DIY_EFI Digest V4 #479

[Greg Hermann]

>I think the simple answer to this question is  a fuel pump is designed to
>pump against head pressure.   In other words push fuel.  Fuel injection
>pumps are not engineered to act as a suction type device.  Therefore,
>restrictions on the inlet side must be kept to a minimum.  This is why the
>pump must always be at or below the fuel supply level to insure the pump
>never runs dry.
>
>If the fuel filter begins to restrict the flow of fuel and the pump runs
>dry it will fail.
>
If you look up and under stand the concept of minimum required NPSH--Net
Positive Suction Head--as one of a pump's performance
characteristics--either in a (good) thorough industrial pump catalogue or
in agood, practically oriented, fluids testbook, you will have gone a long
way toward understanding what is going on here.

A fuel pump has operational problems similar to those faced by a condensate
well pump (in a steam power plant), although not quite so demanding.

Regards, Greg