Whats the extra bypass line on this pump for?



EDIT: I've obviously accidently posted this in the wrong section - maybe a mod could move it please.

maybe a pressure relief valve of some kind?

Ill guess that its for fuel supply to another larger fuel pump that cant lift its own fuel from the tank. Basically, without fuel in the lines, the fuel pump wont be able to suck more fuel as its not efficient enough to remove the air from the lines. This pump supplies the main fuel pump so that it can start shifting fuel. The other line will have a one way valve in it, to stop fuel being recirculated, but to allow fuel to be drawn through it. That way, the inline pump doesnt have to run continously. it will also allow more fuel to flow through than the inline pump will.


Or as said, could be a conversion for a carb'd car to run efi. This way theres no need for a return fuel line. The pressure valve would work like a fuel reg up the front, only allowing a certain amount of fuel pressure in the line, before returning the extra to the tank via the feed line