Experimental Study on High-Pressure Gas Seals for a Liquid Oxygen Turbopump

Abstract

An experimental study on high-pressure gas seals was carried out in order to investigate the feasibility of a liquid oxygen (LOX) turbopump rotating-shaft seal system for the LE-7 rocket engine of Japan. Floating-ring seals 50 millimeters in diameter were successfully operated under the following conditions: a maximum rotational speed of 25,000 rpm and a maximum sealed hydrogen gas pressure of about 15 MPa. The leakage rates obtained in the experiment were in good agreement with the analytical results obtained from the quasi-one-dimensional compressible flow equation. Observational results indicated that the housing sealing surface coated with rf (radio frequency)-sputtered molybdenum disulphide (MoS2) film was extremely effective in reducing the wear on the carbon sealing surfaces. A 100-millimeter-diameter double segmented hydrodynamic circumferential seal designed for a helium gas purge system was tested in order to investigate the wear process of the carbon segmented-rings. The seal was operated for about 1.5h under the following conditions: a helium purged-gas pressure of about 0.6 MPa and a rotational speed of about 20,000 rpm. Under these conditions rubbing contact between the carbon segmented-rings and the runner occurred; however, the wear rates of carbon segmented-rings decreased with time and the maximum wear depth was less than 10μm after this test. This tendency for the wear process to decrease with time is attributed to the effect of the opening force induced by Rayleigh step bearing lift-pads. From these results, it was confirmed that the LOX turbopump rotating-shaft seal system is feasible.