Is it safe ?

[mowhoong]

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

 

[John Popelish]

mowhoong wrote:

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

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

 

[petrus bitbyter]

"mowhoong" <mowhoong@hotmail.com> schreef in bericht
news:b17209bb-f107-4723-aeca-a52d33397d61@e23g2000prf.googlegroups.com...

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



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

 

[Dave22]

On Mar 12, 7:07 am, mowhoong <mowho...@hotmail.com> wrote:

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

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

 

[Don Klipstein]

In <INGdna9o-NaKaEranZ2dnUVZ_uqvnZ2d@comcast.com>, John Popelish wrote:

mowhoong wrote:
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

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.

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 (don@misty.com)