How to Lessen Corrosion Damage After Main Air Valve Failure?

Fishin_Rod

Went through the boiler room yesterday for MORE Christmas decorations and heard a strange hissing sound. Tracked the problem to a failure in my main air valve (Hoffman 75) on the condensate return lines. The valve is remaining open after the end of the boiler cycle and pulling fresh air into my system.

The sight glass shows dirty fluid, and the water was pretty nasty when I dumped some through the low water cut-off. I suspect I have been pulling oxygen into my water system for quite some time and have greatly accelerated the corrosion.

What is my best course of action at this time? (I am not a "steam" guy. I believe my system is described as a "two-pipe" steam system with no condensate pump. Boiler is a Dunkirk Model 400.)

Do I just need to add a water treatment to the boiler? (For example RectorSeal or Rhomar product?) Any and all advice would be greatly appreciated.

Thanks,
Rod

Fishin_Rod

P.S. The main air valve would start hissing immediately when the burner kicked on. I think it was too rapid. There is a check valve at the very downstream end of my condensate return lines. I believe this is not closing, and expansion in the boiler section immediately after heating commences is pushing air backwards through the check valve and then out of the main air valve.

I opened a pipe union upstream of the check valve. This union is slightly below the normal water level in the boiler. Water leaked out of the union until it equalized with the water level in the boiler. There was some sludge in the horizontal pipe and the union.

Should a 1-1/2" brass swing check valve have sealed under those conditions and prevented the water from flowing backwards through the valve? If so, is cleaning the valve of debris an option, or is that a clear choice to replace the valve at this time? (Only $22 new.)

Thanks again,
Rod

Jamie Hall

With very very few exceptions, every steam system pulls air back in at the end of a cycle (this drive @PMJ crazy), but it's the way they almost all work. The way a vent is intended to operate is as the cycle starts, and steam is being created, the vent is open to allow air out of the system so steam can move in. When (and if, in some systems) steam reaches the vent it will close. Then, at the end of the cycle, the vent should open.

Is this the only vent on your system? if so, it may well be too small for a modern system. To decide, though, we'd need to know a good bit more about the system -- and where this one is actually located.

A check valve is almost never required in a steam heating system -- and is frequently nothing more than a maintenance nuisance.

OK. A little more information here. You say you think this is a two pipe system. That would be you have a steam main or mains leaving the boiler area, and each radiator fed by a runout from that steam main. Then each radiator will have a return to a different pipe, usually parallel to the steam main, called a dry return. Do the radiators have traps on the outlets? If not sure, post a picture... Now. What happens at the end of the steam mains and the associated dry returns? There are two possibilities: either they simply end (and are not joined!), and the steam main has a vent at that location. The other is that there is a trap, just like a radiator trap, piped with the inlet attached to the steam main and the outlet dropping into the dry return. That is called a crossover trap. You really have to have either a crossover trap or a vent. In many cases (not absolutely all) there will also be a pipe going down from the end of the steam main to a wet return near floor level, and a similar one going down from the dry return to a wet return.

In either type, the dry return must be vented before it drops to the boiler inlet. If you have crossover traps, that's the only vent needed on the system.

Which type do you have?

In either case, a check valve on the wet return serves no purpose.

Fishin_Rod

Jamie, thanks for all of the help! (Please feel free to correct all of my incorrect terms - in case someone else reads this thread later.)

Do the radiators have traps on the outlets?

Yes. All radiators are plumbed with incoming steam line, then valve, then entry to high port on radiator. Exit is from a low port on the opposite end of the radiator, to a small brass steam trap, then to the condensate(?) return line.

Is this the only vent on your system? if so, it may well be too small for a modern system.

My system is 102 years old. The original boiler finally died about 10 years ago. We had the replacement boiler installed by "the best guys in town". It did not work. (IMO, because they removed lots of lines and equipment they did not understand.) They finally had to get a retired guy to come in and fix our system.

