Vapor Steam working great!

hoffman

Hi, This is my first post!, but I'm no stranger to the wall. Since about two years ago when the plumbing contractor where I work started taking boiler calls I've learned a lot from this site and from Dan's books. I recently purchased a house (Jan 15') with a steam boiler and wanted share details about my own system. I don't really have any questions per say.... well yes I do, I'll get to that later. I wanted to share the details of my system. I feel guilty reading others posts about problems because my system works so well. I don't have any issues, its all good. I think a lot of that has to do with how original the system is. The only major change was a new boiler in 09'.

I have a two story brick house with 20 radiators. The house was built in 1929 with a Hoffman system. It is a two pipe vapor vacuum system. All the radiators have Hoffman valves and Hoffman steam traps. The boiler has a differential loop, and the original hoffman #76 vacuum main vent. Venting is accomplished with crossover traps on the ends of my two steam mains in the opposite corner of the house as my boiler (the house is a big rectangle) the air then travels uphill back thought the dry returns to the #76 vent. Back at the ends of my steam mains the condensate falls into the wet return and around the outside of my foundation to the Hartford loop and into the boiler.

The system works great, there is no noise, no leaks, no problems. It heats fast and even. My boiler is a Weil Mclain EG-75 300,000 BTU. I knew the system still went into vacuum because I had worked on the boiler for the previous owner. We pulled a radiator out for his bathroom remodel in the middle of winter and heard the vacuum as we disconnected it. The first thing I did after I bought the house was purchase a new pressure/vacuum gauge off ebay and install it. The existing gauge was the stock 0-30PSI pressure gauge which we all know is hard to read ounces pressure on and even harder to read vacuum. When I installed the new vacuum gauge I was a little surprised and disappointed not to hear any vacuum sound when I removed the old gauge. I was afraid the system might not be holding vacuum anymore. I opened the drain valve just to be sure and surprise, no water, air was being sucked into the boiler. I could not believe my pigtail was plugged solid! It surprised me because it was a brass pigtail from 2009. What surprised me even more was that this had never caused any problems. It could have been plugged like this for years. The boiler has a standard issue pressuretrol attached to the same pigtail and it was blocked from the boilers pressure. When I replaced the pigtail and installed the new gauge I was even more surprised to find the boiler heats on 1oz of steam. Its heats on 1oz the whole cycle, beginning, middle, end, it never gets any higher, ever. It never gets anywhere near the differential loop or pressuretrols cutoff points ( which was of course set to high). I had planned to buy and install a vaporstat and I probably still will but its just not necessary. The system could really have the 24v transformer wired from the gas valve to the thermostat. It heats on 1oz all day long, the thermostat is the only control I need. It never goes out on low water either, water makes it back before the low water cutoff activates. The gauge I bought is a very accurate, very large (oz indication marks) test gauge I bought on ebay. When the boiler turns off the system starts to dive into vacuum eventually stopping at 12 on the vacuum scale. It does leak vacuum slowly but there is almost always some left when the burner turns on. Either way there is no noise or problems.

The people who installed this new boiler did an okay job. They only used one 3" tapping off the boiler but the original steam header is excellent, a 4" pipe with flanged union in between takeoffs. The hoffman loop was never moved down with the new boiler install. It sits about a foot higher than the current water line but to my surprise it causes no problems.

The water feed is from a manual globe valve I haven't had to open yet. I'm going to ask the previous owner who lived here 6 years if he ever used it. If he says no I would not be surprised. When I first told him he had a steamer he looked at me funny because he was told it was hot water. I doubt he knew anything about adding water. Even the pressure relief valve from the original boiler is still in the system and still holding a seal. I opened it, even thought I know I shouldn't have, and it sealed right back up.

One minor problem I was having was half the time the main burner came on it would light a fire inside one of the steel pilot tubes. It was always a different tube. I had one of the old timers in town come over and check out the system while I cleaned the burners. This seemed to take care of the fire inside the tubes but my friend was concerned that I might be over firing because of how quickly I make steam. He told me how to clock the gas meter and recommended I do that. My results were surprising, my 300000 btu boiler was to my calculations using only 176000 btu's. I checked this against my 40000 btu water heater which was registering 36000 btu's. If the boiler is indeed under firing I suspect it has something to do with my good fortune in having a even heating system. The burner does not look under fired but I don't know how else to check it.

I know the importance of venting and how a manifold with multiple vents is a great way to go when it comes to main venting. What I don't get is how my system vents with one #76 valve and never breaks 1oz. The crossover traps have got to be part of this. I've worked on about half a dozen steam systems through work but this is the first one i've seen with crossover traps. Now I can't believe more systems weren't setup this way because the main vent never sees steam, so it just vents air. I'm sure thats why its still the original vent, because its life has been so easy. I was expecting to see the #15 vent from old Hoffman catalogs but its just one #76. It still holds vacuum like a champ and vents air whisper quiet. The radiator traps themselves don't even really see steam either. Whenever I touch the radiators when the heat is up I just feel the heat along the top. I think its pretty rare that the thermostat is calling long enough that the steam makes it to the trap. So my question is what pressure do vapor systems normally run at? Is it unheard of that they just run at a steady state pressure? To me it seems like everything was sized perfectly and the vapor system is doing exactly what it was meant to do, run on vapor. I don't get to go into other peoples houses and just sit and watch steamers go through a cycle. What kid of cycles do other vapors systems go through? Are they running up against the vaporstat or not?

