ポンプキャビテーション現象の基礎知識第1回

Abstract

This paper presents basic information about the pump cavitation phenomenon. Firstly, the reason why the cavitation occurs is explained using the saturated vapor pressure curve of water. Water vaporizes vigorously when the water pressure drops to the saturated vapor pressure determined by its temperature. This is the principle of cavitation occurrence. In a fluid pipe line, water increases speed at a contraction section, lowering the static pressure at the same time. Then, when the pressure drops to the saturated vapor pressure, cavitation occurs. In the case of pumps, cavitation which occurs at the suction side of a blade because of the pressure drop is typical example. In addition, in transient phenomena, caused by sudden closing of a valve or pump trip, water column separation that is a kind of cavitation occurs. One of the problems caused by pump cavitation is pump head drop which makes non-attainment of a desired pressure. In relation to this, suction performance curve, NPSH required and NPSH available are explained in this paper.