Aprilaire 4040 Solenoid Valve, 24 Volt for Humidifier Models 400, 500, 600, 700 N/A Imported Genuine Aprilaire humidifier replacement part Made in Madison, WI, USA Ensures that the right amount of humidity is delivered into your home Controls how much moisture enters your humidifier, making it possible to maintain proper humidity levels throughout your home Compatible with all Aprilaire humidifiers except for commercial units and residential models 800, 330, 445, 110, 112, 350 and 360