Example of Reversal of Flow – Backflow Backsiphonage Case 2

A rubber hose is submerged in a laboratory sink — No backflow protection device is installed on the laboratory facet.

There must be adequate pressure in the public water distribution system to supply adequate pressure to the top floor of multistory buildings. Multistory buildings connected to the public water distribution system often lack adequate pressure to the top floors during high peak demands. To overcome this situation of insufficient pressure, building owners will install booster pumps to maintain adequate pressure throughout the building.

The two multistory buildings show above are connected to the same water main. The public water system cannot provide adequate pressure to the buildings during high water use days or during perk demands hours. Because of this situation, the building on the right has installed a booster pump. When the pressure is inadequate in the distribution system, the building booster pump starts pumping producing a negative pressure in the main and causing a reversal of flow in the buildings connected to the same water main.

In this situation, there was a submerged inlet without any cross-connection control. A vacuum breaker should be installed on the laboratory sink faucet and the pump should be equipped with a pressure cut off device to cut off the pump when the pressure approached a negative head or vacuum.