To avoid cavitation, which inequality relates NPSH_available and NPSH_required according to the material?

• A. NPSH_available ≥ NPSH_required
• B. NPSH_available > NPSH_required
• C. NPSH_required > NPSH_available
• D. NPSH_available = 0

Answer: (B)

To avoid cavitation, the suction head available at the pump must be greater than the head required by the pump. NPSH_available is the actual pressure head the fluid has at the suction, determined by factors like fluid temperature, elevation, and losses in the suction line. NPSH_required is the minimum head the pump needs to prevent vaporization at the operating flow. If NPSH_available is less than NPSH_required, vapor bubbles form and cavitation can occur, harming performance and causing damage. If NPSH_available exceeds NPSH_required, the pump operates with a safe margin and cavitation is avoided; equality would be a limiting case (incipient cavitation) where any disturbance could trigger cavitation. Therefore, the condition to avoid cavitation is NPSH_available greater than NPSH_required.