The Air Blocker traps water in its chamber to block the head of air from re-entering the control valve body. This helps reduce the iron oxidation that occurs in the control valve on AIO systems equipped with a NWTS or VESTA AIO control. The Air Blocker extends the valves service life and cleaning intervals over systems without an air blocker. It is designed with the twist lock feature that has an O-ring seal on will only work on the 1" control valves with 1.05" riser pilot.