I dismantled a fuel sensor from the petrol tank in my boat. To my surprise, the sensor made up of a roll of bare resistance wires in contact with a wiper arm. This sensor was exposed in the flammable environment, as the electrical flash will occur between the two contact points. It is very dangerous to install the sensor in such position. Do anyone have comment on this ? Thanks Regards
That depends on what petrol is.
If the fuel is diesel oil, it might possibly cause ignition. This is because its low vapor pressure forms an air fuel mixture above the liquid that is in the explosive mixture range.
If the fuel is for a spark ignited engine (called gasoline, in the U.S. Such highly volatile fuel produces so much vapor that little air remains in the tank to burn it. The vapor forms a non ignitable, over rich mixture. Many gasoline engine cars have electric fuel pumps in the tank (with carbon brushes and copper commutator bars) that run either submerged in gasoline, or dry, depending on how much fuel is in the tank. There is a risk of ignition only if the tank is not only low, but also dry, with just a little vapor remaining.
-- Regards, John Popelish
While at first glance this does look bad, this is the way almost all of the fuel gauges on cars work.
The obvious kicker is in the operation of the gauge itself. These use a thermocouple type of action that results in a very low current and voltage on the sensing wires you are looking at. Thus, due to the limited voltage and energy applied to the sensors there is no risk of a spark.
This is also why most gauges are very slow to respond to changes in the tank level.
Dave 22 Master Electrician and JOAT
"mowhoong" schreef in bericht news: snipped-for-privacy@e23g2000prf.googlegroups.com...
Even aircraft use this type of sensors. The voltages and currents are so low that there is no danger for sparks. Seem to remember a case where such a low power signal line short circuited with a high(er) voltage wire and blew the main fuel tank. Some program like "Aircrash investigation".
petrus bitbyter
Gasoline composition varies widely, and depending temperature the vapor concentration at "full vapor pressure for the temperature" is often in the explosive range.
As for diesel - this is usually not the case. Diesel produces less concentrated vapor than kerosene does, and the flash point of kerosene is above 100 degrees F (38 degrees C). However, this is something I would not like to bet my life on.
- Don Klipstein ( snipped-for-privacy@misty.com)
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