Often on high points of steam heated Shell&Tube heat exchangers etc. I've seen a vent specified to allow air and other non condensables to vent. e.g. this sketch http://www.spiraxsarco.com/images/resources/steam-engineering-tutorials/14/6/fig_14_6_1.gif What's this device (I mean the one labelled "Air vent") in practice? It doesn't seem like a regular steam trap. Or is it? Or just a weep hole? But that'd constantly bleed steam. In general, how is venting of steam enclosures achieved.