Dynamic Instability of Undamped Bellows Face Seals in Cryogenic Liquid

The primary motions of an undamped bellows face seal are described along with the displacements and frequencies of the motions experienced during dynamic instability. Subminiature accelerometers were attached to the nosepiece of a 1 34-inch nominal shaft diameter bellows seal and the accelerations and frequencies recorded on magnetic tape for analysis at an expanded time factor. The results of the tests indicated that dynamic instability will occur in undamped bellows face seals operating in a cryogenic environment and be of such a magnitude as to damage the sealing surface causing excessive leakage. Variations in the pressure difference across the seal and in the contact load between the seal nosepiece and the mating surface did not change the characteristics of the dynamic instability. The primary motions of dynamic instability are diametral rocking and torsional oscillation.