Uniweld Nitrogen Flow Indicator with Inlet Connection 1/4" Female Flare and Outlet Connection 1/4" Male Flare. The UNF Nitrogen Flow Indicator is a visual tool that confirms the flow of nitrogen gas through the copper lines during the brazing process. Flowing nitrogen gas through copper tubing while brazing displaces the oxygen, preventing oxidation and the resulting scale inside the tubing that would otherwise be picked up by the refrigerant and contaminating it. Nitrogen flow is confirmed by the flow indicator tube. If the ball does not rise up in the tube, then there is static pressure and the oxygen is not being displaced.