Which statement relates to NPSH in pumping?

• A. Lack of Net Positive Suction Head relates to cavitation.
• B. Excess Net Positive Suction Head
• C. Ambient temperature
• D. Electrical resistance

Answer: (A)

Net Positive Suction Head is the pressure head available at the pump’s suction to keep the liquid from vaporizing. Cavitation happens when the local pressure in the suction area drops to or below the liquid’s vapor pressure, causing vapor bubbles that collapse and damage the impeller. The direct link is that if the available NPSH (NPSHa) is less than the pump’s required NPSH (NPSHr), cavitation occurs. So a lack of NPSH relates to cavitation. Having excess NPSH reduces cavitation risk but isn’t itself a problem; ambient temperature can affect vapor pressure and thus NPSH needs, but it isn’t the primary relation; electrical resistance isn’t related to NPSH.