Safety valve for diver's timepiece

A safety valve comprising a hollowed-out head provided with a skirt and a central core extended by a stem, a tube onto which the head is mounted, such tube being intended to be secured onto a timepiece case and including a bottom traversed by the stem and a helical return spring surrounding the core and the stem, means being operable to enable the head to occupy an "out" position or an "in" position, a first end of the spring bearing under the head and a second end onto a ring which in turn compresses a first packing arranged on said bottom, a second packing being arranged under the head in line with the tube in a manner such when the head is in the "in" position said second packing is pressed against the tube, the valve then being inoperative and totally sealed, and when the head is in the "out" position said first packing is able to rise up against the return force of the spring if the fluid pressure prevailing within the case is higher than that prevailing on the exterior so as to avoid excessive pressure capable of damaging the case.