Fuel pump questions

[Tom Cloud]

>> The return line pressure is based on the vertical distance the fuel 
>> is pumped, not the weight of fuel in the tank.  So there would be 
>> more pressure if the fuel were returned to the top of the tank .  
>> Most gas tanks are lower than the high point of the system so the 
>> return line is down hill. 


>So you mean to tell me that you can just as easily pump water up a 3/8"
>pipe 75' straight up and into the bottom of a water tower and that 3/8"
>line will have LESS pressure on it than the same line going to the top
>of the water tower and dripping in through the top?  I've been wrong
>before, but I really don't think this is right.
>
>If you put the fuel return line into the bottom of the tank, wouldn't
>that be just like pinching the line and creating more pressure?  Or the
>same as using a smaller fuel line diameter?
>
>Please do explain to me as i don't really understand this i guess...

neither do I  ...  someone said it would take more pressure to
put water into a full tank than an empty one (if the line were
to go to the bottom of the tank) ??

as far as I know, the return line is all downhill -- correct me if I'm
wrong -- so, there should be NO backpressure -- other than that caused
by friction in the return line itself and that caused by any pressure
in the tank.  If the tank is at atmospheric pressure, then there should
be NO backpressure (as stated above).  If the tank has a slight vacuum,
then there will be a suction on the return line.

how can there be any more resistance to the water pouring from a glass
into a reservoir if it is (1) being poured directly from the glass or
(2) being poured into the glass through a straw ??  (neglecting the
restriction caused by the straw)

and why would it require anymore "pressure" to return the liquid
to the glass if the straw went to the bottom of the glass ...
the liquid being poured into the straw is actually going to the
surface level of the liquid in the glass -- not to the bottom and then
pushing against the weight of the liquid in the glass .... that is done
by the level of the liquid rising in the straw

if the tank were higher than the return source, then all this is moot
and the height of the liquid in the tank would, indeed, affect the
pressure required to pump gasoline back into it ....  IMHO