Helium escape valve

A helium escape valve is a one-way valve on some professional dive watches that lets helium, which can build up inside the case during saturation diving, escape during decompression without damaging the crystal.

It matters to saturation divers and is otherwise a feature of interest to enthusiasts. On watches that have it, the valve is another seal that needs to be in good condition.

Check the valve is intact and correctly fitted, and include it in any pressure test.