Power Plant Guruji

  Boiler Feed Water Pump  Operation Questions  1.What do you mean by NPSHA & NPSHR in BFPs? NPSHA:  Net positive suction head available is the absolute pressure at the suction port of the pump. NPSHR:  Net positive suction head required is the minimum pressure required at the suction port of the pump to prevent the pump from cavitations. NPSHA should be always greater than NPSHR (NPSHA >    NPSHR) 2. How do cavitations occur? What are the abnormal effects of cavitations? Pump cavitation occurs when the pressure in the pump inlet drops below the vapour pressure of the liquid. Vapour bubbles form at the inlet of the pump and are moved to the discharge of the pump where they collapse and make high sound and vibrations often taking small pieces of the pump with them. Cavitation is often characterized by: Loud noise often described as a grinding or “marbles” in the pump. Loss of capacity (bubbles are now taking up space where liquid should be). Pitting damage to parts as material is