Water Journal : Water Journal March 2011
refereed paper water MARCH 2011 105 Five pits were purpose-built for this trial with valves and the ability to connect hydrophones at each point. The map shows the pit positions and the picture shows the simulated leak. Leak Simulation A hose was attached to the ball valve to measure the leak, and then removed to simulate the leak (Figure 10). As the pit filled with water, the differential in pressure between the water escaping from the pipe would have been reduced, causing a slight reduction in leak noise and frequency. All of these trials were performed during the day; background noise was evident during the trials and filtering was often required to get a clear leak position. It is expected that better results with less need to filter would be achieved if the correlation trials had been performed at night. Stanley and Woods of Sydney Water reported: "The overall results for accelerometers showed that the lowest leak flow that could be correlated was 2L/minute over a distance of 232m with accelerometers. Over a longer distance of 400m, the lowest value correlated was 6L/minute with accelerometers and 3L/ minute with hydrophones." Examples of the correlation results for the Gutermann Aquascan Trunk Main are shown in Figures 11, 12 and 13. Background noise may cause interference, so it is advisable to correlate when pressure is greatest and background noise is lowest. A knowledgeable operator with an understanding of leak frequencies and how to filter background noises may work effectively during the day, as was done during this trial. Part 2: Comparison of Sahara with the Aquascan in Manila Following the Sydney simulation trials, Gutermann used their Aquascan equipment to test for a number of known leak sites in Manila. The leaks had previously been identified during a survey using Sahara, providing a perfect opportunity to compare the results. The objective was to enhance the performance of the correlator in busy Asian cities with large levels of background noise, even in the middle of the night. All of the field testing was performed at night and all of the sites were residential or light industrial areas. asset management Figure 11: Simulated leak 6L/M using accelerometers. Figure 13: Simulated leak 3L/M correlated with hydrophones. Figure 12: Simulated leak 10L/M using accelerometers.
Water Journal April 2011