Which statement defines Net Positive Suction Head (NPSH) and its role in pump operation?

Which statement defines Net Positive Suction Head (NPSH) and its role in pump operation?

• A. NPSH is defined as the sum of suction head and vapor head; it does not relate to cavitation.
• B. NPSH_available − NPSH_required; sufficient NPSH prevents cavitation; inadequate NPSH causes vapor formation.
• C. NPSH is the pump speed at suction.
• D. NPSH is unrelated to cavitation.

Answer: (B)

Net Positive Suction Head is the margin of pressure head available at the pump suction to keep the liquid from boiling as it is drawn into the pump. Cavitation happens when the pressure at the suction falls below the liquid’s vapor pressure, causing vapor bubbles that can damage the pump when they collapse. To avoid this, the suction must provide enough head to satisfy the pump’s needs at a given flow rate. That need is called NPSH_required, while the actual available head at suction is NPSH_available. The practical takeaway is the margin between them: NPSH_available minus NPSH_required. A positive margin means there’s enough head to prevent cavitation; a negative margin means vapor forms at suction and cavitation can occur.

Net Positive Suction Head is the margin of pressure head available at the pump suction to keep the liquid from boiling as it is drawn into the pump. Cavitation happens when the pressure at the suction falls below the liquid’s vapor pressure, causing vapor bubbles that can damage the pump when they collapse. To avoid this, the suction must provide enough head to satisfy the pump’s needs at a given flow rate. That need is called NPSH_required, while the actual available head at suction is NPSH_available. The practical takeaway is the margin between them: NPSH_available minus NPSH_required. A positive margin means there’s enough head to prevent cavitation; a negative margin means vapor forms at suction and cavitation can occur.