High Pressure Main Pump

Fig. 13 Fuel pump:

Fig. 14 Rotor & rollers:

Fig. 15 Fuel pump internal view:

The roller-cell fuel pump is driven by a permanent magnet electric motor and is usually located near the fuel tank, Fig. 13. Steel rollers are held loosely in cut-outs on the shaft-mounted rotor, Fig. 14, so that centrifugal force seals the rollers against the walls of the pressure chamber as the rotor spins; the off-center lay-out of the rotor and pressure chamber "squeezes" fuel trapped between the rollers and forces it out the delivery port, Fig. 15.
The pump is designed to be cooled and lubricated by the fuel flowing through the motor; there is no possibility of fire because there is never a combustible mixture inside the pump; the pump is subject to damage if it is ever allowed to run "dry"-- even for a few minutes. For this reason, the CIS fuel filter is located on the pressure side of the pump.
A non-serviceable relief valve is designed to vent fuel back to the intake side of the pump if pressure ever exceeds system pressure range. A replaceable check valve holds about 2 bar (29 psi) of residual pressure and works in conjunction with the accumulator and the piston seal in the fuel distributor to ensure good hot starting.
The pump delivers several times the amount of fuel required at any time; the excess fuel is diverted back to the tank by the pressure relief valve in the fuel distributor.