Re: No oxygen inside of a fuel tank. But a spark at the filler..


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Posted by David Sherman on Monday, December 04, 2006 at 3:43PM :

In Reply to: No oxygen inside of a fuel tank. But a spark at the filler... posted by chriscase on Monday, December 04, 2006 at 3:02PM :

I don't think the engineers would rely on the lack of oxygen to prevent explosions. Plenty of fools have blown themselves up using a match to see down in the tank to see if there's gas in it. What it really amounts to is an "energy-limited" design. There is a whole class of industrial electronics that are "explosion-proof". There are basically two ways to make a piece of electronic equipment explosion-proof (unable to ignite an explosive atmosphere). One is to enclose it in a heavy, tightly-sealed metal housing, usually cast aluminum or cast iron. The other is ensure that there is no source of energy within it capable of making a spark. There are specific rules for this in terms of volts, amps, and joules. I had to do an explosion-proof design once a long time ago, but I don't remember the details. I'm certain that the resistance of the fuel gage is enough to ensure that even if you touch the sender wire directly to ground and pull it away, you'll never get even the tiniest spark. That means that nothing going wrong inside the sender can caust an explosion. You would need to have the gage fail with a short-circuit to the battery, which is highly unlikely, and the sender fail at the same time, in order to get a spark. Like I said, I've never heard of it happening, so the design must be pretty safe.

As far as the effort goes, once a part isn't available from the local NAPA, it's almost always easier to try to fix it than to try to find a replacement. My 65 D200 has a flaky gas gage that I never could get working right. It came with two old senders in the tool box, which tells me the previous owner had the same problem. The next time I get to working on it, I'm going to try the jumper wire method, and I'm confident it will fix the problem.



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