gioarmani 2 Posted January 7, 2010 The purpose of an HEV (Helium Escape Valve). Certain watches designed primarily for prolonged, deep sea diving (e.g., the Rolex Seadweller, Omega's Planet Ocean & Seamaster, etc.) come with HEVs, generally located on the left-hand side of the case, opposite the crown side. Air cannot be used for deep-sea dives, since nitrogen (the primary constituent of air) becomes toxic at a depth of 60 meters (aprox. 197 feet, below sea-level). Therefor, when carrying out work at great depths, professional deep-sea divers stay in a bell (above water) for several days, breathing a mixture of gases, containing a high proportion of helium (instead of nitrogen). The pressure is gradually increased inside the bell to equal the same pressure at the working depth below. The divers--still inside the bell--are then lowered into the water, and down to the working site. Only then are they safe to leave the bell & perform their work. Once their work is complete, they re-enter the bell, which is then raised back to the surface. After emergence, the pressure inside the bell is then lowered (returned back to atmospheric pressure) and it's during this stage that the HEV must be opened. This is the only proper time an HEV should ever be opened--only for deep-sea dives lasting for several days. Opening an HEV after regular swims and dives is essentially pointless, and does nothing for the watch. However, if your HEV valve is opened while you're in the water, you'll run the risk of flooding the movement with water, ruining the watch. Once opened, the helium molecules diffuse and then penetrate the material of the gaskets. If not released via the HEV, the quantity of internal pressure inside the watch--after prolonged deep-sea exposure--is sufficient enough to explode the crystal out of the watch during the de-pressurization of returning to atmospheric levels. To avoid this situation, this is why true, deep-sea divers watches are equipped with an HEV. Thusly, an HEV on a rep is primarily for decoration and serves no functional purpose (except on the rare occasion--and only ONCE deep-sea dive/compression tested--such as the new Rolex Sea Dweller 16600), as 99.9% of the population doesn't have the means or dreams of ever going that low. So, long story short, no need to ever open your watch's HEV; make sure the gasket inside is silicone greased and your HEV is securely screwed down before each swim. And don't swim in a watch, unless you've paid the $15 to have it pressure tested. Ciao. Share this post Link to post Share on other sites