Air vents are an important, but often overlooked, component in steam systems.  They are used to aid in the removal of air and non-condensable gases.  When a steam system is shut down it will cool and all of the steam within the system will condense.  This creates a vacuum which will cause air to be drawn into the system.  When the equipment is brought back on line all of that air must be displaced before steam can fill, and heat, the system.  Air vents are typically designed with temperature sensitive devices that are open when cool and closed when hot.  Air, being cool relative to steam, will pass through the air vent allowing steam to fill the system.  Steam reaching the air vent will heat the device and cause it to close.

Watson McDaniel manufactures several air vents utilizing the same technology found in our very successful thermostatic steam trap product offering.

Additionally, Watson McDaniel manufactures vacuum breakers, a special configuration of a check valve, which opens on vacuum to admit air into the steam system.  These devices are used to protect equipment from collapsing  due to excessive external pressure.  Vacuum breakers also aid condensate drainage from heat exchangers that are operating under vacuum conditions.