Taking Off the Pressure

Aug. 9, 2018
Indonesian city gives a boost to its aging infrastructure by installing pressure-reducing valves

Malang lies 900 km east of Jakarta on Java in Indonesia. In 2011, the city was supplying water to roughly 120,000 service connections—roughly 600,000 people, which accounted for about 70% of the city’s population. Approximately 30% of the supply to the customers is gravity-fed directly from springs to the users, while the other 70% of the supply is pumped to eight storage reservoirs with a total maximum storage capacity of 18,000 cu m.

The problem

However, Malang was experiencing a lack of water supply and low reservoir levels due to leakage and pipe bursts that had lead to 30% of the population being regularly deprived of water from the normal distribution mains.

With daily pipe bursts, reservoirs dropping to 20% of capacity at night and leakage rates hitting an estimated high of 41%—or 400 liters per second (1 million cu m per month)—the director of non-revenue water (NRW) for the city’s water department, PDAM Malang, brought a team of experts together to create a water loss management plan. Ranhill Water Services, a Malaysian NRW consulting firm, conducted a six-month district meter area (DMA) hydraulic calibration study for roughly 20% of the PDAM Malang water distribution system. PT Pancatama also conducted a test on a standard Singer diaphragm-operated pressure-reducing valve (PRV). The valve proved very effective at controlling pressures, which reduced the leakage and pipe bursts.

The solution

The consensus was to develop numerous control zones—or DMAs—with a single source of water comprising a meter and a pilot-operated control valve at the source of the DMA. Once operators are able to measure the flow into the DMA as well as flow to users, they are able to manage the pressure. With a direct correlation to pressure and leakage—if operators reduce pressure they will reduce leakage—the ultimate goal was to give user just enough pressure to serve their needs while eliminating over pressures.

One of the most difficult aspects of the project was getting senior PDAM Malang water directors and politicians to approve the budget and necessary funding for such an ambitious plan. To demonstrate that the goals were achievable and that the ROI would be favorable, PDAM Malang installed three test DMAs and PRVs near a problem reservoir. The pipe bursts stopped, leakage was greatly reduced and reservoir levels were maintained. The directors were convinced, and so the budget requirements were approved and the project quickly moved forward.

DMA construction began with an initial 42 Singer Valve S106 2-PR-BTs (100 mm to 500 mm) being installed. In Malang, the average pressure in the main distribution lines range from 2 bar (30 psi) to 4 bar (60 psi). In order to reduce this, Singer added two pressure-reducing pilots to the main diaphragm-operated control valve; one pilot is set for night pressure (low demand), while the other is set for daytime pressure (high demand), so they are able to relatively accurately maintain pressure at the critical point. This is typically the most challenging pressure point in the DMA. This technology is controlled by a simple IP68 (waterproof) timing device controlled by a locally available 9-VDC battery that switches pressure at a predetermined time. The new valves were able to reduce the pressure during high demand in the daytime to 2 bar (30 psi) and further reduce the night pressure to 1.5 bar (22.5 psi).

With the initial 42 units installed, leakage was reduced from 41% to 27.7%. In terms of volume, this means that leakage had been reduced from 400 liters per second to 250 liters per second, reducing the leakage rate by 150 liters per second, or 388,800 cu m per month. With the additional 96 PRVs, leakage was reduced to 20%, which resulted in a savings of 750,000 cu m of water per month.

Larger valves were required for larger main DMA areas. In these cases, Malang officials used a single rolling diaphragm (SRD) technology, as opposed to the norm of flat diaphragms that often have seat chatter with fluctuating flow. The SRD provides smooth, steady and precise pressure control from maximum to virtually zero flow without the need for low-flow bypass valves. The effective area of an SRD remains constant, and the bonnet is much smaller and lighter than that of a flat diaphragm. A measured quantity into the bonnet control chamber always gives the same smooth movement of the inner valve through the entire stroke, even during low flows (night time). A smaller bonnet also makes the valve lighter and safer for maintenance, while the control chamber enables it to respond faster to changing pressures. This NRW-specific innovation prevents minor surges entering the downstream side of the PRV and is revolutionizing NRW projects worldwide as flow stability, particularly at low flow, is crucial to minimizing infrastructure damage.

Prior to the installation of the PRVs, operators addressed an average of one pipe burst per day. This has been reduced to an average of one pipe burst per month, which has led to huge savings in the annual maintenance budget for the repair of pipe bursts. In addition, the entire system makes use of GIS technology, allowing for the real-time monitoring of pressure and flow so that leak detection teams can be dispatched to specific DMAs when data readings are unacceptable and repair crews can respond quickly.

Prior to the PRV installation, reservoir levels typically dropped to about 20% of capacity by 4 a.m. each morning due to leakage rates and pipe bursts, resulting in extreme water shortages and, sometimes, no water for those at the ends of the distribution lines. Now the city has reservoir levels at 80% at 4 a.m., resulting in the vast majority of customers in the DMA zones having water all day, every day, regardless of demand.

The results

With increased reservoir capacity and greatly reduced leakage rates, the City of Malang has been able to expand its distribution main lines and make water available to an additional 125,000 service connections, which amounts to roughly 625,000 people.

Another huge cost saving has been in power consumption. Prior to installation of the new PRVs, the DMAs required two pumps to supply the reservoirs, but due to the increased capacity of the reservoirs, only one pump is now required to maintain the levels, despite the additional customers. Electrical consumption has decreased monthly from an original 1.2 billion rupiahs to 800 million rupiahs per month—a 33% savings.

The City of Malang is now able to expand reliable water access to new communities. “I can sleep well at night knowing that the vast majority of customers now have reliable water,” said Teguh Cahyono, director of non-revenue water for PDMA Malang.

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