Pressure Leak Flow Relationships


Updates on Applying FAVAD Concept

Hydraulic Analysis and Fast-Track Applications for Practitioners

Outcomes of collaborative research by the University of Cape Town and several international leakage practitioners, to improve both theoretical understanding and practical application of the Fixed and Variable Area Discharges (FAVAD) concept for pressure:leak flow relationships, will be publicly available by mid-September. A common basic philosophy has been used to model hydraulic laboratory studies of both leakage and intrusion flows through leak openings in pipe samples, with fast-track analysis and prediction applications for practitioners using pressure management to reduce leakage in water distribution systems.

The hydraulic equations for fixed and variable area leak openings in pipes are now available as an open access, free to all peer-reviewed paper ‘Realistic Modeling of Leakage and Intrusion Flows through Leak Openings in Pipes’ by van Zyl, Lambert and Collins, published by the American Society of Civil Engineers.

The first part of the Fast-Track applications for pressure:leakage practitioners will be presented at the IWA Water Efficient Conference at Bath on 18th-20th July, as a Paper and Presentation ‘FAVAD Pressure & Leakage: How Does Pressure Influence N1?’ (Lambert, Fantozzi, Shepherd).The current simplified assumption widely used by practitioners is that Zonal Leak Flow Rate varies with Average Zone Pressure P to the power N1 and that the exponent N1 calculated from a field test at night is independent of pressure over small ranges of pressure. However, extensive international management of excess pressure over the last 20 years, to reduce leak flow rates, frequency of new leaks and bursts and extend asset life, has resulted in lower and wider ranges of pressure in many distribution systems. So the current assumption of a fixed N1 may not be sufficiently reliable for some situations and calculations, particularly at lower pressures.

The Bath presentation will explain how practitioners can use the graph below to rapidly assess how an N1 value which had been calculated or estimated for a particular range of Average Zone Pressures (AZPs), during a field test at night, would vary at AZPs outside that range.

Suppose that a field test at night over a pressure range of 35 to 45 metres results in an N1 of 1.3 (as shown by the red triangle). If the pressure is further reduced, N1 will reduce in accordance with the red dashed line (e.g. N1 will equal 1.0 at 10 metres pressure). The full paper and presentation will be available for free download in late July from LEAKSSuite.

At the Computing and Control in the Water Industry (CCWI) Conference at Sheffield on 5th -7th September, papers will be presented by van Zyl on the hydraulic theory, and Lambert on Fast-Track calculation of leak flow rate vs AZP equations derived directly from N1 tests using FAVAD concepts.

Both authors will then explain the concepts used in more detail at a Post-Conference Workshop at Sheffield organized by Water Loss Research & Analaysis Ltd on the 8th September.

Various additions and updates will be made to existing material on the LEAKSSuite website to ensure compatibility with the improved approaches outlined above.

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