Fuel Flow Question

[agitator]

"IN my Trojan F26 with a singl

"IN my Trojan F26 with a single 318 I have two fuel tanks. The starboard fuel line is 30" long and goes from the tank to a brass 'T' at the separator. The port fuel line is 94" long and runs from the tank to the same 'T'fitting. The shutoff valves are on the tanks. Using a mechanical fuel pump, would the fuel pump from both tanks evenly? If one tank ran out of fuel, would it pull from the other tank? There is not a balancing line between the two tanks. Seems to me it would pull from the one that offered the least resistant (closest, shortest) and if that ran dry, it couldn't pull from the other because air would be pulled in from the empty tank. Do you guys run one fuel valve open and one closed?"

 

[makomark]

"billy:

the biggest driver

"billy:

the biggest driver isn't the distance, it is the 'lift' the pump has to overcome.

Your hunches are correct, the path of least resistance will be the source. The boaters I know in your situation run one open and one closed."

 

[fred70]

"Billy,
<font color=""0000ff

"Billy,
<font color=""0000ff"">(I hate how long this turned out to be)</font>

The balancing line (crossover) between the two tanks, is the fuel lines to the Separator.
The fuel in the tanks will naturally level its self between your two fuel tanks. It's a siphoning action that will occur because of gravity.

I just can't picture that 318 drawing so much fuel that 2 - 5/16 fuel hoses (the back side of the "T") could be flow restricted enough, to cause a problem, being there is only 1 hose between the separator & the fuel pump.


As long as the bottom of the pickup tubes in the fuel tanks, are near the same level (as compared to the water line), things are good.
The only thing that may give you a problem, is IF one of the fuel tanks run low enough on fuel, (or if there is an abnormal restriction, or one of the pick up tubes is higher than the other) that the pick up tube starts to sucks air. Then the siphon will be broken, and you could potentially be setting out in the lake, seemingly out of fuel, even though one of your fuel tanks (the one with a lower pick up tube, or restriction) still has 5, 10, or 15 gallons of usable fuel in it.
At that point, shutting the valve to the fuel tank that is sucking air would make you hero of the day (or Captain of the ship), until there is more fuel added to that empty tank.

After fuel is added to the empty fuel tank, it is a MUST, that air is purged out of the fuel lines, by drawing fuel from that formerly empty fuel tank. Do this by opening that fuel valve, and shutting the other fuel tank valve. Then run the engine for a bit. (5 minutes at idle should do it)
Don't forget to reopen the other valve.

Fred 156-M}"