Abstract: Rotatably engaged to the filter (4, 104) of a pressurized-steam container (5, 105) is a closing member (2, 102) provided at the upper part thereof with an operating cap (6, 108). Through 180.degree. rotations of the closing member (2, 102) the fluid communication between the container (5, 105) and the surrounding environment via a filling header (8, 109) having a supply opening (110) at the upper part thereof, is selectively opened and closed. The closing member (2, 102) is driven in rotation by means of a grip element (20, 117) that, upon command of a diaphragm (17, 113) submitted to the inner pressure of the container (105), is moved to an embedded condition in the presence of pressure in the container, thereby being inaccessible to the user.