An inviolable cartridge (2) and cartridge holder (3; 3A) valve assembly (1) for liquid or gaseous fluid systems, in which assembly (1) the cartridge body (9) is provided with a cartridge bottom (23) defining an inner seat (20) for bearing thereon the bottom (19) of the cup sealing gasket (18) of the spring calibrating assembly (10) of the valve and an inner lug (27) which can be engaged in a seat (28) provided in the cartridge holder (3; 3A). The body (9) of the cartridge and the cartridge holder (3, 3A) being provided with quick coupling means (31) with a removable locking element (33).