HEV working?

[lipjin]

Has anyone actually seen the HEV working before - I haven't see many pictures of it open.

Saturation divers pls share!

[padi56]

Originally Posted by lipjin

Has anyone actually seen the HEV working before - I haven't see many pictures of it open.

Saturation divers pls share!

If I remember the deepest recorded dive just on scuba gear was in the Red Sea a few years back.By a guy called Nuno Gomes total depth was just over 318m.Now it only took him about 20 minutes to reach that depth.But because of breathing different gasses at that depth and pressure, a little over 12 hours with all the safety stops to finally return to the surface safe, and without any decompression treatment.

Now at these extreme depths,there are several diving related problems to overcome nitrogen decompression sickness, oxygen toxicity,sheer dehydration and the different affects of the gases when changing over tanks containing the different gas mixtures.Now while breathing the high helium mix the gas wants to leave the blood while the nitrogen wants to rush in.Now this dive would have not been possible without a huge back up and very careful planning.

Gomes is in a very small group of guys that have gone over 250m with just scuba gear. Fact there have been more guys to go to the moon,that over 250m underwater just on scuba. But most recreational divers today stick to around 39m- 40m max depth.But when saturation diving thats what the SD DSSD was intended for, when divers have finished working in the water. They rest eat do everything and live in a dry pressurised chamber on, or some how connected to a diving support vessel, or say a oil rig.But at the same constant pressure as the main working pressure depth, the whole diving team would be only compressed to the working pressure once.And then decompressed to surface pressure again only once, over the entire work period, of days or weeks or even longer.

The HEV is just a one way valve fully automatic on the SD its only used for saturation divers who work underwater and reside at depth in dry chambers at the same outside water pressure.The gas they breath mainly now a high helium content the gas particles are that small they can pass thought the watch crystal seals etc.And when the divers are being re-compressed to normal atmosphere pressure, any gas thats in the watches escapes though the HEV valve, and movement would be that small I would doubt if it could even be noticed. This is because the gas in the case would expand with the rise to normal atmospheric pressure, and the weakest point the crystal would most probably explode.A normal scuba diver would have no need to use the HEV on any watch.Think of it this way take a balloon down to 10m under water. Thats 2 atmospheres one atm water pressure one atm surface air pressure.Now fill that balloon with air at that pressure of 2 atmospheres.Now because the compressed air is now under-pressure and quite dense. You can fill it but the amount of air breathing gas content would be twice as much as normal above water on the surface.Now release that balloon and let it go back to the surface because of the return to one atmosphere surface pressure balloon would expand and burst simply because there was twice as much air in it at surface atm pressure.
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[Passionata]

^great write up

[Garethmjones1]

Great explanation.

I've read elsewhere that all watches have a He escape valve, it's called the crown.

The automatic valve on Rolex watches just means the diver doesn't need to remember to do anything when decompressing.

[newsboy]

Great explanation thanks for taking the time

[bayerische]

I'm sure the HEV once it will release, will probably not be visible, as Padi says. There's very little space inside the watch, so even if it was pressurized to a very high pressure, say max depth rating on a Sea Dweller, the amount of air sipping out of the watch would be very low.

[accce]

Thanks!

[Tseg]

Interesting vid about helium diving:

http://wn.com/saturation_diving

[T. Ferguson]

Thanks for the explanation. One thing about the need for the HEV I'm unclear about is - if helium can seep into the case because of the small size of the helium atom, then why doesn't it just seep out just like it came in? I'm sure in my ignorance I've overlooked something.

Thanks, Padi.

[T01]

Interesting write up, thank you for sharing!

[Wesley Crusher]

Originally Posted by T. Ferguson

Thanks for the explanation. One thing about the need for the HEV I'm unclear about is - if helium can seep into the case because of the small size of the helium atom, then why doesn't it just seep out just like it came in? I'm sure in my ignorance I've overlooked something.

Thanks, Padi.

Keep in mind that I'm not a scientist so what I'm about to say is most likely BS, but wouldn't the helium atoms become very small under enormous amounts of pressure, but will enlarge as the pressure decreases? If a watch is deep enough that helium can enter the case, once the watch rises (and pressure decreases), wouldn't the helium expand (popping off the crystal or causing other problems?)?

[T. Ferguson]

Originally Posted by Wesley Crusher

Keep in mind that I'm not a scientist so what I'm about to say is most likely BS, but wouldn't the helium atoms become very small under enormous amounts of pressure, but will enlarge as the pressure decreases? If a watch is deep enough that helium can enter the case, once the watch rises (and pressure decreases), wouldn't the helium expand (popping off the crystal or causing other problems?)?

