Helium Release?

[bikemonster]

Hi All

The Omega Seamaster Pro has a helium release valve.

Shamelessly pilfered from the Web:
"This OMEGA innovation is indispensable to divers who must spend several days in a diving-bell. A watch without a helium escape valve could explode from too much pressure inside the case when the diver returns to the surface. By unscrewing the crown positioned @ 10 o'clock, the pressure is released through the valve without water infiltrating the case. "

All very well and lovely, but the question that I have is this: How does helium get into the watch in the first place?

Is it that the guys in the diving bell are breathing a helium-rich atmosphere and the small size of the helium molecules allows them to sneak past the watch seal?

In which case, why does the watch not implode when first exposed to the pressure of the diving bell?

Anyone know?

James

[CommanderJameson]

Dunno. Will I need it when I get out of the bath?

[toohuge]

I think that it is more of a marketing thing. There are plenty of other dive watches that do not have such a device.

[Owain]

wiki said:

When commercial divers operate at great depths, they often spend prolonged hours in diving bells under pressure breathing a gas mix like trimix or similar, that contain the gas helium. Since helium molecules are the second smallest found in nature, the gas is able to work its way inside the watch, around any o-rings or other seals the watch may feature. This is not a problem as long as the divers stay under pressure, but when the decompression stops during resurfacing aren't long enough, a pressure difference builds up between the trapped helium inside the watch and the environment. Depending on the construction of the watch case and crystal, this effect can cause damage to the watch, like making the crystal pop off.

[jshell]

toohuge said:

I think that it is more of a marketing thing. There are plenty of other dive watches that do not have such a device.

It's not just marketing, even the Rolex Subs explode coming out of Saturation chambers, much to the annoyance of the Sat divers not having bought Sea Dwellers.....

No helium release valve is Ok for air diving, scuba etc..but certainly not for saturation.

[Frederick]

bikemonster said:

In which case, why does the watch not implode when first exposed to the pressure of the diving bell?

I dare say if you pressurised a diving bell from atmospheric to full submerged, bottom of the ocean type pressure, it would - but as the pressure change is gradual, the helium can work it's way into the watch more slowly.

Edited by Frederick on Sunday 24th May 23:09

[jshell]

Frederick said:

bikemonster said:

In which case, why does the watch not implode when first exposed to the pressure of the diving bell?

I dare say if you pressurised a diving bell from atmospheric to full submerged, bottom of the ocean type pressure, it would - but as the pressure change is gradual, the helium can work it's way into the watch more slowly.

Edited by Frederick on Sunday 24th May 23:09

Nah, the watch is rated to handle the external pressure so it doesn't matter how quickly external pressure is applied. However, the watch is not designed to handle an internal pressure differential of much and the helium valves vent at around 2-3 bar and do so very quickly - so speed of ascent or descent don't matter and are handled differently.

[ShadownINja]

I will remember this next time I surface from 1000m.

PS Why helium?

[MarkoTVR]

I'll hazard a guess that its smaller molecular size results in a lower pressure for the same volume, but the exact reason why you need that in deep sea excursions, I don't know. Perhaps it's more to do with the ascent, as opposed to the descent?

[jshell]

North Sea divers tend to live in a Helium rich environment (up to 96%) for up to 28 days at up to around 13bar. During that time the very small helium molecules can penetrate the watch seals (where water cannot) and raise the watch internal pressure to ambient (13 bar). Decompression takes a relatively shorter time, so the watch doesn't have time for the Helium to find it's way out past the seals so there is a potential for a 10+ bar overpressure of the watch at the end of the trip. The helium valve allows a quick depressurisation as ambient pressure drops.

[bikemonster]

So, thanks to the contributors to this thread, I now understand that the helium release valve is only necessary on watches which are used in a DRY submarine environment.

Seems to me that if a person were to be going to spend a great deal of time in a helium-rich, high ambient pressure environment, they would be better off with a completely non water resistant watch, which would allow pressures to equalise.

Or am I missing something?

[andy_s]

Slightly off there - they generally spend up to 28 days in sat, but this means they live in a chamber that is pressurised. When they dive they are already at the right pressure and when they've finished the dive they go back to the pressure chamber to eat and sleep until the next shift. They do it like this because if they worked at 130m for a few hours it would take them several more hours to decompress (let the gases saturated in their blood leech out rather than bubble out - that's the bends). Obviously compressing/decompressing every time a) isn't particularly good for you and b) takes a lot of time therefore inefficient.
So, the watch does need to be waterproof if you take it outside (i.e. diving). HTH.

[bikemonster]

Thanks andy_s.

Now it makes perfick sense. Well from a functional point of view.

It really does seem hugely gimmicky for just about every so-equipped watch sold though, doesn't it? Especially when most of those watches will never go deeper than the bottom of a swimming pool.

