The stability characteristics of the porous disk thrust bearing was studied experimentally and compared with a theoretical prediction [3]2. The discrepancy between them was found to be small in the low supply pressure region and large in the high supply pressure region. At instability the pressure in the plenum was found to oscillate in response to the oscillation of the upper thrust plate. Thus the plenum volume emerged as an important factor affecting stability. This finding, which appears to be the first ever reported, led to a preliminary theoretical investigation of the plenum volume effect. A satisfactory explanation of the observed stability characteristics was obtained by using a circuit analogy. In addition to the porous disk bearing, two other types of thrust bearings, viz, the plain disk with a porous insert and the plain disk with a recess and orifice restriction, were also included in the experimental study. The three types of bearings were compared with reference to their stability. Within the same range of the gas flow rate, the porous insert bearing displayed an equal or larger region of stable operation in comparison with the orifice bearing. Besides, the porous insert bearing exhibited a feature which could simplify its construction and make its application very attractive.

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