| Author | Message | ||
| Mark Eberhardt (Me_k)
Junior Member Username: Me_k Post Number: 148 Registered: 5-2002 |
There are 2 numbers that are important, the lower explosion limit and the upper explosion limit. In your garage it's the lower limit you care about, mostly air and a trace of fuel, but well below the amount required to sustain combustion. In your gas tank, it's the upper limit, all fuel with a trace of air, but well below the amount required to sustain combustion. You can (and I have) welded full fuel tanks. You can not weld an "empty" tank, they explode. As long as there is any gas in a closed tank, it will be above the upper explosion limit. If it is open it may or may not be. Boeing had a problem for several reasons. Jet fuel doesn't vaporize very well compared to gas, the stuff sits below the lower limit unless it's heated, then it takes a while to get a tank above the upper limit. They uses a pretty small tank with big engines, so it got empty pretty fast and they put the A/C unit, which gets very hot next to it. Then they had a bad groung which allowed a very high voltage static charge to build up. So 3 things went wrong. An engineer from a big chemical comany told me that 3 is always the number when bad things happen. | ||
| Jim Glickenhaus (Napolis)
New member Username: Napolis Post Number: 49 Registered: 10-2002 |
I would try contacting Boeing and NTSB. They may know. The fuel pumps in my Ford MK-IV are submerged in the cells. I sent them for a rebuild. The comment that came back was "This plane hasen't flown much in the past 30 years." | ||
| James Selevan (Jselevan)
Junior Member Username: Jselevan Post Number: 213 Registered: 6-2002 |
Right you are, Magoo. Big time stupidity filling a spare gas container while it sits in the trunk. Read about those Barb B Q's periodically. However, with respect to this thread, static electricity generates several thousand volts, microamps of current. Certainly sufficient to ignite gasoline vapor, but explicable based on the large potential (volts). A horse of a different color vis-a-vis 12 volts. Jim S. | ||
| J. Grande (Jay)
Member Username: Jay Post Number: 704 Registered: 10-2001 |
It also happens with cell phones, and I don't think cell phones are 12volts. | ||
| magoo (Magoo)
Advanced Member Username: Magoo Post Number: 3463 Registered: 2-2001 |
Jim there have been explosions from static electricity on peoples clothing igniting the fumes at the fill neck. In the news not to long ago a guy, in cold weather, was filling his tank. Got back in the car until the pump cut off. Slid across the seat and got out grabbing the nozzle. The spark from the static electricity ignited the fumes and set the car on fire. | ||
| James Selevan (Jselevan)
Junior Member Username: Jselevan Post Number: 212 Registered: 6-2002 |
Jim - I appreciate your input. However, I suspect that a spark a few microns in length will be sufficient to ignite petrol fumes. If you have ever removed the battery terminal while the ignition is on, you will note sparks. Thus, 12 volts is sufficient to propagate a spark ONCE the current is flowing. I agree, holding the two terminals close to each other will not result in a spark, as the potential is insufficient to ionize air, however, once the current is flowing, the inductive nature of the wiring harness and associated equipment leads to a spark when the circuit is broken. My concern is that the idiot-light contact may make/break several times while gas sloshes around. Anyway, I put my restored sending unit back in the car, connected the battery, turned on the ignition (first placed ear plugs in tight) and the gauge read correctly. Jim S. | ||
| Jim Glickenhaus (Napolis)
New member Username: Napolis Post Number: 46 Registered: 10-2002 |
It takes 60-200 volts to arc electricity through an inch of air. A 14 volt system can't maintain an arc over even a tiny gap. Page 123 Dec 2002 Car and Driver | ||
| magoo (Magoo)
Advanced Member Username: Magoo Post Number: 3443 Registered: 2-2001 |
James also on the soldering of the wires I see your concern. Maybe check a guage, not Ferrari guage, that has the fuel sending option on it at a parts store and trace the wires to the terminals on top of the guage. | ||
| J. Grande (Jay)
Member Username: Jay Post Number: 696 Registered: 10-2001 |
Kabooom!  | ||
| magoo (Magoo)
Advanced Member Username: Magoo Post Number: 3442 Registered: 2-2001 |
Craig, I would think when you took the cap off the tank you would get oxygen. So.... | ||
| magoo (Magoo)
Advanced Member Username: Magoo Post Number: 3441 Registered: 2-2001 |
James , I couldn't remember which it was that went through the rheostat + or - but it should not produce contact of + to - or - to + until it reaches outside the tank on its way to the dash guage. Maybe this sounds confusing but then it has been some time since I had mine out. I don't think Peter has his tank guage out. That is one of the pics from his archives. | ||
| James Selevan (Jselevan)
Junior Member Username: Jselevan Post Number: 211 Registered: 6-2002 |
Magoo - both the schematic, and my tracing the conductors, reveal that the gauge is a voltmeter, scaled as fuel. The meter reads the voltage at the rheostat. Thus, current runs from the battery through the sending unit rheostat to ground. The meter reads the voltage across the rheostat resistor. As there is continuous contact with the rheostat, this does not introduce the potential for spark. However, it is the idiot-light that is of concern as it is an intermittent contact, with 12 volt potential. The more I think about this, the more concerned I get. Not for the obvious reason - how many of you have had your fuel tank explode? - but for my concern that I may have soldered this incorrectly. I am concerned that the "fingers" should not be grounded. Peter (75 308 GT4) - could you check to see whether the "fingers" are in electrical contact with the "boom". That would be a great help. Thanks. Jim S. | ||
