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If we're running two pumps, why aren't we getting twice as much flow?

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An introduction to parallel, series, and parallel-series pumping

(Version 16)

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If we're running two pumps, why aren't we getting twice as much flow?

  1. 1. IF WE'RE RUNNING TWO PUMPS, WHY AREN'T WE GETTING TWICE AS MUCH FLOW? Brian Gongol DJ Gongol & Associates, Inc. October 11, 2017 Iowa AWWA 102nd Annual Conference Council Bluffs, Iowa
  2. 2. Some system designs will never, ever change
  3. 3. Those are not our concern here (If that's you, this is your chance to sneak out the back)
  4. 4. What moves a system head curve?
  5. 5. Inflow and infiltration
  6. 6. Future flows due to new construction
  7. 7. Future flows due to new industry
  8. 8. Multiple pump systems on one force main
  9. 9. Force main restrictions: ARV failure
  10. 10. Force main restrictions: Clogs and sediment
  11. 11. Force main tuberculation (constriction by corrosion)
  12. 12. What moves a pump performance curve?
  13. 13. Wear
  14. 14. Transmission inefficiencies
  15. 15. How do you plan for future flows?
  16. 16. Or big gaps between average and peak wet weather flows?
  17. 17. Wide-range conditions demand wide performance
  18. 18. Easy way out: Oversize the pump system
  19. 19. But that's wasteful
  20. 20. More-elegant solutions are available
  21. 21. You already need a second pump, right?
  22. 22. It's mainly a backup in case of failure
  23. 23. Does running the second pump in parallel help?
  24. 24. Usually not
  25. 25. Ideally, parallel pumping doubles flow at same head
  26. 26. But the system imposes a constraint
  27. 27. Parallel pumping is best on a flat system head curve
  28. 28. Parallel pumping usually does very little good
  29. 29. Parallel pumping into a common force main Each pump handles 50% of the total flow and 100% of the total dynamic head
  30. 30. On a sufficiently steep system head curve...
  31. 31. ...parallel ops may be outside the performance range
  32. 32. Now, the other side of the coin
  33. 33. Series/staged pumping
  34. 34. Two pumps in series: Double head, same flow
  35. 35. Not indefinitely, of course
  36. 36. Limit: Max casing pressure of second stage
  37. 37. Limit: NPSHr of the first stage
  38. 38. On a steep system head curve...
  39. 39. ...series pumping can add significant flow...
  40. 40. ...keeping pumps inside their performance curves
  41. 41. Plain parallel pumping would have done zilch
  42. 42. But wait, there's more!
  43. 43. Parallel-series pumping
  44. 44. Captures advantages of parallel and series  System design remains the same  Each pump sized for full normal flows  Pumps alternate for balanced wear
  45. 45. At high-flow times:  Lead pump can't keep up
  46. 46. At high-flow times:  Lead pump can't keep up  Lag pump gets called into service
  47. 47. At high-flow times:  Lead pump can't keep up  Lag pump gets called into service  Lag pump is converted to series operation
  48. 48. How is parallel-series pumping achieved?
  49. 49. Pipe pump #1 discharge to pump #2 suction
  50. 50. Piping: Isolation/plug valve, tee(s), check valve
  51. 51. Auto-switches into series when lag pump is called
  52. 52. Pressure differential on suction, discharge sides of the pumps
  53. 53. What if two pumps operating in series are required?
  54. 54. Conventional series: Twice as many pumps
  55. 55. But a parallel-series layout can do it with three  Performance of four pumps for the price of three  Eliminates one complete pump unit
  56. 56. Any two pumps auto-shift into series mode
  57. 57. Benefits of triplex parallel-series arrangement
  58. 58. Smaller footprint
  59. 59. Reduced control set
  60. 60. Cost savings
  61. 61. Operationally speaking  A parallel-series pumping system allows each pump to meet average daily flows  When a single pump can't keep up...  ...the station automatically shifts into series mode  ...and the system meets peak flows
  62. 62. Parallel-series pumping solves  Inflow and infiltration  Future flows due to new construction  Future flows due to new industry  Multiple pump systems on a common force main  Force main restrictions: ARV failure  Force main restrictions: Clogging and sedimentation  Force main tuberculation (constriction by corrosion)
  63. 63. Example See handout
  64. 64. Single-pump operation
  65. 65. System "A": High friction heads
  66. 66. System "B": Low friction heads
  67. 67. Parallel pump operation
  68. 68. System "A" in simple parallel
  69. 69. System "A" in simple parallel
  70. 70. Series pump operation
  71. 71. System "A" in simple series
  72. 72. System "A" in simple series
  73. 73. System "B" in simple parallel
  74. 74. System "B" in simple parallel
  75. 75. System "B" in simple series
  76. 76. System "B" in simple series
  77. 77. Questions?  Thank you for coming!
  78. 78. Thank you for your attention!  Contact us anytime with questions  Brian Gongol  DJ Gongol & Associates  515-223-4144  info@djgongol.com
  79. 79. References:  Pump curves generated courtesy The Gorman-Rupp Co. and Patterson Pump Co.  Photos of installed parallel-series stations and some images courtesy The Gorman-Rupp Co.  Photo of pipe tuberculation courtesy Wayne Rickers, City of Beatrice, Nebraska  All other photos and illustrations are original work by and copyright reserved to Brian Gongol

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