Described herein is an inflation/deflation device of the type comprising a portion provided with an intake orifice for taking in a gaseous fluid under pressure, and a portion provided firstly with an inflation/deflation orifice designed to communicate with the confinement capacity, and secondly with a discharge orifice opening out between the two portions; and a valve member control system for inflation/deflation operations per se. In accordance with the invention, one of the portions is provided with arrangements for receiving a washer, which arrangements are suitable for allowing said washer to deform elastically, under the effect of a pressure of a gaseous fluid discharging through the discharge orifice, so as to release face-on bearing by an annular protuberance provided on the other portion, and so as to generate a fluid discharge passage between said annular protuberance and said washer.