An implantable device for the treatment of hydrocephalus syndrome, characterised by a mechanical passive valve device designed to move the cerebrospinal fluid in the cranial site of the patient, comprising a cylindrical body, a piston, and a special spring exhibiting a non-linear characteristic and suitable for applying a force on the piston such that, when the pressure of the cerebrospinal fluid acting on the two opposite faces of the piston exceeds a certain value, a rapid displacement of the piston in the cylindrical body takes place due to the non-linear characteristic of the spring, with consequent aspiration, by the same piston, of a greater quantity of cerebrospinal fluid contained in the ventricle and, when the pressure of the cerebrospinal fluid falls below a certain value, the piston reacts and moves rapidly in a direction opposite to the first, so as to feed into the ventricle the cerebrospinal liquid previously aspirated.
