<VV> Electric fuel pump

[Frank DuVal]

As Seth says, there are different pump types that do things differently, 
but in general, it is better to push a liquid than pull it. In broad 
terms, you can only suck water up 32 feet. That is the limit for 
atmospheric pressure to push the water into the vacuum (or lower 
pressure) area created by the pump 32 feet above the top of the liquid. 
Confused? Think well pump on top of the ground or pump on top of a 
building. These pumps cannot suck water more than 32 feet up. Shallow 
well up to 32 feet deep, no problem. 50 foot well? A jet pump or 
submersible is the answer, not a suction pump.

In car terms, since most are less than 32 feet high, the suction of the 
fuel will work, but since the fuel is going into a lower pressure area 
(the line before the suction pump) it is much more susceptible to vapor 
lock. remember, liquids boil at a lower temperature at lower pressure, 
Boyle's law I think.

So, proper mounting is pump below the top of the fuel level (not an old 
wives's tale, but proper installation), but it can work with the pump 
higher most of the time, just no guarantees.

As far as different pump designs go, remember the well pumps you had to 
prime to get to work? Those didn't pump air worth beans! This design 
would never suck air through a dry fuel line, yet they are a fluid pump.

Frank DuVal

AeroNed at aol.com wrote:

>In a message dated 10/3/2010 12:42:12 P.M. Central Daylight Time,  
>ricknorris at suddenlink.net writes:
>
>They are  designed to push the gas not pull it a long distance 
>through a  pipe.
>Rick,
> 
>
>I disagree (as strongly as I dare) with your statement. This is an old  
>wives tale, not that you're an old wife. There is no difference in the pump  
>design to push versus pull fuel. A fluid pump is a fluid pump. The only  
>difference is that the piping between the pump and the tank has to be free of  
>leaks because air is easier to pump than gasoline.
> 
>My electric pump, which is located behind the rear seat under the  package 
>tray, is higher than the top of the gas tank. It has sucked fuel through  
>empty lines several times without any trouble.
> 
>Ned
>
>  
>