Pressure Transients in Water Engineering - A Guide to Analysis and Interpretation of Behaviour

Table Of Contents

Contents

Acknowledgements XV

Notation xvi

Introduction 1

Chapter 1 Motivation for hydraulic transient analysis 7

1.1 Primary purpose of analysis, 7

1.2 Secondary objectives, 8

1.3 Permitted pressures, 8

1.4 Maximum pressures, 8

1.5 Pipe materials, 8

1.6 Rigid pipes, 9

1.6.1 Grey cast iron, 9

1.6.2 Asbestos cement, 10

1.6.3 Concrete pipes, 10

1.7 Flexible pipes, 11

1.7.1 Ductile iron, 11

1.7.2 Steel pipe, 11

1.8 Overpressure allowance, 12

1.9 Pipe linings for rigid and flexible pipes, 13

1.9.1 Bitumen, 13

1.9.2 Coal tar enamel, 13

1.9.3 Coal tar epoxy lining, 13

1.9.4 Cement mortar, 13

1.9.5 Paint systems, 14

1.9.6 Polyethylene lining, 14

1.10 Plastic pipes, 14

1.10.1 Thermosetting plastics, 14

1.10.2 Thermoplastics, 15

1.11 Failure modes of pipes, 17

1.12 Maximum pressure and allowable amplitude of surge

in plastic pipes, 18

1.13 Minimum pressures, 18

1.14 When is analysis necessary?, 19

Chapter 2 Derivation of basic equations 21

2.1 The rigid-column approach, 21

2.2 Compressible flow theory, 23

2.2.1 Conservation of force, 23

2.2.2 Conservation of mass, 24

2.2.3 Compressible flow equations in terms of total head H, 25

Chapter 3 Interpretation of a 27

3.1 Fluid properties, 27

3.2 Influence of the conduit wall, 28

3.3 Simple expression for a, 29

3.4 Variation of a with conduit shape, 32

3.5 Influence of gas on a, 32

3.6 The effect of sewage, 38

Chapter 4 Characteristic equations 41

4.1 Development of characteristic equations, 41

4.2 Significance of the integrals, 44

4.3 Effect of changing pipe elevation, 44

4.4 Pipeline resistance, 45

4.4.1 Corrosion, 47

4.4.2 Sliming, 47

4.4.3 Evaluation of the integral, 48

Chapter 5 Application of characteristic equations 49

5.1 Use of the characteristics, 49

5.2 'Natural' characteristic mesh, 52

5.3 Using variable wave speed a, 54

5.4 Use of a larger time step, 55

5.5 Use of a fixed wave speed, 56

5.6 Distribution of free gas along the pipeline, 58

5.7 Model output, 59

Chapter 6 Boundaries 60

6.1 Types of boundary, 61

6.2 Reservoirs and tanks, 62

6.3 Branches and changes in pipe properties, 64

6.3.1 Specific cases - number of pipes = 1, 67

6.3.2 Specific cases - change of cross-sectional area, 67

6.4 Response of a large pipe or trunk main, 69

6.5 Actuated valves and pipeline fittings, 71

6.5.1 Terminal valves, 73

6.5.2 In-line valve, 74

6.5.3 Automatic control valves, 75

6.6 Use of more than one time step, 77

6.7 Non-reflecting boundary, 78

6.8 Other bifurcation conditions, 82

6.8.1 Bifurcation with operating valves, 82

6.8.2 Isolating valves, 83

6.9 Continuous drawoff, 84

Chapter 7 Valve closure in a simplified system 87

7.1 Instantaneous valve closure at t = 0, 87

7.2 From 0 ( t ( L/a, 89

7.3 L/a(t( 2L/a, 90

7.4 2L/a ( t ( 3L/a, 92

7.5 3L/a ( t ( 4L/a, 93

Chapter 8 Actual pipelines 95

8.1 Attenuation, 95

8.1.1 Conditions at the wavefront, 97

8.1.2 Conditions when the wave height is of zero

amplitude, 99

8.1.3 Conditions at the closed valve, 100

8.1.4 Conditions downstream of a pump or valve, 100

8.2 A uniform gravity main, 100

Chapter 9 Valve operations 106

9.1 Treated water main, 107

9.2 Improving valve operation, 113

9.3 Two-stage valve closure, 113

9.4 Submerged discharge valve, 117

9.5 In-line valves, 118

9.5.1 Isolating valves, 118

9.5.2 Actuated valve, 119

9.6 Control of transient pressures and estimation of valve

operating time, 122

Chapter 10 Pumps 125

10.1 Types of pump, 125

10.1.1 Pumps which produce transient behaviour only when

changing their mode of operation - that is, starting, stopping or changing speed, 125

