Abstract: A one-way check valve for pressurized fluid is described which comprises the following elements: a cylindrical envelope (1) provided with a chamber (2) having a fluid inlet passage (3) at its base and a fluid outlet passage (4) at its top end, a mobile sphere (5) which moves inside the chamber (2), under the effect of the pressure exerted by the fluid, from a closed position to an open position or vice-versa, and a ring (6) firmly fixed to the base of the envelope (1) and serving as a seat for the mobile sphere (5) in the closed position, the upper part (7) of the ring (6) being shaped so as to present a spherical or conical contact surface (8), the upper part of the chamber (2) having stops (9) separated by passages (10) leading into the fluid outlet passage (4), the lower part of each of the stops (9) being shaped so as to present a spherical or conical contact surface (11), and the mobile sphere (5) being retained by the said stops (9) in the open position, and the envelope (1), the mobile sphere (5) and t