Pressure measurement


Hydraulic Network aNalysis L


arge urban water supply and distribution networks are like complex organisms. Thousands of people in


cities need to be able to get water without delay in their kitchens, bathrooms, washrooms, etc. Pumps can fail or cause pressure surges in pipes. Then there are industrial facilities, which consume large amounts of water in what is sometimes a very irregular manner. Water supply systems need to be


managed professionally if sufficient pressure is to be maintained and damage caused by defective components is to be prevented. Continuous maintenance and the hydraulic analysis of current or potential future problems are effective management instruments in this regard. Hydraulic network analysis makes use of


calibrated models which in turn are based on real measured flow and pressure data. Such an analysis can improve the efficiency and performance of the water supply and distribution system and eliminate energy losses caused by inefficient feed pumps or inadequate water storage technology. Hydraulic network analysis can therefore significantly reduce operating costs for local governments and municipalities.


Network model verificatioN


Water supply network models are like snapshots of a situation that changes as a result of the construction of new residential housing or the establishment of new businesses in a commercial district. This means that every hydraulic water supply model has to be reviewed whenever such changes occur. This is done by subjecting the real network to known operating conditions and


Hydraulic water supply model


or Darcy


comparing calculated and actual flow rates and flow pressure in or- der to detect significant errors. For example, during a low- load nighttime situation, all measured hydraulic grades should display nearly the same hydrostatic values – i.e. there should be no flow influences to speak of. Discrepancies from the calculated model would indicate errors in elevation data or large unknown leaks. In a high- load situation, the hydraulic resistances of the main network pipes are checked, whereby differences here indicate hydraulic blockages caused by defective fittings or clogs, for example.


field measuremeNts for calibratioN


Field measurements are an indispensable component of hydraulic network analyses, as they provide the most important data. A key parameter here is the pipe-roughness coefficient,


formula (λ), which friction factor must be obtained in order to calculate the


pressure drop in a pipe flow. Among other things, this friction value depends on whether the flow is laminar or turbulent, as well as the type of cross-section geometry involved and the


design of a pipe’s inner walls. In order to calculate the real friction


coefficient, the per- formance of various system components must be tested and documented. To this end, the pressure, flow and water consumption values must be recorded, whereby this physical data collection is supplemented by operation data collection. Various measurements are relevant here, including continuous 24-hour flow rate recording at selected key locations, such as water catchment sites and the main network pipes. To this is added flow data col- lected from other key pipes and selected nodes, such as fire hydrants, that are evenly spread over the network. The storage level (hydraulic elevation) also needs to be monitored as well as other factors that influence the mea- sured pressure values, such as inflow and outflow data for pumping stations and booster pumps.


Network model calibratioN


Pressure measurement sensors and data loggers from KELLER are important components for guaranteeing the intelligent management of water supply systems. The data loggers are evenly spread over the network and record synchronised pressure values in realtime, which are then used to calculate and fine-tune realistic pipe rough- ness values and identify punctual resistances in the pipe system. This makes it possible to align measured and calculated hydraulic grades for the purposes of roughness calibration. A verified and calibrated network model helps


detect and correct hydraulic problems in existing networks and avoid similar problems when designing future network extensions.


Realtime recording of pressure values Instrumentation Monthly January 2020


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