The GeneralAire GA4004 strainer screen is an important component of a properly functioning drain-type humidifier. The strainer screen, comprised of crushed brass particles, sits within the solenoid valve, which controls the humidifier’s water flow. A strainer screen is needed to keep the valve free since particles in the water might block it. A handy guide for straightforward installation is included with the strainer screen. To guarantee good filtering, the strainer screen should be replaced every two to three years.