Performances of Very Low Specific Speed Centrifugal Pump with Circular Casing

Efficiency of a centrifugal pump is known to drop rapidly with a decrease of specific speed ns in the range of ns?100. However, below ns=60 [m, m3/min, min-1], the pump efficiency is not yet clear, and the spiral angle of volute casing becomes too small to manufacture. To solve this problem, a circular casing is considered appropriate in the very low ns range. The present study is aimed to reveal the relation between pump efficiecy and a specific speed in the range of ns?60, when a circular casing is used. The results show that a circular casing gives higher efficiency than a spiral casing, and that radial thrust is considerably small in both casings compared with that of ordinary specific speed pump.