Pressurized AAA Stuck Tight

Some time ago I read about a loud pop heard when someone opened their Arc. Forgot the details but it's likely that's what happened to my AAA last night. About an hour after using it for a few seconds I couldn't turn it back on. The head was jammed tight and I could not open it either. The threads and o-ring are kept lubed and it had operated without a problem for the past six months.

I resorted to using a small strap wrench and after a few turns a loud pop escaped. I'm guessing that I didn't unscrew the head enough rhat the light was on in my pocket and the AAA cell outgassed, putting pressure on the threads. The light was not on when I retrieved it from my pocket but was warm and the light wasn't at full brightness when I turned it back on.

Does that sound logical? Next time I'll try pushing the head and body together while unscrewing them.

There was a chemical reaction when your battery leaked. It created a vacuum inside the tube which explains the head being jammed tight. When you got the head out, it would normally pop just like a gerber bottle. You will notice an unusual smell and most likely came from the chemical reaction. Always check your battery for any leak.

Are you sure about a vacuum? I thought alkaline cells produced gas (out gassed). Isn't that why hazard rated flashlights have pressure valves? Maybe I've got it backwards.

When a battery produces gas which is most likely hydrogen, spontaneous combustion will occur with the trapped air in the battery tube. The combustion will induce vacuum (similar to a backdraft).

The above is true especially if you felt that the tube and/or battery is moist as water is a product of combustion.

Not to nitpick, but w/o a source of ignition, hydrogen (h2) gas does not spontaneously combust in air at standard temperature and pressure. I am not sure a regular alkaline cell will vent h2 gas anyway. But even if it did vent h2 and somehow combust with oxygen (o2) the result would not be a vacuum inside the flashlight.

I'm gonna nitpick. /ubbthreads/images/graemlins/grin.gif A perfect vacuum would result in a force of 2.5503 pounds. (14.7psia X .1735 sq in) My AAA head turns quite freely while pressing it towards the battery fith well over 2 1/2 pounds. /ubbthreads/images/graemlins/grin.gif

Larry

What are you trying to say? Was I unclear in my post? Don't think we're talking about a vacuum condition here.

If the head turns easier when pushed toward the body then there's pressre in that thar toob thing...no?

Turbodog,

I was seconding you by pointing out there is no way a vacuum could result in what jayflash experienced.

Larry

Ahhh.

Throw the light in the frezzer for awile to cool it down then try opening it again.

[ QUOTE ]
turbodog said:
Not to nitpick, but w/o a source of ignition, hydrogen (h2) gas does not spontaneously combust in air at standard temperature and pressure. I am not sure a regular alkaline cell will vent h2 gas anyway. But even if it did vent h2 and somehow combust with oxygen (o2) the result would not be a vacuum inside the flashlight.

[/ QUOTE ]

The battery contact is the source of ignition (may not be spontaneous as earlier indicated). Limited combustion is supported via the presence of trapped air (O2), gas (fuel) and the arcing of the contacts (source of ignition) during the rotation of the head. Since the tube is sealed and no air can no longer enter, combustion will create vacuum.

In the thread called Noooooooooooooo! can't open LE, started by (now) ARC's very own TrevorNasko (then called Aragorn) in August 2002 a similar problem was discussed.

Mind you his was caused by an attempt to change the battery at a depth of 9 feet in a swimming pool ...

o I wonder did he ever manage to get it open?
o I wonder does Peter allow him access to the ARC testing dept? /ubbthreads/images/graemlins/grin.gif /ubbthreads/images/graemlins/grin.gif /ubbthreads/images/graemlins/grin.gif

[ QUOTE ]
rajanf1 said:
[ QUOTE ]
turbodog said:
Not to nitpick, but w/o a source of ignition, hydrogen (h2) gas does not spontaneously combust in air at standard temperature and pressure. I am not sure a regular alkaline cell will vent h2 gas anyway. But even if it did vent h2 and somehow combust with oxygen (o2) the result would not be a vacuum inside the flashlight.

[/ QUOTE ]

The battery contact is the source of ignition (may not be spontaneous as earlier indicated). Limited combustion is supported via the presence of trapped air (O2), gas (fuel) and the arcing of the contacts (source of ignition) during the rotation of the head. Since the tube is sealed and no air can no longer enter, combustion will create vacuum.

[/ QUOTE ]

Ok... I forgot about the possibility of a spark when the contact to the battery is made or broken. However, at these prescribed conditions, there still can be no vacuum. Why? Take an arc aaa, put the battery in and close it. Basically, except for a theoretical SLIGHT increase from screwing the head in, internal pressure is the same as outside pressure. Assume the battery vents gas. Assume this gas is NOT flammable... we now have a pressurized condition inside the light. Ok, assume the gas is flammable and in the right concentration to combust. Combustion takes place, but after combustion we are still left with a pressure condition inside the light.

I will go along with one assumption, that there is more fuel present than oxygen. After combustion, there is no more free oxygen in the light body. However, there is a new gas present... the by product of the combustion.

The other way works also... if there is more oxygen than fuel. You have leftover oxygen, no fuel, and a pressure condition.

Look at the ideal gas law.

I stand by my statement that a vacuum would only produce a 2.5# axial loading of the threads, which would not impair being able to easily turn the head. A Q&D calc for the case volume minus the battery gives abt .034 In^3. Were an AAA to discharge 1 In^3 of gas into this volume, the internal pressure would rise to over 400psi! (Didn't bother using Barlow's to calculate approx burst on one. /ubbthreads/images/graemlins/grin.gif ) That would result in a 50-60# axial load on the threads and would probably result in it being difficult to turn the head.

I read the TrevorNasko post again, and what I can't understand is how he was able to reassemble it under water! It should have gone essentially solid when the O-ring engaged!

Since I don't know what alloy Peter is using, maybe he should hydrostatically test a few to failure just for chuckles. /ubbthreads/images/graemlins/grin.gif
(Edited to correctly spell alloy.)
Larry

I feel sure that in the water episode there was some trapped air in there as well.

td,

/ubbthreads/images/graemlins/grin.gif Had to have been! /ubbthreads/images/graemlins/grin.gif

Larry

Come on Trevor,

Tell the CPF community what happened to the LE. Please?

[ QUOTE ]
arab said:
Come on Trevor,

Tell the CPF community what happened to the LE. Please?

[/ QUOTE ]

Go on,

Surely you're not embarrassed ??? /ubbthreads/images/graemlins/blush.gif /ubbthreads/images/graemlins/blush.gif /ubbthreads/images/graemlins/blush.gif