If a centrifugal pump sounds like it has rocks in it, what does this indicate?

The sound of a centrifugal pump resembling rocks indicates cavitation. This occurs when the pressure in the pump drops below the vapor pressure of the liquid, causing vapor bubbles to form. When these bubbles move into areas of higher pressure, they collapse violently, creating shock waves. The resultant noise can be likened to rocks or gravel bouncing around within the pump. This condition not only leads to the unwanted noise but can also cause significant damage to internal components such as the impeller and volute over time.

In contrast, blockage in the intake generally results in different symptoms, such as a drop in flow rate or pressure but not a distinct gravel-like noise. A worn impeller may produce a different sound associated with reduced performance or inefficiency, while lack of lubrication would generally lead to a whining or grinding sound rather than a noise resembling rocks. Therefore, the characteristic sound effectively indicates that cavitation is occurring within the pump.