Mystery Fitting

SteamySwede

Any ideas what this square fitting may be attached to a vertical section on a dry return in a 2-pipe residential steam system?  There are 2 vents (Hoffman's?)nearby.  Please see photos.  Thanks.

Steamhead

Might be an air vent

from the way it's piped, but I've never seen one like that.



The other two are Hoffman #4A vents. These cute little vents are almost certainly too small for your system.



If the square vent is the only thing that might be a vent on the dry (overhead) return, and the 4A vents are on the ends of the steam mains, we've established that it is the dry return vent.



A Vapor system like yours is designed to operate on a few ounces of steam pressure, that's why it's called Vapor. The design also eliminates vents on the radiators. The steam comes in thru the rad valve, and the air leaves thru the return connection along with the water produced when the steam condenses. There is usually- but not always- a thermostatic trap or some other device at the rad's return connection to keep the steam out of the dry return.



When the dry return reaches the boiler area, the water is returned to the boiler, and there is a venting device to get rid of the air. The vent may have a small check-valve in it to keep air from returning. This was a great feature when boilers burned coal but not so good on oil or gas.



In order for this system to work well, not only do the rad valves need to work properly (as in your other thread) but the air must vent quickly. There are main-line vents available that make those 4A vents look like toys, specifically the Gorton #2.



Where is this system located? Have you been able to see a name on the square vent?

SteamySwede

JV73R

There is an embossed, cast number on side - JV73R. Hard to make out so a few digits could be something differnt. It is definitely a vent as I was able to see what looks like a 4-way vented cylinder sticking out the top.