What can cause constant cavitation in pump?

there are more than one reason such

1 low level in tower/tank, (low head pressure

2 product interfere into the pump ;(different density, visco ets)

3 air interfere; pump not primed before start it up.

when NPSHr is higher than NPSHa

the couse of constant cavitation in pump is when  NET POSITIVE SUCTION HEAD REQUIRED (NPSHr) is higher than NET POSITIVE SUCTION HEAD AVAILABLE (NPSHa).

Setting pump at level higher than NPSH