A volumetric compressor comprising: a casing provided with a suction chamber and a delivery chamber, between which a pair of screw rotors is included; a pan containing oil, and a delivery adjustment unit equipped with a slide valve, cooperating with the rotors and with a fluid-operated actuator, in which it is possible to identify an active chamber with a sliding piston connected to the slide valve. The adjustment unit comprises a flow switching unit, that connects the active chamber of the actuator to the pan and to the suction chamber and comprises a static flow switch removably associated with a switching solenoid valve electrically connected to a control unit. The switching solenoid valve is suited to be associated, alternatively, with different static flow switches that make it possible to obtain deliveries of compressed fluid varying discretely or continuously, depending on the position of the slide valve with respect to the rotors.