Cavitation

Cavitation is the formation and subsequent collapse or implosion of vapor bubbles in the pump. It occurs because the absolute pressure on the liquid falls below the liquid’s vapor pressure. If the vapor bubbles collapse with enough energy, they can remove from the internal casing wall and leave large indent marks on the casing wall.

When cavitation occurs in a pump, its efficiency is reduced. The effects of cavitation are noise and vibration. If the pump operates under cavitating conditions for enough time, the following can occur:

• Pitting marks on the impeller blades and on the internal volute casing wall of the pump.
• Premature bearing failure.
• Shaft breakage and other fatigue failures in the pump.
• Premature mechanical seal failure.
• Cavitation problems can be resolved either by increasing the external pressure on the fluid or decreasing its vapor pressure.
• The external pressure could be increased by:
• Increasing the pressure at the pump suction.
• Reducing friction losses at the entrance to the pump.
• Using a larger pump.

The vapor pressure of the fluid is decreased by:

• Lowering the temperature of the fluid.
• Changing to a fluid with a lower vapor pressure.

Cavitation leads to one or more of the following:

• Problems with pump packings.
• Problems with mechanical seals.
• Problems with alignment.
• Problems with the bearings.