Water Hammer

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Water Hammer

• Travis Meyer, P.E.
• Richard P. Arber Associates

2
INTRODUCTION

• Background
• Water Hammer Modeling
• System Improvements
• Results
• Conclusions

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City of Black HawkDistribution System
Dory Hill Tank
3
4
2
5
1
Pressure Reducing Station
Mesa Tank
Pump Station
4
Distribution System Profile
Grade
Mesa Tank (8775 ft)
Hydraulic Grade
Pressure Reducing Station
120/40
Pump Station
1
160/70
Dory Hill Tank (8375 ft)
2
140/90
3
140/65
140 psi
3
70
4
5
Pump Suction Line
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Problem
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Water Hammer - Causes

• Sudden Velocity Change
• fire hydrant
• fire sprinkler system
• pumps
• Vapor Cavity Formation
• pressure down surge at a low pressure dead end
• Equipment Malfunction
• fire hydrants, valves, PRVs

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SURGE 5 MODELSUDDEN VALVE CLOSURE
2,000 GPM TO 0 GPM IN 3 SECONDS
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SURGE 5 MODELSUDDEN VALVE OPENING
0 GPM TO 2,000 GPM IN 3 SECONDS
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SURGE 5 MODELSUDDEN VALVE OPENING
0 GPM TO 2,000 GPM IN 3 SECONDS
PUMP SUCTION ISOLATED
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Water Hammer ModelingConclusions

• Sudden Large Demand Changes Can Initiate a Water
  Hammer Event
• Vapor Cavity Formation and Collapse Can Occur in
  the Pump Suction Line
• Unable to Model PRV Behavior During Water Hammer
• Cause of Extended Hammers?

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Water Hammer - Solutions

• Sudden Velocity Changes
• Pressure Relief Valves
• Surge Tanks
• Surge Anticipation Valves
• Standpipe
• Vapor Cavity Formation
• Eliminate Low Pressure Dead Ends
• Connect System High Points to Open Tanks

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Recommended Improvements

• Reconfigure Pump Suction to Eliminate Possibility
  of Vapor Cavity Formation and Collapse
• Install Pressure Relief Valves in Pressure Zones
  3 and 4
• Reconfigure Existing, Unused 12 Pipe as a
  Standpipe
• Optimize PRV Settings
• Lower System Pressures
• Require Surge Tanks for New Construction with
  Fire Service

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System Improvements
Standpipe
6
3
4
2
5
Pressure Reducing Station with Pressure Relief
Valve
1
Pump Station
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System Improvements
Mesa Tank (8775 ft)
Grade
Hydraulic Grade
Pressure Reducing Station
120/40
Pump Station
1
160/70
Dory Hill Tank (8375 ft)
2
140/90
140/65
3
3
70
4
5
Pump Suction Line
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Initial Implementationof Improvements

• Isolated Pump Suction Line
• Installed Temporary Pressure Relief Valves
• Put Locks on Fire Hydrants
• Lowered System Pressures Where Possible (Zone 4)

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Initial Implementation
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Initial Implementation
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Water Hammer Test

• Fire Dept Indicated That One Fire Hydrant Always
  Seemed to Cause Water Hammer
• Initiated a Water Hammer Event on Purpose
• Monitored System Pressures and PRV Behavior
  During Water Hammer

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Water Hammer Test
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Water Hammer TestConclusions

• Damaged Stem Extension on Fire Hydrant
• City Subsequently Inspected All Fire Hydrants for
  Damage
• Pressure Regulating Valves
• Appeared to Operate Smoothly During Water Hammer

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Final Implementationof Improvements

• Pump Suction Line Reconfigured
• Standpipe On-Line
• Two New PRV Stations with Pressure Relief Valves
  On-Line
• System Pressures Lowered to Final Levels

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Another Water Hammer
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Probable Cause

• Contractor Started Work Approximately Same Time
  as Water Hammer
• May Have Filled Water Truck from Fire Hydrant
• Pressure Regulating Valve
• Corrosion Buildup on Stem Guide Caused Valve to
  Stick and Operate Unevenly

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Another Water Hammer
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Final Adjustments - PRV Stations
Secondary Supply 95 psi
Primary Supply 100 psi
Emergency Supply 90 psi
Pressure Zone
100 psi
100 psi
Pressure Zone
100 psi
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Success!!??
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Conclusions

• To Avoid Water Hammer
• Eliminate Potential for Vapor Cavity Formation
  (Low Pressure Dead-End Lines)
• Maintain Fire Hydrants, System Valves, Fire
  Protection Systems, Pressure Regulating Valves
  for Proper Operation
• Try Alternate PRV Strategy for Multiple PRV
  Pressure Zones

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Conclusions

• To Protect System and Customers
• Install Pressure Relief Valves
• Install Standpipes
• Require Surge Tanks on Fire Service Taps
• Lower System Pressure

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Proud Papa
Jeffrey - Born 9/10/02