Cavitation is the source of many problems in pumping applications, but it takes experience and system knowledge to understand where to find it and how to solve it
18. Discharge-side cavitation, more formally
When the pump fails to produce
enough discharge pressure to overcome
the fluid already in place,
discharge-side cavitation results
27. Telltale symptoms of cavitation
Remember: Under the right conditions,
any pump can cavitate.
It can happen on the suction side
or on the discharge side.
This includes flooded-suction and submersible pumps!
28. A growling sound: Suction cavitation
Often like gravel or rocks banging around
29. A pinging sound: Discharge cavitation
Much like the sound of falling hail
45. Vapor pressure: Water versus gasoline
Vapor pressure for water at
sea level and 100°F:
0.95 psi, or about 2'
Vapor pressure for gasoline
at sea level and 100°F:
9 psi, or about 21'
46. Vapor pressure: Water versus gasoline
Higher vapor pressure under the same conditions
means gasoline wants to evaporate before water
48. Vapor pressure: Liquid water vs. boiling water
Vapor pressure at sea level,
70°F:
0.36 psi, or about 1'
Vapor pressure at sea level,
212°F:
14.67 psi, or about 34'
51. How much safety factor is enough?
The law:
Rules vary (though some
regulations require up to 6'
of safety factor)
The facts:
The deepest hurricane low
ever recorded in the Atlantic
basin was Hurricane Wilma
(2005), with a central low
pressure of 882 mb, or 29.55'
That departure is less than
4.5' below standard
atmospheric pressure (34') at
sea level
52. High vs. low elevations: Different calculations
Higher elevations mean less atmosphere above you
53. High vs. low elevations: Different calculations
Less atmosphere above means less available "push"
54. High vs. low elevations: Different calculations
Liquids boil at lower temps because vapor pressures at
lower temperatures overcome atmospheric pressure
61. Cavitation issues are really system NPSH issues
Atmospheric pressure available
minus vapor pressure
minus safety factor
minus total dynamic suction head
minus NPSH required by the pump
100. Temperature is rarely a factor
Very small differences in vapor pressure
between "cold" and "warm"
...but do keep it in mind if dealing
with boilers or HVAC
101. What's in the water gets in the pipes
Wastewater solids
Sewer gases
Entrained air
Mineral deposits
102. Pipe diameters matter exponentially (item 1)
Small constrictions can matter a great deal
over long distances
103. Pipe diameters matter exponentially (item 2)
4" ID pipe
12.56 in2
cross-section
3" ID pipe
7.07 in2
cross-section
25% reduction in diameter
44% reduction in cross-section
Thanks a lot, πr2
113. To recap
Cavitation is a hydraulic matter
It is systemic -- you have to address the system to fix it
Other issues cause similar problems and damage
The issues may overlap
Cavitation won't go away just by hoping
114. Remember!
Hydraulic problems can happen to any centrifugal pump
Submersible, flooded-suction, and suction lift alike
Hydraulic problems are system problems
Fix the system or the problem will remain
115. Thank you for your attention!
Contact us anytime with
questions
This presentation is linked
at gongol.net/presentations
for you to review and share
Brian Gongol
DJ Gongol & Associates
515-223-4144
www.gongol.net
info@djgongol.com
@djgongol on LinkedIn,
Facebook, and Twitter
116. References:
Gasoline vapor pressure data:
http://www2.epa.gov/gasoline-standards/gasoline-reid-vapor-pressure
Hurricane low pressure record:
https://www.aoml.noaa.gov/hrd-faq/#record-setters
Willis Tower Skydeck elevation:
http://theskydeck.com/for-kids/fun-facts/
Photos of corroded impeller was submitted to our office for
troubleshooting assistance; client to remain nameless out of courtesy
Photo of diver taken from the public domain:
https://www.loc.gov/resource/thc.5a48300/
All other photos are original work by and copyright reserved to Brian
Gongol