The City of Farmington Hills is the second-largest city in Oakland County, Mich., with a population of more than 80,000. Most of the city has excellent water pressure and adequate fire protection, but as the name suggests, hilly terrain presents pressure challenges in certain areas.
With roughly 468 miles of pipe in its water distribution system, the city uses an average of 8.6 million gal per day (mgd) from the Detroit Water and Sewerage Department (DWSD). DWSD offers lower rates for communities that reduce their maximum day and/or peak hour demands. While the city’s average daily consumption is good, its peak hour factor of 4.4 mgd and maximum daily consumption of 21 mgd comes at a high cost.
The desired operating pressure for a water system is 50 to 80 lb per sq in. (psi), with a state required minimum normal working pressure of 35 psi. To ensure adequate pressure for fire protection, 20 psi is the required minimum during emergencies. When pressure is too high, leakage rates go up, and when it is too low, fire protection is compromised. Upon closer inspection, nine areas were identified with pressure concerns that needed to be addressed.
To reach the desired operating pressure, two styles of pressure-reducing valves (PRV) needed to be installed at five different points in the distribution system, ranging in size from 6 to 24 in.
The Singer S106-2SC-PCO-PR-SC-SPI-MV was the first type of PRV installed. This model provides for remote supervisory control and data acquisition (SCADA) control of flow and pressure. In the event there is a loss of power or SCADA control, a pressure- reducing override takes over, ensuring pressure is maintained through the system. The city also needed the valve fully open in the event of low pressure differential across the valve. The valve-opening pilot on the low inlet pressure setting ensures that the valve can go to a full open position on low inlet pressure to maintain fire flow and operating pressures in the system. The valve was fitted with upstream and downstream pressure transducers tied into the SCADA to provide for this functionality.
The Singer S106-2PR-SC-SPI-MV was the second type of PRV implemented in the system. This valve is equipped with two pressure-reducing Model 160 pilot controls with different set points. Through SCADA control, the city now remotely sets the system maintenance pressure. In addition, non-revenue water loss and pipe breakage has been reduced because of the utility’s ability to lower pressure in off-peak usage times, typically during the night and non-summer seasons.
All valves have the SPI-MV, a single point electromagnetic flowmeter that is built into the valve and ensures an accuracy of ±2% throughout the specified velocity range. This enables Oakland County to measure flow into each of the corresponding pressure zones, track usage and detect pipe breakage. It also allows the county to control and regulate the flow from DWSD during the peak flow hours. The SPI-MV allows the city to fill its tank at off-peak hours and control the total draw by reducing flow to districts as needed.
“The valves have exceeded the county’s expectations by allowing them to smoothly and effortlessly control flow rates within a 20-[gal per minute] dead band,” said Carrie Cox, assistant chief engineer for Oakland County.
With the construction of a 3-million-gal storage tank and accompanying controls, peak demands could be reduced, resulting in an annual savings of $3.3 million.