Our flow valve was inspired by a customer who wanted some way to reduce oxygen flow without having to call for his wife. It is usually connected between the cannula and extension hose where it can easily be reached. When the valve is open, the oxygen flow is set at the concentrator as needed. Closing the valve reduces flow to a calibrated level which is specified at checkout. It doesn’t harm the concentrator and is the same as turning down the flow on the control panel. In some cases it can cause a problem when used with a humidifier.