The Spirovent PJR000HA Vent Head is a replacement vent head assembly designed for Spirovent Jr. Series Air Eliminators used in hydronic heating, radiant heating, and HVAC water circulation systems. It works by automatically releasing trapped air and microbubbles from the system, helping maintain smooth fluid flow and efficient heat transfer https://www.partshnc.com/pjr000ha-spirovent-head-only-for-spirovent-junior-includes-o-ring