latest practical advances in pressure management marco
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119/12/2017 1
Latest Practical Advances in Pressure Management
North American Water Loss Conference 2017
SAN DIEGO - December 3-5, 2017
Allan Lambert, Water Loss Research & Analysis [email protected] Fantozzi, Studio Marco Fantozzi, [email protected] van Zyl, University of Cape Town, Kobus Van Zyl, [email protected] Shepherd, JOAT Consulting, South Africa, www.joat.co.zaJulian Thornton, Thornton International, [email protected]
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Overview of Presentation
Pressure:leak flow rate relationships• 1994: John May: Fixed & Variable Area Discharges
• 1995 to date: N1 Power Law approximation
• 2017: Van Zyl et al prove FAVAD hydraulically valid
• 2017: Lambert fast-tracks FAVAD for practitionersStep 1: Calculate N1 from N1 night test (simple spreadsheet)
Step 2: Identify Fixed and Variable area leaks %s at AZPave in N1 test (easy)
Step 3: Show how N1 changes with pressure (equation, graph)
Step 4: Calculate leak flow rate vs AZP equation (with graph)
Step 5: Calculate leak flow rates from AZP pressures (graph)
Step 6: Improve Night Day Factor calculations (graphs, equation)
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John May (1994)
Free download from LEAKSSuite website at:
http://www.leakssuite.com/wp-content/uploads/2016/10/JOHN-MAY-SEMINAL-1994-ARTICLE-4.pdf
with permission of Water Environment Federation (USA), which now holds the copyright.
Pressure Dependent Leakage
(World Water and Environmental Engineering, October 1994)
The original article that explained the FAVAD concept
(Fixed and Variable Area Discharges)
for pressure:leak flow rate relationships
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Fixed and Variable Area Leakage Paths
Fixed area leakage
Lf varies with P0.5
Includes ring cracks, corrosion holes …….
Variable area leakage Leak area varies with PVelocity varies with P0.5
Leak flow varies with P1.5
includes background leakage at joints and fittings, and splits in
flexible pipe materials
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N1 Power Law approximation of FAVADLeak flow rate L varies with PN1
• Initial average pressure Po
• Initial leak flow rate Lo
• Assume Lo = A x PoN1 …(1)
• New average pressure P1
• New leak flow rate L1
• L1 = A x P1N1 ……………(2)
For small changes in pressure , assume A and N1 almost constant
• Divide 2nd eqn by 1st eqn
• ‘A’ cancels out
• L1/Lo = (P1/Po)N1
Numerous tests show that N1 usually lies within the range 0.5 to 1.5
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Experimentos - Relacao dentre Vazao e Pressao
0
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0:00
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Hora
Vazao
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ora
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mca
Flowrate m3/hr Pressure m
AZNPo
AZNP1
AZNP2
Customer night use
LoL1 L2
A 2-step N1 Night Test on Zone Vila Maria, SABESP, Brazil (1998)
L1/L0 = (AZP1/AZP0)N1 so N1 = ln(L1/L0)/ln(P1/P0)
Zone inflow rate m3/hr Average Zone Night Pressure (m)
Increased inflow to roof storage tanks
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Current use of N1 by Practitioners
• Since 1994, the N1 power law FAVAD is being widely used by practitioners internationally
• Most users tend to assume a constant N1• 1.0 (linear), or 1.15 (Japan)
• Some users try to predict N1 using component analysis, or pipe materials and snapshot ILI
• Some consultants carry out N1 tests• but most practitioners have never done so
• and more systematic training is needed
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Pressure Control expands after 1995
• Thousands of pressure control schemes installed internationally since 1995 to reduce leakage; justified economically due to• better methods to predict reductions in leak flow rates (FAVAD,
simplified to N1 Power Law)• advanced pressure control with flow modulation • methods to predict reductions in new burst frequency on mains,
and services, and extend infrastructure life
• As a consequence many systems now are operating at lower and more variable pressures
• It became necessary to review concepts used for calculations
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Recent collaborative research on FAVAD
• By Prof. Kobus van Zyl, Allan Lambert, Amanda Cassa, Dr Richard Collins and post-grad University of Cape Town students• Leakage Numbers for lab tests on pipe samples:
• Leak Area vs pressure relationships
• Influence of low/negative pressure on leak flow rates
• Open Access paper on hydraulic analysis by van Zyl, Lambert and Collins ASCE Journal of Hydraulic Engineering / Vol 143 Issue 9 - Sept 2017 ( 1000+ downloads)• summarised in Presentation 2017S on LEAKSSuite
• Allan Lambert has now applied FAVAD concepts to N1 tests, to get fast-track methods for practitioners to use
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The Leakage Practitioner Concept
• For valid results, Zonal N1 tests must follow rules, just like taking a blood pressure test at the Doctor’s
• Step 1: Pressure MUST be measured at the correct place• At Doctor’s: sitting, on upper arm at the same level as the heart
• not the neck and not the ankle!
