Product review (3 stars): INLET AND OUTLET TUBES SWITCHED......
This valve replaced the original valve for our Aprilaire 550 humidifier.  The old valve was half plastic.  This one is all brass.  ONE NOTE OF CAUTION.....THE VALVE DID NOT ATTACH TO THE HUMIDIFIER LIKE THE OLD ONE.  THE INLET AND OUTLET TUBES ARE SWITCHED.  I WAS UNABLE TO SCREW IT BACK IN PLACE ON THE BOTTOM OF HUMIDIFIER.  I think I will end up using duct tape........BUT the valve worked well.