Air eliminators are used in liquid systems to aid in the removal of air and other gases.  Many systems designed for liquid service do not operate well when air is present.  One example would be flow metering.  Most flow meters are designed around volumetric measurement principles.  Air passing through a flow meter gets measured just as if it were a liquid, causing large flow measurement errors.  An air eliminator, mounted to the top of a stilling chamber and installed upstream of the flow meter, will vent this air, and only liquid will be presented to the flow meter.

Liquid heat transfer systems are another application where air vents are commonly used.  Air will tend to adhere to the tubes in the heat exchanger, in effect insulating the tubes from the liquid.  This will significantly reduce the amount of heat transfer and can also promote corrosion as the oxygen in the air provides a key ingredient for oxidation.  Again, a properly installed air eliminator will rid the system of air or other gases, ensuring superior heat transfer.

Watson McDaniel manufactures air eliminators that sense the density difference between liquids and gases - the buoyant force acting on a float actuates the valve plug.  Both soft seated and metal seated products are available.