Main Vent on Boiler

RPK

My employer (small commercial HVAC company) took a job replacing a steam boiler. It a Peerless 210-8-S, atmospheric burner, about 1,000,000BTU/H. Apparently the new boiler will be almost identical to the old, and the bid was to replace the boiler only. Not a great situation to be in, I know.

I haven't see all the piping or radiators in the building, but it's a two-pipe system with TRVs and thermostatic traps on all radiators. The mains appear to be vented via crossover traps. I don't know how many, how big, or where all of them are located, but there are two in the boiler room (main leaves, two supplies circle the perimeter of the building in opposite directions and end up back in the boiler room).

I'm trying to figure out why there would be a main vent (Hoffman 75) and a vacuum breaker installed directory on the boiler. I'm thinking perhaps the crossover traps are not large enough (or failed at some point) causing pressure to build and shut the boiler down prematurely. Does that theory hold water? Could water expansion in the boiler be building pressure? Obviously the vent closes as soon as there's any steam being made, so I don't see how the vent on the boiler would do much of anything.

What other reasons might there be for that vent? I was surprised to see it there, but my steam experience is limited so I thought I'd ask the experts.

Next time I'm on site, I'll take picture of everything.

nicholas bonham-carter

Is there a vacuum gauge on the system? Hopefully, the piping according to manufacturer's requirements will present no problem.
Maybe this was an old vacuum system like a Dunham, and with a few failed traps causing problems, the vacuum breaker was put on as some sort of bandaid, when it was observed to operate as designed, or when the boiler was converted from coal to oil/gas.
Any boiler replacement should include the possibility of checking for, and replacement of failed radiator, and crossover traps.Sailah here can supply new internal parts so making it easier.
Don't forget the cleaning/skimming of the boiler several times after the installation, (you could show the owner how to do it, as a cost-cutting feature).--NBC

JUGHNE

The 75 would open and also serve as a vac breaker once it cooled off?
But located right at the boiler it would be a long cool down time.

Fred

Are you sure it's not a Hoffman 76, vacuum vent? They look the same. Not sure why it's there?
http://www.supplyhouse.com/Hoffman-401432-76-1-2-x-3-4-Straight-Main-Steam-Vacuum-Valve-11742000-p

RPK

NBC: Yes there is a vacuum gauge on the boiler. And the main control is a vaporstat.

Fred: It is indeed a 75, not 76. The 75 had been changed in the relatively recent past, as evidenced by a used, relatively new one in a box in the boiler room.

Steamhead

The presence of the condensate pump explains the vent. They were using it as a vacuum breaker to keep the vacuum from pulling water from the tank into the boiler, which would flood it.

I sure hope you're going to re-do the near-boiler piping and go back to gravity return!

RPK

Steamhead, I doubt I'll be able to talk my superiors into doing anything beyond installation of the new boiler. Apparently it's identical to the old one in terms of connections and dimensions. I'll certainly give it a try if it's the better way to go. Why is a simple gravity return preferable to having that pump there? Would the pump have been added for some reason other than easier return piping?

It sounds like we should keep the vent if the condensate pump stays. Are there any reasons to keep it if we do away with the condensate pump?

SWEI

These days, installation of a new boiler must include a review of and corrections to near-boiler piping in order to ensure proper operation.

KC_Jones

Might be good to remind your employer once you touch it you will be responsible for the good and bad. I have found in the company I work for once we redesign something we hear about all the problems with the previous design, after it's "too late".

There may be assumptions on the part of the owner that any "issues" will be fixed with the replacement, whether they tell you about them or not. Hint: your employer should be asking these questions.

I am having a hard time finding anything correct with the existing piping. I'm assuming your employer didn't add up the system EDR to verify boiler sizing either? I'd be willing to put money on it being over sized.

RPK

I know the drill all too well. All I can do is make recommendations and say "I told you so" when things don't work out so well. I'm afraid this train has already left the station. I'm trying to make the best of a bad situation and at least learn how this install should be going so I can do things right when I'm in charge one day. For now I'm going to reread Dan's book (Lost Art) and the boiler install manual and make up a list of changes that should be made that I can submit to those in charge of the job.

KC_Jones

RPK said:

I know the drill all too well. All I can do is make recommendations and say "I told you so" when things don't work out so well. I'm afraid this train has already left the station. I'm trying to make the best of a bad situation and at least learn how this install should be going so I can do things right when I'm in charge one day. For now I'm going to reread Dan's book (Lost Art) and the boiler install manual and make up a list of changes that should be made that I can submit to those in charge of the job.

Not sure how the wording is on the boiler you are installing, but some of them typically have wording that if it isn't piped to manufacturers spec they will void the warranty. Just some food for thought for your boss.

Many of us work for someone else making the decisions...I feel your pain.

RPK

After thoroughly reviewing the boiler install manual I see the following differences: Header not constructed per install manual. Supply takeoffs should not tee together. Equalizer/drain should be elbow at end of header downstream of main.


I would like to summarize the potential issues we are risking by leaving the existing piping.

I know incorrect piping can cause:
1. wet steam
2. Issues with surging and water level

What am I missing? Can anyone help me elaborate?

JUGHNE

No swing 90 joints on the steam boiler risers to the header. Could stress the sections of the boiler, especially if they come off the top.
No skim tapping?

Fred

Also Looks like the equalizer comes off of the bottom of the header instead of the end, like it should.

JUGHNE

Are the ends of the mains the double tee connected together with lines going to 2 F&T's......the ones with the drip nipples with the bell reducer couplings with boiler drains installed.

Could the 2 boiler drain locations been the end of main drips going to a wet return for a Hartford loop?

With this being a 2 pipe system where do the dry returns end up coming back to the boiler room.

As you said the train has already left the station; but you can learn a lot by studying others mistakes......the ones that happen a long time ago and the ones that are about to happen.

RPK

Jughne, Yes the end of the mains are the two bell reducer couplings.

The dry returns enter opposite ends of the boiler room and both end up at the condensate pump (picture attached).

There was no skim tapping on the old boiler. The new boiler will have one as called for in the Peerless manual.


I lost the fight over repiping (for now anyways).

Next issue is the Vaporstat. Old boiler had a Vaporstat, new boiler was ordered and shipped with pressurestat. I recommended we either keep the old Vaporstat or replace with new. I need to list some potential issues that could be caused by inability to run pressures as low as the old boiler was running and control them accurately. Those in charge don't want a used control on the new boiler and want to know why we should spend the $$.

ChrisJ

Fred said:

Also Looks like the equalizer comes off of the bottom of the header instead of the end, like it should.

The equalizer can come off of the bottom, in fact bottom is best as long as it's after any main connections into the header. It all must be in a row and the equalizer is last.

Jamie Hall

The problem with a pressurestat instead of a vapurstat is that you cant control the pressure to as low as you want to. There are three areas of potential problems.

The first is that each psi raises the water level in the returns in most properly piped boilers. You, unhappily, have a condensate pump in there so that isn't a problem, assuming that it is working properly and that its check valves are also working properly.

The second is that higher pressure puts more stress on all the traps and vents. They won't last as long, even if they don't actually fail from the high pressure. This is an economic issue, but since it is "down the road" it seems likely that your paper pushers and bean counters won't care.

The third is that it takes more fuel to reach the higher pressures, and the system won't heat as evenly. This also is mostly an economic issue.

Good luck.