Pardon me, but I think that cavitation is much different than air flowing through the pump. Cavitation is actually the formation (and eventual collapse) of vapour cavities. The collapse is associated with very high water velocities that can be very damaging to the impeller or housing.
However, it occurs when the pressure in the liquid being pumped falls below its vapour pressure. This can happen several ways:
- if the suction lift is too great
- impellor speed is too fast
- liquid temperature is too high
To aviod cavitation the pressure in the suction line must be greater than the vapour pressure of the liquid (that's where the net positive suction head comes in). Now, I seriously doubt (though I have been wrong before

) that any of us have pumps capable of causing cavitation in our small systems.