A safety valve (300; 400a; 400b, 400c, 400d, 400e; 500; 600) adapted to be coupled to a tank of fluid to adjust a pressure in the tank, the safety valve comprising a coupling portion (370; 485d; 685) for fluidly coupling the valve with the tank of fluid, and at least one pressure relief valve portion (372; 572; 485d) adapted to reduce an over-pressure in the tank when the pressure in the tank equals or exceeds a maximum pressure value and/or at least one vacuum relief valve portion (375; 480; 685) adapted to allow in the tank a vacuum-compensating fluid when the pressure in the tank equals or falls below a minimum pressure value, characterized in that at least one among the connecting portion, the pressure relief valve portion and/or the vacuum relief valve portion comprises at least one valve body (100, 100', 100"), the valve body defining a cavity inside the valve body, the valve body comprising: a plurality of openings ( 110a, 110b, 110c, 110d) provided in the valve body to allow accessing the internal cavity of the valve body, at least two openings ( 110a, 110b, 110c, 110d) of said plurality of openings being provided on the valve body in such a way to lie on substantially parallel planes one with respect to the other, and a plurality of mechanical coupling portions ( 120a, 120b, 120c, 120d), each mechanical coupling portion being provided in correspondence of a respective one of said at least two openings of the valve body and adapted to couple with a corresponding coupling portion of a further valve body, each mechanical coupling portion comprising a respective border ( 120a, 120b, 120c, 120d) adapted to delimit a corresponding opening of said at least two openings, each border comprising a plurality of coupling elements for coupling with a corresponding plurality of coupling elements comprised in a corresponding border of the further valve body, wherein: -- the valve body has a box-like structure generally prism-shaped with a quadrangular base, and wherein said at least two openings include four openings provided on four of the six faces of the prism with a quadrangular base; further characterized in that - the valve body has a groin-vault structure comprising a first wall and a second wall each with a groin-vault structure, and each comprising four perimetric arcs, the first and second walls being connected together with each perimetric arc of the first wall that is coupled with a corresponding perimetric arc of the second wall defining an outer perimeter of a corresponding opening of said at least two openings. a plurality of openings ( 110a, 110b, 110c, 110d) provided in the valve body to allow accessing the internal cavity of the valve body, at least two openings ( 110a, 110b, 110c, 110d) of said plurality of openings being provided on the valve body in such a way to lie on substantially parallel planes one with respect to the other, and a plurality of mechanical coupling portions ( 120a, 120b, 120c, 120d), each mechanical coupling portion being provided in correspondence of a respective one of said at least two openings of the valve body and adapted to couple with a corresponding coupling portion of a further valve body, each mechanical coupling portion comprising a respective border ( 120a, 120b, 120c, 120d) adapted to delimit a corresponding opening of said at least two openings, each border comprising a plurality of coupling elements for coupling with a corresponding plurality of coupling elements comprised in a corresponding border of the further valve body, wherein: -- the valve body has a box-like structure generally prism-shaped with a quadrangular base, and wherein said at least two openings include four openings provided on four of the six faces of the prism with a quadrangular base; further characterized in that - the valve body has a groin-vault structure comprising a first wall and a second wall each with a groin-vault structure, and each comprising four perimetric arcs, the first and second walls being connected together with each perimetric arc of the first wall that is coupled with a corresponding perimetric arc of the second wall defining an outer perimeter of a corresponding opening of said at least two openings. -- the valve body has a box-like structure generally prism-shaped with a quadrangular base, and wherein said at least two openings include four openings provided on four of the six faces of the prism with a quadrangular base; further characterized in that - the valve body has a groin-vault structure comprising a first wall and a second wall each with a groin-vault structure, and each comprising four perimetric arcs, the first and second walls being connected together with each perimetric arc of the first wall that is coupled with a corresponding perimetric arc of the second wall defining an outer perimeter of a corresponding opening of said at least two openings.