What is NPSH and why is it important?

NPSH (Net Positive Suction Head) is the absolute pressure head at the pump suction above vapor pressure. NPSHa (available) is provided by the system: NPSHa = P_atm/rho*g + h_static - h_friction - P_vapor/rho*g. NPSHr (required) is specified by the pump manufacturer. If NPSHa < NPSHr, cavitation occurs - vapor bubbles form and collapse causing noise, vibration, impeller damage, and loss of head. Adequate NPSH margin (typically NPSHa > NPSHr + 0.5-1m) is essential.