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AprilAire #4640 Humidifier Scale Control Insert, Replacement Part

AprilAire Humidifier Scale Control Insert Replacement Part # 4640

This is the u-shaped component which encases the Water Panel Evaporator. 
 
 
Used with water panel number 10 and the water distribution tray number #4331 ,  sold separately
 
Fits:
Aprilaire Model   500, 500A and 500M