helium escape valve

[gan1hck]

Anyone know at what psi the HEV on a Sea-Dweller opens?

[Ed Rooney]

Sounds like a Subfiend question.

[Letsgodiving]

Interesting question and a tough one. Ironstark?

[tonelar]

and all this time I thought it was a 1 way valve... that pretty much allowed helium molecules (smaller than hydrogen or O2 for that matter) to escape at anything greater than an atmosphere.

Are you planning a sat dive for this coming weekend?

[chevycorvette]

it is like a blow off valve of a turbo.

i am sure u have no chance to use it. because if you dive over 1k meter, you should be the one that need the helium escape valve

[Jedi]

Um, doesn't it work like this:

- helium will accumulate inside the watch when under lots and lots of pressure
- the risk is that the helium will blow off the crystal when the watch is resurfacing, ie decompressing
- the valve allows the helium to escape when decompressing so that the crystal is not blown off

[SPACE-DWELLER]

I have read somewhere that the HEV released stored gas as soon as decompression begins, basically already when moving just 1 atmosphere up.

[Stratton]

I wonder what percentage of HEVs actually get used? Sometimes I think that most HEVs made in the last 40 years, or for how ever long they have been made, could have seized up through not being used, ever.

[Jedi]

Regular servicing should take care of that!

Lots of talk about servicing recently!

[gan1hck]

doesn';t have to be helium ...it'll open for any gas aslong as there is a pressure differential...like HIGH altitude situations...or the vacuum of space...

but at what pressure differential is my question.

[Letsgodiving]

Originally Posted by tonelar

and all this time I thought it was a 1 way valve... that pretty much allowed helium molecules (smaller than hydrogen or O2 for that matter) to escape at anything greater than an atmosphere.

Are you planning a sat dive for this coming weekend?

I'm not an engineer but I would think it would be difficult and maybe impossible to develop a mechanical one way valve within the tolerances that would be required to differentiate between molecules without and an actual opening under a certain amount of pressure.

I'm sure I'll never use the HEV but it is an interesting bit of trivia that I would like to know.

[petespendthrift]

The HEV is for divers who are breathing types of Hellium mix used to prevent Nitrogen or Oxygen narcosis. The mixes are either Trimix (Helium, Nitrogen, Oxygen) or Heliox (Helium and Oxygen). The deeper the diving operation the less Oxygen and Nitrogen used as the pressure causes too much to be absorbed into the blood stream. Between dives it is not practicle to decompress to surface pressure so divers will remain in a pressurised chamber breathing the same gas mixture. Over a period of days in a chamber Helium which has the smallest particles will permeate into the watch case (possibly with some other gases). When the operation is complete or a change in working depth is required and the divers slowly decompress (in the chamber), the HEV safely allows the pressure build up to release.

I have read that a 2.5 ATM differential is required to operate an SD HEV (but cannot veryify the accuracy of this). If it is the case then going from sea level at 1 ATM into a vacuum (such as space) at 0 ATM would not operate the HEV.

[simmonjam1]

Would you see the gas escaping? That would cool to see.

[Letsgodiving]

Originally Posted by simmonjam1

Would you see the gas escaping? That would cool to see.

Helium has no color, odor or taste.

[Mrdi]

I change the helium in my SD
every 3,000 hours.

[simmonjam1]

So it would vent out of the water? Not while you are coming up slowly? I'm not a diver; forgive my ignorance.

[wanasub]

Sorry, meant to respond specifically to "I change the helium every 3000 hours"....again, Ha!!

[CPCC]

So how do you know that your valve is malfunctioning?

[Leighton]

Originally Posted by cpcc

So how do you know that your valve is malfunctioning?

If your watch crystal blew off during decompression.

[robrtx]

Originally Posted by Leighton

If your watch crystal blew off during decompression.

A friend of mine who used to be a commercial diver had that happen to his Submariner on a 500' sat dive

[Andad]

The watch is not in the water when the valve operates.

[ErikAalto]

From what I understand, it is only of use if you are in an environment (e.g.; diving bell) where you would be breathing a mixture of air with helium. There is no need for it if you are simply going on a dive from the surface.

