Lebro Posted October 14, 2020 Report Share Posted October 14, 2020 Nice photo David, it shows the resistance wire & the wiping contacts very clearly. Bob. Quote Link to post Share on other sites
Richardtr3a Posted October 16, 2020 Report Share Posted October 16, 2020 A picture like that makes it so much easier to understand. Thanks Richard & B Quote Link to post Share on other sites
Charlie D Posted October 17, 2020 Report Share Posted October 17, 2020 Something I’ve always wondered about was how dangerous it seems to have a coil of resistance wire inside a fuel tank. One side is earthed, and if the other side accidentally touched full battery (Quite possible when playing around with wires behind the dash) would the coil of wire not become a heating element, like in an electric fire. The same with the wiper rubbing against the resistance wire. I always picture sparks (Albeit very small ones) coming from the wiper as it rubs along the coil. The only thing I can think of it that the tank is 100% full of petrol vapor and would need a fuel air mixture to explode. I would be grateful of some scientific explanation as to why my thoughts must be in error. Charlie. Quote Link to post Share on other sites
RobH Posted October 17, 2020 Report Share Posted October 17, 2020 (edited) 2 hours ago, Charlie D said: I can think of it that the tank is 100% full of petrol vapor and would need a fuel air mixture to explode. That's correct. Liquid petrol itself does not burn so although it sounds completely wrong, immersing electrics in petrol is quite safe. it's the vapour that is flammable but that is only over a very restricted range of fuel/air mixes - 1.4 to 7.6 % petrol to air by volume or thereabouts. The vapour concentration in the tank is very much greater than that so there is no risk of fire*. ( Petrol vapour is heavier than air, so air will not readily enter the tank to dilute the mix even when the cap is off). That does mean the risk increases greatly if the tank is completely empty of course as the vapour then becomes more dilute, which is why one should be very wary of repairing tanks using hot methods. *The partial pressure of petrol is about 4.5psi under normal ambient conditions so as long as there is liquid petrol in the tank, as an approximation there will be around 30% vapour by volume. Edited October 17, 2020 by RobH Quote Link to post Share on other sites
Charlie D Posted October 17, 2020 Report Share Posted October 17, 2020 6 hours ago, RobH said: ...Petrol vapour is heavier than air, so air will not readily enter the tank to dilute the mix even when the cap is off... Thanks for that Rob, I now feel reassured. Charlie Quote Link to post Share on other sites
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.