James

[rhinochopig]

ShadownINja said:

I will remember this next time I surface from 1000m.

PS Why helium?

Why helium? Sat diver use a heliox misture, where the Nitrogen of surface air is replaced by helium. The reason - Nitrogen becomes a narcotic under pressure - google raptures of the deep for more info.

[andy_s]

Most diving watches are over-engineered, I was an army diver in my youth and just used a Seiko chrono, 100m rating but not specifically a diving watch. My mate is in sat at the moment and has a Seiko diver that he doesn't wear outside the bell, he's got a team looking after him and his dive computers.
The great irony is that I am after a diving watch now but my forays will be no further than the bottom of the pool - I think part of the attraction is a) an appreciation of the engineering (like auto vs quartz) b) Over engineered is better than under-engineered if you do fancy a splash and c) they are evocative of a certain style, like military watches, pilot watches etc.

[Vipers]

jshell said:

North Sea divers tend to live in a Helium rich environment (up to 96%) for up to 28 days at up to around 13bar. During that time the very small helium molecules can penetrate the watch seals (where water cannot) and raise the watch internal pressure to ambient (13 bar). Decompression takes a relatively shorter time, so the watch doesn't have time for the Helium to find it's way out past the seals so there is a potential for a 10+ bar overpressure of the watch at the end of the trip. The helium valve allows a quick depressurisation as ambient pressure drops.

At last a sensible response. I couldn't work out the early Sub Mariners (Rolex), rated to 300 msw DIDNT HAVE A HELIUM RELIEF VALVE, and a diver at depths over 50 msw (Commercially) can only be in an Helium environment. Nice to see the latest Rolex is rated to something like 12,000 fsw, maybe no one has told Rolex how deep man can go.

Wika post is slightly incorrect, divers dont spend hours in diving bells, a bell run in UK is 8 hours seal to seal, but they do spend up to 28 days in a saturation chamber breathing an O2/He mix. Splitting hairs I know.

For those interested, 13 bars is 130 msw - 426 fsw in old money, and decompression is around 4.8 days.

Edited by Vipers on Monday 25th May 10:11

[andy_s]

Vipers said:

jshell said:

North Sea divers tend to live in a Helium rich environment ..................... The helium valve allows a quick depressurisation as ambient pressure drops.

At last a sensible response. I couldn't work out the early Sub Mariners (Rolex), rated to 300 msw DIDNT HAVE A HELIUM RELIEF VALVE, and a diver at depths over 50 msw (Commercially) can only be in an Helium environment. Nice to see the latest Rolex is rated to something like 12,000 fsw, maybe no one has told Rolex how deep man can go.

In technical sports diving you can go deep if you're breathing mixed gases and not just air. In sport diving you'd go and do the dive and decompress on the way up to the surface rather than live in a bell for 4 weeks. This means although you are breathing mix, the watch is just subjected to the ambient water pressure and not gas under pressure - if that makes sense?

For reference - here is the ISO for a divers watch, which features a few more things than just depth rating. Annex A is for gas saturated watches and there is no mention of needing an escape valve, just that the watch should be able to survive the under pressure.

[Vipers]

andy_s said:

In technical sports diving you can go deep if you're breathing mixed gases and not just air. In sport diving you'd go and do the dive and decompress on the way up to the surface rather than live in a bell for 4 weeks. This means although you are breathing mix, the watch is just subjected to the ambient water pressure and not gas under pressure - if that makes sense?

Yes of course Andy, that makes sense, saw some good footage recently on Sky, some fish scientiest swimming around 100 msw on various gas's looking for specises of fish, commercially we are governmed by UK legislation, and restricted to 50 msw max on air, and we have to use a diving bell below this depth. But I still don't know why Rolex bothered with their need for a super dooper watch rated to 3900 msw???? bit like making a road car which will do about 900 mph.

Edited by Vipers on Monday 25th May 11:16

[ShadownINja]

rhinochopig said:

ShadownINja said:

I will remember this next time I surface from 1000m.

PS Why helium?

Why helium? Sat diver use a heliox misture, where the Nitrogen of surface air is replaced by helium. The reason - Nitrogen becomes a narcotic under pressure - google raptures of the deep for more info.

Ah! Ta.

[Vipers]

bikemonster said:

Thanks andy_s.

Now it makes perfick sense. Well from a functional point of view.

It really does seem hugely gimmicky for just about every so-equipped watch sold though, doesn't it? Especially when most of those watches will never go deeper than the bottom of a swimming pool.

James

Some of us brought them coz we were offshore North Sea commercial divers, some buy them because they think they look cool. Also in the 80's there was only a couple of watches rated for deep diving, now days, divers buy Seiko for about £90.00 does everything, why on earth would you now pay over 2.5K for a Rolex Sea Dweller which only tells the time, and date, you even have to wind it on for a 30 day month.