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| Joined: | Thu Nov 3rd, 2005 |
| Location: | USA |
| Posts: | 1783 |
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The purpose and function of the helium relief valve is a common point of confusion. It has nothing to do with normal underwater diving. Helium does NOT seep into the watch while the watch is in water at any depth. At approximately 250 feet, air becomes toxic due to changes caused by the high pressures at such depths. Special types of ocean exploration vessels are used by those who do very deep sea research. In some of these, a highly helium-saturated atmosphere is used to avoid the air toxicity effect. The purpose of a helium release valve is for people who wear their watch inside the helium-saturated environment for an extended period.
Because helium is the smallest atom, it will seep through the watch's seals under the high air (not water) pressures in this environment. If the watch stays in this environment for an extended time, helium will continue to seep into the watch until the air pressure inside the watch (initially surface air pressure) equalizes to the air pressure in the environment. This becomes a problem when the vessel is brought back up and depressurized. The helium which seeped into the watch over a couple of days cannot seep out any faster. The excess pressure inside the watch needs a way to release faster than it seeped in. It is only in this situation that a watch needs a helium relief valve at all. If a relief valve was not on the watch, the excess pressure would likely escape by pushing the crystal out.
More info:
http://en.wikipedia.org/wiki/Helium_release_valve
http://home.xnet.com/~cmaddox/helium_diving.html