An Experimental Study of Static and Dynamic Characteristics for Annular Plain Seals with Porous Materials

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The static and dynamic characteristics are experimentally investigated for three types of damper seals with round-hole pattern and a plain seal with sintered metal bush. The damper seals consist of an inner perforated ring of 0.5mm thickness (SUS304) having about 3800 round holes of 0.4mm diameter at intervals of 2mm and a bush (SUS304) holding the ring. These holes lie in the axial plain, and are made perpendicularly to the inner surface (radial direction) for damper seal 1, from the 60 degrees direction to one for damper seal 2 and from the 30 degrees direction for damper seal 3. The other type of seal (porous seal) has the sintered metal bush which is inserted into the inlet part of the seal, and consequently, the seal surface consists of two different materials: solid (SUS304) and sintered metal (SUS304).The results of this test program support the following conclusions.A comparison of the damper seals and the ordinary solid annular plain seal shows that the damper seals take higher values of the friction loss coefficient lambda and the nominal inlet-pressure loss coefficient xi , and smaller leakage flow Q than the solid seal. The value of lambda becomes higher and Q smaller in order of the solid seal, damper seal 1, damper seal 2 and damper seal 3. Furthermore, the tangential fluid forces for damper seal 2 and3 are reduced, which facilitate the backward whirling motion and lead to a high stable operation at relatively high rotational speed as compared to that for the other seals.On the other hand, it is observed that the quantitative difference of performance characteristics between the porous seal and the solid seal is insignificant. This fact is ascribed to the reduction in the hydrostatic force induced by the sintered metal owing to higher clearance ratio.