Abstract: An airvessel for molding articles comprises a tank, a highly elastic membrane formed as a valve element and fixed in the tank by flanges to a support plate to form an annular chamber which may be pressurized via an air supply conduit to deform the membrane towards a closure position in which the membrane falls upon a valve seat. An opening is established in the center of the membrane-support plate assembly to which is axially coupled an outlet conduit for release of residual air which is present in a diffuser positioned below the membrane and coupled to a mold box.