I believe the Hoffman 75 is the only main vent on our system. One large radiator that is farthest from the boiler has a small radiator (torpedo?) air valve that still seems to work.

I believe our system has dry returns that come together in the boiler room. Instead of the crossover traps you describe, we just have the Hoffman 75 main vent where the dry returns converge, and then drop back to the boiler inlet.

I believe we also have a wet return on our system. We have radiators on three floors. It is a 2-story house, but there is lots of living space in the basement. (We live in tornado alley in Kansas.) The radiators in the basement have return lines that gather to a single line that comes in to the boiler room at the level of the basement floor. This line then comes up about 2' and tees into the downcomer line from the dry returns. (I believe this matches your description of a "wet" return.)

I believe there is a CHANCE that the operation of my main vent has NOT changed. However, I am pretty sure it used to close when warm steam/air finally hit it from the dry returns. It now immediately goes on a vacuum as soon as the boiler fire goes off. I did confirm that it vents air out shortly after the boiler fires. However, I did not confirm that it ever closed at some point in the middle of the heating cycle. It must close at some point, or you could just leave a piece of open pipe at the top of your dry returns manifold?

I also thought keeping oxygen out of our boilers and pipes was one of the key factors for longevity. However, I do not have a local expert to consult, since there are very few residential steam systems remaining in my city.

I hope that gives you a little more information to evaluate my situation. If you need more info, just keep asking specific questions that I will try to answer about my system.

Thanks.

Jamie Hall

It does -- well done!

Given the age, it is quite possible that the original system didn't have either crossovers or main vents on the mains. Whether you need them or not... some would say, of course! But me, I'd say that at some point you could put a low pressure gauge on the same pigtail as the pressure control and see what it reads. If it stays below half a pound or less, and the radiators all heat reasonably quickly and reasonably at about the same time... leave it be.

What I would do, though, is add to the main venting on the dry return. The Hoffman 75 is a very good vent, but they do get tired. I'd see if I could cleverly figure out a way to mount two Gorton #2s in the same place instead. And stop right there... you can leave the stray air vent on that farthest radiator. It will do no harm.

And... yes indeed. Odd as it may seem, if all the radiator traps are working as they should, steam can never get into the dry return, and it is entirely possible that the main vent will never close. And, as you note, it could just be piped to the atmosphere! In fact, that was done not infrequently.

Therefore... it really is helpful to check the radiator traps. You can do it with an IR thermometer, although those can be misled by different finishes on the pipes -- or by yeouch approach. Which is -- the inlet to the trap may be hot, even steam hot, but the outlet should be noticeably cooler.

Now on nasty water... if there is a blowdown valve on the low water cutoff, as you seem to suggest, that should be operated somewhere between once a week to once a month -- and the first burst of water coming out will, indeed, be pretty horrible. You don't have to run enough to get it clear, just freely flowing. A gallon or two is usually ample.

It's quite true that oxygen isn't all that desirable, but in steam systems it rarely causes any trouble in the piping. What can cause trouble is if you have to add a good deal of water -- say more than a gallon a week beyond whatever you blow down (you shouldn't have to, by the way -- more than that suggests a leak somewhere). That does bring in oxygen -- in the water. Which can cause the boiler to rust below the water line. Not good. The solution to that is if you do add water, run the boiler up to steam. That will drive the oxygen out.

Fishin_Rod

Jamie, thanks again.

The needle on the 30# gauge on the pigtail that was installed during the boiler replacement never moved off of the pin. I recently installed a 15# gauge. It shows 0.5#-0.75# of steam pressure at the boiler.

The radiators seem to all heat reasonably well and at about the same time. (Of course, where the pipes are exposed sufficiently for me to know the steam path, it is clear they heat up in order.)

Who knows what the old system had before the workmen ripped it out? I do know that there are three new 1/2" plugs in the dry return lines just before they all join together (where the Hoffman vent is installed). Those pipes are all original, so there may have been a series of small vents.

