Alex Wong1697456877 Posted October 11, 2000 Share Posted October 11, 2000 I've just been replacing my petrol pump and was wondering why they don't explode every now and then. There are two uninsulated electrical connections in a injection tank. The fuel pump and the rheostat for the fuel gauge. Surely a single spark from either of these points (especially the rheostat as it's in the fumes above the petrol when the tank isn't full) and the petrol would ignite. I know it doesn't cos we're all still here but I wondered why. Can anybody reassure me that it can't happen? Alex Wong www.alexwong.net _________ / / ___ _/______ /_ ___ / (_) (_)/ /`-'/o/ _______ o/`-'/ / /// ( VDU7X ) \/ / /___/--_________/--/___/ Link to comment Share on other sites More sharing options...
CHRIS CLARK Posted October 11, 2000 Share Posted October 11, 2000 Alex Good anorak subject this. I too have had the same thought but presumed that they rely on the fact that the fuel sender wiper is always in contact with the windings & so this won't give rise to a spark. I'm still not convinced though!!!!!!!! Over to Peter C! Link to comment Share on other sites More sharing options...
Peter Carmichael Posted October 11, 2000 Share Posted October 11, 2000 Have a look here . Link to comment Share on other sites More sharing options...
Alex Wong1697456877 Posted October 12, 2000 Author Share Posted October 12, 2000 Peter, You are worthy of the title Anorak!!!! Thanks. smile.gif I'm still not convinced though. Alex Link to comment Share on other sites More sharing options...
Alex Wong1697456877 Posted October 12, 2000 Author Share Posted October 12, 2000 Reassembled it. Turn key - fuse blows. After tracking down most of the live feed to the pump, (thanks Roger) I found the offending short circuit. Where the electrical feed goes into the pump is a resin filled block. This is resin filled to hide the appaling electrical connection inside. After chipping the resin away, I re-soldered it and filled it with epoxy. I've got about 10 cable ties to re-fit but hopefuly everything's ok now. Anybody else had this problem? Alex Wong www.alexwong.net _________ / / ___ _/______ /_ ___ / (_) (_)/ /`-'/o/ _______ o/`-'/ / /// ( VDU7X ) \/ / /___/--_________/--/___/ Link to comment Share on other sites More sharing options...
John Alston Posted October 12, 2000 Share Posted October 12, 2000 Alex All flamable substances have a volume to air range ABOVE or BELOW which they will NOT ignite. Some gasses like Acetylene have a very wide range and anything between 2.5% to 80% by volume in air will give you a very flamable mixture indeed. However, by comparison petroleum has a very narrow range and requires 1.4% to 7.6% by volume in air to make a flamable mixture. Therefore, with a normaly sealed Seven petrol tank, you will never under normal circumstances, get the petroleum to air mixture existing above the liquid level within the flamable range required. It will allways be far too rich to support combustion. So rest in peace you should never go 'BANG'. John Alston Link to comment Share on other sites More sharing options...
Nick Posted October 12, 2000 Share Posted October 12, 2000 Ah, that makes sense, thanks. So less is more. Link to comment Share on other sites More sharing options...
Alex Wong1697456877 Posted October 12, 2000 Author Share Posted October 12, 2000 Thanks! The cars running again and..... No explosions! More to the point, the misfire is gone. I suspect the original pump was ok and the intermittent short caused it. That would explain the 30amp fuse that was fitted to the fuel pump! 15amp fuse now and everything is ok. Alex Link to comment Share on other sites More sharing options...
gareth Posted October 12, 2000 Share Posted October 12, 2000 I am afraid I beg to differ, I am but a humble racer but at Cadwell Park I came up behind Richard Hassell in an SLR with fire coming nicely from his fuel tank. He pulled over as I passed and jumped out and proceeded to break all known 100 and 200 metre records in his dash for safety. He was very quick I swear he was catching my Caterham on foot. But for a brave marshall his 7 would have been toast, but it still was a mess Link to comment Share on other sites More sharing options...
Peter Carmichael Posted October 12, 2000 Share Posted October 12, 2000 It was not Richard's fuel tank that was on fire, but the fuel tank vent pipe. In their wisdom, Caterham decided to run an open pipe as the breather on Superlights and Superlight Rs. It tends to piddle fuel out in left hand bends, then you just need something hot to come along and there is bound to be some combination of vapour and oxygen in a flammable range. Link to comment Share on other sites More sharing options...
Graham Perry Posted October 12, 2000 Share Posted October 12, 2000 Indeed the amount of Oxygen required to ignite Petrol is really quite large. In some parts of the States Oxygen is added to petrol at the refinery to improve its emmissions but even then though its Oxygen rich they still don't go bang. I have often wondered though if this remains the same if you run the tank down to its last drop of Petrol, as one could see a situation where there was very little petrol in the pump when its on its last few drops of fuel and an awful lot of air. Anyone care to comment ? Link to comment Share on other sites More sharing options...
gareth Posted October 12, 2000 Share Posted October 12, 2000 Peter You are correct, I did know that, my point in humour was there is a possibility of a petrol tank going boom, and the way you described it is the most probable IMHO Link to comment Share on other sites More sharing options...
Peter Carmichael Posted October 12, 2000 Share Posted October 12, 2000 Gareth, I enjoyed your story. I remember Richard recounting the tale on the Sevens List. On Le Sept 1998 my car was spotted piddling fuel in the manner described and I have an extra long vent tube routed up and down the FIA bar. Shame we didn't spot that Richard's had the same tendency on the same trip. Link to comment Share on other sites More sharing options...
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