The helium escape valve exists to solve a specific physical problem: helium atoms are so tiny that they penetrate through the seals of a watch even when it's perfectly waterproof. This happens during saturation diving, where professional divers breathe gas mixtures rich in helium — HeO2 or trimix — and live in hyperbaric chambers for days or weeks at a time. Under those conditions, helium accumulates slowly inside the case. The problem isn't the descent: it's the ascent. When external pressure drops, the trapped helium tries to expand. If it can't find a way out, it pushes from inside against the crystal and seals until they're damaged — in the worst cases, the crystal detaches cleanly.
The solution is a one-way valve integrated into the case, usually positioned at 9 o'clock or 10 o'clock on the left side. It works like a safety valve: when internal pressure exceeds external pressure beyond a set threshold, it opens and lets the gas out; then it closes again. There are two design variants. The manual valve requires intervention from the diver — you unscrew it a few turns before ascending to open the passage, then screw it back in. The automatic valve, adopted by Rolex on the Sea-Dweller since 1967 and later by other manufacturers, handles the process without external intervention. Rolex developed the automatic solution working with Doxa; the exact attribution is still debated among industry historians, and I prefer not to assign it with certainty to just one of the two brands.
During the seventies and eighties, the valve was considered the distinctive marker of a true professional dive watch. Today the situation is more nuanced. Omega removed the valve from the fourth generation Planet Ocean while maintaining 600 meters of water resistance: modern manufacturing processes and new-generation seals significantly reduce helium penetration. Some brands still mount decorative valves — meaning components that mimic the appearance but don't perform the function — and this is something I always verify when a used watch arrives for professional use.
For a watch intended exclusively for sport diving, even extreme diving, the helium escape valve isn't necessary. It only serves those who work in saturation or hyperbaric chambers. Those who see it as an essential requirement on any dive watch are confusing professional use with recreational use.