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Leakage characteristics of the screw gas seal having a rectangular screw groove on a shaft were investigated by varying the peripheral velocity up to 250 m/s and by using room temperature air. The various effects of helix angle, groove width ratio, aspect ratio, number of threads, etc, were examined both in stationary and rotating states. As a result, it was found that the seal performance was optimized by using a dimensionless parameter, the ratio of the cross-sectional areas of screw groove to screw rotor. Thus, the seal performance was optimized when this parameter was nearly equal to 1 × 10-3 or when the cross-sectional area of screw groove became nearly 0.1% of the cross-sectional area of screw rotor. The effects of aspect ratio, helix angle, groove width ratio and number of threads on the seal performance appear to be relatively unimportant.

The leakage characteristics of the stepped type labyrinth gas seals were investigated both in stationary and rotating states by varying the thickness and position of the throttling fin. As a result, it was found that the leakage in the downward stepped type labyrinth seal was less than that in the upward stepped type. It was also found that, when compared with the conventional straight-through type labyrinth seal, the downward stepped type had a better sealing effect where the leakage rate decreased by about 70% in the stationary state and by 80% in the rotational state.