The non return isolation duo valves commonly known as duo valves are used at the cold supply line to the hot water services. The non return isolation valve's main job is to isolate the mains supply to the hot water system by using a one way check valve internally and can be switched off manually by using either a quarter-turn ball valve or a jumper valve mechanisam. These features can ensure that the hot water do not back flow back into the mains supply even when presurized. The non return isolatio ball valves can be switched off during services and maintenance.
