Frustrated with the two pipe air vent system...

drtom

Does anyone understand these systems? My system does not have any MAIN vents, but still seems to work okay. It has two VENTRITE #33s on the return pipes, does this make any sense? There are no vents on the supply lines at all.

Some of you say that these systems should not have any main vents. Some of you advise putting main vents on the supply lines, and others advise removing the vents from the dry returns. There are no wet returns on this system, there is a small area just before the pipes go back into the boiler that is "wet" but it is very small.

What books can I read that have specific information about "Two Pipe Air Vent" systems?

Steve_210

I Rember

your pictures and steamhead expert advise. after the returns leave the rads there should not be any vents, it look like you have one?

nicholas bonham-carter

books on steam

go to the shop here and order a copy of "the lost art of steam heating", and "greening steam". both are very informative.

i believe you have a "vapor system", the cadillac of steam systems, and you can do a search here for that term, and then post specific questions. a few pictures of your piping, and radiator shut-off valves would help to identify it.--nbc

Charlie from wmass

You could call for a service call

I would be happy to look at your system but I do charge for travel one way and my time on site.

drtom

Long Drive

How much is your hourly? It looks like it's about a two hour drive one way.

drtom

Good point...

I am just having a hard time connecting with the concept of an air vented system without any main vents.

Jamie Hall

It does

sound as though it may be a vapour system.  Among other characteristics, they had no vents on the steam mains (but crossover traps connecting to the dry returns at the ends) and one or more vents on the dry returns right at the boiler.  What you are describing makes a great deal of sense.  Do get the Lost Art -- it describes these systems in detail (and is a fun read).  While you are waiting for it to come, why not give Charles a call, as he suggests.  Rhode Island isn't all that far from where he hangs out, and he really does know his stuff.  And while you are waiting for him to come, check your mains and dry returns.  I'd bet that if you follow them along to the end, you will find a nice crossover trap lurking there, connecting the two.  I could be wrong; have been before.  But if you do, that trap is acting just like a main vent.



And it's not true that nobody understands these systems!  They're just a little different from "normal" two pipe systems, that's all.

TomM

post a print

tom, you should post a schematic of your complete system.  I think you posted one before, but it didn't include the return piping.

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also, there's not much in LAOSH about true two pipe air vent systems, except a description about how each radiator must have its own wet return to work properly.  but dont let that dissuade you from buying hte book.  I have been unable to find any good info about two pipe air vent systems either.  It seems odd that they would use the extra piping for no really good reason. 



and remember, they didn't do much venting other than rads sometimes when boilers were coal fired.

Jamie Hall

A very quick rule of thumb...

which doesn't always work.  But usually does.



Are there vents on the radiators?  If so,it is either one pipe steam (one pipe into the radiator, that's all) or a true two pipe air vent system (Lost Art, pg 228 - 229).  These latter are scarce as hen's teeth, but they do exist.  Assuming they haven't been knuckleheaded, they are also distinguished from anything else by having a valve (not a trap) on both the "inlet" and the "outlet".  There was a lot of experimentation in the piping for these things, but they really are fancy one pipe systems with a bunch of extra pipe and valves, and can be treated in much the same way.



Now and then you will run into a true two pipe system which has vents on the radiators, or on some of them.  That's a knucklehead job, and you would need to go back to square one to fix it.  Can be done.  Adds to the vocabulary...



OK.  No vents on the radiators.  Then it is either a vapour system, designed to operate on very low (ounces) pressure, or a conventional two pipe system. 



There were a whole raft of vapour systems; as was common a hundred years ago, there were a lot of ingenious folks inventing things.  All of them, however, have some means of keeping steam from passing through a radiator, but letting air and condensate out.  This may be a thermostatic trap (very common) on the outlet.  It may be an orifice on the inlet, or a reduced valve opening (also common).  It may be any one of a number of fascinating patented outlet fittings.  But one way or another, steam was never supposed to get past the radiator.  Condensate did, and went through a dry return (mostly) back to the boiler.  Air also did, and went through the dry return back to the boiler, too, where there was one or more vents to let it out (the earliest systems had just an open pipe, no vent at all -- just an open pipe).  The earliest systems also often did not have a connection from the steam main to the dry return; the air vented out of the mains through the radiators.  Later systems did have a connection: a crossover trap, which was the same as a radiator thermostatic trap (sometimes bigger) which connected the end of the steam main to the end of the associated dry return and let air go over, but not steam (they'd let water go over too, but the water is taken care of by a drip to a wet return, or by counterflow in the steam main).  This helped even things out.  There are also a variety of interesting contraptions which cope with the possibility of excess pressure -- but we needn't worry about that right now.  I might add that many vapour systems also have wet returns, to handle the condensate -- but they always have dry returns.



One thing about vapour systems (and, by the way, from your description I'd bet that that is what you have): the pressure must, must be kept low.  By low, I mean no more than 8 ounces per square inch, and often less (the one in the museum I supervise runs at 6.5 ounces per square inch maximum).  Otherwise, one or more of the contraptions used to regulate where the steam goes won't work right.



Last, but not least (and certainly quite common) are what might be called conventional two pipe systems.  They depend on the action of the thermostatic traps to prevent steam from getting through the radiators and into the returns.  They may have dry returns, but not necessarily.  In these, it is important to vent the ends of the steam mains, to get even distribution.  If they have dry returns, these could be vented too -- there's no harm to it -- but it isn't important to do so.  These can run happily at slightly higher pressures -- up to say 2 psi, although 1.5 psi max. is better.



As I said above, my betting is that you have a vapour system.  As others have said, these were the Cadillacs of steam heat.  They are simple enough to maintain, although exactly what maintenance might be needed to tune them up to run properly varies somewhat with the system.  First, pressure: as I said above, ounces.  Not pounds.  Ounces.  You will need a vapourstat to control the pressure; pressuretrols just won't do the job.  Second, if you have traps they must be working right.  If they were never overpressured, they can last a long time.  They can also fail, either open or closed.  If they fail open, that radiator will heat like mad -- and other radiators nearby will heat very little, if at all.  If the outlet pipe is steam hot (a good IR thermometer is a big help, although the yeouch test also works) the chances are the trap is bust.  Conversely, if the radiator won't heat at all, either the valve is closed or the trap is failed closed.  Easy enough to figure out.  Either way, trap replacement parts are easily available.  If you have no traps, but have one or more radiators which are much too hot too fast, odds are that somebody, sometime, messed up the valve setting or removed an orifice.  This is a little trickier to diagnose and fix, but not that bad.  If you have water hammer, odds are that there is a sag in a pipe somewhere, or a pipe has gotten pitched wrong -- check everything with a good level (not just end to end on longer runs; they do sag in the middle!) (this assumes the near boiler piping is good -- if it isn't that can cause hammer in even the best piped otherwise systems).



And so on, for starters.  I hope this helps; come back with more questions as you have them.

Charlie from wmass

After looking at the photos

It is a two pipe air vent system. It has been knuckleheaded a bit but nothing that can not be fixed.

TomM

carbon dating

in the future, you could also use dating techniques to determine if it ever had traps or not.  according to dan, the trap was not invented until 1903.  if you're house was built before then and the system looks original, then you probably never had traps.  if you dont' know when your house was built, you could look at the nails.   cut nails vs wire nails.  if the house is completely built (original stuff) with cut nails, it is probably built before 1893.  if completely buit with wire nails, probably built after 1910ish.  if it is a mixture of the two, then sometime in between.   just a thought