What is cavitation? 

The first step in understanding cavitation is realizing that the term simply refers to the formation of a cavity (sometimes referred to as a “bubble” or “void”) within a solid object or liquid body. 

However, what causes the formation and what is contained within the cavity is not always the same.  Cavitation may fall under one of two categories: vaporous or gaseous. 

Vaporous Cavitation

The introductory example of pump erosion damage is due to vaporous cavitation.  This occurs when the fluid pressure drops below the vapour pressure and allows local regions within the fluid to rupture.  As soon as the saturated vapour pressure is reached, a local phase change occurs causing many small bubbles (or “cavities”) to be instantaneously created, similar to boiling. 

To demonstrate this phenomenon, let’s explore the engine oil pump example in more detail.