The UNF3 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 at low pressure through copper tubing while brazing displaces the oxygen, preventing oxidation and the resulting scale. Scale inside the tubing can cause blockage within the TXV valve. Nitrogen flow is visually confirmed by the float ball rising in the flow indicator tube. If the ball does not rise in the tube, then there is static pressure [no flow] and oxygen is not being displaced. Controlling the flow of Nitrogen gas conserves its consumption and cuts operating costs.