How does closing the suction valve of a running centrifugal pump affect cavitation?

Closing the suction valve of a centrifugal pump while it’s running significantly increases the risk of cavitation. Here’s why:

For the mathematical relation of NPSH (available), you can refer to this link

• From the NPSH relation as mentioned in the above link, as the velocity of the fluid in the suction side of the pump increases, NPSH (available) reduces.
• When NPSH (available) become less than NPSH (required), pressure in the pump drops below the liquid’s vapour pressure.
• Cavitation Formation: When the pressure drops below the liquid’s vapour pressure, bubbles or cavities form in the low-pressure area – this is cavitation.

The following graph represents the pressure profile without cavitation.

The following graph represents the pressure profile with cavitation.

• Bubble Collapse: As the liquid moves through the impeller, these bubbles collapse violently when exposed to higher pressure zones.
• Pump Damage: The collapsing bubbles create shockwaves that can damage the impeller, housing, and other pump components.