Abstract: An automatic device for the regeneration of a bed of ion-exchanging resins s constituted by a valve body internally provided with two communicating seats, in whose inside pistons which are caused to move by a couple of cams keyed on a motor-shaft slide. The valve body is provided with openings, alternately intercepted by the pistons, to realize different flows of the fluid. In running conditions, water passes through a tank containing a bed of ion-exchanging resins, whose regeneration takes place in counter-current with solutions of sodium salts. This operating stage and the following one of resin washing are carried out according to an automatic sequence by way of cams, which act on the piston.