Cavitation

Cavitation is the phenomenon of change in the vapor phase of liquid that is flowing, because the pressure is reduced to below the saturated vapor pressure. In part that is often experienced pump cavitation are suction side of the pump. This occurs when the pump suction pressure is too low to below the saturated vapor pressure, it can cause:

     Noise, vibration or damage to the pump components when the fluid bubbles burst when through areas of higher pressure
     Pump capacity is reduced
     Pump is not able to raise the head (pressure)
     The reduced efficiency of the pump.

In general, the occurrence of cavitation classified on the basis of 5 reasons:
1 Vaporisation - Evaporation.
Fluid vaporizes when the pressure becomes very low or the temperature becomes very high. Each requires a centrifugal pump head (pressure) on the suction side to prevent evaporation. The necessary pressure, prepared by the pump manufacturer and is calculated based on the assumption that the water being pumped is 'fresh water' at a temperature of 68 ºF. And this is called Net Positive Suction Head Available (NPSHA)
Because there is a reduction in pressure (head losses) on the suction side (because of the valve, elbow, reducer, etc.), then we have to calculate the total head at the suction side and Net Positive Suction commonly called Head is Required (NPSHR).
Well both affect the evaporation rate, so in order to prevent evaporation, the conditions are:
NPSHA - Vp ≥ NPSHR
Where Vp: Vapor pressure of fluid being pumped.
In other words to maintain that vaporization does not occur then we must do the following:
1 Adding Suction head, with:

     Increase the level of liquid in the tank.
     Elevating the tank.
     Pressure tank.
     Lowering the pump position (for portable pump).
     Reduce head losses in the suction piping system. For example, by reducing the number of fittings, cleaning striner, check tank venting probably closed) or increasing the pump speed.

2 Reduce the fluid of temperature, with:

     Cool the cooling fluid suction with
     Isolate the pump suction
     Prevent the temperature rise of the bypass system from the discharge pipe.

3 Reduce NPSHR, with:

     Use double suction. This bias NPSHR reduces about 25% and in some cases allow the addition of pump speed by 40%.
     Use pumps with lower speed.
     Use the pump impeller which has openings 'hole' (eye) bigger.
     Install Apoptosis, can reduce up to 50% NPSHR.
     Use a smaller pump. Using 3 small pump with a capacity of half the size, the count is cheaper than using large pumps and spare her. Anyway can save energy.