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TECHNICALLY SPEAKING

Reducing the pressure

Media pressure from consumers is having a positive effect on leakage figures, says Frank Rogalla of Aqualia. But pressure from water in pipes is what causes leakage in the first place

P

ressure management, particularly in areas where the pressure is high, is universally accepted as a major tool for reducing losses in water distribution networks. Pressures are reduced by installing a

fixed outlet pressure reducing valve (PRV) on the inlet to the monitoring zone or district meter area (DMA). A typical DMA with a PRV installed at the inlet is shown in the photo. The critical point is that point which is either the furthest or at the highest elevation or both in relation to the DMA inlet. It is the point that will normally see the lowest pressure. There is a further point shown, the AZP point, where the average zone pressure (AZP) can be measured. Basic pressure management has been introduced by many water companies. A fixed outlet PRV reduces the pressure from the PRV inlet pressure (P1) to the PRV outlet pressure (P2). This outlet pressure is set manually after installation of the PRV. Because it cannot be varied easily, it must be set to a conservatively high level that ensures the critical point (P3) receives good service under the worse case conditions. Some contingency is also applied to allow for new housing developments. Flow modulation is an improvement – it can be used to reduce average

pressures in the network by adjusting the valve outlet P2 to compensate for flow related head loss in the network. However, this does not fully optimise pressures since the modulation relationship is crudely calculated and fixed with high safety margins, leading to a high value setpoint for the minimum

“The objective of the system is to achieve a quantum leap over current pressure management technologies, by continuously adjusting the level of the valve outlet”

pressures at the critical point P3. This in turn keeps the overall pressure of the DMA unnecessarily high, with related increase in losses. To improve the current state of the art, and to reduce water leakage, a

new methodology of advanced pressure management has been introduced by i2O Water, which is based at the University of Southampton Science Park. Founded only in 2005, the company has already installed its innovative water-saving technology to 12 UK water companies and has grown to 25 employees. The objective of the new system is to achieve a quantum leap over

current pressure management technologies, by continuously adjusting the level of the valve outlet P2 to a minimum level. To guarantee a good service to all customers in the area, P2 is varied in order to achieve at the critical point P3 a steady level just above the reference. This is achieved by integrating three important features:

■ A new advanced pilot valve (APV) which reliably adjusts pressures with minimum power

■ A central mathematical algorithm which continuously self learns the primary relationships between flow and pressure in a district and has the ability to learn other parameters including time of day, day of week and season of year

■ A central server that stores and processes all DMA data received wirelessly from a network of i2O devices in each installation, including

36 Water & Wastewater Treatment May 2010

Checking for leaks outside the houses of Parliament

the algorithms created automatically and downloaded to the controller using the GSM network

To achieve the aim of keeping the critical point pressure P3 stable and

close to the minimum pressure for good service, the PRV outlet pressure P2 must be continually adjusted as the head loss in the DMA between the PRV and the critical point changes with changing demand patterns. Existing controllers for pressure management tend to use a fixed table that gives a value for P2 depending on the flow. There are a number of drawbacks to this system:

■ The table has to be entered manually following a logging exercise ■ The controller does not take into account demand patterns that vary depending on the day of the week or time of year

■ Neither does it take into account changes to the demand pattern in the DMA caused by a factory closing or new house building Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64