Alex,
I think you will find that an electric pump needs no return line. They have a pressure switch which shuts them down at a certain pressure. Fuel injected vehicles require return lines for other reasons but not older carb engines. The diagram of the gun tractor fuel system shows no return line.
If you invent a return line without some sort of sophisticated pressure regulating valve the fuel will take the easiest path and just run back down the big hose into the tank rather than having to squeeze through the needle and seat.
If you have owned a Landrover, Jaguar or any one of many British types you will have heard the pump rattle away when you first turn the ignition on then slow down and stop as fuel pressure rises. If you just sit with the ignition on the pump will not continue to run unless it has a faulty shut-off switch (a highly likely situation if it is a Lucas pump!).
The reverse also happen with those Lucas pumps and several times the driver behind me has wondered what this lunatic is doing as he jumps from the car (Mark II Jag) and smashes his hand repeatedly on the rear of the vehicle to get the Lucas pump running after the fuel pressure drop was not sensed by the pump and it failed to get going.
Modern Japanese pumps and motor shop after market pumps do not need bypass lines.
Lang
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