The answer to 'types of backflow preventer' is that there are several main types of backflow preventers used in plumbing systems to protect against the reverse flow of water or other liquids. The most common types are atmospheric vacuum breakers, pressure vacuum breakers, double check valve assemblies, and reduced pressure zone (RPZ) assemblies.
Atmospheric vacuum breakers are the simplest type, designed to prevent backflow by allowing air to enter the system if the water pressure drops. Pressure vacuum breakers add an additional check valve for more protection. Double check valve assemblies have two independently acting check valves, while RPZ assemblies have two check valves plus a relief valve to safely discharge any backflow. The type of backflow preventer required depends on the level of hazard and local plumbing codes.