Does petrol conduct electricity? Odd question I know!
Discussion
Just watching Wheeler Dealers and Ed China is working on a nice Volvo P1800. The fuel sender wasn't working so he has replaced the sender unit (and tank and fuel gauge). It's never occurred to me before but of course the sender sits in the tank and works on a similar basis to the volume control on a radio, a slider moves against a coil of wire and increase or decreases the resistance in the current which is sent to the gauge. Now I assume that over the years petrol, being the invasive substance it is, must seep into the unit so do they work wet sitting in fuel or is it essential that they remained sealed and isolated from the fuel? Also, is there absolutely no chance of sparks from the sender unit as it moves across the wire coil? Surely this could be final but again I have no idea. All things I have never thought of until I saw the inside of a fuel gauge sender unit! 
I'm no boff on the subject, but I'm pretty sure that fuel tanks are pretty much void of any oxygen required to create a combustion event. Also petrol isn't as easy to ignite as you may think without putting it under pressure.
I'd also imagine that the voltage passing through the sender is tiny and not capable of mustering up a spark if it tried.
(someone feel free to take me down a few pegs tho)
I'd also imagine that the voltage passing through the sender is tiny and not capable of mustering up a spark if it tried.
(someone feel free to take me down a few pegs tho)
Edited by jimxms on Friday 9th December 21:04
jimxms said:
I'm no boff on the subject, but I'm pretty sure that fuel tanks are pretty much void of any oxygen required to create a combustion event. Also petrol isn't as easy to ignite as you may think without putting it under pressure.
(someone feel free to take me down a few pegs tho)
Ok so that answers my point about a spark igniting the fumes so now I am just left wondering about the sender working in petrol. Interesting point about oil cooled transformers though. (someone feel free to take me down a few pegs tho)
AFAIK petrol "liquid" wont ignite that readily its the Vapour that is volatile
and the design of the track & wiper in the sender is such that an arc cannot happen
if you look closely at the wiper track interface its relatively wide so you
have a broad point of contact thus low resistance so no arc or heating
OR i made it up.
and the design of the track & wiper in the sender is such that an arc cannot happen
if you look closely at the wiper track interface its relatively wide so you
have a broad point of contact thus low resistance so no arc or heating
OR i made it up.
ShayneJ said:
...if you look closely at the wiper track interface its relatively wide so you
have a broad point of contact thus low resistance so no arc or heating...
Right okay but do they sit in petrol? And if so that suggests petrol is non conductive because if it was in a tank of water it would all short out. have a broad point of contact thus low resistance so no arc or heating...
Petrol itself isn't flammable, only its vapour. In theory, if a swimming pool was filled with petrol, you would be able to swim underwater (underpetrol as such), while the top was on fire, although I don't think this has been tried. If anyone cares to try, please post back with the results.
What happens when you spray WD40 on the ends of your spark plug leads and hook them back onto the plugs? They still work. So I reckon as it's a petrolem based product, that petrol will conduct electricity. But there will be such a thin film between the contacts on the sender, that it wouldn't really make much of a difference.
What happens when you spray WD40 on the ends of your spark plug leads and hook them back onto the plugs? They still work. So I reckon as it's a petrolem based product, that petrol will conduct electricity. But there will be such a thin film between the contacts on the sender, that it wouldn't really make much of a difference.
I don't think I've expressed myslef clearly. Forget the spark igniting the fuel vapor issue. My main thought was that a fuel gauge sender unit is basicsally a a volume control which sits inside the tank. Okay so it's in a unit but I imagaine petrol must seep in over the years. If that was water it would stop working immediatly the slightest amount of water shorted out the slider and contacts. This doesn't appear to happen in the petrol tank 
Or... is the sender unit so well sealed that petrol never seeps through the gaskets and seals into the slider?
Or... is the sender unit so well sealed that petrol never seeps through the gaskets and seals into the slider? Astra Dan said:
RichB said:
Not talking about fuel pumps, fuel gauge sender unit was the point of my random thinking.
I know, but it's exactly the same principle. I just realised I only typed half of what I meant to! Never mind me...RichB said:
ShayneJ said:
...if you look closely at the wiper track interface its relatively wide so you
have a broad point of contact thus low resistance so no arc or heating...
Right okay but do they sit in petrol? And if so that suggests petrol is non conductive because if it was in a tank of water it would all short out. have a broad point of contact thus low resistance so no arc or heating...
I love Pistonheads forums, my wife's gone out to a Xmas dinner so I've watched Wheeler Dealers 9with a glass of red) and come up with a stupid question to which I now have the answer. Thanks! Mind you I still think it seems counter intuitive to me that something that looks like water doesn't conduct electricity 
RichB said:
I love Pistonheads forums, my wife's gone out to a Xmas dinner so I've watched Wheeler Dealers 9with a glass of red) and come up with a stupid question to which I now have the answer. Thanks! Mind you I still think it seems counter intuitive to me that something that looks like water doesn't conduct electricity
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