Compressor device that is at least provided with: - a screw compressor with a compression chamber that is formed by a compression housing, in which a pair of meshed compressor rotors (5,6) in the form of a screw are rotatably mounted; - a drive motor that is provided with a motor chamber formed by a motor housing, in which a motor shaft is rotatably mounted that drives at least one of the aforementioned two compressor rotors (5,6); - an inlet to the screw compressor for the supply of air; - an outlet from the screw compressor for the discharge of compressed air, and which is connected to a pressure vessel via an outlet pipe; - an air outlet on the pressure vessel for the supply of compressed air from the pressure vessel to a consumer; whereby - the compression housing and the motor housing are connected directly to one another to form a compressor housing, whereby the motor chamber and the compression chamber are not sealed off from one another and whereby the outlet pipe between the pressure vessel and the screw compressor is free of closing means in order to enable a flow through the outlet pipe in both directions; - the screw compressor is a vertical screw compressor, whereby the two compressor rotors (5, 6) have rotor shafts (8,9) that extend along a first axial direction (AA') and a second axial direction (BB') and the motor shaft extends along a third axial direction (CC') and whereby the aforementioned axial directions (AA', BB', CC') of the compressor rotors (5,6) and the motor shaft are vertical, the compression housing forms a base or bottom section of the compressor housing, and wherein the motor housing forms a head or top section of the compressor housing, - the screw compressor is provided with a fluid, with which both the drive motor and the compressor rotors (5,6) are cooled and lubricated, wherein a return circuit is provided for removing the fluid from the outlet in the base of the screw compressor, and for returning the removed fluid to the head of the compressor housing, wherein the aforementioned return circuit is connected to a cooling circuit for cooling both the drive motor and the screw compressor and through which the fluid can flow from the head of the compressor housing to the base of the compressor housing; wherein during the operation of the screw compressor, or when air is drawn off from the pressure vessel by a consumer in the outlet pipe, a mixture of air and the aforementioned fluid flows; wherein the fluid is an oil and wherein the pressure vessel is provided with an oil separator that, when the aforementioned mixture flows, separates the mixture into two flows, on the one hand a flow of compressed air via the air outlet of the pressure vessel and on the other hand a flow of oil via a separate oil outlet on the pressure vessel; wherein an oil return pipe is provided at the oil outlet of the pressure vessel, which is connected to the screw compressor for the reinjection of oil; characterised in that a part of the oil return pipe is constructed as a radiator that is cooled by means of a forced airflow of surrounding air originating from a fan, in that a bypass pipe is also provided in the oil return pipe that is affixed in parallel over the part of the oil return pipe with the radiator; and in that the compressor is further provided with a control system for controlling one or more liquid or gas flows in the compressor device; said control system being provided with: - an inlet valve on the inlet of the screw compressor; and - a tap or valve to close and open the air outlet of the pressure vessel; and whereby the inlet valve is a non-controlled or self-regulating valve embodied as a check valve. - a screw compressor with a compression chamber that is formed by a compression housing, in which a pair of meshed compressor rotors (5,6) in the form of a screw are rotatably mounted; - a drive motor that is provided with a motor chamber formed by a motor housing, in which a motor shaft is rotatably mounted that drives at least one of the aforementioned two compressor rotors (5,6); - an inlet to the screw compressor for the supply of air; - an outlet from the screw compressor for the discharge of compressed air, and which is connected to a pressure vessel via an outlet pipe; - an air outlet on the pressure vessel for the supply of compressed air from the pressure vessel to a consumer; - the compression housing and the motor housing are connected directly to one another to form a compressor housing, whereby the motor chamber and the compression chamber are not sealed off from one another and whereby the outlet pipe between the pressure vessel and the screw compressor is free of closing means in order to enable a flow through the outlet pipe in both directions; - the screw compressor is a vertical screw compressor, whereby the two compressor rotors (5, 6) have rotor shafts (8,9) that extend along a first axial direction (AA') and a second axial direction (BB') and the motor shaft extends along a third axial direction (CC') and whereby the aforementioned axial directions (AA', BB', CC') of the compressor rotors (5,6) and the motor shaft are vertical, the compression housing forms a base or bottom section of the compressor housing, and wherein the motor housing forms a head or top section of the compressor housing, - the screw compressor is provided with a fluid, with which both the drive motor and the compressor rotors (5,6) are cooled and lubricated, - an inlet valve on the inlet of the screw compressor; and - a tap or valve to close and open the air outlet of the pressure vessel; and