10.1.2 Pumps which generate surge effects as a by-product of

their operation, 126

10.1.3 Pumps which produce transient events in order to fulfil

their function, 126

10.1.4 Pumps which do not by themselves produce surge

effects, 126

10.2 Turbine pumps, 126

10.2.1 Centrifugal or radial flow pumps, 127

10.2.2 Mixed or semi-axial flow pumps, 128

10.2.3 Axial flow or propeller pumps, 128

10.3 Turbine pump performance curves, 128

10.4 Including turbine pumps in hydraulic transient analyses, 132

10.4.1 Transfer pump, 134

10.4.2 Booster pump, 136

10.4.3 Other pumping station and pipeline configurations, 137

10.4.4 Station losses, 139

10.5 System curves and pump duty, 139

10.6 Turbine pump start, 140

10.6.1 Direct start, 140

10.6.2 Star/Delta and transformer starting, 140

10.6.3 Variable speed or 'soft' start, 141

10.7 Case studies of pump start, 141

10.7.1 Simulation of direct start in solo pumping, 141

10.7.2 Direct start in multi-pump operation, 143

10.8 Initial conditions of flow, 146

10.9 Pump failure or 'trip', 146

10.10 Other pumps, 150

10.10.1 Reciprocating pumps, 150

10.10.2 Pneumatic ejector, 152

10.10.3 The hydraulic ram, 155

10.10.4 The jet pump, 156

Chapter 11 Flywheels 159

11.1 Moment of inertia, 159

11.2 Flywheels, 160

11.3 Limitations on flywheel size, 161

11.4 Pipeline limitations, 162

11.5 Case study with different pump speed options, 163

11.6 Flywheels on a larger system, 167

11.7 Booster pump installations, 170

11.8 Multi-pump installations, 170

11.9 Advantages of flywheels, 171

Appendix Moment of inertia, 171

Chapter 12 Pressure vessels 173

12.1 Modelling a pressure vessel, 173

12.1.1 Polytropic relationship, 174

12.1.2 Rational heat transfer (RHT) equation, 176

12.2 Role of a pressure vessel in surge suppression, 176

12.3 Initial estimation of required pressure vessel volume, 177

12.3.1 Graphical techniques, 177

12.3.2 Simple numerical method, 178

12.3.3 More detailed numerical assessment, 178

12.3.4 Subsequent investigations and criteria, 178

12.4 Case study of a sewage pumping system, 179

12.5 Worst-case conditions, 181

12.6 Reversed flow and refilling a pressure vessel, 183

12.7 Low-lift systems, 189

12.8 Vessels at a booster pumping station, 193

12.8.1 The upstream pumping station, 194

12.8.2 The downstream pumping station, 196

12.9 Summary of response with a pressure vessel included, 199

Appendix Equations for estimating air vessel parameters, 200

A 12.1 Equation of motion, 201

A12.2 Solution ignoring resistance to flow, 203

A12.3 Including resistance to flow, 205

A12.4 Complete equations, 207

A12.5 Application of the equations, 207

A12.5.1 Maximum expanded gas volume, 207

A12.5.2 Peak upsurge pressure head, 209

A12.5.3 Required throttling, 212

A12.6 Pipeline system of varying cross-section, 214

Chapter 13 Further aspects of pressure vessels 215

13.1 Pressure vessel types and their fittings, 215

13.2 Vessels having an air-water interface, 215

13.2.1 Air compressors, 215

13.2.2 Control of gas chargeAiquid level, 217

13.2.3 Other vessel fittings, 218

13.3 Bladder vessels, 219

13.4 Positioning a pressure vessel, 221

13.5 Installation with air valves, 225

Chapter 14 Surge tanks and related structures 230

14.1 Purpose of a surge tank, 230

14.2 Simple analysis, 232

14.3 Long connection to a chamber, 233

14.4 Full-size connection, 236

14.5 Extent of protection, 236

14.6 Other aspects, 239

