Installing Main air vents

Jerry Withers

Tomorrow I am having my annual steam system maintenance done and in addition to that some main air vents installed.



I spent a lot of time in determining where they should go. I am hoping that the contractor reaches the same conclusion.



I have 13 radiators. Nine of these are one pipe with counter flow and 4 are two pipe without an F&T traps or thermostatic vents on the returns. these 4 are all off of the same main and in essence seem to function as one pipe radiators. I have been getting at times steam into the returns so here is what I am planning to have done.



Install main air vents at the end of the mains for the "normal" one pipe radiators.



The 4 two pipe radiators all have thier returns pipes flow into a single return pipe (they all feed from a single supply and end up in a single return), so I am planning of having a main air vent installed right where the 4 returns reduce to a single return and between that and the boiler a 5 foot water seal as described on page 106 of "We Got Steam Heat". I figure that way all the radiators will have a main vent and the water seal will prevent steam from backing into the returns.



Al it is, with all the supply valves open on these 4 radiators I do not have any problems (no water hammer), but if the supply valve is closed a bit I did notice the radiators will heat from both sides and be cold in the middle. So, obviously I am getting steam through the returns. With the supply valves totally open and the air vents on the radiators (I know... not sure if they should be there with this 2-pipe hybrid ) set to vent very slow I am getting good heat.



What does everyone think?



Thanks!