CAT Engine Course (Part 6) Fuel System

FUEL SYSTEM
The fuel transfer pump (2) pulls fuel from the tank through the inlet line (1) and forces it through a check valve and into the line to the fuel filters (3). After the fuel filters, the fuel flows to the fuel manifolds (6) along the inside of each cylinder bank. The top inlet passage of the manifold sends fuel through lines connected to each cylinder head. (Early engines had fuel filter screens in the connectors.) Fuel flows into a circular space around the injector (5). Part of this fuel is used for injection and part to cool the injector. (Later engines have fuel filter screens in the injectors.) The extra fuel that cools the injector is returned through lines to the bottom outlet passage of the fuel manifolds, through a pressure regulating valve (7) and then through a return line and to the tank.

The priming pump (4) has a supply line from the inlet side of the pump and sends fuel through the filters, into the fuel manifolds. The location of the pressure regulating valve is on the front of
the right fuel manifold (7). The pressure regulating valve is made to hold a constant pressure of approximately 415 kPa (60 psi). The valve makes a high resistance to the flow of fuel to 415 kPa (60 psi), but little resistance to air. In this way, air can be removed from the fuel system. A small orifice connects the inlet and outlet passages to make a siphon break when changing filters, thus making it less possible that the system will need to have the air removed after a filter change.

The fuel transfer pump is on the rear of the oil pump and is driven by the lower oil pump shaft. The pump sends fuel through the fuel filters and into the fuel manifolds located along each bank of cylinder. The pump capacity is approximately 21 litres/minute (5.5 gpm) or several times as much fuel as needed for combustion.

Here we can see the:
1. transfer pump
2. supply inlet
3. check valve fitting
4. fuel line to fuel filter housing base
5. fuel line to priming pump
6. fuel filter housing base and filters; and
7. priming pump
On the vehicular engine, the transfer pump (1) and filter housing base and filters (7) are on the right side of the engine. Fuel from the supply tank goes in the transfer pump at the supply inlet (2). A check valve (4) is in the fitting at the transfer pump for the fuel line (2) that goes to the filter housing base. The check valve prevents fuel flow back through the transfer pump when the priming pump (8) is used.

The transfer pump bypass valve (10) limits the maximum fuel pressure of the transfer pump.
The bypass valve will open at 520 kPa (125 psi) and send the extra fuel to the inlet side. This prevents damage to the fuel system components caused by too much pressure.

On vehicle arrangements, the spin-on replacement type fuel filter elements (the filter element and filter case are one unit) are located along the left side of the engine. On marine, industrial and generator set arrangements, the filters are located in a housing across the front of the engine as seen earlier.

Two (2) spin-on fuel filter elements are used for vehicular engines having 250 hour oil changes.
Each filter turns on the screw threads of the filter base. All of the fuel from the fuel tank goes through the filters for cleaning (a full flow filter).
There are five (5) fuel filter elements used on engine arrangements with 500 hour and 1000 hour oil change periods. In this way, the fuel filter elements may be changed when the lubrication oil is changed. When you remove the old filter, be sure the old gasket comes off with the filter.

Change the fuel filter elements at the recommended interval. Remove and discard the old fuel filter element. Clean the gasket sealing surface of the filter base. Make sure all of the old gasket is removed.

Apply clean diesel fuel to the fuel filter gasket. Install the new filter and tighten by hand until the filter gasket contacts the base. Tighten the filter 1/2 the 3/4 turn more with a filter wrench.

The optional priming pump is installed on the filter base/housing. It is used to prime a completely dry fuel system, or prime the system after the filters have been changed.

Here we can see:
1. fuel supply line
2. adapter with pressure regulating valve
3. fuel manifold (right side)
4. return line (from cylinder head)
5. inlet line (to cylinder head)
6. pressure regulating valve; and
7. connection for return line to tank

A fuel inlet line goes from the top passage of the fuel manifold to a fitting on the right side of each cylinder head.
A fuel return line goes from the left side of each cylinder head to the bottom passage of the fuel manifold where it goes through the return line to the fuel tank.

On Industrial, Generator Sets, Marine and Marine Auxiliary Engine Arrangements, and fuel filter housing (1) is on top of the oil filter housing (3).
Here we can see:
1. fuel filter housing
2. drain valve
3. oil filter housing
4. adapter with pressure regulating valve; and 5
5. fuel manifold (right)
The drain valve (2) is used to drain fuel from the filter housing when the filters are changed.
Also, we can see the adapter with pressure regulator valve (4) and the fuel manifold (5) on the right side.