Water Leakage and Pressure
Progress in practical predictions since 2005
An overview paper was recently presented by Allan Lambert to a mainly academic audience at the 12th International Conference on ‘Computing and Control in the Water Industry’ at Perugia.
The multiple benefits of pressure management
Regarding pressure:leak flow rate relationships, the Cape Town University group (van Zyl, Cassa, Schwaller) has developed a ‘Leakage Number’ concept to gain a better understanding of the variability of FAVAD N1 exponents for different types of cracks in pipes which experience elastic deformation.
Also, FAVAD N1 predictions for distribution systems now include Infrastructure Condition Factor ICF (a measure of undetectable background leakage) as well as Infrastructure Leakage Index and % of rigid mains.
Prediction methods for the reduction of burst frequency on pipes in distribution zones have also progressed significantly.
The latest prediction models include an allowance for a non-pressure dependent component of burst frequency (BFnpd), and a pressure-dependent burst frequency which varies with the cube of AZPmax, the maximum pressure at the Average Zone Point. The burst frequency in each Zone will follow its own individual path, depending upon its current ‘starting point’, if AZPmax is reduced
It is also important to make separate predictions for mains and services, as their burst frequencies usually respond differently to changes in AZPmax.
A practical technique for assessing BFnpd, and good comparisons of recorded and predicted changes in zone burst frequency, are shown in the paper. Reductions in seasonal burst frequencies are particularly evident, following reduction of excess pressure, and the latest conceptual equation provides a plausible overview of why this may be expected to occur.
Changes in repair frequencies for mains, and for services, in Durban Central Business District
Reproduced with the permission of Ethekwini Water
The latest prediction methods have now been successfully tested in several different countries (Australia, South Africa, UK) and are being incorporated in new and updated versions of LEAKSSuite water loss management software.
The additional benefits of burst reduction, extension of asset life, and reduced use of energy are likely to become fundamental influences on the selection and economic justification of future pressure management schemes, which have previously been largely justified only on the expected reduction of leak flow rates.
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