Tailcaps under pressure. Solution

Why do tailcaps get too hard under pressure? Is there anything we could to to avoid it?

Most of the people here won't dive with their lights. but pressure can be inside or outside the light. You can find that an overdischarge, or a failed battery have generated too much pressure inside the tube of the light, and it is very difficult to open it. The solution proposed here does work pretty well, but...

IMPORTANT!!!: If you ever need to open a flashlight that probably has pressure build up inside the battery tube don't forget to take as much precautions as possible. No flammes nearby (most of the times gas is hidrogen), clear all the way of the tailcap because it could be "shot" or projected with liquids, batteries...to anything or anybody, use protection gloves, safety googles. A safe environment.

Here is a drawing we made time ago. (it is in spanish, but translated)



Presión: Pressure.
Grasa: Grease.
Superficie de contacto: Contact/Friction surface.
Antigripaje: Antiseize

This is the way things happen. Pressure forces a movement that makes surfaces of the thread area to increase friction, as all the grease or oil is moved away (Red lines show the maximum friction area). When we are using an antiseize grease the micro balls of graphite or MoS2 are not moved away because they are solid, and they act as bearings, not allowing surfaces of the thread to get in contact.

So simply use your graphite pencil and your regular oil or silicone grease, and things will get easier.

Regards,

Javier López

BTW: I was not sure about what was the correct sub-forum to post this, but as this is an issue related to safety and flashlights I thought the general flashlight was the best one.

So the graphite particals help to fill the gap and stop the stiction.

Yes, that is.

Probably my technical explanations haven't been as precise as they should be because my english is not so precise either...so if anyone wants to help me to improve them, it would a good idea.

Regards,

Javier López

Javier, your english is fine as was your explanation. I never thought of adding graphite to my lights. I have a Maglite that could benefit from this. If people want to buy graphite powder, I recommend this brand Mr.Zip Extra Fine Graphite

If I may throw in my 2 cents on a subject I know enough about to be dangerous with but not enough to be expert on.

If the graphite is in contact with raw Al and there is saltwater present, I believe you have a situation for galvanic corrosion at a significant level. If your seal is exterior to this contact region and precludes the presence of saltwater then you are in much better shape to be certain.

It has been my experience with UW gear that the most effective switches are ones that do not alter the volume of air which is trapped and under pressure nor are they subject to this pressure, ideally.

The Gladius has an interesting tail cap design which leaves the switch "outside" of the pressure chamber and not subject to pressure differentials. Unfortunately, IMHO, the design also opens the door to corrosion and other mechanical issues with the switch indeed "outside" and exposed to the elements. It is cool though that the Gladius clicky switch will not be bothered by external or internal pressure in the battery chamber.

Well I ramble and go off topic. I agree that the solution for ease of rotation to a threaded mate of components which are under either a compression or tension load is to minimize the total surface friction present, between the threads. Not only do lubricants make a difference here but also the nature of the thread contact surface and its total area of contact. I believe pitch and shape of threads play a part here and I suspect the physics can get rather complicated.

Great idea! Also graphite is conductive too. When a light has been under pressure from a battery out-gassing I've always pushed in as I twist to relieve the pressure and thus allowing me to turn it easy. I'm sure there are times when the pressure could be too high though...