Successfully reported this slideshow.
Your SlideShare is downloading. ×

Troubleshooting pump cavitation - v.19

Ad
Ad
Ad
Ad
Ad
Ad
Ad
Ad
Ad
Ad
Ad
Loading in …3
×

Check these out next

1 of 116 Ad

More Related Content

Similar to Troubleshooting pump cavitation - v.19 (20)

More from Brian Gongol (20)

Advertisement

Recently uploaded (20)

Troubleshooting pump cavitation - v.19

  1. 1. Troubleshooting Pump Cavitation Brian Gongol DJ Gongol & Associates, Inc. January 28, 2022 Iowa Water Well Association Altoona, Iowa
  2. 2. What is cavitation?
  3. 3. What is cavitation? The formation of vapor cavities due to a hydraulic imbalance in a kinetic fluid
  4. 4. Where all our trouble begins Pumps create low pressure and discharge to high pressure
  5. 5. Pumps rely on atmospheric pressure
  6. 6. Pumps don't really suck...
  7. 7. ...atmospheric pressure pushes
  8. 8. When there isn't enough "push"...
  9. 9. The liquid behaves like it's being pulled apart
  10. 10. Vapor cavities form
  11. 11. Then the cavities collapse
  12. 12. The collapse releases a blast of energy
  13. 13. Put more formally When atmospheric pressure is insufficient to supply the low-pressure zone created by a pump, suction-side cavitation results
  14. 14. The other half of the story ↑↓
  15. 15. If the pump is pushing...
  16. 16. ...but the resistance is too great...
  17. 17. ...then internal dynamics will cause cavitation
  18. 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
  19. 19. What does cavitation look like?
  20. 20. Suction-side cavitation illustrated [Let's see the video]
  21. 21. Discharge-side cavitation illustrated [Let's see the video]
  22. 22. Those vapor cavities only look harmless
  23. 23. Cavities form...
  24. 24. ...and then collapse...
  25. 25. ...releasing significant energy... Estimated in the tens of thousands of PSI
  26. 26. ...which creates cavitation wear or pitting
  27. 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. 28. A growling sound: Suction cavitation Often like gravel or rocks banging around
  29. 29. A pinging sound: Discharge cavitation Much like the sound of falling hail
  30. 30. Visible damage near the impeller eye: Suction
  31. 31. Visible damage on vane tips: Discharge
  32. 32. Gauges swing left: Suction [Watch the gauges in this video]
  33. 33. Gauges swing right: Discharge [Watch the gauges in this video]
  34. 34. Other symptoms of cavitation (possibly)
  35. 35. Broken shafts
  36. 36. Seal failure
  37. 37. Changes in performance
  38. 38. A deeper dive into the nature of cavitation
  39. 39. NPSH balance Positive Atmospheric pressure
  40. 40. NPSH balance Positive Atmospheric pressure Negative Vapor pressure
  41. 41. NPSH balance Positive Atmospheric pressure Negative Vapor pressure Safety factor
  42. 42. NPSH balance Positive Atmospheric pressure Negative Vapor pressure Safety factor Total dynamic suction head
  43. 43. NPSH balance Positive Atmospheric pressure Negative Vapor pressure Safety factor Total dynamic suction head NPSH required by pump
  44. 44. Vapor pressure: Water versus gasoline
  45. 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. 46. Vapor pressure: Water versus gasoline Higher vapor pressure under the same conditions means gasoline wants to evaporate before water
  47. 47. Vapor pressure: Liquid water vs. boiling water
  48. 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'
  49. 49. What's the safety factor for?
  50. 50. Atmospheric pressure changes with weather
  51. 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. 52. High vs. low elevations: Different calculations Higher elevations mean less atmosphere above you
  53. 53. High vs. low elevations: Different calculations Less atmosphere above means less available "push"
  54. 54. High vs. low elevations: Different calculations Liquids boil at lower temps because vapor pressures at lower temperatures overcome atmospheric pressure
  55. 55. Consider carbonation in pop in an airplane
  56. 56. Consider carbonation in pop in an airplane Lower atmospheric pressure means more bubbles
  57. 57. Deduct total dynamic suction head Static lift plus any friction losses through pipes, valves, strainers, etc.
  58. 58. TDSL even counts against submersibles...
  59. 59. ...and positive-suction applications
  60. 60. Also deduct the NPSHr for the pump
  61. 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
  62. 62. The conditions causing cavitation are specific...
  63. 63. ...so the damage is specific as well
  64. 64. Not corrosive damage
  65. 65. Not abrasion damage
  66. 66. But different types of damage can overlap
  67. 67. Some forms of damage can cause/accelerate others
  68. 68. Related but not identical conditions
  69. 69. Some overlap with symptoms of air problems
  70. 70. Vapor cavities are not the same as air
  71. 71. Vapor cavities are not the same as air Vapor is water after a phase change
  72. 72. Air entrainment and its problems
  73. 73. How does air get inside the system?
  74. 74. Cascading water entrains lots of air
  75. 75. Also look for vortex formation
  76. 76. Air also comes out of solution naturally Seasonal temperature changes can enhance the effect
  77. 77. Piping, valves, fittings, and gaskets can leak
  78. 78. How to diagnose air entrainment with gauges [Watch the gauges in this video]
  79. 79. A pump is not a fan Air entrainment is a problem because pumps are meant to move water, not air
  80. 80. Entrained air isn't system hydraulic imbalance It's still a serious problem, but it isn't hydraulic in origin
  81. 81. Other similar but non-air problems
  82. 82. Vibration or misalignment
  83. 83. Chemical attack
  84. 84. Abrasive wear
  85. 85. Accelerated corrosion
  86. 86. Where else can you find cavitation?
  87. 87. Valves
  88. 88. Piping
  89. 89. Constrictions
  90. 90. Inlets
  91. 91. Ways to fix cavitation
  92. 92. #1: Fix the system There is no substitute
  93. 93. Reduce losses in piping
  94. 94. Simplify piping Leave the spaghetti bowls at the Olive Garden
  95. 95. Correct valve problems 50% closure is rarely 50% flow
  96. 96. Adjust clearances and tolerances Tighten up!
  97. 97. Replace under-performing parts
  98. 98. Look for seemingly-innocent changes Who moved my VFD?
  99. 99. Consider what's flowing
  100. 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. 101. What's in the water gets in the pipes Wastewater solids Sewer gases Entrained air Mineral deposits
  102. 102. Pipe diameters matter exponentially (item 1) Small constrictions can matter a great deal over long distances
  103. 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
  104. 104. #2: Adapt to unresolved problems
  105. 105. Metallurgy: Use hardened parts
  106. 106. Counter-compensate with valves
  107. 107. Avoidance mechanisms Plot today's system head curve and tomorrow's system head curve
  108. 108. Avoidance mechanisms Consider the slope of a changing system head curve versus the slope of your pump performance curve
  109. 109. Steep pump curve / Flat system curve
  110. 110. Flat pump curve / Flat system curve
  111. 111. Flat pump curve / Steep system curve
  112. 112. Steep pump curve / Steep system curve
  113. 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. 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. 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. 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

×