NPSHr is provided by the pump manufacturer for a given flow; it indicates the minimum suction head to avoid cavitation; ensure NPSHa > NPSHr.

• A. NPSHr is the head required by the pump to avoid cavitation and is provided by the manufacturer for a given flow; ensure NPSHa > NPSHr.
• B. NPSHr is the head loss in the suction line due to friction.
• C. NPSHr is the vapor pressure of the liquid.
• D. NPSHr is the pressure at the vapor bubble.

Answer: (A)

Cavitation in a pump happens when the pressure on the suction side drops low enough that the liquid’s vapor bubbles form. The two key terms are NPSHr and NPSHa: NPSHr is the head the pump itself requires on the suction side to avoid cavitation for a given flow, and it is provided by the pump manufacturer. To operate safely, the system must provide more suction head than the pump needs, so NPSHa (available suction head) should exceed NPSHr.

This is the best answer because it directly defines NPSHr as the pump’s required suction head and emphasizes the safety condition: available head must be greater than the required head. The other options describe related but different concepts. Head loss in the suction line refers to friction losses in the piping, which affect NPSHa but are not NPSHr itself. Vapor pressure is a property of the liquid that sets the cavitation threshold, and while it influences NPSHa, it is not NPSHr. The pressure at the vapor bubble describes the condition during cavitation but again is not the pump’s required suction head.