Water Journal : Water Journal March 2011
refereed paper water MARCH 2011 107 started to correlate this section, and lots of people were up, coming out of their homes and the traffic was picking up. The pressure is very low and there are a couple of bends and a couple of tees in this section. The correlator has identified four peaks, accounting for four out of the five known leaks in the area, as previously detected by the Sahara survey. These were a small leak at 19m, a large leak at 43m, a medium leak at 82m, a small leak at 84m and a small leak at 242m (all distances from sensor B.) One of the challenges for operators of a correlation-based product is being able to confirm that the peak is a leak and to pinpoint it on-site. The leak noise on trunk mains is typically such a low frequency that it cannot be heard by the human ear, even with amplification equipment like ground microphones. The engineers at Gutermann have created a new Aquascope ground microphone and listening stick kit with significantly greater amplification and a frequency multiplication option, enabling the operator to enhance low inaudible frequencies to an audible frequency. The Aquascope 550 is shown in Figure 18. Conclusions Despite having lower pressure, multiple leaks and a larger pipe diameter in Manila, the results were better than obtained in Sydney. The most noticeable difference in comparing these two test sites is that the simulation was a part-open valve, while the others were real leaks. The Aquascan has been programmed to recognise the frequency signature of a leak and performs better with real leaks than simulated leaks. The testing in Manila proved the Aquascan is effective at finding leaks in busy Asian cities over distances of 600m or more. The setup time for each correlation is about half-an-hour, with the processing time being 15--30 minutes. This makes the Aquascan a fast and effective solution for finding leaks on trunk mains. There are now advanced automatic filtering options to enable the operator to quickly identify potential leak locations and suppress some of the background noise. In addition to the site preparation work required to create access points for Sahara, it will often take five hours or more to survey a stretch of about 600m. Nonetheless, Sahara seems to provide the most thorough and accurate survey on trunk mains, finding very small leaks. Engineers may question whether it is economical to repair these small leaks. SmartBall is a little more efficient with time and can find small leaks, but it is unlikely to be as accurate as Sahara. In complicated networks it might be difficult to catch the ball. With the installation of an accelerometer sensor only requiring a magnetic connection to the pipe or pipe fitting, and a hydrophone needing a tapping point in the line for water access, the ease and cost of installation greatly favours the accelerometer. The performance of hydrophones is greater than accelerometers on most occasions; however, the results are always similar. After field testing the Aquascan we are confident that correlating over distances of 400--600m with accelerometers will locate leak positions for leaks of 10L per minute or greater. The Author Andrew Clark (email andrewc@ gutermann.net.au) is currently the Asia Pacific Regional Manager for Gutermann and has been involved in the training and supply of a wide range of pipe location and water leak detection equipment to the water industry for over 10 years. He has travelled extensively throughout Asia and is familiar with the extreme conditions many leakage operators face in busy cities with very low pressures. References (Copies of these documents can be obtained from the author.) An overview of innovative leak detection technologies for large mains in Sydney, by Aravinda Stanley & Roger Wood (Sydney Water). Trunk Main Leak Detection, by Alan Marlin (Sydney Water). Misconceptions of Leak Detection, by Stuart Hamilton & Dale Hartley (Gutermann International). Trunk Main Leak Detection at Lansdowne Rd, Sydney, by Andrew Clark (Gutermann International). Trunk Main Leak Detection in Manila, by Rolixto Jodieres (Maynilad Water) & Andrew Clark (Gutermann International). asset management Figure 18: The Aquascope 550 digital sounder is used to pinpoint trunk main and PVC leaks. Figure 17: Correlation result with hydrophones -- small leak at 19m, large leak at 43m, medium leak at 82m, small leak at 84m and small leak at 242m (all distances from sensor B).
Water Journal April 2011