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Prevention or Action measures to be taken
The dynamic process formation of bubbles inside the liquid, their growth and subsequent collapse is called cavitation.
The pump always need to have a sufficient amount of suction head present to prevent vaporization at lowest pressure point in the pump. So NPSH is important.
NPSH (Net positive suction head) is the total head at suction flange of the pump less than the vapor pressure converted to fluid column height of the liquid.
Cavitation can be avoided by increasing the NPSHa (Net positive suction head) available greater than the NPSH required.
NPSH available= Pressure head in suction reservoir + Static suction head + velocity Head at pump suction flange - friction head in suction line - vapor pressure of liquid at that temperature.
So as you see in the equation to increase the NPSHa you will have to
1-MAKE SURE THAT THE PUMP WORK IN ITS WORKING RANGE
1. NPSH Available should be greater than NPSH Required means available suction head must be greater than required suction head.
2. Proper priming of the pump should be done so that no air is left inside the casing.
3. Discharge of pump should be uninterrupted to prevent recirculation inside casing.
Pump cavitation is the formation of bubbles or cavities in the liquid, developed in areas of relatively low pressure around the eye of an impeller. As the bubbles/cavities travel to the discharge side of the pump, moving to a high pressure area, the cavities implode. The imploding or collapsing of these bubbles triggers intense shockwaves inside the pump, causing damage to the impeller, vibration, and excess noise.
base should be good bearings must be in good condition
A. NPSHa in the system (the available energy in the system), must be higher than the NPSHr of the pump (the pump’s minimum energy requirement).
B. If Caviation Due To Internal Circulation.
This condition cannot be corrected on pumps with an enclosed impeller.
by eliminating any loses or obstruction could be exist in the suction line
1.REDUCING MOTOR SPEED
2.INSTALL AN IMPELLER INDUCER
3.INCORPORATE A BOOSTER PUMP INTO YOUR PUMP SYSTEM
4.REDUCE THE TEMPERATURE OF THE PUMP