The invention relates to a proportional volumetric doser (10) comprising a motor (20) to which a pump (30) is connected, 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 amount 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 variation of the volume of the dosing chamber (48), said proportional volumetric doser (30) 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.

The invention relates to a proportional volumetric doser (10) comprising a motor (20) to which a pump (30) is connected, 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 amount 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 variation of the volume of the dosing chamber (48), said proportional volumetric doser (30) 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.