Water Hammer: Practical Solutions

187 Pages·1995·5.732 MB·English

by  Bruce Sharp, David Sharp

WATER HAMMER: PRACTICAL SOLUTIONS
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WATER HAMMER:
PRACTICAL SOLUTIONS
B. B. Sharp and D. B. Sharp
Burnell Research Laboratory, Victoria, Australia
["lUTTER W O R TH
E I N E M A N N
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First published 1996
Transferred to digital printing 2003
Copyright © 1996, B. B. Sharp and D. B. Sharp. All rights reserved
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Contents
Contents V
Nomenclature vii
Introduction ix
1. The Valve (Gate) 1
2. The Pump 9
3. The Booster 15
4. Inertia 19
5. An Optimum Pump Location 25
6. The Non-return Valve (check valve) 35
7. Non-return Valve as a Protection Method 41
8. The Complex System 48
9. The Separation Problem 55
10. The Non-elastic Conduit 61
11. The High Point 65
12. Fire protection 69
13. The Plumbing Problem 73
14. Structural Interaction 79
15. The Open Surge Tank 85
16. The One-way Surge Tank 89
17. The Pressure Reducing Valve 95
18. The Resonance Problem 101
19. Series Pumping 107
20. Compounding of Pipes - System Alternatives 111
21. The Impact of Waves - Coastal Defence Problem 115
22. The Air Vessel 121
23. A Hydroelectric Example 129
24. Expansion Loops (Lyres) 133
25. Dead End 137
26. Cooling Water Systems 141
27. Sewage Pumping 145
vi Contents
28. Blowdown from High-Temperature/Pressure Systems 149
29. Classification Discussion 153
Appendix 1 Liquid and Material Properties 155
Appendix 2 Data File for Complex Network Example 159
References 165
Index 171
Nomenclature
The diagrams and notations for the data follow the basic scheme of the
computer analysis with the following conditions. The velocity is used as
the basic flow variable and because the water-hammer wave propagation
is a celerity the symbol C^ is used.
Pipes ; numbered from the downstream end, have n(j) -f 1 internal
points /, numbered from 1 to n{j) + 1 from the downstream node to the
next upstream node.
The wave propagation, shown by the arrows in the figure below, is asso
ciated with a sign for CJg that is positive when passing in the direction of
negative velocity and conversely negative when passing in the direction of
positive velocity.
NP«5 \ > ^ /
\ ^ ^ T
NPB«7 -CJg ^CJg
—< /a
HC ,HSTAT
J-']/^^V
JmS \^ j-T^
JmT * 1
x«0 /./V(J)+1 x»
area Horizontal area of air vessel, uppermost level = top (also HAB)
ACT Valve to open or to close
AV Area of pipe connection to air vessel
Core, Wave speed
Constant Delivery storage level constant Y or N
d pipe diameter
ef pump efficiency
viii Nomenclature
exponent for air vessel volume change, p V = constant
n
/ Darcy friction coefficient
GD Plant inertia, short for GD^/4
Air vessel levels, see Chapter 22
HC Pump suction level
HPU Pump head
HSTAT Static pump lift
/ Point within pipe segment, downstream = 1, upstream = n(j)-^\
JPU Pipe downstream of pump
JVALVE Pipe upstream of valve
LNS Pump specific speed type, 1,2, or 3
NAV Number of pipe downstream of air vessel
Number of pipe segment divisions
NR Pump rated speed
NRV Non return valve Yes or No
PS Initial pump start=l, stop=0
Q Main line pump discharge
t Time valve starts operation
I
Time valve ceases operation
Velocity
V
VAV Initial volume of air vessel or surge tank (also V)
X. Y Main pipeline distance, elevation
p, a Density, surface tension
Introduction
Water hammer is the result of an event which is associated with a rapid
velocity (or pressure) change, the result of an accident or a normal oper
ational matter in a pipeline system.
The basic theory is well developed for the single fluid phase, but still
requires refinement for unsteady friction; although there are models
already for friction, it is only recently that the complexity of the velocity
profiles during transients has been demonstrated by experimental obser
vation. One such example by Jonsson (1992), shown in Figure 1, indicates
the beginning of flow reversal close to the wall and the shift of the loca
tion of the maximum velocity away from the centre of the pipeline fol
lowing a valve closure in 1 s.
The observations were close to the downstream valve with an initial
velocity of 0.312 m s', 150 mm dia. pipe.
Centreline
500 ms
600 ms
900 ms
1000 ms
Wall
Fig. 1 Variation of the velocity profile after valve closure