What condition will decrease the capacity of a centrifugal pump?

Insufficient suction head is a critical condition that can significantly decrease the capacity of a centrifugal pump. Suction head refers to the vertical distance between the surface of the liquid in the source (like a tank or reservoir) and the pump's impeller. If the suction head is not sufficient (often due to a low liquid level or obstruction), it affects the ability of the pump to draw fluid into the impeller effectively.

When insufficient suction head exists, it can lead to cavitation, a phenomenon where vapor bubbles form in the liquid and collapse violently, potentially damaging the impeller and other pump components. This cavitation reduces the overall flow and pressure output of the pump, thus diminishing its capacity to deliver the required volume of water.

Understanding this concept highlights the importance of maintaining an adequate supply and pressure of liquid at the pump's inlet to ensure optimal performance and efficiency.