Backflow preventers prevent the possibility of pollution in the water systems. Thus, the good water does not come into contact with the sewage or other pollutants. This is the same function that the vacuum breakers play. Therefore, in essence, vacuum breakers are types of backflow preventers. They are in the shape of plastic disks, and when there is water pressure, they move forward and cover the vents. One of the common types is the atmospheric vacuum breaker. It is the cheapest of the backflow preventers. The other type is the pressure vacuum breaker.