# Passive Gate The passive gate is a simple one-way valve that prevents gasses from flowing backwards. The valve's input is on the side of the [color=red]red[/color] circle. The valve also shows the current flow rate of the pipe when examined. It's useful in many applications, for example: - Preventing a pure gas from getting contaminated via a mixed gas flowing back through the pipe. - Preventing pressure or temperature changes across two [textlink="pipenets" link="PipeNetworks"] in the opposite direction. - Quickly checking the flow rate on a pipenet without needing a [textlink="gas analyzer" link="AtmosTools"].