Ford Car pump

"Colin Keith Williams" wrote in message news: snipped-for-privacy@autobanter.co.uk...

I've no explanation, but to add to your puzzlement, when I replaced the missus Ka fuel pump (same as on other Fords, too, by the look of things), there is an exposed 'rheostat' (nearest word I can think of, because the track is not continuous) for the fuel guage sender. I, too, am amazed that they even consider such an arrangement. The thing is certain to cause sparks with 12V across it. I can only assume that there isn't enough Oxygen in the tank to sustain anything more than the tiniest of ignitions. A bit like how you can light a flame at the end of a gas pipe, without it going inside. Or something.

Exactly the same thing. In order to get ignition you need fuel and an oxidant. In the case of electrics submerged in fuel tanks, there's no oxygen. We're just too used to operating in an atmosphere containing

petrol vapour to air ratio must be in a very narrow range for it to burn. between 1.2 percent and 8 per cent, so you need an open tank or a leak to have real danger of a spark from the sender unit setting it off (the sender only uses very low power in any case) the fuel pump is sealed and a spark inside liquid petrol would not ignite it in any case.

The current flow through it is tiny - so no spark. Rather the same as you don't get sparks when you fit a new watch battery.

Would you actually get a 'spark' in the absence of oxygen?

Chris

IIRC the only time a spark would not be able to travel is in a serious vacuum, otherwise there will always be some atoms of something for it to propagate across.

I was thinking of HV mains distribution switches; these are oil-filled in order to quench any possible arcing.

Chris

I thought you were talking about in the vapour above the fuel (you mentioned oxygen)

True. When I was a draftsman I did the drawings for an OCB (Oil Circuit Breaker) casting. Due to inexperience I left a couple of sharp edges on the inside of the casting, but I got the bollocking before the pattern was made, and rounded them off.

Even they can arc, on the higher voltage ones you switch to SF6

In message , Duncan Wood writes

To be honest, I don't know what they filled the huge 132/264kV tanks in the '50s, I was an apprentice then, and we climbed inside to wire the heaters, so I imagine it was still oil.

Aaargh. I guess they hadn't heard of H&S or polychlorinated biphenyls then.

Silly! They put the oil in afterwards!

D'uh. I are an eejit.

(In my defence, I do Usenetty things in the pauses between doing real work, usually during very dull meetings, so it doesn't always get the attention it deserves.)

I've always wondered why that doesn't happen; now I know why! Thanks.