school me please, why a fuel sender will never ever spark

[perello]

title says it all...

to me a fuel sender is basically a reostat with a contact jumping between wires..


what obvious thing am i missing?
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Aug '58 pressed bumper SO23
1974 German Thing
1978 Bug 1200

[slayer61]

It's not jumping between wires. It's the same wire. Different locations on the same wire.

Kinda like putting both your volt meter leads on the same hot/ground wire. There's no difference in potential.
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[baldessariclan]

I'm no electrical engineer, but would venture to guess that it's because the voltage is so low and resistance high in that circuit -- suspect it's nearly impossible to make a spark form/jump in those circumstances. Or perhaps any spark which would form is still too weak and cool to ignite the fuel + air vapor mixture in a gas tank -- ? Those are just SWAGs, though...
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baldessariclan -- often in error, never in doubt...

[jeffrey8164]

It must be settled science though I don’t know anything about it.
They’re putting entire fuel pumps inside the tank on modern cars.
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[busdaddy]

Even if it did the atmosphere in the tank is far too rich to ignite:

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[Schepp]

Where do I add the fluid to my blinkers?
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Bandit #19
1972 Baja Rallycross Bug

[67rustavenger]

I too have wondered why but, never questioned the issue since things were working as designed.

I recently changed the FP in my Eurovan and the pump power connection are exposed to the fuel in the tank. Hmmm, no fuel fire when energized. Lol!
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[perello]

thank for the inputs...

i get the point, the voltage drop in a single wire turn is too low...or low enough to make absolutely sure it will never create any spark.

Is something that made me wonder always (i did repair fuel senders), thinking that this works in an atmosphere that basically is gasoline fumes...
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Aug '58 pressed bumper SO23
1974 German Thing
1978 Bug 1200

[finster]

my interest was piqued and this is from a boat forum where the same question was asked.
In any "hazardous location" (as defined by safety regulations) and for every atmosphere (gasoline, propane, etc.) there is a graph of voltage versus current showing the level at which a vapour will ignite. These graphs have been determined in a laboratory and are used as the basis for approving equipment to be used in these locations.

also gasoline will only ignite within a limited range of fuel/oxygen mix. about 1.4% to 7% fuel in the air mixture. again this has all been studied and defined so that limits can be set.
https://en.wikipedia.org/wiki/Flammability_limit
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[RUNKLE]

.

Simply put as busdaddy stated, “the atmosphere in the tank is far too rich to ignite”.

Submerged electric fuel pumps don't cause explosions because gasoline is in a liquid state, and only its vapors can burn. The pump is submerged, which prevents sparks from igniting the fuel. Additionally, the concentration of gasoline vapors in the tank is too high for combustion, as there isn't enough oxygen in the "headspace" above the liquid to create an explosive mixture.

.
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Type 1
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[liquidrush]

But........ we're supposed to believe that this is what brought down TWA flight 800 right? I mean even the cia made a video......the gov would never lie. Right?

[Who.Me?]

[Abscate]

[RUNKLE]

.

[Abscate]

It is a little freaky to mix electrics in liquid gasoline but the safety thing is worked out.

Is this a good time to point out that all( most) mainline generators run in a Hydrogen environment? With high voltage sparky slip rings?
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[HarrysRatBug]

I worked with a welder when I was in the Air Force that welded on active jet fuel lines on the ramp where they refueled the planes. He told me the principal, but I never really understood it. The lines would have to be full and running under pressure. Told me if a pocket of air came through, he'd be gone. There were always at least two firemen fully suited in special suits with a crash truck sitting at ready. Told him he was crazy and he proved it at a later assignment in Korea when I was talking to somebody and he used a spray can as a torch by my head!

[Xevin]

Public Broadcasting Service was pretty neat, growing up for me in the 70s
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[zerotofifty]

A buddy of mine used to weld natural gas pipelines, repair leaks with welding. The gas was flowing, even coming out of the leaks, and he'd weld, sure the leaking gas burnt, but the flame never could sustain inside the pipe, as the pipe had too little oxygen in it to support a flame.
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[EVfun]

If one is really concerned you could run a marine reed switch type fuel gauge sender. I have KUS sender in my buggy, but have not connected it to a gauge yet.
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[Heiferman]