Sam Ziemann From - Region of Waterloo

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August 26, 2011Sam ZiemannPage 8 of 12Reference: Fluid Transient Analysis for Strange Street Raw Water Supply System – Draft TechnicalMemorandumof the truncated model. Results for Scenario 2, which are shown in Figures 4a and 4b,are similar to those of Scenario 1 and indicate full vacuum conditions occur over most ofthe segment of watermain from the K18/K19 Well House to the end of the truncatedmodel.Model results show that the maximum transient pressures within the pipeline during apump shut-down can exceed steady-state pressure conditions by as much as 710 kPa.Results also indicate it is likely the pressures within portions of the raw water supplysystem reach atmospheric or subatmospheric conditions when there are no wells inoperation and that a segment of the system may empty into the Strange StreetReservoir subsequent to shut-down of all the wells. This is because the high waterelevation of the Strange Street Reservoir is below the well head elevations. It isundesirable to allow pressures within the raw water supply system to reach atmosphericconditions as it increases the potential for contamination of the watermains and canallow air to enter the raw water supply system. If air within the raw water supply systemis not managed correctly, air binding could occur and reduce the watermain carryingcapacity by causing an increase in head loss.Scenario 3 – Well K18 Start-up: 5 secondsFor this scenario start-up of Well K18 over a 5-second period was modeled. Figures 5aand 5b show the head and pressure experienced along the raw water supply systempiping from the K18/K19 Well House to the end of the truncated model for a 5-secondwell pump start-up. Results indicate the maximum pressures experienced within the rawwater supply system can exceed steady-state pressures by approximately 330 kPa.Pressure Control AlternativesFor the second stage of the transient analysis effective means of controlling thepressure fluctuations calculated for Scenarios 1-3 during pump start-ups, shut-downs,and power failures were examined.Controlling Pressures During Power Failure Induced Pump TripsPower failure induced pump trips cause a sudden drop in discharge header pressure asthe pumps suddenly de-energize. The installation of air valves within the raw watersupply system to allow air to enter the system can help prevent column separation.Scenario 4 modeled the same power failure (pump trip) event with all of the wellspumps in operation as Scenario 1 except that air valves were input along the watermainand at each well in an attempt to prevent macro-cavitation conditions from occurring.Double acting surge-suppression air valves with 50 mm inlet and 7.93 mm outlet orificeswere used to model the air valves. The valves were sized based upon manufacturer’spublished information. Figures 6a and 6b, which illustrates the pressure and headexperienced along the raw water supply system piping from the K18/K19 Well House to
August 26, 2011Sam ZiemannPage 9 of 12Reference: Fluid Transient Analysis for Strange Street Raw Water Supply System – Draft TechnicalMemorandumthe end of the truncated model, indicates that, although negative pressures within theraw water supply system piping occur immediately downstream of the K18/K19 WellHouse and at the downstream end of the model, full vacuum conditions and columnseparation (macro-cavitation) are avoided. The double acting surge-suppression airvalves input along the raw water supply system piping within the model are the reasonmacro-cavitation conditions are avoided.Model results show that the maximum transient pressures within the watermains forScenario 4 do not exceed steady-state pressure conditions by more than approximately80 kPa. Model results also show that the modeled air valve size is sufficient to preventcolumn separation from occurring in the raw water supply system piping.Controlling Pump Shut-down PressuresPump shut-down pressures should be such that negative pressures within the watersupply system are avoided. For normal pump shut-down this can be accomplished withthe use of variable speed drives, soft-stop controls, pump control valves, or acombination of these.Scenario 5 was developed to minimize the occurrence of negative pressures within theraw water supply system subsequent to a pump shut-down and assumed the soft-startat the wells were programmed with a ramp down time of 60 seconds. Figures 7a and7b, which display the Scenario 5 results, demonstrate that shutting the pumps downover a 60-second period essentially eliminates negatives pressures within the raw watersupply system.Controlling Pump Start-up PressuresScenario 6 models the use of soft-start controls to start-up Well K18 over a 30-secondperiod. Figures 8a and 8b, which display the Scenario 6 results, show that the pressureincrease within the water supply system from the K18/K19 Well House to the end of thetruncated model is limited to approximately 135 kPa above steady-state conditions.Maintaining Raw Water Supply System Pressure during Normal Operating ConditionsPressures within the raw water supply system should remain above atmosphericpressure during normal start-up and shut-down of the wells. This can be accomplishedwith the use of control valves and/or a reservoir placed at the location where flowconditions transition from full pipe/pressurized flow to partially full pipe/gravity flow tomaintain pressurized flow conditions downstream of these points.Scenario 7 models the installation of a control valve, specifically a pressure sustainingvalve, on the Strange Street Reservoir fill line to maintain positive pressure within theraw water supply system subsequent to shut-down of Well K18 over a period of 60
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Page 14 and 15: Pressure (kPa)K18/K19 Well House to
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HYDROGEOLOGICAL ASSESSMENTSTRANGE S
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25Pumping Rate20Pumping Rate (L/s)1
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TABLE 2SUMMARY OF GROUNDWATER ANALY
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CALCULATION OF SPECIFIC CAPACITY FR
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March 2, 2011Reference: 006-189Stan
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TABLE 1REGIONAL MUNICIPALITY OF WAT
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July 23, 2010Lisa Lachuta, P.Eng.Pa
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TECHNICAL MEMORANDUM A1 -STRANGE ST
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TECHNICAL MEMORANDUM A1 -STRANGE ST
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TABLE 1SUMMARY OF GROUNDWATER ANALY
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Sam Ziemann From - Region of Waterloo

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