The RTD-CB back-flow restrictor prevents radiator back-flow and heat transfer at the return pipe in a one-pipe system. The back-flow restrictor is installed in the radiator return pipe with the bow pointing upwards. The RTD-BR bypass restrictor decreases flow through the bypass in a one-pipe system, thus forcing the correct amount of system water to pass through the radiator. The bypass restrictor will decrease the bypass with one dimension ( e.g. DN 20 > DN 15). The bypass restrictor is installed in the bypass by the radiator