A self-balancing type axial-thrust balancing system referred to as “balance piston” was applied to the LE-7 LOX turbopump, the discharge pressure of which exceeds 30MPa. A research model turbopump showed that pressure distribution in the balancing chamber deviated greatly from the predicted distribution and that the axial clearance of the balancing-chamber inlet orifice became too small to maintain safety. Consequently, we attempted to determine the cause of these phenomena and to find methods of ensuring sufficient axial clearance of the inlet orifice. Two methods were attempted. In the first method, balancing holes directly connecting the balancing chamber and the main impeller inlet were made. In the second method, grooves were made on the casing wall facing the main impeller front shroud.
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