• In Zone: at the Average Zone Point AZP
• not the inlet point and not the critical point!
• Step 2: Change the pressure• Doctor: when patient is relaxed, raise pressure to a maximum, then allow to fall back
to minimum
• Zone: wait for steady inflow and AZP pressure at night; reduce pressure to achieve lower steady minimum flow and pressure
• Step 3: Summarise results of analysis quickly and clearly• in units and format the patient/Utility can easily understand
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Inlet Point
Critical Point
NOT ENOUGH !
Average Zone Pressure (AZP)
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Fast track approaches for practitioners
• Use Fast-track FAVAD calculations, customised for practitioners, for improved leakage calculations
• WLR&A’s ‘Leakage Practitioner’ fast-track approach for Utilities using FAVAD in 6 steps:
1. Calculate N1 from an N1 test, or assume N1, at a specified Average Zone Pressure
2. Identify % split of Fixed and Variable Area leaks from N1
3. Then calculate N1 vs Average Zone Pressure equation
4. Use N1 test to define Leak Flow Rate vs AZP equation
5. Predict zonal leakage from AZP pressures in real time
6. Improve reliability of assessment of Night-Day Factors
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N1 Leakage Practitioner test: Fast track Steps 1 to 3
CAUTIONIf you extrapolate the N1 vs AZP equation to
higher AZP pressures than the maximum in the N1 test, you risk creating new leaks which may
change the N1 vs AZP relationship
For methodology and derivation of N1 vs AZP equations,
see ‘FAVAD Pressure & Leakage:How does pressure influence N1?’
(Lambert, Fantozzi, Shepherd, 2017) at Paper 2017L and Presentation 2017K
on 7th May 2017
1000 2000
Start 64.0 psi 88.00 USgpm 8.80 USgpm 79.20 USgpm
Finish 51.2 psi 68.20 USgpm 8.80 USgpm 59.40 USgpm
Step 1 At Average AZNP = 57.6 psi N1 = ln(L1/L0)/ln(AZNP1/AZNP0) = 1.29 Lave = 69.3 USgpm
Step 2 0.21 0.79
15.4 psi
psi
15.4 psi
N1 Night Test for Anyzone
01:30 to 02:15
Sunday
02:30 to 03:15
MNF
AZNPo =
AZNP1 =
Night Use Leakage Rate LNo. of Properties Test
Data
General Equation for N1 vs AZP is Step 3
Population
Variable Leakage Area VAL% = N1 -0.5 =
Average Zone Pressure AZP when N1 = 1.0 is AZPN1 =1 = AZPave x FAL/VAL =
) where units of AZP are in
Fixed Leakage Area FAL% = 1.5 -N1 =
N1 = 0.5 + AZP /(AZP + AZPN1 =1 ) where units of AZP are in
Equation for N1 vs AZP is N1 = 0.5 + AZP /(AZP +
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Step 3: General relationship between N1 and AZP:N1 reduces as average zone pressure reduces
• N1s from individual Zonal tests can be plotted on this graph
• Always quote N1 with its corresponding Average Zone Pressure
• N1 always reduces as Average Zone Pressure decreases
• Rate of change increases as Average Zone Pressure decreases
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Step 4. Derive Leak Flow Rate vs AZP pressure from N1 test
• Predict current Leak Flow rate vs AZP equation direct from reliable N1 test
• Using FAVAD, L (volume/unit time) = A x AZP0.5 + B x AZP1.5
• From N1 test, we know L0 and AZNP0 , and L1 and AZNP1
• Solve simultaneous equations, derive A, B in units to suit user’s data
• Extrapolate L vs AZP equation from N1 test to full range of lesser AZPs
• This defines the current L vs AZP equation at the time of the N1 test
Sunday 01:30 to 03:36 02:30 to 03:15 Date
AZNPo = 64.0 psi MNFo = 88.00 USgpm 8.80 USgpm 79.20 USgpm
AZNP1 = 51.2 psi MNF1 = 68.20 USgpm 8.80 USgpm Night Leakage Rate L1 = 59.40 USgpm
USgpm = 1.907 x AZP0.5 + 0.1249 x AZP
1.5
AZNPave = 57.6 psi MNFpred 77.87 USgpm 8.80 USgpm Predicted Leakage Rate = 69.07 USgpm
N1 at 57.6 psi = 1.29 with 79% 21%
15.4 psi 15.4 )
Night Consumption
Fixed Area Leaks
FAVAD equation is
variable area leaks and
Leak Flow Rate L in
Average Zone Pressure at N1 = 1.0 is AZNPave x % Fixed /% Variable Area = N1 = 0.50 + AZP/(AZP +
Night Consumption
Calculations by A.N.Other
07-May-17 03-Jun-17 [email protected]
Night Consumption
Night Leakage Rate Lo =
Day and Date of N1 Test Initial Steady State Lowered Steady State
Leak Flow Rate in USgpm
Pressure at Average Zone Point in psi
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0
Le
ak
Flo
w R
ate
in
US
gp
m
Pressure at Average Zone Point in psi
Leak Flow Rate L in USgpm vs AZP in psiL = 1.91 x AZP0.5 + 0.125 x AZP1.5
N1 Test
Calibration Point