14.7 Initial estimates of surge tank parameters, 240

14.8 Related structures, 240

14.8.1 Service reservoir as a one-way surge tank, 241

14.8.2 Operation of an existing service reservoir, 242

14.8.3 Filtration plant, 243

14.8.4 Seawater intake system, 245

14.8.5 Seal weir, 248

14.8.6 Water towers, 249

14.8.7 Special structures, 253

Chapter 15 Feeder tanks or volumetric tanks 259

15.1 Components and location of a feeder tank, 259

15.2 Mode of operation, 261

15.3 Abnormal behaviour, 264

15.4 Mains duplication: Example 1, 267

15.5 Mains duplication: Example 2, 270

15.6 Aspects of feeder behaviour to consider, 276

15.7 Preliminary estimation of feeder tank volume, 277

Chapter 16 Discharge conditions 279

16.1 Vertical bellmouth, 279

16.2 A tank or chamber of finite area, 280

16.3 Back-flow connection, 282

16.4 Siphon breakers, 284

16.4.1 Above-ground storage tanks, 284

16.4.2 Vacuum disconnecting valves, 286

16.5 Air valve operation, 292

16.6 Summary of influence of discharge arrangements, 293

Chapter 17 Air valves 295

17.1 Normal air valve locations, 297

17.2 Air valves for surge alleviation, 298

17.3 Events following flow reversal, 302

17.4 Air valve closure, 308

17.5 Case study of a sewage pumping station, 310

17.6 Pump restart with air in a pipeline, 314

17.7 Other considerations, 318

17.7.1 Uncertainties in simulation, 318

17.7.2 Liquid being conveyed, 319

17.7.3 Inspection, 320

17.7.4 Valve chamber and cover, 320

17.7.5 Valve materials, 321

17.8 Buffer tanks and estimation of required volumes, 321

Chapter 18 Air and gas 325

18.1 Pump start-up with an air-filled riser, 325

18.1.1 A more restricted air outflow device, 332

18.1.2 Soft-start of the pump, 333

18.1.3 Use of an accumulator, 334

18.2 Pump start with slow valve closure, 334

18.2.1 Air venting through a standard air valve, 336

18.2.2 A butterfly valve for air venting, 336

18.3 Air venting through a 'sparg' line, 339

18.4 Gas evolution, 339

18.5 Gas pockets in a pipeline, 340

18.6 Throttled outflow air valves, 343

18.7 Case study of a sewage rising main, 345

18.8 Pump blockage, 351

18.9 Pumped outfall pipeline, 354

18.9.1 Pipeline configuration, 354

18.9.2 Viking-Johnson coupling failure, 356

18.9.3 Hydrodynamic forces, 356

Chapter 19 Relief valves 359

19.1 Relief valve types, 359

19.2 Initial valve sizing, 362

19.3 Valve positioning, 363

19.4 Analysis of behaviour, 363

19.5 Automatic surge control valve, 365

19.6 Surge anticipation valve, 366

19.7 Pumping station pressure relief valve, 366

19.8 Grove regulator, 369

19.9 High head relief valves, 371

19.10 Bursting disk, 375

Chapter 20 Check valve dynamics 376

20.1 Check valve response, 376

20.2 Pumping station check valves, 377

20.3 Consequences of an unsuitable check valve installation, 377

20.4 Prediction of pumping station hydraulic transients, 380

20.5 Reopening of a check valve door, 382

20.5.1 Check valve reopening due to pressure wave reflections, 383

20.5.2 Valve reopening in longer term, 385

20.6 Check valve response in a multi-pump installation, 388

20.7 Surge behaviour as a check valve shuts, 388

20.8 Modelling a pumping station, 390

20.8.1 Non-reflecting boundary with allowance for external pipeline resistance, 390

20.8.2 System curve boundary, 393

20.9 Reduction of transient pressures following valve closure, 394

20.10 Maximum pressures at a check valve, 396

20.10.1 Initial valve closure, 396

