This Aprilaire 4001 Humidifier Saddle Valve replacement is used in many Aprilaire humidifier models in combination with the Aprilaire 4040 Solenoid Valve. This Aprilaire 4001 Saddle Valve is the humidifier component that supplies the necessary amount of water to your Aprilaire humidifier with copper tubing to the Aprilaire solenoid valve.