injection occurs near the end of the compression stroke. The fuel injection pump regulates the amount of fuel that is delivered to the fuel injection nozzles. This action controls the engine rpm by the governor setting or the position of the throttle control.

During operation, extra fuel is used as coolant and lubricant for pump parts that move. The extra fuel is circulated through the pump housing. The extra fuel is then returned to the fuel tank. The return lines also remove air that is trapped in the fuel injection nozzles or the fuel injection pump housing.

The fuel injection pump transfers fuel to the fuel injection nozzles at high pressure. The camshaft for the fuel injection pump is driven by a gear in the timing case. Lobes on the camshaft cause the plunger for each cylinder to reciprocate. The reciprocating motion first draws the fuel. The reciprocating motion then pressurizes the fuel. A fuel valve for each cylinder acts as a check valve in order to prevent a loss of pressure to the fuel injection nozzle.

The fuel which leaks back to the fuel filter performs the following functions before being discharged through the fuel return line:

  • The housing is filled with fuel, which helps prevent any buildup of air.

  • Internal components are lubricated.

  • The fuel injection pump is cooled.

  • Small air bubbles are removed.

The fuel injection pump must be full and airtight in order for the pump to function correctly. The fuel injection pump is self-lubricating.

Fuel Injection Nozzle




Illustration 4g00376593

(1) Connection for the fuel return line

(2) Bolt for the clamp

(3) Clamp

(4) Connection for the fuel supply line

(5) Spacer

(6) O-ring

(7) Fuel injection nozzle

(8) Seat washer

(9) Fuel injection nozzle orifice

(10) Threaded hole for bolt

Each fuel injection nozzle is fastened to the cylinder head by a bolt (2) and a clamp (3). The seat washer (8) functions as a seal in order to prevent blowby. The seat washer also sets the projection of the fuel injection nozzle into the cylinder in order to prevent contact with the piston.

Note: When a fuel injection nozzle is installed in the cylinder head, a new clamp (3), a new O-ring (6), and a new seat washer (8) should be installed.

The operating pressure of the fuel injection nozzle is set and tested at the factory. Refer to Specifications, "Fuel Injection Nozzles" for the settings of the pressures on the fuel injection nozzle.

The fuel injection nozzle in the 3034 engine is a two-stage nozzle. A two-stage nozzle has two springs. Each spring releases the fuel through the orifices of the nozzle into the cylinder. Each spring provides a different pressure. The two-stage process for fuel injection creates an even distribution of the fuel. This also prevents condensation of the fuel in the cylinder. The result is more complete combustion of the fuel at a lower temperature. The improved combustion of the fuel reduces the emissions. The power of the engine is increased and the fuel consumption is reduced. The emission of oxides of nitrogen is especially reduced.

The two-stage nozzle holder has two springs and two plungers. A clearance is provided between the two plungers. This clearance is called pre-lift.

The nozzle opening pressure is set by the first spring. When the nozzle is opened, the needle valve is lifted. The valve opens the distance of the pre-lift. In order to adjust the opening pressure of the nozzle, a shim is installed with the first spring. This shim establishes the pre-lift.

The force of the second spring is adjusted by an adjusting screw.

When the fuel pressure from the fuel injection pump exceeds the force of the first spring, the needle valve and the first pushrod are pushed up. This action opens the needle valve, which injects fuel into the cylinder.

The needle valve stops for a moment when the first pushrod is lifted into the second pushrod. When the fuel pressure exceeds the force of the first spring and the second spring, the needle valve is pushed up again. This action results in the injection of additional fuel into the cylinder. Most of the fuel which is injected into the cylinder is from the second injection.

Fuel Transfer Pump




Illustration 5g00390462

Components of the fuel transfer pump

(1) Outlet valve

(2) Inlet valve

(3) Diaphragm

(4) Diaphragm assembly

(5) Arm

The fuel transfer pump creates suction in order to draw fuel from the fuel tank. Pressure is created in order to pump the fuel to the fuel injection pump. The diaphragm (3) prevents leakage of the fuel into the cylinder block. This also creates the vacuum of the fuel transfer pump. The outlet valve (1) and the inlet valve (2) operate as check valves.

A lobe on the camshaft for the fuel injection pump causes the arm (5) to move up and down. When the arm moves down, the diaphragm assembly (4) moves down. This increases the size of the chamber above the diaphragm assembly. This suction opens the inlet valve (2) which draws fuel into the chamber above the diaphragm assembly.

When the arm moves up, the diaphragm assembly moves up and the chamber above the diaphragm assembly is pressurized. This pressure opens the outlet valve (1) which allows fuel to flow toward the fuel injection pump.

Glow Plug

Each cylinder has a glow plug in order to aid the cold starting of the engine. The glow plugs may be energized by two different methods:

  • The ignition switch is moved to the auxiliary position (if equipped).

  • The starting aid switch (if equipped) is moved to the ON position.

Usually, energizing the glow plug for six seconds will heat the cylinder sufficiently for easy starting of the engine. The glow plug should not be activated for more than 15 seconds at one time.

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