Pressurized Dive Light

[Aquamaniac]

Pressurized Lighting Canister.

I just finished some trials with a lighting canister and thought I would pass on the data.
The cause of leaks in a canister are at the seal location and caused by the differential in pressure between the internal canister pressure and the outside environment.
For example: The internal pressure will always be about 0 PSI because the canister is sealed at sea level (theoretical). At a depth of 100ft the outside pressure would be about 43 PSI , so the differential is 43 PSI.
Therefore if the seal begins to leak at a differential of 43 PSI. The max depth of the canister is 100ft.
If the canister is pressurized at the surface to 43 PSI and taken to a depth of 100ft, the differential will be zero. If it is then taken to 200ft the differential will be 43 PSI.
So it can be assumed that by pressurizing the vessel to its maximum depth rating, the actual depth rating can be doubled.
The second advantage of this system is that a faulty seal can easily be detected by the presence of bubbles at the start of a dive.
On my system I actually fitted a small pressure gauge inside my canister (clear acrylic) so I could monitor the internal pressure. If I noted a drop in pressure, I knew I had a potential leak.
I fitted the canister with a standard tire inflator and a tank adapter. (Capped off of course).
This method will never be available commercially due to the regulation of commercial pressure vessels. But its easy to do, and may have some benefits.
I know that most canisters are rated well above most divers limits, but It certainly is a good insurance.

I did this exercise purely out of interest and not for economical gain or to attempt to improve on already well built lights.

Dave

 

[nickjb]

This could help with some designs but the main problem is that most (all) canisters are designed for negative pressure (pressure outside greater than inside). By pressurising the cannister you will be putting a completely different load onto the seals and fixings, especially the ones that hold it closed which currently take hardly any load and are often designed accordingly. You will also put pressure onto parts inside the canister. Most of these will probably take the pressure but some might not (A spare bulb defintely wont!)

An alternative might be to pressurise the cannister as you dive and vent it as you ascend so it stays equalised like a drysuit. A bit complicated though.

 

[sheck33]

when you seal a cannister light or any other light for that matter at sealevel the pressure inside will be 14.7 PSI and not 0 PSI.
Also i think the seal the o-ring makes on say a cannister light will be a better one if the pressure outside is larger then inside because the water pressure will press the lid firmly onto the o-ring. I think it is more important that the o-ring is not damaged and the o-ring groove is clean and not damaged. No need to have some complicated failure prone way of pressurizing a simple light. Keep it simpel

 

[Aquamaniac]

Nick.
Yes I agree. But firstly the reverse pressure will not do any harm, Secondly If a canister is rated at 300' and the seals are onlt half effective in the reverse ( most are better than that) you can still improve the rating (or increase insurance) by 150'.
Most canister seals are O ring, which work bi-directional. It is an issue as to how the ends are clamped or fitted, but 45-100 PSI is not a great deal of force on any good catch or thread arrangement.
Most cable gland seals are also very effective in the reverse direction, they use a long rubber compression sleeve that is not sensitive to neg/pos pressure. Switch boots can be a problem, but they are problem anywat and should be avoided, opting for reed type switches.
My Light is a modified Dive-rite (wreck2) And i can pressurize it to 100 PSI without a leak.

Sheck.....(big Sigh) Let me say it again.

"I did this exercise purely out of interest and not for economical gain or to attempt to improve on already well built lights."

 

[sheck33]

i take things too seriously sometimes:crazyeyes

do you have pictures of your light?

 

[Aquamaniac]

psia describes an absolute pressure per square inch that starts from a perfect vacuum. psia is influenced by weather and elevation. A good frame of reference is at sea level there is 14.7-psia

psi describes a relative pressure that starts from atmospheric pressure. Therefore if you are on a mountain and the pressure vessel gage reads 1000-psi and relocate the pressure vessel to sea level the gage will read 1000-psi. We can further say that at sea level there is 0-psi. Example, when purchasing a new gage the pressure gage reads zero.

We can now say psia is an absolute pressure reading, and psi is a relative pressure reading. In most cases, psi is used on pressure vessels.



I'd love to take some pics.....Anyone wanna give me a nice new nikkon Digital!!!

 

[jonnythan]

Aquamaniac once bubbled...
psi describes a relative pressure that starts from atmospheric pressure. Therefore if you are on a mountain and the pressure vessel gage reads 1000-psi and relocate the pressure vessel to sea level the gage will read 1000-psi.

Not quite.. if you're on a high mountain where the air pressure is, say, .5 atmospheres, when on the mountain the gauge reads 1000 psi. When you go down to sea level it'll say about 993 psi. psi is a general term.. psia is absolute, psig is psi guage (difference)

 

[Aquamaniac]

Yeah Yeah Yeah, man you guys can get pedantic. ( no doubt Ill get corrected on the spelling!!!)