Posted by Clint Dixon [172.70.131.217] on Tuesday, July 04, 2023 at 07:04:57 :
In Reply to: Re: Gas tank filler tube posted by Jerry in Idaho [172.71.147.9] on Sunday, July 02, 2023 at 02:11:46 :
Very common problem. The vent tubes on my two trucks extend past the inlet tube of the tank well into the interior of the tank. If you take a look at fill tubes and vent tubes on modern vehicles, the vent tube may be 1/10th the size of the fill tube, or even larger. Compare the vent tube size to the fill tube on a Power-Wagon. It may be 1/50th the size at best.
For every cubic foot of fuel entering the tank, a cubic foot of air must escape. Not all that big of a problem with the older pumps that pumped a lot slower. But with modern pumps that blast the fuel out of the nozzle, the shape of the filler neck causes that fuel to swirl in a crazy vortex unless you get the flow aimed in exactly the right direction. The vent tube then becomes even more important now, but it is so small in comparison, also has a dogleg shape to it, and the escaping air has to flow out at a very high velocity to equal the same volume.
If you get the filler neck full of fuel to overflowing, watch how long it takes for it to drain down the fill tube as the displaced air escapes through the vent tube. As long as there is no gurgling and bubbling in the fill tube, the vent tube is doing its job. What length of time you witness is about as fast as the fill tube is going to take fuel without backing up unless one compensates somehow and gets additional downward angle to the fill tube, whether it be alteration to the truck, or parking in a way to make the slope near the gas pumps work to your advantage.
One has to consider that in 1946, there were still a lot of gravity flow "visible" pumps still in use. Even the early electric pumps had flow rates not all the much greater.
Junior