I'm no expert either, LOL, but I'm not sure the actual atoms of any gas or air actually get bigger as pressure goes up but rather they simply become more active and therefore take up more space. But I suppose it is possible that the pressure could build faster than the helium can leech out and that may cause the problem.

I don't know really, just something I've wondered about regarding the HEV. I'm sure there's a reason.

[bayerische]

A diver can take sudden drops in pressure, as long as the equalizing pressure is long enough, thus creating a drop on the pressure around the watch.

[dysondiver]

Originally Posted by T. Ferguson

Thanks for the explanation. One thing about the need for the HEV I'm unclear about is - if helium can seep into the case because of the small size of the helium atom, then why doesn't it just seep out just like it came in? I'm sure in my ignorance I've overlooked something.

Thanks, Padi.

hi it would ,,, given time ,, but thats the issue ,, its time , so as an increase in external pressure forces things together and seals tighter its ok , but if the pressure was greater inside as the diver rises up the water column , the pressure would be greater inside than out , do it slowly and the he would leach back out as suggested ,,, but do it quickly and the crystal would pop , as its design is to be waterproof from the higher pressure on the outside... so the he valve just unseats a minute fraction and the internal presure releases until its at the same pressure as the outside , more or less , allowing for hev spring tension ,,,,,
some pilots watches have crystals that are secured in incase of sudden cabin depressurization ,,

[Tseg]

Originally Posted by dysondiver

hi it would ,,, given time ,, but thats the issue ,, its time , so as an increase in external pressure forces things together and seals tighter its ok , but if the pressure was greater inside as the diver rises up the water column , the pressure would be greater inside than out , do it slowly and the he would leach back out as suggested ,,, but do it quickly and the crystal would pop , as its design is to be waterproof from the higher pressure on the outside... so the he valve just unseats a minute fraction and the internal presure releases until its at the same pressure as the outside , more or less , allowing for hev spring tension ,,,,,
some pilots watches have crystals that are secured in incase of sudden cabin depressurization ,,

This. Saturation divers stay in helium saturated environments for weeks at a time, allowing helium to slowly seep in. They do not decompress for weeks at a time.

[RollieVerde]

Padi's explanation is exactly correct. Now, for bonus points, you're on a plane at 40,000 ft MSL, and the pressurized cabin is at about 10,000 ft. Bang! There is a sudden, instantaneous decompression. The watch will in theory have more pressure in it than ambient, so would the HE valve purge this excess so the crystal doesn't pop off? BTW, I hope this never actually takes place to you or anybody you like.

[Andad]

I think my watch crystal popped off just as I died Billy.

[vman]

Originally Posted by RollieVerde

Padi's explanation is exactly correct. Now, for bonus points, you're on a plane at 40,000 ft MSL, and the pressurized cabin is at about 10,000 ft. Bang! There is a sudden, instantaneous decompression. The watch will in theory have more pressure in it than ambient, so would the HE valve purge this excess so the crystal doesn't pop off? BTW, I hope this never actually takes place to you or anybody you like.

I am not sure if it would work there... From what I understand the valve is designed to work with helium molecules which are quite small. However, how exactly would extra helium enter a watch in the scenario above? The gas mix you breathe in an airplane (air) is not the same as the gas you'd breathe in a saturation chamber.

[padi56]

Originally Posted by T. Ferguson

Thanks for the explanation. One thing about the need for the HEV I'm unclear about is - if helium can seep into the case because of the small size of the helium atom, then why doesn't it just seep out just like it came in? I'm sure in my ignorance I've overlooked something.

Thanks, Padi.

Read my explanation with the balloon.

[T. Ferguson]

Originally Posted by dysondiver

hi it would ,,, given time ,, but thats the issue ,, its time , so as an increase in external pressure forces things together and seals tighter its ok , but if the pressure was greater inside as the diver rises up the water column , the pressure would be greater inside than out , do it slowly and the he would leach back out as suggested ,,, but do it quickly and the crystal would pop , as its design is to be waterproof from the higher pressure on the outside... so the he valve just unseats a minute fraction and the internal presure releases until its at the same pressure as the outside , more or less , allowing for hev spring tension ,,,,,
some pilots watches have crystals that are secured in incase of sudden cabin depressurization ,,

Originally Posted by Tseg

This. Saturation divers stay in helium saturated environments for weeks at a time, allowing helium to slowly seep in. They do not decompress for weeks at a time.

Thanks guys.

