2007 年 2 巻 1 号 p. 130-138
Efficiency of a centrifugal pump is known to drop rapidly with a decrease of specific speed ns in the range of ns ≤ 100 [m,m3/min,min-1]. However, below ns = 60, the pump efficiency is not yet clear, and the spiral angle of a 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 efficiency 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.
