Cavitation in pumps and ...

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Cavitation in pumps and ...

  1. 1. CAVITATION IN PUMPSAND IMPORTANCE OFCALCULATINGNET POSITIVESUCTION HEAD INPREVENTING IT by: Siavosh Nasiri K
  2. 2.  Pressure drop on propeller vane Formation of vapor bubbles Implosion of bubbles Damaging the vanes Causing disorder in continuity Even stopping pump discharge
  3. 3. CavitationDamage to propeller vane due to Cavitation
  4. 4. Cavitation There is a corresponding pressure in liquid saturation in front of each temperature Evaporation due to decrease in pressure:
  5. 5. Cavitation Vapor bubbles flow with liquid to other points with higher pressure Collapse (implosion) of vapor bubbles Generating high-pressure pulses Erosion of pump vanes Dangerous and damaging to pumps in short period of time
  6. 6. Cavitation Major pump parts Cavitation and Implosion
  7. 7. CavitationImplosion of bubbles
  8. 8. CavitationPotential Cavitation Areas
  9. 9. Cavitation Symptoms:  1. Reduction of volumetric flow rate (Débit)  2. Decrease in efficiency (Rendement) of the pump  3. Vibration  4. A special discontinues noise: similar to sound of some bullets hitting a metal surface!
  10. 10. Cavitation
  11. 11. NPSH Total pressure of fluid in suction eye of pump compared to evaporation pressure of fluid in pumping temperature Unit:  SI:metre  Imperial: foot Types:  NPSHAV  NPSHreq
  12. 12. NPSH NPSHAV or NPSHA :actual pressure of the fluid in the suction eye of the pump NPSHreq: Minimum pressure needed in the suction eye of the pump in order to prevent cavitation (presented by Manufacturer)
  13. 13. NPSHPump Factory Head-Capacity Diagram
  14. 14. NPSH To reduce the NPSHreq:  pump with less circular velocity  more pumps or using a double-suction eyed pump  specially designed suction-eye propeller (only specific volumetric flow rates)
  15. 15. NPSH Ways to increase NPSHA:  putting suction source or total system under pressure to increase pump suction pressure  if fluid temp. is high, feed source should be on a higher position than pump and under pressure  low fluid velocity  reducing the losses in suction pipe
  16. 16. NPSH Maximum suction height (Zs max): maximum altitude that pump can be installed upper than free surface of the liquid if Zs max < pump altitude  Cavitation

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