Designed for use in heating system to continually remove air which builds up in the system. This means the system wont need to be manually vented. It consist of a float connected to a valve. Air will exceed a level inside the float chamber resulting in the float dropping, opening the valve and releasing trapped air within the chamber. When the air is released it is replaced by water resulting in the float moving back into the up position and sealing the valve. Comes available with a quick releasing isolating valve which negates the requirement for an additonal isolating ball valve.