Pressure and Bursts

Pressure : Burst – Frequency Relationships

Predicting Reductions in Bursts on Mains and Services

 The influence of pressure reduction on background leak flow rate has been well known since the mid 1990’s; the FAVAD NI value is around 1.5, so a 10% reduction in average pressure produces a 15% reduction in background leak flow rate. As the frequency of new background leaks may also reduce, reductions in background leakage may be even greater than predicted using leak flow rates alone.

PRESSURE: BURST FREQUENCY RELATIONSHIPSThe influences of pressure reduction on unreported leakage will be fewer unreported leaks, and reduced unreported leak flow rates. Approximately, a 10% reduction in pressure may be expected to produce a 20% decrease in the Rate of Rise of unreported leakage, a 10% increase in economic intervention interval, and a 10% decrease in the Annual Budget for intervention.

The influences of pressure reduction on reported bursts on mains and services, will be reduced leak flow rates and possibly reduced frequencies of reported bursts. For mixed pipe materials, a 10% reduction in pressure may produce a 10% reduction in flow rate (assuming FAVAD N1 = 1.0). The prediction of changes in frequency of bursts has been the subject of ongoing research since 1994, and 2013A provides an 18-year overview.

Source: Fantozzi and Lambert (2007)

Significant progress has been achieved since the Pressure Management team of the IWA Water Loss Task Force became involved in 2003. Allan Lambert is a leader in the international research on how best to model and predict these relationships.

In 2006M, burst frequency data ‘before’ and ‘after’ pressure management in over 100 individual zones by IWA Task Force members clearly demonstrated that remarkable reductions in new burst frequencies can be achieved in some cases, by quite moderate reductions in maximum pressure (including reduction of pressure transients). The overview concept of ‘the straw that breaks the camel’s back’ was also introduced, to explain why reductions in burst frequency could be large in some cases, and absent in others.

Allan Lambert is a leader in the international research on how best to model and predict these relationships

Simple practical concepts of Burst Frequency Index (BFI), were introduced (2007P) to target Zones with high potential for burst reduction; predictions for Zones with high burst frequency could then be made using the equation:

% reduction in burst frequency = 1.4 x % reduction in maximum AZP pressure

Further research between 2007 and 2011 led to the development of an improved more general equation for predicting pressure:burst relationships.

Burst frequency BF = BFnpd + A x AZPmax^N2

Separate predictions of reductions in burst numbers and repair costs on mains, and on services, can now be made for individual Zones, leading to predictions of economic benefits of extension of asset life.

Predictions of reductions in bursts on mains, and separately on services, can now be made for individual Zones

Published papers and presentations on pressure:bursts can be downloaded from links  at 2011G, 2012L, 2012M, 2012N, 2012P, 2012S, 2013C, 2013F, 2013J, 2013K, 2013M, 2013N and 2014E and Blogs ‘Pressure Bursts Update’, Perugia 2013’, ’Water Leakage and Pressure Management Masterclass’.