Device for shifting the seats of a ball valve

A device for shifting the seats of a top entry ball valve comprising a valve body provided with an inlet duct, an outlet duct and an upper closure cap, the said inlet and outlet ducts being each provided with a seal carrier ring or valve seat, which are elastically pressed by series of springs against the spherical valving element, characterised by consisting of, inserted permanently into said valve body as an integral part of the valve, two identical portions, one for each valve seat, which are interposed between said valve body and the relative valve seats, each portion of the device being formed from a stop ring which, made rigid with the valve body by first locking means, acts as an external guide for the axial sealed sliding, via an O-ring, of a seat shifting second ring of said portion which, coaxial to and cooperating with the relative valve seat via at least one O-ring, is moved, together with said valve seat by friction, by a first operating means, into a withdrawn position to enable said valving element to be extracted and, by a second operating means, into an active position or a repositioning of the valve seat, said seat shifting second ring being maintained in said active position by second removable locking means.