subject: The Ten Pump Rules For Optimum Pump Performance - Part 1, Cavitation #1 [print this page] Pump cavitation is one of the most befuddling problems plant engineers can face. The literature on the subject can be quite technical, some of it misleading, and much of it offers limited practical guidance on how to get rid of the problem. Worse yet, there are different types of cavitation, and different definitions of "acceptable" suction conditions.
In any case, cavitation is fairly easy to define. It is basically the formation of vapor bubbles in the pumped fluid, with the vapor bubbles subsequently imploding as they are exposed to higher pressure as they pass through the pump. These implosions can create massive forces which result in mechanical damage to impellers, loss of efficiency, noise and vibration, and overall poor reliability.
In an effort to minimize cavitation, a logical place to start is by identifying what type of cavitation is occurring. We can break cavitation down into two basic categories: suction cavitation and recirculation cavitation.
Suction cavitation can be categorized into 4 general causes:
* Inadequate NPSHA
* Air entrainment
* Vortex formation
* Turbulence
Recirculation cavitation can be subdivided into 2 categories:
* Suction recirculation
* Discharge recirculation
Pump users generally suspect cavitation is a problem due to two factors: impeller damage and/or the classic "pumping gravel" sound when the pump is running. For most people, the sound will provide ambiguous information regarding the type of cavitation. Instead, impeller damage provides a much clearer picture of which type of cavitation is occurring.
Suction cavitation damage will appear on the visible side of the impeller vanes at the suction eye of the impeller:
Source: http://ow.ly/daVp5
Recirculation cavitation has two forms: discharge recirculation and suction recirculation. The damage from each appears at different places on the impeller.
Discharge recirculation cavitation damage will appear at the outside of the impeller vane tips:
Source: http://ow.ly/daWq0
Suction recirculation cavitation occurs on the non-visible side of the impeller vanes and is generally only visible by using a small mirror""like a dental mirror""to see the back side of the vanes. The diagram below shows the 3 locations where the different types of cavitation damage can occur:
