Fuel Pump Return Line Question

[Ronno6]

I am curious about the fuel return line on a mechanical pump.
I have read that the return system is designed to keep fuel moving to prevent vapor lock.
Does that mean that there is always fuel being returned?
Of, is there a back pressure requirement in the pump that only returns fuel once a pressure threshold has been met?
If that is the case, what is that pressure??

 

[AuroraGirl]

I am curious about the fuel return line on a mechanical pump.
I have read that the return system is designed to keep fuel moving to prevent vapor lock.
Does that mean that there is always fuel being returned?
Of, is there a back pressure requirement in the pump that only returns fuel once a pressure threshold has been met?
If that is the case, what is that pressure??

im pretty sure you could technically flow the full amount of fuel pumped, but its designed to return a portion of the fuel thats pumped continually, if you were to open the pump , im sure youd find that the return has an orifice or its placed in such a way that most fuel will go to the carb, but that the internal piping returns some by design. I saw recently someone posted a photo of the orifice on the outer pipe ,but most i see appear to be full bore at the outlet at least. most vapor lock is going to be between the pump and the carb, the pump is at engine temp and the line is near engine (but not touching, so moderately cooler. radiant insulation can help lower problem. possibly phenolic gasket for the pump?