Technical Glossary

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Corrosion Resistant Pump

Cavitation

Cavitation is the forming and subsequent collapse of bubbles in a liquid when water at normal temperature is pumped up more than 10m and the saturated vapor pressure falls below the static pressure. It's a phenomenon that occurs when the static pressure drops below the saturated vapor pressure, evaporates or condenses the liquid, thus creates bubbles. When these bubbles collapse, it creates a shockwave, noise and vibration and reduces the efficiency of the machinery, such as screws or pumps. The erosion of the machinery could cause the machinery to be destroyed during cavitation.
When the available NPSH is greater than the necessary NPSH, depending on the given conditions of pipe or pump installation, cavitation will not occur.

Available NPSH

There is a need for a higher static head pressure when the total pressure at the impellor suction is equivalent or higher than the saturated vapor pressure, cavitation in the pump will not occur. This available NPSH (Net Positive Suction Head) can be calculated as follows.

NPSHav=Ha-Hvp±Hs-hl

・Ha:working atmospheric pressure at suction surface (m)
・Hvp:Saturated vapor pressure at that water temperature (m)
・Hs:Suction Total Head (m) (when pumping in +, when pumping up - )
・hl:Suction loss from all piping

Dynamic Seal

In the case of a vertical Molded pump: when the pump is in operation, the centrifugal force at the back of the impellor blade pushes the liquid to the casing, forming a liquid membrane. This effect at the rear of the blade prevents leakage.

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