20.10.2 Cavitation upstream of the valve and resulting peak pressures, 397

20.11 Other applications of check valves, 400

20.11.1 Check valve at the start of a rising main, 400

20.11.2 Check valve on vessel connection, 400

20.11.3 Bypass check valve, 400

20.11.4 Check valves along a rising main, 401

20.11.5 Inclusion of air valves with in-line check valve, 406

20.11.6 Backflow check valve, 407

Chapter 21 Check valve characteristics 409

21.1 Check valve response, 409

21.2 Swing check valves, 411

21.2.1 Free-acting modifications, 414

21.2.2 Valve damping modifications, 415

21.3 'Recoil' valves, 416

21.4 Tilting disk valve, 417

21.5 Rubber flap valve, 418

21.6 Split disk valve, 420

21.7 Butterfly valve used as a check valve, 421

21.8 Nozzle valves, 422

21.9 Moving ball, 424

21.10 Sleeve or duckbill valve, 425

21.11 Membrane valve, 434

21.12 Prediction of valve behaviour, 435

21.13 Use of the charts, 445

Chapter 22 Flexible pipe 446

22.1 Review of pipe materials and properties, 446

22.2 Pressure transient effects, 448

22.3 Strain and deflection, 449

22.4 Establishing the rate of ovalisation in the longer term, 451

22.5 Long-term buckling pressures - unconstrained surroundings, 452

22.6 Long-term buckling pressures - constrained pipelines, 454

22.7 Deformation of a circular section and its effect on wave speed, 458

22.8 Short-term elastic buckling under hydraulic transient effects, 463

22.8.1 Unconstrained conditions, 463

22.8.2 Constrained conditions, 463

22.9 Application of a flexible pipe model, 465

22.9.1 Long horizontal pipeline, 465

22.9.2 Descending outfall, 467

22.9.3 Uniformly rising main, 468

22.9.4 Pipeline of differing properties, 470

22.10 Cyclical oscillations, 472

Chapter 23 Amplification of transient pressures 474

23.1 Transmission of pressure waves through a branch connection, 474

23.2 Pressure wave transmission through a change of cross-section, 476

23.3 Meeting of opposing pressure waves, 478

23.4 Pressure waves in a suction main, 479

23.4.1 Protection of the rising main, 479

23.4.2 Conditions in the gravity main, 479

23.5 Amplification within a network, 481

23.5.1 Kirkleatham Lane Pumping Station, 481

23.5.2 System modelling, 484

23.5.3 Recorded pipe bursts and pressure extremes, 485

23.6 Wellfield transients, 488

23.6.1 Collector pipeline system, 488

23.6.2 Borehole and wellhouse configuration, 490

23.6.3 Wellfield operating conditions, 490

23.6.4 Pumpset inertia, 492

23.6.5 Sequenced pump operation, 493

23.6.6 Pumping failure, 494

23.6.7 Air valve operation, 496

23.7 Potential for amplification, 497

Chapter 24 Flow instabilities 499

24.1 Types of oscillation, 499

24.2 Pumping system - Glasgow East Main and Daer network link, 501

24.2.1 Burnside booster pumping station, 503

24.2.2 Hydraulic transient computations, 503

24.2.3 Castlemilk Low pumping station, 503

24.2.4 Transient pressures, 504

24.2.5 Spread of unstable oscillations and consequences, 506

24.2.6 Possible remedies, 506

24.3 Gravity flow system, 507

24.3.1 The break pressure chamber, 508

24.3.2 Head losses, 508

24.3.3 Flow regulation, 508

24.3.4 H1 valve movement, 511

24.3.5 Remedial measures, 512

24.4 Small hydro station, 513

24.4.1 Observed behaviour, 513

24.4.2 Comments on observed behaviour, 515

24.4.3 Modelling behaviour, 516

24.4.4 Remedial measures, 518

24.4.5 Final comments, 519

References 520

Further reading 525

Index 527