Bad AvGas Problem

I'm based at H19, a small municipal airport in Northeast Missouri. The City has an above ground fuel tank, and recently installed an expensive credit card reader and pump. They don't sell much fuel and it sits in the tank for up to a year. For the last year, the City has failed the State Fuel Vapor Pressure test. Evidently, they are really close, but it always comes in a decimal or two off. They have had the supplier drain the tank, put new fuel in etc., but shortly after it always fails the test.

The tank has an unusual arrangement in that the pickup tube for the pump is 18 inches above the bottom of the tank, so the bottom rarely gets drained. We first noticed the problem when Aaron Christensen was visiting with his RV-7 and noticed some off-color fuel. Shortly after, it began failing the test.

I'm not a chemical engineer, and neither are any of the city employees. Since they tend to just sit on the problem and worry about what it will cost, they are doing nothing. I would appreciate any help someone might be able to lend us. Do we have a supplier issue? Feel free to contact me off line and lets discuss.

Thanks,
Jerry Folkerts

I had a new system that exhibited those same symptoms. I found the engineers had mis-measured the surface height and the installers added a nonstainless section of pickup pipe. Orange color 100ll and rusty steel bits in the filters. The pickup must be well above the bottom. The nasty fuel has to be sucked out through somewhere else with a drop hose or drained out on a surface tank. Tell the town they can have their shorts sued off if a plane goes down.

caution; address problem first....

I work for a 'city'. Sounds like they are typical in their inaction.
but........
if you even start to say the word.....'Liable'....the tanks will be gone.
......that's how all liability problems are solved these days.

so, think about the end game, do you want fuel, dirty fuel, or no fuel?

perhaps when that tank gets 1/2 empty or 6 months old, you need to advertise a fly-in with heavily discounted ( but clean) fuel to turn it over more often?

my $.02

Bad Gas

I have personally used 7 year old avgas (many, many hours worth) in both carbureted and injected engines without problems. I personally have no fear of 1 or even 2 year old fuel unless there is some other contaminant present.

My experience, your experience may differ.

My guess is that when they put new fuel in, they extracted the old fuel through the regular pickup, leaving 18 inches of it in the bottom; then pumped new good fuel in, which mixed with the bad.

Probably should have drained it out through the tank's sump.

Drain it completely, and sell it (undiscounted) to car racers. Clean the tank, check for corrosion, and fill it with new stuff. And don't fill it all the way to the top, because then the new fuel will get old and cranky before it's sold, and you'll get the same problem all over again.

I've seen algae growing in kerosene. There are bugs that grow in avgas too, so it might be a biological contaminant rather than corrosion or water ingress, and it really should be tested, because the tank might need disinfecting before it's refilled.

- mark

Possible Contaminant

Has the system been checked for water contamination? There are a couple of scenarios that come to mind, but do not quote me on anything. The reason they are checking the vapor pressure is because Avgas has a certain vapor pressure based on the molecules it contains. For example propane has a high vapor pressure than isobutene. When you mix propane with isobutene you have can calculate the resulting pressure based on the partial pressures of the two and you will therefore get a pressure somewhere in between, depending on the mixing ratios. So when someone is telling me the vapor pressure is reading low, it is an indication of a contaminant of a lower vapor pressure (higher b.p.) such as water. I wont get into the details, but normally water separates and sinks to the bottom, so one question is, when was the last time the tank was drained, but it is also possible for a surfactant to have been some how introduced, which would cause the water to stay in suspension. On the other hand, it is very possible the calibration of the cities pressure gauge is off and reading incorrectly, or the person taking the ready is ill-trained.

While I am not a chemical engineer, I am an organic chemist.

Mike Zenner

zennermd said:

So when someone is telling me the vapor pressure is reading low, it is an indication of a contaminant of a lower vapor pressure (higher b.p.) such as water.

Click to expand...

To the OP: which way was the vapor pressure out of spec - high or low? I'd be much more concerned about high vapor pressure than low, in the summer on a hot day after a heat-soak re-fuel.

Only concerned about low vapor pressure if there's so much of whatever contaminant that the fuel doesn't burn. Doesn't sound like that's happening - yet.

edit: I see that there's no fuel information on AirNav for this airport (H19). Perhaps they'd sell more fuel if they advertised to transient pilots that fuel is indeed available.