A method of calibration of a valve, wherein a mobile element, housed in a seat, defining an axis, and associated with a spring, carries a ball, arranged in abutment against a reference element, housed in the seat, said method using a calibration tool, provided with a motorised punch, mobile in use, along said axis, and provided with a point coaxial to the motorised punch, connected to a loading cell and provided with a front end which protrudes from an end of the punch, the method comprising the realization of a calibration cycle wherein the following steps are carried out: - achieving the movement of the motorised punch, which is arranged in abutment against the reference element, said reference element being axially moved and interference fit tightly in the seat; - achieving contact between the front end of the point and the ball and measuring a force F, said force F resulting from the elastic reaction of the spring, said spring starting to be compressed; - comparing the measured force F with an objective force F t and blocking the movement of the motorised punch when the measured force F is equal to an objective force F t; - storing, a position x t of the motorised punch, when the requirements of said comparison are met, said position x t being related to the objective force F t; said method being characterised in that it comprises the realization of a second control cycle of the calibration that has been carried out, wherein: - the motorised punch is arranged again in the stored position and a current calibration force F' applied on the point is detected; - the acceptability of said current calibration force F' is checked, wherein, if said current calibration force F' is considered acceptable, the method is ended; instead, if said current calibration force F' is not considered acceptable, a correct quota Δx' is calculated based on a force difference ΔF and based on the elastic constant k of the spring, said force difference ΔF being defined as the difference between the objective force F t and the current calibration force F'; - the motorised punch is moved so as to arrange it in a position related with the correct quota Δx' and detect the force value applied on the point in said position; and the calibration control cycle is repeated. - achieving the movement of the motorised punch, which is arranged in abutment against the reference element, said reference element being axially moved and interference fit tightly in the seat; - achieving contact between the front end of the point and the ball and measuring a force F, said force F resulting from the elastic reaction of the spring, said spring starting to be compressed; - comparing the measured force F with an objective force F t and blocking the movement of the motorised punch when the measured force F is equal to an objective force F t; - storing, a position x t of the motorised punch, when the requirements of said comparison are met, said position x t being related to the objective force F t; - the motorised punch is arranged again in the stored position and a current calibration force F' applied on the point is detected; - the acceptability of said current calibration force F' is checked, wherein, if said current calibration force F' is considered acceptable, the method is ended; instead, if said current calibration force F' is not considered acceptable, a correct quota Δx' is calculated based on a force difference ΔF and based on the elastic constant k of the spring, said force difference ΔF being defined as the difference between the objective force F t and the current calibration force F'; - the motorised punch is moved so as to arrange it in a position related with the correct quota Δx' and detect the force value applied on the point in said position; and the calibration control cycle is repeated.