Proportional volumetric doser with improved dosing regulation

Proportional volumetric doser (10) comprising a motor (20), provided with an inlet conduit (24) of a main fluid and an outlet conduit (26), and a pump (30) adapted to supply an auxiliary fluid to the motor (20), which pump (30) comprises a tubular sleeve (80) inside which a cylinder (85) is housed in which a small doser piston (62) slides, mechanically connected to an output shaft of the motor (20), wherein an inner surface of the cylinder (85) and the small piston (62) partially define a dosing chamber (48) of an auxiliary fluid to be mixed in the motor (20) in a prefixed quantity with the main fluid, where said cylinder (85) has a threaded outer portion that meshes with a threaded portion of a ring nut (70) so that a rotation of the ring nut (70) causes an axial translation of the cylinder (85) and the volume variation of the dosing chamber (48), said proportional volumetric doser (10) being characterized in that the sleeve (80) comprises a locking system (100) configured to mechanically lock the cylinder (85) with respect to the tubular sleeve (80) by creating a shape constraint.