How do fuel pumps operate?

[darthapple35]

I am not talking about the mechanics of them, I am talking about what factors influence how much fuel they pump in a given system(EFI return style) at a given time. What do numbers such as maximum pressure and free flow rate mean? Can you have a pump that is too powerful for a system like say if you had a factor of safety of 4:1? Would this just require more power from the electrical system or can it actually be bad for the fuel system itself?

 

[jerromyjon]

I don't know much about the engineering side of you questions, but as far as practicality goes, you only need enough fuel pressure to facilitate an effective fuel atomization at the injector nozzles and enough flow rate to exceed peak fuel consumption. All fuel systems include a excess pressure relief valve which regulates the pressure in the fuel rail, many adjusted automatically through engine vacuum. Some vehicles such as many Volkswagon turbo engine gasoline vehicles have an electric feed pump in the tank with a mechanical high-pressure pump driven by the engine's camshaft.

 

[CWatters]

Turn on a water tap/faucet and experiment by trying to stop the water with your thumb. The harder you press with your thumb the higher the pressure and the lower the flow rate.

The free flow rate is the flow rate at zero pressure (nothing restricting the flow).

Max pressure usually occurs at zero flow rate (maximum restriction).

Most systems operate somewhere between these two points. Pump suppliers usually supply a graph of pressure vs flow rate.

 

[David Macclain]

It consists of a rubber diaphragm that is sandwiched between two halves of the housing and actuated by some sort of arm. More about that later, but for now we must distinguish between pusher and puller pumps.