Example of Reversal of Flow – Backflow Backpressure Case 4

A single valve connection exists between the public water system and the fire-sprinkler system. The fire-sprinkler system is connected to an auxiliary water source and the public water system.

The fire-sprinkler system is normally supplied from a nearby lake through a high pressure pump. The fire pump water pressure is greater than the public water system pressure. The fire pump is activated for testing the first Monday of every month. When the pump is activated, there are complaints from residents near the mill building of odor coming from the drinking water.  When the fire pump is tested, non-potable water from the auxiliary supply is pumped into the public water system distribution system. The valve separating the two systems is not drip tight and is leaking or is left open during the fire pump test. The valve separating the two systems would normally be left open for firefighting purposes. It should be closed during the fire pump test.

To prevent a cross-connection incident, a backflow prevention device should be installed on the public water system service line to the fire-sprinkler system. All fire-sprinkler systems that utilize an auxiliary water supply shall be equipped with cross-connection protection.