2nd Gen Non-Engine/Transmission Need some fluid dynamics help - VP44 fuel return line

[rweis]

I am trying to figure if the VP44 return line size of 3/16" ID will flow the maximum possible return of 70% of 45 gph (= 31. 5 gph) without creating back pressure on the VP44 bypass valve.



The VP44 bypass valve is set to open at 14 psi, but has a very small constant bore that is always open (to vent air I think is the reason). When it is open supposedly it can return 31. 5 gph back to the tank (which is the cooling fuel)



I have very limited knowledge of fluid dynamics.



I think I have figured that to pass 31. 5 gph (. 525 gpm) through a 3/16 diameter ID the velocity has to be at least 6. 1 ft/sec. I am not sure what that tells me though in terms of pressure.



Supposedly the return line should not be under any pressure as it is open ended as it terminates into the tank, which means as the VP44 bypass valve opens at 14 psi it must drop that psi to zero as soon as the fuel gets through the VP44 bypass valve orifice into the 3/16 ID line.



Is that possible to go from 14 psi small orifice in the VP44 bypass valve to ~ 0 psi in a 3/16 ID line passing . 525 gpm at (I think) 6. 1 ft/sec? OR is this another issue we need to address in the DC fuel system?



Everyone feeds the VP44 with pleanty of fuel (RASP, FASS, Walbro pumps), but is the return line sized correctly to not put back pressure on the VP44 bypass valve?



Thanks,



Bob Weis

 

[MRiley]

Bob ,thanks for asking this question. I was wondering the same thing. I went with the 95gph fass pump because I was worried about back pressure on the VP with the 150 in a stock set up. I'll be watching for post from those smarter than me!:-laf