Where is the air going?

gizmo

We are a mfrs rep in the midwest. Not a lot of steam, but usually we can get it figured out. This one has us stumped. We were called to look at a 7 year old steam boiler that was leaking. Top of the section was paper thin. Looked like a classic case of what we know as oxygen corrosion. The homeowner confirmed that weekly she was dumping 5-10 gallons of water to "clean out the system." OK, so that is part of the problem. Started looking around upstairs and immediately noticed that this 2 pipe system was a little different. Turns out it has Mouat radiator valves and Mouat return fittings (a non-mechanical trap) on all of the radiators except one.

Back in the basement to look at the piping. Two 2" steam mains head away from the boiler in opposite direction eventually meeting at the far end of the basement opposite the boiler. there they join into a single 2" pipe which heads back to the boiler room. Pitch is away from boiler room, around, and back. Returns from the radiators follow a single pipe which increases from 3/4" to 1 1/4" in the boiler room. Now here is the weird part. When the steam main and return line get back to the boiler, they just drop and are plugged into tappings on opposite sides of the boiler. There is no f/t trap, there is no air vent! there is no equalizer or Hartford loop. Yet for at least 7 years, this system has worked in some fashion or another! Where is the air going?

None of the original Mouat vent or regulating equipment was there. All the near boiler piping is just 7 years old.

Two other weird things. Where the two steam mains come together, there is a short piece of pipe that was was replaced and instead of a coupling there is a flange that looked original (1927). Also, the one radiator that does not have the Mouat valve and return fitting has a regular boiler valve, thermostatic trap, and an air vent.

We want to help the contractor get this right. Shouldn't we have him add a f/t trap at the end of the main where it drops to the boiler and an air vent to vent both the main (after the trap) and the return line? I never worked with a Mouat system before, but this seem to be missing enough components to now be considered a standard 2 pipe system.

But I still want to know where the air has been going.

Sorry, no pictures. Thanks for any help.

Dave in QCA

Mouat system diagram and explanation

Here is a link to a file on this site that has an excellent description and diagram of a Mouat System.  http://www.heatinghelp.com/files/articles/1376/541.pdf

This system, as shown, worked entirely on very low pressures, never vacuum.  All venting was through the radiators and water seal fittings at the outlets.  The return main had one non-mechanical vent /seal.  It is shown in the diagram.  Are you sure that device is not still there?  If it is not, then all venting is occurring through the one radiator vent in the system.  Since all radiators are venting into the return mains, the air flow in the return mains would be running backwards into the one odd radiator that has a trap and a vent.   Flow would be backwards through that trap, into the radiator, and out the vent.   Perhaps an oversight and error that has allowed the system to function.

I am going to step back and let the pros offer proper corrective solutions.  I know there are several who work with Mouat systems.

Pictures would sure be nice.

gerry gill

Mouat

vented his systems in two ways..one through air vents that may not look like anyone Else's air vents, ..or..he would not vent the supply at all and run a pipe off the dry return into the chimney..the negative pull of the coal boiler would aid in venting the returns..just about all we do is work on Mouat systems..he was a local Cleveland Hts fellow, so his systems are the dominant ones around here..I'll help your contractor out if he wants to get a hold of me.

gizmo

Thanks

Dave and Gerry: Thanks for responding. I am absulutely certain that there are no vents on the system other than the one radiator vent. What I don't know is what was there 7 or 8 years ago when the boiler was replaced. The old chimnet was abondoned because it was falling apart. The replacement boiler was pwer vented.

The fitting on the return side of the radiators looks like the one that Gerry has posted on this website. The radiator valves say "Mouat" on the side.

My real dilemma is how to take what's there and make it work. I am pretty sure that some components have been removed over the years. But for the last 7 years, the system limped along as described. I am simply truing to help this contractor and homeowner. The homeowner isists that the system worked better before the boiler was replaced 7 years ago, but no one can say what other work has been done on the system over the years.

Suggestions?

Dave in QCA

vent needed

It certainly sounds like you need to add a vent to the system.  I am going to let one of the pros that if familiar with Mouat Systems make the recommendation.  Hope Gerry is watching.

Steamhead

I agree

the air has to get out of the system some way. If the air can't get out, the steam can't get in.



What you're looking for is a device on the dry (overhead) return line that vents the air. This may also be a tee that was plugged, especially if that system originally vented its air to the chimney. I'd say it probably did vent to the chimney and someone screwed it up so that it allowed steam to get that far, which would explain what happened to the chimney.



The solution will be to add one or more Gorton #2 vents to the dry return.



Take some pics of what's there so we can see it.

jpf321

invisible vents?

This may be completely unjustified here, but it's worth a reminder perhaps .. I remember Dan saying that he once ran across radiators that had internal air vents with simply a pinhole showing on the side of the rad that was of course painted over several times and therefore invisible and inoperable. Before you go crazy, make sure you don't have these "invisible" internal rad vents.

The Steam Whisperer (Formerly Boilerpro)

Leaks......

I have seen systems with no official vents that still heated because there were enough leaks at supply valves, etc to let the air out.  Then the owner repaired all the valves and guess what, the heat stopped working.  Sometimes the world is very comical and cruel at the same time.  He added a vent and the system worked better than it ever had. 

Steamhead

A Mouat system

would not have had those internal In-Airid radiator vents. It was designed to route the air into the dry returns and vent it near the boiler, usually into the chimney.



That one radiator vent may be venting the whole system if there is no vent on the dry return. Air would go up the rad return line and out the vent. That would be one slow rad since air would be coming at it from both directions.



Gerry is our resident Mouat expert, I'd go with what he says.