A valve is provided to fill a chamber for holding a rotation shaft of a rotating anode in an X-ray tube. The valve has a needle supported on a seat. The needle maintains the vacuum in the tube. A sleeve can engage in the valve. The sleeve is hollow and has a cavity. This cavity can be connected to the vacuum or to a bottle under vacuum filled with a lubricant liquid. The sleeve is used to handle the needle. The sleeve furthermore bears on a rim of the valve by an O-ring joint. This joint maintains the vacuum when the needle is raised and when the tube under vacuum is connected to the cavity of the sleeve.