Effects of Running Clearance of Semi-Open Impeller Pumps under Air Admitting Conditions

Abstract

The performance of pumps with semi-open impellers was tested under air admitting conditions and the effects of running clearance between the impeller vanes and the stationary casing were discussed. The results were compared with those of closed-impeller pumps. when the clearance reduces, the pump ability under no air admission increases continuously, but the performance is much decreased by air admission. When the clearance relative to the channel depth of impellers λ is increased beyond 0.1, the drop of pump head due to air admission is much weakened, and it tends to a definite value, regardless of impeller shape. When two pumps with a closed-impeller and with a semi-open impeller show the same performance under no air admission, both pumps develop nearly the same performance under air admitting condition. The clearance range of λ=0.033∼0.086 is suitable for the duty of delivering air-water mixture.