| 摘要 |
PURPOSE:To prevent a pump from lowering its efficiency, by providing, in addition to a high output type impeller having a wide outlet port and a small diameter, a low output type impeller having a narrower outlet port and a larger diameter in order to carry out the impeller-cut upon adjusting of the pump head. CONSTITUTION:By limiting the use of a low output type impeller A in part, a high output type impeller B having a high efficiency is used in a substantial part. The shape of the impellers is determined such that, estimating that the ratio between the outlet port width W and the outer diameter is mu, the rate of the mu of the high output type impeller B to that of the low output type impeller A is set more than 1:1, and the number of stages in the low output type impeller A is set below 30% of the number of the all stages. Both low output type impeller A and high output type impeller B have the same specific point, and therefore, when the head upon manufacturing exceeds the specific point, the impeller-cut is carried out with the low output type impeller being alone controlled.
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