Operation

The roller cell fuel pump is driven by a permanent magnet electric motor that is located near or inside the fuel tank.
Steel rollers are held in "cut-outs" on the rotor. Centrifugal force seals the rollers against the walls of the pressure chamber as the rotor spins. Fuel that is trapped between the rollers is then forced out the delivery port.
The pump is designed to be both cooled and lubricated by the fuel flowing through it.
Since there is never a combustible mixture inside the pump, there is no possibility of fire.
The pump is subject to damage if it is ever allowed to run "dry."
A non-replaceable relief valve is designed to vent fuel back to the intake side of the pump if pressure ever exceeds the normal pressure range.
A replaceable check-valve holds about 2 bar of residual pressure in the system with the engine shut off and seals in conjunction with the pressure regulator to insure quick hot-starting.
Since the pump delivers a greater amount of fuel than is required by the engine at any given time, excess fuel is diverted back to the tank via the pressure regulator, which is located near the fuel distributor.