Why didn't it explode?
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  1. #1
    Official RnS Addict zephyr's Avatar
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    QuestionWhy didn't it explode?

    Had a fuel leak - ended up pulling the sender unit out. The fuel gauge needle has always jumped around from zero up to where it should be. There's a brassy metal strip about 1/4" wide from the potentiometer up to inside of the flange that bolts to the tank where it attaches to an insulated bolt that the wire to the gauge connects to. The metal strip had broken and was making and breaking contact with the bolt, hence the needle jumping around.

    Soooo.....an electical circuit was constantly making and breaking, which must surely have resulted in a spark inside the tank!!??!? Near the top, above the level of the fuel, where there would have been air and petrol vapour. So how come it didn't just go bang? As the tank is right behind the back of the seat, I reckon I'd have noticed! So was I lucky or am I missing something?

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    Official RnS Addict chris's Avatar
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    very lucky i reckon

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    Flange Dealer Paul G's Avatar
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    Probably all fume & very little oxygen , or the broken bits too dull to make a contact. Still damned lucky though!
    No longer selling anything Hot Rod related. Not on this site anyway. Don't bother searching Ebay either, they got too greedy.........

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    Official RnS Addict zephyr's Avatar
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    Spose I'd better fix it then! Seriously though, the truck's only had a gerry can of petrol at a time and it's been started and left running while I try and stop it leaking vital fluids all over the drive lots and lots of times. Surely I'm not that lucky? There's bound to have been plenty of air in there. Anyone know what ratio of air to fuel is needed for ignition and normal atmospheric pressure?
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    Official RnS Addict fozwanger's Avatar
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    You generally find that the air/furl ratio in the tank is too high, the "atmosphere" in the tank will be above the UEL (upper explosive limit) and therefore there will not be enough oxygen to sustain a fire, hence no bang. On the other hand, if there is too much oxygen, there is not enough fuel to feed the fire, this will be below the LEL (Lower Explosive Limit)The "explosive" band is roughly between 8 - 15% fuel to air ratio (God, I'm sad)
    Also, fuel is conductive ( the fuel companies add additioves) as fuel generally tends to build up a static charge when tanks are charged / discharged (for refinery and transportation purposes) so they need to be conductive to disipate the charge. (Am I boring you yet?)
    finally, your fuel gauge will probably be of the potentiometer type, only Eddy current, V low voltage, just measure the difference across the device.
    And remember, it's only "explosive" if the mixture is "contained", it'll just burn really unimpressively in open air.

    I think I need to get out more (time for a career change too, been in fuel testing and on fuel farms for far too long......... :-$

    Lol
    Last edited by fozwanger; 13-05-2009 at 18:47.

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    I'm a grown up member now !
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    You'd crap yourself if you thought too long about the in-tank pumps. They have electric motors running submersed in the fuel.
    Mart.

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    Official RnS Addict fozwanger's Avatar
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    You'd crap yourself if thought thought about a lot of the things you use everyday, washing machines and kettles and electric showers, hmmm, electric and water, now there's an accident waiting to happen.....
    :-)

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    Rods 'n' Sods Junkie pop-dreamer's Avatar
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    Quote Originally Posted by fozwanger View Post
    You generally find that the air/furl ratio in the tank is too high, the "atmosphere" in the tank will be above the UEL (upper explosive limit) and therefore there will not be enough oxygen to sustain a fire, hence no bang. On the other hand, if there is too much oxygen, there is not enough fuel to feed the fire, this will be below the LEL (Lower Explosive Limit)The "explosive" band is roughly between 8 - 15% fuel to air ratio (God, I'm sad)
    Also, fuel is conductive ( the fuel companies add additioves) as fuel generally tends to build up a static charge when tanks are charged / discharged (for refinery and transportation purposes) so they need to be conductive to disipate the charge. (Am I boring you yet?)
    finally, your fuel gauge will probably be of the potentiometer type, only Eddy current, V low voltage, just measure the difference across the device.
    And remember, it's only "explosive" if the mixture is "contained", it'll just burn really unimpressively in open air.

    I think I need to get out more (time for a career change too, been in fuel testing and on fuel farms for far too long......... :-$

    Lol
    If that was boring, then I am boring too, because I found it quite interesting!

  11. #9
    Rods 'n' Sods Junkie
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    YouTube - Nutter sets fire to a petrol pump

    Notice how when the static spark lights the vapour, it's a big floppy flame, not a small blue one, and there is no BANG.

    It probably only lit because it mixed with the extra air outside the tank.

    Still a brown undergarments moment though!!!!!!!!!!

  12. #10
    Exceeded sell by date Plumpcars's Avatar
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    Just had a fuel hose split on the 34 whilst driving it. I smelt fuel but had just filled up and it always smells a bit on rh bends for the first few miles so wasn't worried. Holley comp pump so high pressure over the right hand exhaust manifold for at least 4 miles. Pulled into my garage adjacent to my brother working on his Panhead. He was screaming at me to get it back out as he didn't want his bike destroyed!
    Still not sure why that didn't go up.

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