A hydrodynamic retarder device for installation in a driveline to a vehicle, wherein the retarder device comprises: a blade-equipped stator which, together with a blade-equipped rotor, forms a blade system with a workspace for receipt of an aqueous working medium, and a retarder circuit connected to the workspace to control the inflow of a working medium to the workspace, wherein the retarder circuit is installed to be connected to the vehicle's ordinary cooling water circuit. The retarder circuit comprises valve elements to shut off the flow of working medium to the workspace, and a negative pressure generator is connected in the retarder circuit, which is installed to reduce the pressure in the workspace to or below the vapor pressure for the working medium, so that the workspace is thus evacuated of the liquid working medium. The invention also pertains to a method and a vehicle.