Pressure vacuum breakers ensure fluids travel in one direction through a system, preventing contaminants from flowing backward and entering a facility's water supply. They're used for continuous supply applications and installed above the point of use, such as a sprinkler system. Pressure vacuum breakers rely on an air vent to create an air gap. Negative air pressure on the outlet side of the valve traveling through the air vent activates the valve and stops the backward flow of liquids.