Cap with valve system provided with flow reducer

A fluid vent valve for a fuel tank, comprising:

• a valve body having an inlet opening connected or connectable to a tank, and an outlet opening, said valve body having at least one main chamber interposed between said inlet opening and said outlet opening;
• a piston inserted or insertable in said main chamber and movable inside said main chamber so as to define a closed configuration, wherein said piston occludes a passage between said inlet opening and said outlet opening, and an opening configuration wherein said inlet opening and said outlet opening are in fluid communication;
• a pendulum hinged to said valve body and coupled to said piston so as to promote a movement of said piston from said open configuration to said closed configuration and vice versa as a function of an orientation assumed by said pendulum, wherein said pendulum has a cam and wherein said piston comprises a lower portion hinged in said cam;
• and
• characterised in that it comprises a flow reducer operatively interposed between said outlet opening and said piston.