Why Backflow Occurs 3

Repairing a pump may cause the pressure in the public water distribution system to change pressure creating a cross-connection incident.  Pumps are used to move water from a lower elevation to a high elevation. Centrifugal pumps are typically used in the transmission of water. High booster pumps are used to increase the pressure in a public water distribution system and to supply water to elevated tanks. If the pump is shut down for repairs the pressure on the discharge side of the pump may not be adequate to supply water and maintain the pressure needed to and are a section of the distribution system or to buildings that are elevated above the hydraulic grade line of the of the public water system distribution system.  The hydraulic grade line is defined in American Water Works Association Reference Handbook Basic Science Concepts and Applications to mean a line, which connects all piezometric surfaces along the pipeline.  The hydraulic grade line is used to determine the pressure at any given point on the public water distribution system. Any building floor located above the hydraulic grade line will not have water pressure. If the building relies on booster pumps to maintain the pressure at a certain elevation and the booster pumps are shut down for repairs, portions of domestic internal water system in that building may become sub-atmospheric. If the cross-connections are not protected and there is an unprotected submerged inlet, the non-potable water will flow into the potable water system creating a public health threat. All cross-connection shall be controlled where they exist especially when a booster pump is needed to maintain pressure.