Ranco Water Solenoid Valve Part Number 4040-001. The Ranco 4040 Series Solenoid Valve controls water flow to the humidifier to ensure proper humidity is delivered creating a more comfortable living environment. The 4040-001 solenoid valve has a strainer screen to filter out contaminants and eliminate build up in the humidifier. The 4040-001 kit includes an inlet compression fitting and ferrule to make installation simple. The solenoid valve controls the water flow to the humidifier by turning the water flow on and off. When the solenoid valve is closed, it will cut off the water flow to the humidifier. When the valve is powered it will open the flow of water to the humidifier. The solenoid valve is controlled by the humidistat.