| Craig Dewey (Craigfl)
Member Username: Craigfl Post Number: 484 Registered: 1-2001 |
As long as you don't provide any oxygen(or anything that will provide oxygen), it can't burn. Now maybe at a microscopic level there might be a free oxygen molecule available but the burn won't last long.... | ||
| magoo (Magoo)
Advanced Member Username: Magoo Post Number: 3438 Registered: 2-2001 |
Great, I'm having a little sauce myself. You know sometimes a guy can't fly on one wing. Magoo | ||
| magoo (Magoo)
Advanced Member Username: Magoo Post Number: 3437 Registered: 2-2001 |
I think the resistance from the rheostat operates on the negative side and the 12volt positive side picks it up outside the tank sending it to the dash guage that works on 12 volts. JMO | ||
| Hans E. Hansen (4re_gt4)
Member Username: 4re_gt4 Post Number: 424 Registered: 4-2002 |
Yup | ||
| magoo (Magoo)
Advanced Member Username: Magoo Post Number: 3436 Registered: 2-2001 |
Hans, I like that. Are you on the sauce again????? | ||
| Hans E. Hansen (4re_gt4)
Member Username: 4re_gt4 Post Number: 423 Registered: 4-2002 |
James: Maybe it really is a problem, we're all dead, and don't know it. PS - hoping you can do LA | ||
| James Selevan (Jselevan)
Junior Member Username: Jselevan Post Number: 210 Registered: 6-2002 |
I assume that 12 volts reaches the sending unit. I will test this tomorrow with my voltmeter. However, 12 volts is sufficient potential to lead to a spark. Try rubbing battery terminals. However, as close as one holds a terminal to a battery at 12 volts, it won't spark. Once current is flowing, such as when touching, and then the terminal is removed, the separating connectors will spark due to the close proximity during initial separation. The idiot light contact makes and breaks while fuel sloshes around. So why no spark? I suspect Mitch Alsup is on the right track. Perhaps the oxygen content is insufficient due to the fuel vapor-pressure forcing air out. I am perplexed. Jim S. | ||
| J. Grande (Jay)
Member Username: Jay Post Number: 688 Registered: 10-2001 |
Interesting. I may not understand why the fuel doesn't ignite but at least I know why Brits drink warm beer!  | ||
| Edward Gault (Irfgt)
Intermediate Member Username: Irfgt Post Number: 2214 Registered: 2-2001 |
I see fuel pumps on all types of cars that have the in tank pumps that fail and some times the wiring connectors are burned black and the insulation is burned away. Still no fire or problems. Just one of the mysteries like crop circles that you just accept. | ||
| Edward G. Salla (350hpmondial)
Junior Member Username: 350hpmondial Post Number: 197 Registered: 2-2002 |
Hans, Are you sure it's dark? (You know, I used to think that about my refridgerator too.) Soooooo ,,,,,,,,,, Why, do the Brit's drink warm beer? Because their refridgerators are built by LUCAS. | ||
| Matt Lemus (Mlemus)
Member Username: Mlemus Post Number: 392 Registered: 8-2002 |
Didn't Boeing have this problem on the 747's? | ||
| Hans E. Hansen (4re_gt4)
Member Username: 4re_gt4 Post Number: 412 Registered: 4-2002 |
At least you know it'll be dark in there. (Oh, gawd. Now I've done it. Even I'm doing Lucas jokes.) | ||
| Joel Ames (James)
Junior Member Username: James Post Number: 57 Registered: 4-2001 |
Jay, my 62 E-Type has the fuel pump in the tank. Now you want something scarry? A Lucas electrical device in a fuel tank. | ||
| Mitch Alsup (Mitch_alsup)
Junior Member Username: Mitch_alsup Post Number: 204 Registered: 4-2002 |
The vapor mixture in a tank is extremely rich and not that easy to ignite. As yo fill the tank, you displace all the air and with it the oxygen. As the tank empties, there is plenty of time for the gasoline to vaporize and create an extremely rich mixture. | ||
| Hans E. Hansen (4re_gt4)
Member Username: 4re_gt4 Post Number: 409 Registered: 4-2002 |
I realize that low voltage/low current is probably the correct answer to this, but I *think* that on at least a microscopic level, there is always a spark. I.e. if you close contacts with 1000 volts on them, big spark. 500 volts, the contacts have to get closer before ionization allows current flow and produces the resulting spark. 100 Volts, contacts closer yet, etc., etc. I can't see that there is some magic voltage level where the spark disappears completely. I do find the entire concept a little scary, however it's been done for decades. What's probably scarier are those submerged fuel pumps. Electric motors have sparks around the brushes, regardless of the voltage involved. If completely submerged, OK. But when tank near empty? | ||
| Erik R. Jonsson (Gamester)
Junior Member Username: Gamester Post Number: 181 Registered: 11-2000 |
It sends an extremely low voltage, low current signal only. Too low to cause a spark. Have you ever seen a spark jump when you test a resistor(out of circuit) with a multimeter? That is what a sender and gauge are... an analog multimeter with E-1/4-1/2-3/4-F on the meter face rather than resistance values. This is tied to a variable resistor(the sender) | ||
| J. Grande (Jay)
Member Username: Jay Post Number: 686 Registered: 10-2001 |
If you've followed the other thread on fuel senders you'll know that this question arised. What stops a spark from the sender unit igniting the fuel inside the tank? I realize that if it is submerged under fuel it can't spark, but what about when the fuel level is down? The fumes are more flameable then the liquid, so why isn't there an explosion when the connections make contact? This is true with all fuel senders that are inside the tank not just Ferraris. |