The following guidelines for flushing of distribution system may be followed:
(a) Need to flush Distribution lines
The purpose of flushing is to remove sediments and stale water and to help maintain chlorine residuals throughout the distribution system. It helps to reduce the occurrence of unsightly deposits in the water and eliminates unpleasant odour.
(b) Rules of Flushing
(i) Prepare a map of the distribution system, showing the position of all valves and hydrants.
(ii) Always flush individual section of mains, by isolating valves at intersections during the flushing. This allows a better velocity for given conditions.
(iii) Never flush a large main from a single smaller one - the volume will be insufficient to flush the larger main. Trunk mains should be flushed prior to flushing branch lines.
(iv) Be careful not to shut down an area or mains inadvertently. This can happen when working around mains already flushed and left isolated from unflushed mains.
(v) In most cases, a fully opened fire hydrant will provide adequate velocity to stir up the debris in a watermain.
(vi)Ensure that ‘slugs’ of discoloured water have been removed from junctures with mains previously flushed.
(vii)Avoid opening or shutting fire hydrant valves rapidly to avoid water hammer.
(viii) Never leave an area practically shut down overnight, as fire protection may be severely impaired. Schedule work so that each zone can be completed by the end of the shift.
(ix) Avoid damage to streets or lawns. Direct the flow from hydrants into the wheel of a truck or drain, or devise on energy dissipater.
(x) Marked closed valves on a map and erase the marks when the gate valves are re-opened.
(xi) Watch out for construction projects or open manholes.
(xii) Ensure that all water contributing to a flow comes from cleared areas or from mains large enough to resist being stirred up by the flow.
(xiii) Notify consumers in the area who might be affected by the flushing, such as the inconvenience caused by reduced pressure or dirty water.
(xiv) Keep lengths of main being flushed, as short as possible, especially on small diameter pipes. Velocities must be kept high to be effective and the shorter the ‘run’, the higher the velocity attainable.
(xv) Do not hurry the flushing. Make sure that all debris are eliminated. In some areas if the water never really becomes clear, site judgement must be made by the supervisor on when to stop.
(xvi) As part of the flushing exercise, the team should take the opportunity to inspect all the valves, hydrants, air valves, pipelines, etc.
(xvii) Flushing should be carried out during the non-peak hours preferably at night to minimise supply disruption and for maximum effectiveness.
(c) Equipment and Manpower
A two-man team is generally sufficient for a flushing operation. The team should be equipped with a pick-up truck and the necessary valve keys, picks and other equipment.
(d) Records and Samples
(i) The flushing team must provide the engineer with the following information:
a. Rate and time of flushing.
b. Flushing points and location.
c. Time required for water to run clear.
d. Description and nature of the water. Presence of odour, discolouration and/or turbidity.
e. Samples of the dirty water and final clear water.
f. Reports on any defective valves, hydrants, air valves and leakages.
(ii) The volume of water used for flushing must be recorded and should be considered as accounted for water. To measure the volume of water used, always install a hydrant standpipe and a standard 65mm diameter flow meter.
Sarawak ID
