Southern Plumbing has trained staff to meet your safety compliance and filtration needs. Reduced Pressure Zone Devices (RPZDs) These backflow control valves are used to prevent contamination of the water supply by physically stopping water running back to the supply. They differ from other backflow preventers in that they are designed with added safeguards, and … Continue reading Safety & Filtration: RPZD, TMV, Billi & Zip