AWWA WQTC59012

This AwwaRF project was conceived primarily to test certain assumptions about low-pressuretransients in drinking water distribution systems. The basic assumptions tested werethat low and negative pressure transients actually occur in real distribution systems (not justwithin large transmission mains) and that they can cause liquid external to the pipe to be intrudedinto a drinking water main through a leaking pipe barrel, pipe joint, or other orifice. Pressuretransients can result in contamination when the pressure of water surrounding the water mainexceeds the internal pressure. Under these conditions, water external to the main may flow intothe main through leakage points, submerged air-vacuum valves, cross connections, and faultyseals or joints.Pressure transients can travel throughout a distribution system and cause significantpressure fluctuations in some portions of the system. Many of the causes of pressure transientsare a part of regular water distribution system operations, and therefore, pressure transients mayoccur frequently in certain water distribution systems.The overall aim of pilot testing was to verify the occurrence of intrusion during surgeevents in the distribution system by constructing and operating a pilot-scale test rig apparatus(test rig) at Tulane University. A second objective was to quantify intrusion volume undervarious test conditions. Hydraulic transients were induced in the test rig by closing a valvequickly. Intrusion was facilitated by applying an external column of water on the plate of a blindflange with a pre-drilled orifice that was mounted on the test rig. Experiments were conductednear maximum attainable velocity conditions to enhance hydraulic responses in the test rig. The field study phase of this research included three primary objectives:Locational and Event Monitoring - determine the frequency and location of lowand negative pressures in representative distribution systems under normaloperating conditions and during specific operational events such as flushing, fireflow tests, valve operation, and pump starts and stoppages;Comparison of Different Monitoring Technologies - document differences inpressure monitoring equipment capabilities to measure instantaneous pressuretransient occurrences in distribution systems (i.e., compare electronic monitors toconventional mechanical pen and chart recorders); and,Verification of Model Predictions - compare field monitoring results to surgemodel findings in order to verify the ability of such models to accurately simulatelow and negative pressure occurrences in distribution systems.Pressure monitoring was performed both long-term to record any and all pressurevariations at a specific location ("locational monitoring"; two weeks to 1.6 years), and short-termto monitor effects from a specific type of distribution system operation ("event monitoring";hours). For the long-term locational monitoring, high-speed electronic pressure data loggerswere connected to distribution system piping at a minimum of three different locations in each ofthe seven participating distribution systems studied, typically for a period of at least two weekseach. The monitoring was intended to capture events of any origin, known or unknown. In twoof the systems the monitors were left in place continuously for over a year and a half. Short-termevent monitoring was performed to detect pressure changes during the following types ofscheduled operational events:pump tests (including starts/stoppages);high demand periods (e.g., system flushing, fire fighting practices, tank filling,and high-demand consumers);valve operation (e.g., butterfly and pressure reducing valves); and,surge tank operations.The primary electronic pressure monitor used was a high-speed single-channel pressuretransient datalogger (Model RDL 1071L/3 Pressure Transient Logger; Radcom Technologies,Inc., Woburn, MA). In some cases a slightly older model of the

Product Details

Edition:

Vol. - No.

Published:

11/02/2003

Number of Pages:

20

File Size:

1 file , 440 KB