I also remember a large cast iron(?) cylinder about 10" in diameter and 18" long on the original system. It had a large weight on an angle arm to make adjustments. (I had no idea they would remove it.)

I do have a cheap IR thermometer. I have been using what you call the "yeouch" approach. I suspect the IR thermometer will be both an improvement in accuracy and pain avoidance.

Since all of my traps appear to be the same, I am sure the IR thermometer is accurate enough to determine the difference between a good and bad trap.

I am worried about the "nasty" water. I only know one system, so I can't judge what is a normal level of "nasty". However, the sight glass pictures I see on the forum all show fluid that looks much cleaner than mine!

I will keep dumping 1/2 to 1 gallon a week through my blowdown valve to clean up the water a little. If I am not losing water over the course of the week, then my system should be good to go?

Thanks,
Rod

mattmia2

The cylinder and weight thing was some sort of pressure regulator that moved the dampers on the coal boiler to make the boiler burn faster or slower. If you post some pictures of the radiator valves and traps and where supplies and returns connect and anything else unusual someone here might be able to identify what system it is. Pictures of the cylinder would help a lot if you have any.

Jamie Hall

Basically, sounds like you're good. I wouldn't worry too much about the nasty water out of the low water cutoff -- it will be. Now if it's murky in the sight glass too, sometime or other -- like come spring -- you might want to actually drain and refill the boiler. But in the meantime? Not to worry.

I expect @mattmia2 is right on the cylinder thingy. It would have been nice to have it for a museum, and it was doing no harm being there -- but the usual reaction to something like that is "I don't know what it is or what it does, so tear it out and bury it".

Fishin_Rod

Good call, Matt!

Yes, the original boiler (1918) was coal fired and later converted to gas.

I didn't know anything about boilers when ours needed to be replaced, so I didn't take pictures of anything.

BIG MISTAKE!

That would have helped when we had to have an "expert" come in and fix the mistakes of the installers of our replacement boiler.

I think there were two dampers in the original exhaust vent pipe off of the boiler(?). However, I don't trust my memory on our original design, because I did not study it closely.

Jamie Hall

The cylinder would have controlled the inlet draught damper of the coal boiler, not the exhaust, and would have been disconnected when it was switched to gas.

The system worked wonderfully well. There was probably also a mechanical thermostat upstairs somewhere which acted in concert with the cylinder -- and the heat was constant and even. The efficiency and emissions, however, were... lamentable?

Fishin_Rod

The cylinder definitely could have been connected to an air inlet system.

I thought my gas bills would have gone down after we installed the replacement boiler. They did not, even adjusted for gas price variability.

I think my 100-year-old system was pretty efficient, since it was designed and installed by experts for their given time period.

I think my current system could be run more efficiently. That is why I have posted here about the main air vent, etc.

What can I do to possibly boost my efficiency?

1.) I think clean water converts to steam with less energy than dirty water? If true, what is best way to optimize steam generation?

2.) Check my steam traps on the downstream end of my accessible radiators? No reason to have live steam in dry returns behind the walls.

3.) My original boiler and the largest steam lines were clad in asbestos. My replacement two main steam header pipes(?) are just bare steel. As are the steam pipes leaving the boiler room. Any insulation recommendation for those?

4.) Other ideas?

Thanks.

Jamie Hall

On 1 -- no difference between dirty and clean, unless the "dirt" is excessive dissolved solids content -- but it has to be really excessive to be a problem. Oil, however, is a problem -- not because the water takes more energy to boil, but because the steam has a harder time breaking through the surface and you get surging and other evils.

On 2 - oh please do. Steam in the dry returns is very very unfortunate!

On 3 -- Snap on fiberglass. There are several sources for it (but not the big box!). 1 inch thickness seems a good compromise. It does increase efficiency some -- but not so much because it reduces heat loss from those pipes, though it does, but because it allows steam to get to the radiators faster, which shortens run times.