What is Net Positive Suction Head (NPSH) and its importance?

• A. NPSH is the pressure at the discharge; ensures flow.
• B. NPSH relates to ambient temperature.
• C. NPSH is the energy stored in the suction tank.
• D. NPSH is the suction energy available to the pump; adequate NPSH prevents cavitation and maintains flow.

Answer: (D)

Net Positive Suction Head describes the suction-side energy that is available to push liquid into the pump. It is the head (feet or meters of liquid) representing the energy in the liquid on the suction side, incorporating static suction head, velocity head, and suction losses, minus the liquid’s vapor pressure. The important idea is that the pump must have enough suction energy so the pressure at the impeller inlet stays above the liquid’s vapor pressure. When the available suction energy is insufficient, cavitation forms bubbles that collapse inside the pump, causing noise, reduced flow, efficiency loss, and possible damage. By ensuring adequate NPSH, the pump can draw liquid smoothly and maintain the desired flow. This concept is typically expressed by comparing NPSHA (actual suction energy available) to NPSHR (the amount the pump requires); keeping NPSHA above NPSHR prevents cavitation and preserves performance.