Abstract: A collapsible beam element is provided, including: (a) an elongated flexible structural member having a predetermined cross section; and (b) a hollow defined by the cross section of the flexible structural member, wherein the flexible structural member is collapsible so as to enable folding of the beam element from an open configuration into a packed configuration, and wherein the flexible structural member readopts the predetermined cross section when unfolding the beam element from a packed configuration into an open configuration. The beam element is preferably made of material having predetermined shape. The beam element may be used so as to construct any collapsible three dimensional construction. Amongst other possibilities, the beam element may be used as a stretcher beam or a ladder or bridge beam.

Abstract: Pressure control device, characterized in that it comprises, in combination with valve means having an open and a closed position and urged to said closed position by a pressure thrust, elastic means opposing the closure of said valve means by exerting thereon an elastic counterthrust opposed to said pressure thrust, said means being normally in a condition of normal strain or stress wherein it creates a first level of elastic counterthrust such as to be overcome by said pressure thrust when it exceeds a first predetermined level; and means for bringing said elastic means to at least another condition of strain or stress, wherein it creates a second level of elastic counterthrust such as to be overcome by said pressure thrust when it exceeds a second predetermined level.