Fuel pressurized at the transfer pump travels to the charging annulus. The annulus has eight slots. From the charging annulus, fuel is distributed to two places (figure 5-13):
• the pump housing
• the pumping plungers of the rotor
Fuel delivery to the plungers is most important for the understanding injection pump operation. Fuel reaches the plungers from two sources.
The first is through two inlet ports in the rotor. As the rotor spins, these ports align with two of the eight annulus slots. Pressurized fuel passes from the slots through the rotor inlet ports. Passages in the rotor carry fuel from the ports to the plungers.
The second source of fuel distribution to the plungers occurs at the front of the rotor, in the fill/spill chamber. Fuel enters through the open control valve. The valve’s movement is controlled by the fuel solenoid. When the solenoid is off, the spool-type control valve unseats to allow fuel to pass through.
Fuel in the rotor is metered for delivery to the injection nozzles.
