Abstract: An improved device for shifting the seats of a top entry ball valve, consisting of two identical portions, one for each valve seat, which are permanently interposed between the valve body and the relative seats; each portion comprises a stop ring made rigid with the valve body by first locking means, and a seat shifting second ring cooperating with a valve seat and movable axially by operating means into a withdrawn position to enable said valving element to be extracted or into an active position in which it is locked in position by second locking means. Preferred embodiments of said means are also described.