Originally Posted by padi56

Read my explanation with the balloon.

I did. But unless the balloon is tied off I don't see how it would explode on its way to the surface. The air would just rush out the same place it went in, through the open end. A Rolex watch isn't sealed off air tight after helium gets in. But the above explanations helped clear it up for me. As the guys pointed out it could seep out the way it came in, but there isn't enough time.

[S52]

Originally Posted by RollieVerde

Padi's explanation is exactly correct. Now, for bonus points, you're on a plane at 40,000 ft MSL, and the pressurized cabin is at about 10,000 ft. Bang! There is a sudden, instantaneous decompression. The watch will in theory have more pressure in it than ambient, so would the HE valve purge this excess so the crystal doesn't pop off? BTW, I hope this never actually takes place to you or anybody you like.

I wore my 16710 in an altitude chamber ride during my Air Force training where we simulated a rapid decompression... from sea level to about 25,000 feet in a couple seconds... absolutely zero effect on my watch.

[The Joker]

Originally Posted by Garethmjones1

Great explanation.

I've read elsewhere that all watches have a He escape valve, it's called the crown.

The automatic valve on Rolex watches just means the diver doesn't need to remember to do anything when decompressing.

What I don't get is on the seamaster their HEV is a 2nd crown on the left side of the case, that you have to manually unwind. Why bother have this, why not just use the regular crown? Anyone?

At least with the Rolex it does it automatically in case you forget.

[padi56]

Originally Posted by T. Ferguson

Thanks guys.



I did. But unless the balloon is tied off I don't see how it would explode on its way to the surface. The air would just rush out the same place it went in, through the open end. A Rolex watch isn't sealed off air tight after helium gets in. But the above explanations helped clear it up for me. As the guys pointed out it could seep out the way it came in, but there isn't enough time.

Well of coarse the balloon would be tied to contain the gas otherwise it would not rise to the surface.But because you filled it under pressure say 2 atmospheres there would be twice the amount of air in it.So as it rises the gas in balloon would expand and burst the balloon.This is why a diver that has been breathing any gas under pressure say at 10m underwater or more.If he had to make a emergency ascend to surface say out of air he would have to exhale his lungs all the way to surface.Otherwise possible same thing would happen to his lungs as with the balloon.

[nGage7962]

Here is a picture of the HEV working... ;)

[Andad]

Originally Posted by T. Ferguson

Thanks guys.



I did. But unless the balloon is tied off I don't see how it would explode on its way to the surface. The air would just rush out the same place it went in, through the open end. A Rolex watch isn't sealed off air tight after helium gets in. But the above explanations helped clear it up for me. As the guys pointed out it could seep out the way it came in, but there isn't enough time.

[Andad]

Originally Posted by padi56

Well of coarse the balloon would be tied to contain the gas otherwise it would not rise to the surface.But because you filled it under pressure say 2 atmospheres there would be twice the amount of air in it.So as it rises the gas in balloon would expand and burst the balloon.This is why a diver that has been breathing any gas under pressure say at 10m underwater or more.If he had to make a emergency ascend to surface say out of air he would have to exhale his lungs all the way to surface.Otherwise possible same thing would happen to his lungs as with the balloon.

Having one of those days Pete?

[HogwldFLTR]

Diffusion is the key issue. A dive at depth and maintained at depth give a lot of time for He to infiltrate a watch. If the time down and up were equal then there would be no issue since the "He in" would equal the "He out." The real issue is the time spent at the bottom which generally isn't added to the ascent time. Hence the gas can't escape fast enough and the watch expands to compensate for the extra molecules.

[samsam]

Padi, this is the best and simplest explanation I've read about the topic. Thanks for sharing.

[lipjin]

Originally Posted by directioneng

I think my watch crystal popped off just as I died Billy.

Lol

Padi thanks for the detailed explanation.

[Tseg]

Originally Posted by padi56

Well of coarse the balloon would be tied to contain the gas otherwise it would not rise to the surface.But because you filled it under pressure say 2 atmospheres there would be twice the amount of air in it.So as it rises the gas in balloon would expand and burst the balloon.This is why a diver that has been breathing any gas under pressure say at 10m underwater or more.If he had to make a emergency ascend to surface say out of air he would have to exhale his lungs all the way to surface.Otherwise possible same thing would happen to his lungs as with the balloon.

Here is an honest question... they call it a Helium Escape Valve vs. a Decompression Valve. Why? Does the issue arise during any decompression or only in a helium saturation environment over extended periods of time?

Of course my Orient Saturation Diver luckily does not have to worry about any of this.