REFLECTOR: Fuel venting and grounding

[Chuck]

Since everybody seems to have weighed in on this issue, I felt left out, so 
here's my view. Before I retired, I was a fire protection engineer, and part 
of that job was to ensure that the vacuum breaker (a low pressure spring 
loaded check valve) was regularly checked so that the plant's tanks would 
not implode (from negative pressure) from draining, if the normal vent was 
plugged.Thus, it made sense to have a vacuum breaker on the V fuel line vent 
system. It  is very important to have a very low cracking pressure on the 
vacuum breaker because most tanks can't take hardly any negative pressure. 
Since the only time this would open was if the main vent line was plugged 
(ice, mud daubers, etc), I felt it was okay to have it vent into the cabin 
since air would only be flowing into the valve. I could see of no scenario 
where fuel or vapor could flow out, and if you vented it to the outside of 
the plane, it could get plugged. My vacuum breaker is at the very top of the 
plane, so it should not be exposed to any liquid fuel.

I didn't separately "ground" my fuel caps or fuel ring, but I did connect a 
metal chain and triangle to the bottom of the metal fuel cap which touches 
the metal fuel fill ring when I open it. All my life I've believed that if 
the the potential (voltage) between 2 metal pieces is the same (aka 
grounded), their can't be a spark. Following this logic, I first connect the 
fuel truck grounding wire to the fuel cap which is 6" outside the plane 
before I put the fuel filler nozzle into the plane. Since the filler nozzle 
is connected to the fuel truck grounding wire, I don't see how there could 
be a spark. BTW this is the similar system that large plants use for fuel 
handling from trucks (although they actually are earth grounded, as well). I 
have investigated explosions where they forgot to attach the grounding wire 
and the fuel vapors ignited and exploded. With gasoline, you can expect that 
the vapors coming out of the fill hole are within the explosive range at all 
times. If the vapors ignite, you can blow the strake tank apart followed by 
a nasty fire, so remember to hook up your ground strap first away from the 
fill hole.

Let me know if I'm wrong on this.

Chuck H

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>
> Has anyone used coarse steel wool in the vent line
> that exits the bottom of the cabin to stop the dirt
> dobbers from pluging this line. I would think that
> coarse steel wool could be tamped tight enough not to
> move but loose enough not to plug the vent. I am
> working on my tanks at this time and am planing to try
> this on my vent line. Just a thought.
>
> Andy Ellzey
>
>
> --- reflector at velocityxl.com wrote:
>
>> Yea, the horse is definitiely dead on this one, and
>> folks have to do what
>> they're comfortable with, but a reliable vent is
>> vital.
>>
>> But the only way I can see vapor getting into the
>> cabin is on the ground.
>> If you're running the motor, fuel (mass) is draining
>> from the tank pretty
>> rapidly, and it has to be replaced or a vacuum will
>> be created (and the
>> tank crushed). So air is going to go INTO to tank,
>> vapor isn't going to
>> come out.
>>
>> Also, in my experience, check valves fail because
>> they're used 'normally
>> open', and the spring/closer gets worked. A check
>> valve that is always
>> closed has very little chance to accumulate gunk in
>> the seat, etc, though
>> you could do a double-check-valve installation which
>> is typical for
>> backflow preventers or get self-venting caps if you
>> were concerned.  Fuel
>> vapor in between the [LINK:
>> http://en.wikipedia.org/wiki/Explosive_limit]
>> lower and upper explosive limits is going to be
>> quite obvious to the nose,
>> and so would have plenty of time (IMHO) to make a
>> precautionary landing.
>>
>> B
>>
>> > -------Original Message-------
>> > From: Scott Derrick
>> > Subject: Re: REFLECTOR: Fuel venting issue
>> > Sent: 02 Jul '07 09:09
>> >
>> > I was thinking the same thing, of installing the
>> tee/valve and then
>> > running an auxiliary vent line to exit outside
>> somewhere else. Thus
>> > requiring both vent ports to be clogged before
>> there was a problem.
>> > Definitely not in the cabin, thats just asking for
>> trouble.
>> >
>> > The major failure mode of having the vent port
>> inside the cabin is
>> having
>> > the main vent plugged and the one way valve
>> failing open, thus providing
>> > fuel and fumes venting into the cabin. An
>> explosive situation, not to
>> > mention that fuel vapors are toxic to humans. I
>> just replaced a one way
>> > valve a few months ago because it was not sealing
>> anymore and flowed
>> both
>> > ways. It happens. And these one way valves do
>> seep, they are not a 100%
>> > one way.
>> >
>> > You would never ever see this design in a type
>> certified aircraft. Not
>> > that that is a prerequisite since nobody
>> manufactures a plane as good as
>> > the Velocity.
>> >
>> > I'm sure there are rules (common sense?) about
>> having a fuel vent port
>> > inside the cabin. Though maybe I'm flogging a dead
>> horse on this issue?
>> >
>> > Scott