Valves series 3030 are safety devices according to the definition given in Article 1, Point 2.1.3, 2nd dash of 97/23/EC Directive and are the subject of Article 3, Point 1.4 of aforesaid Directive. The valves above mentioned are standard type, unbalanced, direct-loaded safety valves. Valve opening is produced by the thrust the fluid under pressure exerts on the disc, when said thrust exceeds, under setting conditions, the opposing force of the spring acting on the disc