Helium Escape Valve

Definition

A one-way valve in the case of a saturation-diving watch that lets helium out. Divers who live in a pressurised habitat breathe a helium mix, and helium atoms are small enough to seep into a watch case over days; on decompression they expand faster than the case seals can release them and can blow the crystal off. The valve, developed by Rolex and Doxa in the 1960s, vents the gas safely. It is only needed by saturation divers, but it became a mark of a professional dive watch: the Omega Seamaster Diver 300M carries a manual one at 10 o'clock, the Planet Ocean the same, and the Rolex Sea-Dweller an automatic one at 9 o'clock. The Submariner, rated to 300 m, has none, because it was never a saturation watch.