Why don't in-tank fuel pumps cause explosions O/T? - Vintage Mustang Forums
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Old 08-18-2002, 05:14 AM   #1 (permalink)
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I figured I'd ask and see what you people think about this one. I just finished reading the post about why the senders don't cause fires and figured you guys might want to ponder this one.

And by the way, I am referring to the in-tank pumps that are 12 volts and are actually submerged in the fuel, cummutator sparks and all. And if it doesn't ignite when full, why doesn't it ignite if you run it empty?

I have yet to figure this out myself, but maybe someone out there has engineered these things and can give us an answer.
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Old 08-18-2002, 09:21 AM   #2 (permalink)
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Probably the same reason blowers in boats don't cause a fire or explosion..I believe they use what is reffered to as a sparkless motor..now what that means I have no idea..but it works in a boat where the motor is turned on to vent gas fumes from the bildge, could be the same principal.
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Old 08-18-2002, 10:26 AM   #3 (permalink)
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Take a look at one of those fuel pumps, they are sealed so tight nothing can get in or sparks can't get out...
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Old 08-18-2002, 10:48 AM   #4 (permalink)
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Kinda why en empty gas tank is dangerous and will explode and a full one won't, lack of oxigen! The fuel pump is submerced and isn't in contact with oxigen, hence no ignition, along with being sealwd up very well as Dave has said.
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Old 08-18-2002, 12:59 PM   #5 (permalink)
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Talking about in tank pumps, I read a good article on those pumps, yesturday.
The article said that you needed to keep your gas tank no less than 1/2 full with in tank pumps. They are cooled by the gas temperature around them. The less gas in the tank, the more heat the pumps develop. This shortens the pump life. Guess that makes sense, just had never thought about it....Anyone else ever heard of that
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Old 08-18-2002, 01:18 PM   #6 (permalink)
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But have you ever taken one apart?

The one I took apart pumped the fuel in one end and then it went out the other. The fuel actually got pumped through the motor itself, commutator, brushes, windings, all the way through to the other end. Take apart an old inline fuel pump some day, and you will see what I am talking about.
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Old 08-18-2002, 01:21 PM   #7 (permalink)
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Sounds feasible. I wonder.....
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Old 08-18-2002, 01:25 PM   #8 (permalink)
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Gas dont like to burn unless its in a vapor form . as long as the pump is submerged it wont burn . That is how they all work threw the filter in the back out the line in the front .
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Old 08-18-2002, 03:17 PM   #9 (permalink)
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there is really no danger of electricity in gasoline. you would have to run so much current to cause the gas to vaporise, and you would have to have enough gas vaporising to cause it to form enough of a boil to bring enough air to the gas vapor to even support combustion and it is at that point the wire would need to melt and form a spark.

Gas really isn't as dangerous as i think your believe it is. A ruptured gas tank was not an automatic death sentance. In fact it was quite the opposite. They ruptured all the time. I was in a wreck that spilled 15 gallons of gas on the road. Spill about a pint of gas in the middle of driveway and take a book of matches and try to throw a lit match into the gas and make it light. The gas will keep putting out the matches. You will suceed when you throw it just next to the puddle. Where it has just long enough to start the vapors on fire. That is where gas is scary. the vapors hover just above the floor. Rags soaked in gas can form a large enough vapor cloud to build up on the floor that it reaches a gas pilot light. The same thing happend in car wrecks. the gas pouring all over the highway would form a vapor and seek out flame. There was a very rare event that a fuel tank would rupture on impact and throw fuel into the car and also light.

A much larger danger is present in fuel injected cars. They work on a closed loop so it is expected to pump large volumes of fuel under high presure from the tank to the engine and back. The problem in the fiero was in the first years model they had a metal fuel line linking the engine to the chassis. Over time the flex caused the line to break. At this point fuel blew onto a hot manifold at 20 pounds pressure and it vaporised where it filled the engine compartment with gas fumes. Any combustion point would make the car go boom. The fiero is just an example. This is like using the pinto as an example of fuel tank explosion. It was a glaring example like the fiero but the problem was not unique to them. I've seen far more fires in fuel injected cars than i ever have in mustang era cars.

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Old 08-18-2002, 03:23 PM   #10 (permalink)
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electric motors most often spark (grab your electric drill in the dark, pull the plug and wala! let there be light.

when electricity runs through a wire, it generates a magnetic field, "winding" the wire in a particular manner adds the fields together, and this field can push/pull a shaft. At some point a couple of conductors seat themselves on the spinning shaft and I think this is where the spark occurs. Generators work in reverse, a spinning magnet induces current in wires.

I think maybe these sparkless motors are purely using the magnetics to make a less efficient motor but one that doesn't spark.

It's been a good 6 years since I've seen the theory, so I may not be totally accurate, not my field.

you might try "howstuffworks.com", and look for electric motors, i love that site, good articles on engines, trannies, etc.

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Old 08-18-2002, 04:52 PM   #11 (permalink)
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The fuel pump is a sealed unit. If the seal breaks then it is submerged. There is no oxygen to let it catch fire and the fuel is conductive so it acts as a resistor so there is no spark. Its sort of like a pilot light on a gas stove. they only thing that keeps the flame from running into the pipe and blowing up the entire city is that there is no oxygen in the gas lines.

Fuel pumps also have fuses so in the event of a short the fuse will blow.

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Old 08-18-2002, 09:48 PM   #12 (permalink)
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It's a weird concept, but I guess it works. I am glad I didn't have to be the first one to plug the motor in while it was submerged in fuel!

I guess gasoline really needs a lot of air to ignite, 14.7 to 1 ideally. This translates to about 18 cubic feet of air to burn 1 ounce of gasoline. That is a lot of air if you think about it.

Thanks all for humoring me. I have kinda always wondered why, and I could sorta figure it out, but it just seems unbelievable at times.
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Old 08-19-2002, 01:51 PM   #13 (permalink)
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You mean those big explosions in the movies when a car crashes or a bullet hits the tank aren't real? What's next? Mustangs can't fly like "Gone in 60 seconds"?
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