Originally Posted by Searanger50
I think you've misunderstood my idea. I was looking at the possibility of taking an outlet from halfway down the tank so for the first half it would be gravity fed and the second half the pick-up would be a lot shorter.
Perhaps I am misunderstanding it often difficult to convey ideas typing.
However, if the fuel pipe is full of fuel it makes no difference where the pickup is on the tank.
With a pickup on the top, middle, or bottom the fuel will rise to same level. The suction required by the lift pump is the same no matter where the pickup is.
Try it with some water
and a syphon transferring water
from one bucket to another. Moving the pickup from the bottom to the top of the donating bucket will make no difference to the flow rate. (providing it stays below the water level)
Moving the pickup to the top of the bucket does not help the flow even though the drop in height between the ends of hose is now greater.
Water can be even made to flow "uphill" from a pickup that is below the level of the exit point of the pipe, providing the water level in the donating bucket is above the level in receiving bucket.
It is the fluid level that is important.
The lift pump has to lift the fluid from the top of fluid level in the tank to the engine. The tank can be 1 foot or 10 foot deep with a pickup at the bottom and the suction required is the same, if the fuel level is the same. (ignoring minor frictional effects)