Figure: Schematic of Ngau Tau Kok distribution main

The water system belongs to the Water Supplies Department (WSD) Pressure Management Area PMA PKE013. It serves about 1,100 consumers neighboring Hong Lee Road in NTK, Hong Kong (HK). The distribution main is located in a residential area with low traffic neighboring a local road that ends in a cul-de-sac. The area has a single point of water delivery at the inlet with pressure and flow monitored by a SCADA system. There is a PRV and an electromagnetic flowmeter at the inlet. The flow rate in the main varies between 0.5 and 13 L/s. Water is supplied through a ductile iron main pipe that is about 450 m long with a diameter of 200 mm and connected to the consumer units via service connections down to 80 mm as shown in the figure above. Three fire hydrants (PH1597, PH1598 and PH1601) are located at roughly 120 m intervals along the water main and the pipes increase in elevation as they follow the upward-sloping road to the end of the street. The freshwater fire hydrants are the monitoring access points to this system. The hydrants are implemented with an appurtenance consisting of a 50mm-diameter steel pipe attached sideways to each hydrant (see Figure below). The appurtenance has flexibility to insert various sensors without disturbing the normal operations of the system. The pressure response was measured previously using low-frequency transducers GE Druck UNIK 5000 (0.04% full scale accuracy, calibrated to 0.1%) up to 1000 Hz during active wave probing. Hydrophones for high- frequency measurements can be easily inserted to the connecting ports of the appurtenances, e.g. B&K (Bruel & Kjaer) hydrophone, model 8104 or 8103. The B&K8104 has a flat response close to 80 kHz (device-dependent) and receiving sensitivity of –205 dB re 1 V/μPa; whereas, the 8103 model has a flat response up to about 100 kHz and receiving sensitivity of –211 dB re 1 V/μPa. The data acquisition can be accomplished by using cRIO 9030 controller from NI (National Instruments) imbedded with a 1.33 GHz dual core intel processor and 4 GB hard drive for long-term background pressure noise record in field. NI 9223 modules will be inserted to the cRIO controller to collect data up to a maximum rate of 1 MS/s (10⁶ samples per second) to resolve high-frequency measurement. Cross-correlations from high-frequency pressure-measurement points require refined levels of synchronization. Synchronization between transducers at each hydrant is accomplished using cable connection. Alternatively, radio frequency synchronization system with accuracy below 1 ms is used depending on selected sampling frequency.

Figure: Detailed schematic of access appurtenances to insert sensors in a fire hydrant line