Cavitation is the formation of vapor cavities in a liquid – i.e. small liquid-free zones (“bubbles” or “voids”) – that are the consequence of forces acting upon the liquid. It usually occurs when a liquid is subjected to rapid changes of pressure that cause the formation of cavities where the pressure is relatively low. When subjected to higher pressure, the voids implode and can generate an intense shockwave.
Cavitation is usually due to low pressure, when the water vaporizes (boils) and higher pressure implodes into vapor bubbles as they pass through the pump. It is primarily a situation in which the pump is discharging less liquid than its rated capacity due to a reduction or lack of liquid supply to the pump intake. Basically cavitation is caused by a pump trying to pump more fluid/water than is available to pump. A pinging sound can sometimes be heard when cavitation is occuring.
Cavitation in a distribution system booster pump station or in a high or low service pump may indicate a flow problem to the pump. This could be caused by a partially closed valve, an airlock or a stuck foot valve that is causing a reduced flow to the pump causing the pressure drop that causes cavitation/bubbles.
Why do we care about this? As these micro bubbles burst, they cause pitting to the volute, the impeller or to the piping causing a drop in efficiency, pressure and volume. What can we do? We can make sure that we are using the right size pump, and the net positive suction head is high enough to give the flow through the pump to not allow cavitation to occur.