Sam Ziemann From - Region of Waterloo

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