In the development of the advanced Rankine space power system technology the rotating machinery is to run on potassium-lubricated bearings. The alternator rotor cavity is evacuated either by venting to space or through artificial means. This reduces rotor windage losses to an acceptable level from the standpoint of alternator efficiency and rotor cooling. The problem investigated was the dynamic seal between the pressurized liquid potassium in the bearing cavity and the vacuum in the alternator rotor cavity. No rubbing seals are permitted because of the high rubbing speeds and the design life in excess of three years. In such a seal there must be a liquid-vapor interface. The objective was to keep the leakage rate at this interface below 10 lb/yr. The experimental development of two dynamic seals meeting the leakage tolerance objective is described. Easily resolved was the problem of maintaining a significant pressure difference across the seal. In the first development the main accomplishment was to solve the problem associated with the breakdown of the liquid-vapor interface which resulted in “sputtering”, an intermittent leakage of liquid droplets. The main accomplishment of the second development was a significant reduction in power consumption by the seal.

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