In Fuel Tank Electrics....

[WallerZ]

Hi all, this may seem simple but thought I'd envoke a discussion on it...

 

I have decided to re-use as much of the MX5 stuff as possible, specifically the fuel sender unit...however I have used an out of tank pump as the zero fuel tank. The MX5 sender unit also included an in-tank fuel pump which I've removed but still aim to use the float for the gauge.

 

But here is the problem: the sender unit came out of the tank (whole thing is all inside, which has an open back which exposes the electric terminals). I would have thought that this should be a sealed unit as it could cause a spark/ignition which in even a nearly empty fuel tank, is not going to go down to well at all.

 

In essence, inside the mx5 tank it was exposed, I'm not 100% sure on the tank design, but I don't see how this sender could have been sealed away from fumes/petrol. My question is (if you've followed this far) should I be worried that I may potentially be wiring up a kit bomb car or am I just making myself worry about something that is impossible to happen?

 

Thanks all for any help/ advice

[Grim]

There isn't enough oxygen for it to ignite, even if it did spark. The petrol fumes fill a large proportion of the 'air' space in the tank.

[WallerZ]

Are the fumes not an issue for igniting? Thought it would be more combustable than oxygen?

[agent_zed]

you need oxygen for it to burn. In an engine its in a ration of 15:1 air to fuel to burn correctly.

[Longboarder]

Petrol vapour in air must be present in a ratio of between 1.4% and 7.6% to burn. Its flashpoint is about 220C which almost any spark will achieve.

What keeps petrol tanks safe is the petrol vapour concentration is always too high to burn. This is why the electrics can happily spark away in the tank with no problem. It's also why it's dangerous to empty a fuel tank for welding without steam cleaning and filling it with a flow of carbon dioxide to flush the oxygen out. An empty tank is more dangerous than a full one.

 

Nigel

[Grim]

Thank you longboarder for the figures! Interesting that it's such a small range, and low amout.

[stevedohc2b]

I had the same with serria sender and fuel pump all in tank with exposed electronics all worked fine now removed in tank pump and fitted outside swirl potand pumps.

 

If the MX 5 has a swirl pot fitted with pump i would use it all so Keep It Simple

 

Stephen

[WallerZ]

Fantastic, cheers all. It's help settle my nerves on it for now. I'll probably forget all about it once my foot goes down

 

Cheers,

Zach