OEM 4231 AP-4231 Aprilaire Humidifier Yellow Water Orifice- For Models 500 500..

This simple but critical part regulates the flow of water into the humidifier. Be sure to clean or replace your In Line Strainer (Aprilaire part # AP-4231) when you replace the orifice. This Item is used in Aprilaire Humidifier Models: 400, 400A, 500, 500A, 550, 560, 600, 600A, 600M.