Thanks for reading, if anyone has questions let me know.

nicholas bonham-carter

What a cool system!
Because the crossover traps are working properly, you don't have to worry about the returns connecting above the waterline.
The continuing vacuum must help in a quick responce to drops in temperature, as the Hoffman 76 is a rather slow vent for a large system like yours. If you want to experiment, you could always put a 3/4 inch check valve on in place of the Hoffman, and see if there was any improvement in response from cold to hot in the shoulder season. The functioning crossover traps will have taken care of the steam.
Have you solved the mystery of the lower gas consumption from the boiler rating plate?--NBC

PMJ

These old vapor/vacuum systems are something else all right. All that is needed is big enough installed pipe - thanks to those who came before us who paid the up front cost that made life so much better for generations to come.

1 oz maybe 2 is all I ever see in my system just like yours. Too low to do any control with. Rads rarely need to be more full than hot across the top to heat the place. I think you are in good shape. Enjoy!

BTW, don't see an automatic damper on your boiler. That is the single biggest cost saver you could add. Makes a huge difference in time to steam. Without it you just exhaust air you already paid to heat cooling down your boiler fast between firings for no good reason.

Jamie Hall

If it ain't broke... The only thing you might consider doing would be to add another Hoffman 76 at the same location as the existing one -- but if it were mine I wouldn't bother.

That Hoffman loop setting should be fine; they didn't need to be below or even near the water line. Just above it. It should trip at about 12 ounces or maybe less pressure -- but you really don't want it to do that, so keep the pressure down.

The system I care for is very similar to yours -- they last forever.

nicatniter

My system is very similar to the O.P.'s - it's a 1929 Webster System R (vapor/vaccum) with crossover traps. Instead of the (original) check valve someone had installed a Hoffman 75 on the return trap, but I replaced this with a 3/4" check valve (I removed the spring so the cracking pressure is essentially nil). It runs smoothly on less than an ounce of pressure, and goes into vacuum between cycles. Just a beautiful system. I will note that I replaced all the radiator trap and crossover trap inserts, so the returns never see steam at all.

vaporvac

I'm very impressed with 12" of vacuum... jealous really. I get 6" on a goo day, but I still have a lot of leaks. My Trane VV system is hitting up to 1lb of pressure on set-back now that I've changed the CPH to 1 and am tightening up the leaks. I'm thinking of going to three (No 2 option) and see if that helps things. Mine will stay in vacuum until the next cycle.

Dave in QCA

Amazing and beautiful system. If you try Nicholas' suggestion, just do it as a test and then put your #76 vent back in place. This system is designed to see steam in the returns if the boiler pressure rises and therefor, a vent device that stops steam is critical. Although the venting capacity seems less than what we would recommend today, the fact that you are dropping into vacuum and preventing air returning to the system at the end of the cycle, means that you have much less air to vent in the following cycles.

Congratulations on your system.

Jamie Hall

I can't say that I can endorse nicatniter's suggestion. If that Hoffman Loop ever does trip -- which it is designed to do at a certain pressure, typically around 8 to 12 ounces -- it puts live steam right at the vent, which is why the vent is where it is. That vent promptly closes, and the returns are pressurized to equal the mains. This allows the condensate to return to the boiler, and also protects the traps from over pressure.

Once that steam condenses, the system goes back to normal operation.

That's how it is supposed to work, and it works beautifully.

With a check valve instead of a proper vent, the check valve would open and you would have live steam all over the basement, as well as defeating the pressure balancing. Neither is good.

Dave in QCA

Jamie, I had always imagined that when a Hoffman Differential Loop "tripped", that it equalized the pressure in the returns to that of the mains. I recently found this description on g w Gill's website. I also read the patent description and I think he's got it right. When I first found it a few months ago, I thought of you and your Hoffman system. I was going to send it to you but never got around to it. You have probably already seen it, perhaps. Anyway, this is a good thread to post it to.
http://www.gwgillplumbingandheating.com/webapp/p/525/hoffman-differential-loop

Jamie Hall

Dave -- that's exactly what it does do; equalize the pressure in the returns to that of the mains. The thing is that it does it by effectively connecting the main to the returns -- and closing the vent(s) at the same time.

Good short description there... thank you!

ChrisJ

Beautiful system thanks for sharing!

vaporvac

This post does bring up an interesting point concerning two-pipe vaporvacuum systems: they need some sort of system equalizer. On mine it's just a pipe going from the mains to the returns...there may be some sort of valve there. I'm not sure how that would be easily achieved in the conversations we've had on converting two-pipe to natural vacuum.

PMJ

vaporvac said:

This post does bring up an interesting point concerning two-pipe vaporvacuum systems: they need some sort on system equalize. On mine it's just a pipe going from the mains to the returns...there may be some sort of valve there. I'm not sure how that would be easily achieved in the conversations we've had on converting two-pipe to natural vacuum.

On mine the traps are never closed so supply mains and dry returns are always directly connected through the rads. Supply mains are an oz or 2 higher when actually pushing steam but they quickly equalize through the rads when the burner is off.

vaporvac

So you don't have an equalizer pipe?

Jamie Hall

My system has no equalizer pipe, either. However, like PMJ many of the traps never close (the crossovers always do! Also some of the radiators were I am too lazy to have adjusted the valves... sigh... oh well). So when the boiler stops boiling, the pressure in the mains drops almost immediately to equal the pressure in the returns -- and the traps which had closed, particularly the crossovers, open very quickly.

I have one Gorton#2 and a Hoffman 76 as main vents -- as a result, the only time the system will hold a vacuum is when the Gorton has been closed because the Hoffman Loop activated; if the system chances to shut down right after that, before the Gorton opens (it's kind of slow opening) the system will go into a vacuum until it opens. If I had only vacuum type vents, it would go well into a vacuum -- and stay there for a while. Haven't gotten that far. Works OK as is, so not likely to bother!