Lotus Elan and Lotus Elan Plus 2 Forums

Good evening to all Elan Community!

I did purchase a new fuel level sensor, but I'm a bit worried about the construction of such part because it's all open, the potentiometer inside the case is in contact with the petrol, no sealed, for sure is not EEX explosion proof .



Can anybody explain how it works?





For sure inside there is a point of contact where the movable stick scratches the variable resistance of the potentiometer: what's happen if a spark is originated by this friction point?
Ok you could say that the tank is vapour saturated and there is no oxygen inside, but before light my cigar with my own baby Elan, it would be great to get some comfort from you all.
thanks

Ciao da bella Italia
Paolo

That worried me too, but they are all like that and given that I have never heard of a fuel tank explosion, I guess they are safe after all.

It?s a long time now since I needed to do the calculations but I think you will find the answer under Intrinsic Safety.
Basically not enough energy available to cause problems.

These rely upon the vapour space above the tank contents always being above the upper flammability limit of petrol and therefore non explosive/flammable.The level sender itself is quite capable of generating a spark as it is connected to the car's 12V electrics with almost unlimited current available!! To be designed as intrinsically safe would require supply through zener barriers or other devices to limit to around 1.5V and 0.1A. Even if your tank is empty the vapour will stay above the upper explosive limit unless you start blowing air into it .........

Tank unit has the resistance of the gauge in series.

Very true, but the minimum ignition energy for petrol vapour is about 0.8mJ or 0.001watt seconds.....not a lot at 12V

2tmike.
Brings back my mining electrical career with Intrinsically safe equipment.
Same script with methane and flamable mixture range. Small volatile window. Lots of zener barriers, low voltages power supplies with high impedance and even atmite discs in signal bells to quench back emf.
An interesting point was the creation of an incentive spark created by the blow of and object against silver paper on metal. The cause of an explosion! Demonstrated with a hammer blow. So much so that silver paper was contraband. Our Kit Kats, Wrigley spearmint chewing gum and various chocolate buscuits were supplied in paper.
Sorry for thread drift but it brought back some memories.
Mike

I know that absence of evidence isn't the same as evidence of absence but I'd guess that the fact that we, as well as the owners of countless other vehicles using the same sender technology, are still here is some comfort. The odds look as though they're on our side.

Do check the unit VERY carefully before you fit it. You will see in the photos that there is a circular plastic grommet which the terminals for the electrical connection passes through. The second wire connects to the body of the unit.
I recently purchased one of these from one of the bigger parts suppliers and fitted it. Fine until the tank was filled above the level of the gauge. At this point fuel poured out.

As it was an older tank I assumed that the boss on the tank had failed so I emptied the tank, removed it and ordered a new one (Gulp ?????). When it arrived some 6th sense told me to check the whole thing once I fitted the sender to the new tank so I put a gallon in and then tipped the tank so the fuel was over the gauge. Fuel poured out.
So I looked at the gauge which was virtually brand new. It had TWO plastic grommets for terminals but the second one had no terminal, just a slot in the plastic for the blade but which the fuel was pouring through. When I called the supplier and they asked the mechanics they said "Oh, we have had a few like that. We just use a soldering iron to melt the plastic and seal the hole". Grrrrrrrrrrrrrrrrrr

So check your gauge before you fit it!

My point reinforcing 2tmike's point about volatile mixture not being present.
No worries!

I understand why but what has ignited? Our tanks are vented to atmosphere.
https://www.youtube.com/watch?v=6A5qUir3b2k

Most likely displaced vapour from filling the tank. Vapour mixes with air just outside the fuel filler and somewhere around there will be a mixture within the flammable range. Then an ignition source from an electrical device or static and off it goes....

If it's of any use I show the fuel level sensor in this video: https://youtu.be/yKiuTU5hZTE
Mine is an Elan S2. I think the later Elans have a different resistance sensor to mine.

Regards,
Paul