The 433-6 from Taco is a Cast Iron Air Scoop for 1-1/2” NPT. The Air Scoop is designed to slow the water velocity in order to separate air from solution. The unit is manufactured from cast iron and features equal threaded inlets on both sides. Top of the air scoop features a 1/8" NPT outlet (for connection of a regular air vent such as Taco 400-4) and an additional 3/4" FNPT outlet for the expansion tank. Bottom of the air scoop has a 1/2" NPT threaded outlet, which also allows to connect a plain steel diaphragm expansion tank.