Pipe flushing is performed to scour and remove deposits, encrustations, sediments, and other materials from the main. Complaints from consumers reporting taste, odour, turbidity, biological growths, red water, and staining of fixtures is a signal that the pipes need flushing or cleaning. The frequency of flushing can usually be determined by the number of consumer complaints and past experience with the system. Dead end pipes, for example, may require more frequent flushing. Flushing should be performed in advance of consumer complaints and should be scheduled during low flow periods.
Steps in the procedures for flushing include the following: 1) Planning; 2) Safety; 3) Flushing Progression; 4) Valve Closures; 5) Flow Velocity; 6) Discharge Location; 7) System Pressure; 8) Records; 9) Sampling; and, 10) Open Valves.
- Planning
Before undertaking the flushing program, schedule and plan the work, and notify consumers of the dates and times of flushing. Inform fire departments, affected utility companies, and other high or critical water users.
- Safety
Erect barricades, signs, and warning lights as needed to protect the public and workers.
- Flushing Progression
Start nearest the source and work outward into the distribution system so that material is carried away from the pipes that have already been flushed.
- Valve Closures
isolate the section of pipe to be flushed. Close valves slowly to prevent water hammer. RECORD the valves that were closed.
- Flow Velocity
A minimum flushing velocity of 0.75 m/s (2.5 ft/sec) is needed to scour material from inside the pipe. Increase velocity to 1.5 m/s (5 ft/sec) if high capacity pumps are available.
- Discharge Location
Open hydrants or blow-off valves slowly to prevent water hammer. Direct the flushed water away to prevent flooding and soil erosion. Keep the hydrant open for at least 5 to 10 minutes and longer if needed for longer pipe lengths. Observe the clarity of the water. Once clear water is observed, close the valve slowly.
- System Pressure
Assure that system pressure does not drop below 200 kPa (30 psi) anywhere in the system
- Records
Record time, dates, procedures, and general water quality.
- Sample
Take samples before and after flushing as needed to verify and check water quality.
- Open Valves
Reopen valves that were closed in Procedure 4. Use records to determine which valves have been closed in order to ensure that they are not left closed.
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