1. CAVITATION IN PUMPS
AND IMPORTANCE OF
CALCULATING
NET POSITIVE
SUCTION HEAD IN
PREVENTING IT
by: Siavosh Nasiri K
2. Pressure drop on propeller vane
Formation of vapor bubbles
Implosion of bubbles
Damaging the vanes
Causing disorder in continuity
Even stopping pump discharge
4. Cavitation
There is a corresponding pressure in liquid
saturation in front of each temperature
Evaporation due to decrease in pressure:
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. Cavitation
Major pump parts Cavitation and Implosion
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!
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. 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)
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. 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. 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