Predicted VariableArea Leak flow
Predicted Fixed
Area Leak Flow
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Step 5: Calculate leak flow rate profile from AZP pressures• Example: Zone in Mexico with roof tanks: continuous measurement at AZP point
• Recovering from intermittent supply with pressure management, AZP 12 to 18 m
• Derive L vs AZP equation using automated N1 test every Sunday morning
• Use L vs AZP equation to predict 96 x 15 min leak flow rates, add for daily leakage
• Check: predict 15 min leak flow rates from N1 vs AZP equation + Sun night leak rate
• Check: predicted night leak rates agree and do not exceed MNF on any week night
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Step 6a: Overview of Night-Day Factor
• Calculate ratio of AZPave/AZP at time of mnf, for X-axis
• Read off possible range of Night-Day Factors from Y-axis
• Measure or assess N1 at daily AZPave for Zone if more accurate estimate of NDF is needed
048
12162024283236404448525660646872768084889296
100
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 2.2 2.3 2.4 2.5
Nig
ht
Day
Fac
tor
Ho
urs
pe
r d
ay
Ratio of 24 hour Average AZP/AZP at time of Minimum Night Flow
NDF vs AZPave/AZPmnf, with Fixed + Variable Area correction
N1 =1.49 at AZPave
N1 = 1.40 at AZPave
N1= 1.30 at AZPave
N1 = 1.20 at AZPave
N1 = 1.10 at AZPave
N1 = 1.00 at AZPave
N1 = 0.90 at AZPave
N1 = 0.80 at AZPave
N1 = 0.70 at AZPave
N1 = 0.60 at AZPave
N1 = 0.51 at AZPave
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Step 6b: NDF using Correction Factor method• Calculate ratio of AZPave/AZP at time of mnf, for X-axis
• NDF = CF x 24 x AZPave/AZPmnf , where CF is a Correction Factor
• Derive CF from graph below; CF varies with AZPave/AZPmnf and N1 at AZPave
• The equation which defines the graph below is used for automatic data processing
0.50
0.60
0.70
0.80
0.90
1.00
1.10
1.20
1.30
1.40
1.50
1.60
1.70
1.80
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5
Co
rre
ctio
n F
acto
r C
f
Ratio of Average AZP/AZP at hour of Minimum Night Flow: AZPave/AZPmnf
Night Day Factor = CF x 24 x AZPave/AZPmnf
N1 at AZPave = 1.49
N1 at AZPave = 1.40
N1 at AZPave = 1.30
N1 at AZPave = 1.20
N1 at AZPave = 1.10
N1 at AZPave = 1.00
N1 at AZPave = 0.90
N1 at AZPave = 0.80
N1 at AZPave = 0.70
N1 at AZPave = 0.60
N1 at AZPave = 0.51
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Summary and Conclusions
• FAVAD concept remains best available, now hydraulically validated
• N1 Power Law simplified FAVAD, assuming constant N1 for small pressure range, but N1 decreases as pressures reduce
• Leakage Practitioner approach: use Fast-Track FAVAD to • quickly identify Fixed and Variable components from N1 night test • quickly calculate N1 vs AZP Type Curves, to check assumed N1s• quickly calculate Zonal L vs AZP equation derived from N1 test• derive continuous leak flow rate profile from recorded AZP pressures• split Zonal 15 minute inflows into leakage and consumption• check validity of Night-Day Factor calculations, improve where needed
• Combination of Academics and Practitioners is mutually beneficial if the different approaches, experiences and communication needs of both communities are recognised when disseminating the outcomes
• Additional free references are available at http://www.leakssuite.com/influences-of-pressure/
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Acknowledgements
• John May, for laying the foundations of these studies 23 years ago
• Prof. Kobus van Zyl, Richard Collins and post-graduate students of University of Cape Town for reinvigorating Fixed and Variable Area concepts.
• Many other colleagues in the Pressure Management Team of the IWA Water Loss Specialist Group, for ongoing successful international promotion of the benefits of well targeted pressure management.
• The LEAKSSuite website for making so much material available, free to all; now over 26,000 users worldwide
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Latest Practical Advances in Pressure Management
North American Water Loss Conference 2017
SAN DIEGO - December 3-5, 2017
Allan Lambert: Water Loss Research & Analysis [email protected] Fantozzi, Studio Marco Fantozzi, [email protected] van Zyl, University of Cape Town, Kobus Van Zyl, [email protected] Shepherd, JOAT Consulting, South Africa, www.joat.co.zaJulian Thornton, Thornton International, [email protected]
Thanks for your attention !