[BiG JeEzY]

Originally Posted by directioneng

The watch is not in the water when the valve operates.

Yes exactly, you operate the valve after you have surfaced from the dive to relieve the watch of some of the pressure build up. I never really heard about crystals popping out like that in a dive, kinda unusual for me.

[BigHat]

Originally Posted by Letsgodiving

Helium has no color, odor or taste.

Maybe someone that actually knows about this could post something. For some reason, I thought dive watches were filled with helium. I doubt that's likely. So why a "helium" relief valve. Does the helium content in air act differently under pressure than nitrogen, oxygen or any of the trace elements in air?

Do you operate the valve or does it operate on it's own? How do you know that you need to do it? Do you just vent after each dive?

On a side note, have any of you seen the dive watches filled with liquid (incompressible) to avoid this problem?

[666 Bandit]

The valve contains a membrane that alows small molecules the size of helium to escape. It is not a valve that is preset at a specific pressure so there is no adjustment or moving parts for that matter. Hope this helps explain.

[gan1hck]

It would appear that a number of folks here have some misconceptions about the HEV.

For dives where you go into the water (no matter how deep) and then re-surface....the HEV does nothing.


The HEV only becomes necessary when a diver does "saturation" dives...meaning you go into the water (DEEP) and rather than coming back to the surface, you go into a HYPERBARIC chamber where the air pressure is EQUAL to the water pressure that you are diving in.....so no decompressing to get "dry".

Now because in hyperbaric environments both Nitrogen AND oxygen become toxic.. N2 becomes an anesthetic and O2 can actually cause seizures and pulmonary edema....the "saturation" diver breathes a mix of LOW percentage oxygen and HIGH concentration helium...to prevent the toxicities of normal air in a hyperbaric environment.

It is during these dives while the dive is "dry" in a hyperbaric chamber that dive watches can become saturated with helium....

Now during decompression...if you do it SLOW enough, you don't need a HEV...but because humans can tolerate a rate of decompression that is faster than helium can seep back out of a watch, you need the HEV to prevent the crystal from blowing off....

So back to my original question....at what pressure differential does the valve open.....I guess someone already answered 2.5 ATM....if that's the case, then watches with HEV should be able to tolerate the Vacuums of space ...one of the requirements for a NASA certified watch.

[gan1hck]

Originally Posted by 666 Bandit

The valve contains a membrane that alows small molecules the size of helium to escape. It is not a valve that is preset at a specific pressure so there is no adjustment or moving parts for that matter. Hope this helps explain.

that's not correct... the valves are mechanical one way valves...as seen on the patents.

[steel4me]

Originally Posted by cpcc

So how do you know that your valve is malfunctioning?

if you are having trouble breathing!

[666 Bandit]

Where can I see these patents?

[simmonjam1]

Originally Posted by gan1hck

It would appear that a number of folks here have some misconceptions about the HEV.

For dives where you go into the water (no matter how deep) and then re-surface....the HEV does nothing.


The HEV only becomes necessary when a diver does "saturation" dives...meaning you go into the water (DEEP) and rather than coming back to the surface, you go into a HYPERBARIC chamber where the air pressure is EQUAL to the water pressure that you are diving in.....so no decompressing to get "dry".

Now because in hyperbaric environments both Nitrogen AND oxygen become toxic.. N2 becomes an anesthetic and O2 can actually cause seizures and pulmonary edema....the "saturation" diver breathes a mix of LOW percentage oxygen and HIGH concentration helium...to prevent the toxicities of normal air in a hyperbaric environment.

It is during these dives while the dive is "dry" in a hyperbaric chamber that dive watches can become saturated with helium....

Now during decompression...if you do it SLOW enough, you don't need a HEV...but because humans can tolerate a rate of decompression that is faster than helium can seep back out of a watch, you need the HEV to prevent the crystal from blowing off....

So back to my original question....at what pressure differential does the valve open.....I guess someone already answered 2.5 ATM....if that's the case, then watches with HEV should be able to tolerate the Vacuums of space ...one of the requirements for a NASA certified watch.

Thanks for the explanation.

Safe to say the average Joe diver wouldn't need the use of the HEV?

Interesting none the less!