This document discusses why two pumps operating in parallel do not necessarily provide twice the flow, and introduces parallel-series pumping as a solution. It explains that parallel pumping provides little benefit on a steep system head curve due to hydraulic constraints. Parallel-series pumping allows each pump to handle average daily flows, but converts one pump to series operation at high flows to meet peak demands. This configuration provides the performance of four pumps with only three, reducing costs. The document provides an example comparison of single, parallel, and series pumping configurations on systems with high and low friction heads.

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. Some system designs will never, ever change

3. Those are not our concern here
(If that's you,
this is your chance
to sneak out the back)

4. What moves a system head curve?

5. Inflow and infiltration

6. Future flows due to new construction

7. Future flows due to new industry

8. Multiple pump systems on one force main

9. Force main restrictions: ARV failure

10. Force main restrictions: Clogs and sediment

11. Force main tuberculation (constriction by corrosion)

12. What moves a pump performance curve?

13. Wear

14. Transmission inefficiencies

15. How do you plan for future flows?

16. Or big gaps between average and peak wet weather flows?

17. Wide-range conditions demand wide performance

18. Easy way out: Oversize the pump system

19. But that's wasteful

20. More-elegant solutions are available

21. You already need a second pump, right?

22. It's mainly a backup in case of failure

23. Does running the second pump in parallel help?

24. Usually not

25. Ideally, parallel pumping doubles flow at same head

26. But the system imposes a constraint

27. Parallel pumping is best on a flat system head curve

28. Parallel pumping usually does very little good

29. Parallel pumping into a common force main
Each pump handles
50% of the total flow
and 100% of the total dynamic head

30. On a sufficiently steep system head curve...

31. ...parallel ops may be outside the performance range

32. Now, the other side of the coin

33. Series/staged pumping

34. Two pumps in series: Double head, same flow

35. Not indefinitely, of course

36. Limit: Max casing pressure of second stage

37. Limit: NPSHr of the first stage

38. On a steep system head curve...

39. ...series pumping can add significant flow...

40. ...keeping pumps inside their performance curves

41. Plain parallel pumping would have done zilch

42. But wait, there's more!

43. Parallel-series pumping

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. At high-flow times:
 Lead pump can't keep up

46. At high-flow times:
 Lead pump can't keep up
 Lag pump gets called into service

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. How is parallel-series pumping achieved?

49. Pipe pump #1 discharge to pump #2 suction

50. Piping: Isolation/plug valve, tee(s), check valve

51. Auto-switches into series when lag pump is called

52. Pressure differential on suction, discharge sides of the pumps

53. What if two pumps operating in series are required?

54. Conventional series: Twice as many pumps

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. Any two pumps auto-shift into series mode

57. Benefits of triplex parallel-series arrangement

58. Smaller footprint

59. Reduced control set

60. Cost savings

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. 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. Example
See handout

64. Single-pump operation

65. System "A": High friction heads

66. System "B": Low friction heads

67. Parallel pump operation

68. System "A" in simple parallel

69. System "A" in simple parallel

70. Series pump operation

71. System "A" in simple series

72. System "A" in simple series

73. System "B" in simple parallel

74. System "B" in simple parallel

75. System "B" in simple series

76. System "B" in simple series

77. Questions?
 Thank you for coming!

78. Thank you for your attention!
 Contact us anytime with
questions
 Brian Gongol
 DJ Gongol & Associates
 515-223-4144
 info@djgongol.com

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