Quote:
Originally Posted by Darren69
fuel pressure regulator is there to prevent any damage due to over pressure
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Actually, no. What you've described would be an over-pressure relief valve. I don't know of any vehicle that has one of these in the fuel system (although everything has at least one - and some have multiple - in the oiling system).
Before the mid-80's, fuel pumps were "roller cell" type; however, almost all modern fuel pumps are "positive displacement", which cannot develop any pressure without a restriction or control in the circuit. Hence the FPR.
Without one, you get flow, but no pressure - the injectors need a certain pressure range to work correctly. 3 bar (or 45 PSI) is pretty typical for EFI.
Carbs generally want a lot less (like 3 PSI or so) - or you tend to overcome the float needles..
The fuel gets continuously pumped (circulated and returned to the tank) both to avoid localized overheating (eg in a fuel rail over the cylinder head) and because the fuel is used to cool and lubricate the pump.
Interestingly (well, I thought it was anyway), very common in turbo systems to use a rising-rate FPR - the regulator has a vacuum reference, that off-sets regulated fuel pressure by the amount of pressure "seen" in the intake manifold. So when there's 1 bar of boost in the intake manifold, the fuel system is regulated to the nominal 3 bar + 1 bar. Which both proportionally provides extra fuel (assuming the injector duty cycle remains the same duration) and maintains the advantage (pressure differential) of the injector over the intake for a good spray pattern.