Large spark in CMS motor

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Leon wrote:

I don't think it is totally fool-proof except that the conditions for flammability are much more limited than you think owing to the high vapor pressure that does, as another poster noted, keep positive pressure in the tank as long as there's any fuel surface at all.
And, I'd venture that most of the cases you're talking about there's still a residual of fuel in the tank, only that it is below the pickup level.
Added to that that the brushes are undoubtedly built to be non-arcing so that there really isn't a continuous ignition source, the conditions just aren't satisfied.
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That makes sense to me.
According to a table I have, for 100 octane gasoline vapor, when mixed with air, the explosive (flammable) range is from 1.4% to 7.6%. vapor/air mixture, - a condition which, as you say, would rarely be met.
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And rarely is the event that I am talking about. Rarely does not equal absolutley not, and with millions upon millions of these vehicled out there you still don't hear of a problem. There has to be a stop gap safe guard that takes care of those rare situations such as when there is an accident with a ruptured tank and no explosion by fault of the fuel pump. There are simply way too many conditions that can and do occour that would create the right rare situation.
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Leon wrote:

I don't think there's any evidence to support that hypothesis that the conditions can be made right so easily as you suppose--in fact, I think the evidence clearly demonstrates the opposite--that is, despite the number of vehicles, the conditions under which the fuel pump is an ignition source _and_ the tank vapors are in an explosive mixture state is simultaneously, are, simply not events that occur with any frequency at all.
Again, all these scenarios you've brought up simply don't lead to nothing but a dilute air:vapor mix in just the right proportions--there's still far to much fuel.
Again, I don't think it is impossible, only highly improbable.
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Ok, and I'll end with this, I think. What keeps the improbable scenario from exploding? Those improbable scenario's actually do not explode.
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Leon wrote:

They would. That the don't is indicative of just how improbable they are (because they simply don't happen).
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Ok you and he are both missing the point. I realize that the with and absence of air the possibility of an explosion is nil. I am specifically looking at the situation where there is air present, ie. a rupture in the tank where air absolutely will displace the gasoline that is leaking out. We saw this all the time in the shop. Car died on the freeway, completely empty tank.

If there is a hole in the bottom of the tank, it is absolutley below the pick up level. Out of the millions of vehicles built with this configuration you have to know that there will be a deviation that will negate the situation that relies on the lack of air to prevent an explosion. Because I have not ever heard of a tank explosion caused by an electronic fuel pump I know that the system works under normal conditions but normal conditions do not always exist.

That may be the case. Non arcing brushes and again the brushes were in a strongly built contained steel enclosure behind a steel ball check ball.
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Leon wrote: ...

But are the pumps mounted in a well? Are there not formed hollows/ridges for structural rigidity in the tanks? Even if it leaks to the point of not running, I'd expect there to be a little gas in almost all cases left in such areas. If the tanks were a perfect sphere and you punched a hole at the very bottom, all the liquid would run out, yes. But there still wouldn't be air intrusion in most cases, only almost pure vapor.

So, there's the design feature(s) you're after which are simply part of the design. I'm not saying the pumps are built w/ no thought of preventing an ignition source; only that I'm convinced there's no secondary protective device or system other than the base design and the physics of gasoline combustibility.
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It may also be that even when the fuel/air ratio conditions for combustion are met, the arcing from the brushes may not provide a high enough temperature to instigate ignition. (The article in the url below gives an ignition temperature of 600F for gasoline vapor.)
http://tinyurl.com/yanzowk
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And there in lies the probable answer as a fowled spark plug will spark but not necessarily ignite the fuel mixture. Gasoline running past the brushes keeps every thing cooled down under normal operating conditions. And with electrical wiring running into the fuel tanks even for the tank units to measure the level of fuel you have to know that sooner or later there is going to be a short and that does not seem to present a problem either. that has veen a fact long before electric fuel pumps wer even being used. There is absolutely air in the tank otherwise the tanks would colapse or fuel would not exit. Fuel vapor may be too dense to burn unless the conditions are right. Vapor literally does not exist with out air, vapor is simply difused matter suspended in air.
Either way I believe your explanation that the spark in not hot enough is the stop gap safety measure. That is indeed a constant vs air and vapor conditions around the fuel pump.

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Leon wrote: ...

Not necessarily--there are other gaseous materials other than O, N, etc., that are the constituents of air.
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dpb wrote:

Or, more visible way to think of it, if were to start w/ a liquid in a closed container w/ a movable wall and if retract that wall creating a vacuum there will become a new equilibrium of two phases--liquid and gas. The concentration will be dependent on the specific liquid. There's no air needed...
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It might seem so, but that is not the case.
Gasoline vapor is heavier than air. With air given a vapor density of 1, the vapor density of gasoline is between 3 and 4.
In an undisturbed tank, vented to the outside, as gasoline evaporates, the vapor will displace the air. In the case where all of the gasoline has been drained and air has entered the tank, the remaining vapor will be concentrated at the bottom.
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Disturbed, I suspect that a shaken tank would not qualify as undisturbed. There is an awful lot of shoshing around going on in there when the vehicle is moving and if there is a hole in the bottom of the tank from a damaging impact the vapors will "grain out" after the fuel.
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And some fool will try to weld the 'empty' tank ....
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Sadly, it does happen.
Many years ago a young neighbor of mine was using an oxy-acetylene torch to cut open a fuel tank which he had emptied some time beforehand and thought was safe. It exploded, leaving him with serious permanent brain damage.
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How could anyone tell?
Sorry, that was thoughtless and cruel, but it's the mood I'm in at the moment.
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Friend of mine was working on a gas tank from a 1979 Ford Bronco washed the gas tank out several times was trying to solder the tank and all of a sudden there was a big bang what had happened the tank actually expanded,he finished soldering it but we had a hellova time getting it back onto the truck as it had expanded so much. Dan
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RE: Subject
First liar doesn't have a chance.
Lew
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No. They are typically flat and generally tilt towards a low end of the tank for all the gunk to collect at. The pump is suspended by the tank unit up from that position. There are ridges for rigidity on some tanks but those ridges generally run in a direction so as to drain to the low spot of the tank and the low spot is typically the forward end facing towards the front of the vehicle. This allows for more ground clearance under the back of the vehicle. That area is also the most vulnerable and typically will be the damaged/ruptured area when a driver drives over an obstacle.
Are there not formed

I would say that a pint of fuel could collect, maybe depending ont he damaged area but if the damage is located on the front bottom it is likely very very little will remain. Keep in mind a puntcture on the bottom of the tank will act exactly like a can of juice. Hold the juice can and poke a hole in it from the bottom. Juice will come out and as it comes out air will replace the leaking juice otherwise the fluid would not drain. Gasiline works the same way.

Yeah I am sure there is a secondary back up measure there are countless others in the fuel lines and in the old days the carburetors had preventatice features to limit fuel flow.
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