The dynamic behavior of a coned-face noncontacting seal is experimentally observed by means of three proximity probes monitoring the motion of the flexibly mounted stator. The various tilts of the stator are analyzed and the relative misalignment between stator and rotor is found. The effects of both the rotor runout and the flexible support on the relative misalignment are discussed. The tests demonstrate both stable and transition to unstable modes of seal operation. Reasons for failure and other phenomenon during stable seal operation are explained.Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in Hartford, Connecticut, October 18–20, 1983