2 Pipe Steam, recent overheat, and return blow out.

superheathermo

First of all, I want to thank the site, and all the prior posts that I have been digging through, studying, reading, in order to help solve my problem(s). I am a engineer, but not really experienced in Steam Systems, although I have a technical background. I have learned alot by reading prior posts with issues similar to mine.
Here is the background:

Weil Mclain 300,000 (Circa 1960) btu, boiler, I believe it is a vacuum type 2 pipe steam system. The steam layout is such that one main steam riser comes off the top of the boiler, and splits into two symmetrical steam feed pipes. One handles 1/2 the house and the other handles the other 1/2. Running parrallel to each steam riser is a return, about 5 feet off the basement floor and within 6 to 12 inches of the Steam risers. Each return goes separately into the bottom of boiler, one on each side. On top of each steam return, at the boiler are Hoffman 76's. I have some photos and a diagram. The boiler has a White Rogers Pressure Switch Mcdonnel Miller Low water cutoff, and a vintage single set Honeywell Thermostat.

My elderly mother "heard a bang" in the basement of her 2 Story Tudor home. The basement filled with steam. She called 911. Fire department, water department, police shut down all water, gas to the house.

A Licensed Plumber came in, and replaced about 20 feet of the return that had pin hole blow out areas, and fired the boiler. 1/2 of the house heated up well. On the side that the 20 feet of return had been replaced, heat only came up to the closest radiators to the boiler, the rest were cold. The boiler used to run on 1/2 # with all radiators heating uniformly. The plumber then raised the pressure to 1.5#, this caused major water hammer, and maybe 2 more radiators came up. The boiler keeps short cycling on the pressure switch. The basement is hot as heck. The supply and return are scalding hot to a point, then cold as you get farther from the boiler. These radiators do not heat.

I learned that there is a loop seal at the end of each run, the loop seal has a cap. What do these things do, is is possilbe that the steam blow out caused these to run dry, it seems like the steam is fighting to supply and return with ease like it used to. Any thoughts, or help would be fantastic.

superheathermo

Layout

neilc

Start with turning the pressure all the way down as low as it can go,
post a up close picture of that device, and inside the cover also for any differential setting,
you're looking to cut in around 0.5, and out at 1.5.
Also, and importantly, is its pigtail clear ?
you would remove the Ptrol and be able to easily breath into the pigtail, back to the boiler, exhale only, cool boiler, refill the pigtail with water upon reassembly.
For something to POP, and fill the basement, it sounds like pressure built and blew the safety valve,
check the pigtail.
Then check the 2 main vents for operation.
Post a picture of the radiator outlets, traps?
if you overpressured, they may have jammed shut, you might try breaking each cap free and seeing if they free up.
You could check those 2 drip mud legs, but only if they look like they will unscrew easy, or wait til warmer times and open them when weather isn't against you. Be prepared for muddy waters.

JUGHNE

Did the loop seal get primed with water?
I assume that is what the top "clean out" cap is for.
The water seal would keep steam out of the returns if no pipe slopes were changed and the pressure lowered to where it was.

Does each rad have a trap on the outlet?
Steam in the return will back up to those traps and close them preventing air from venting thru the rad and keeping steam out.
Raising the pressure would just push a little steam into the rads with closed traps.

neilc

yeah, actually, that boiler piping leaves much for correction also.
no header or equalizer ?
those loop seals will prime fast enough , , , ,

superheathermo

Thank You neilc, I will get additional photos tomorrow of the radiators, outlets. As I understand it, the plumber did unclog the pigtail, and put a new pressure gage. Also I do not believe that there are any visible traps at the radiators, but i will check carefully tomorrow. The two main vents do whistle, but Im not sure what I am looking for. Those "mud legs" will be a challenge for me, but I will ask the plumber on Monday. I have a feeling that steam systems were not his forte. Thanks Again!

Jamie Hall

All of the above ^^^. Plus. It is imperative to get the pressure down. 1.5 psi will be close to, or will, blow those loop seals and allow steam into the returns.

The loop seals should refill on their own after a few cycles -- if you get the pressure down.

Then... I hate to say this, but the odds are good that if the pressure went high enough to blow the pressure relief -- which is what it sounds like -- it also went high enough to damage those two vents. One of them -- the one on the side which is working -- may have survived. The other one... probably not, and without it working, you'll get no heat or very little on the radiators which it serves. You need to replace it. In fact, I would replace both of them with Gorton #2s.

It is also possible that the overpressure damaged or destroyed some of the radiator traps. They all need to be checked.

Then, and last (for the moment), a system this small may not have had crossover traps. These are like radiator traps -- indeed, they usually are exactly the same, but piped so that the inlet is a vertical pipe up, then horizontal over a short distance from the steam main to the trap, then the outlet piped vertically downwards to the return. Is there any evidence that an one time they may have existed? There would have been one at or very near the end of each steam main. The system will work without them, but not as evenly or as quickly as it would if it had them.

superheathermo

More photos of system.

superheathermo

One more detail,
When I went to drain water from the bottom of the boiler tonight, a huge vacuum occured when I opened the drain valve, and water shot up in the sight glass??? The pressure gage was pinned at 0. Thanks again for your thoughts.

JUGHNE

I see no traps or orificed type control valves.
Possibly there are fixed orifices in the unions of the steam inlet valves. They rely upon a fixed steam pressure. Probably low as possible.

If the system was in vacuum for some time after shutting down then the air vent vacuum part is working as far as letting no air back in. But high pressure may have damaged the air venting part of the vents.

mattmia2

Might not be a bad idea to see how that beast of a boiler compares to the radiation connected to it. It isn't in itself the problem but will make things much worse if the aquastat fails to shut to down on pressure.

this is really great if you want to understand how it works:
https://heatinghelp.com/systems-help-center/the-ten-common-mistakes-made-about-steam-heating/

Maybe the dry portion of that boiler is large enough that the incorrect near boiler piping isn't so bad.

Jamie Hall

That vacuum you noticed after a pressure surge is not, unfortunately, surprising. The big Hoffman mains vents are known to do that. They aren't happy about it, though, and I'd really think about replacing them.

That system is designed to run on no more than 8 ounces per square inch. That's ounces. You should have a vapourstat to control it -- and a low pressure gauge to verify that the vapourstat is doing what it's supposed to be doing.

Steamhead

@superheathermo , where are you located?

superheathermo

Queens NY,
UPDATE, I opened up the loop seal mud leg on the side that was not getting heat, and found it to be totally clogged on the steam supply side, I jambed a flexible plumbing snake up about 3 feet to the top elbow, and hot water came rushing out, with half a pail of rusty sandy crud. I dont believe that any water came out of the return side of the loop seal. Is that normal? I will re check. could this have caused the water hammer and no heat to some radiators?. I did not re fire the boiler yet. Still learning. Thanks

STEAM DOCTOR

Good morning. Good detective work over there. If the loop is clogged, the steam condensate will not be able to get its way out of the main.. Results will be that the main will filled with water and prevent your radiators from Heating and will also cause. Water hammer.

STEAM DOCTOR

It's also possible that the return is not properly pitched. The results will be water buildup in the return which will block the main vents from operating. It's very possible that a water buildup in the return is what caused it to corrode and leak in the first place.

BillyO

Does that Rotary phone still work?

Jamie Hall

Your discovery that no water came out of the return side would be expected if the return is pitched to the boiler -- there's no condensate to get into it.

The rotary phone on my desk still works, @BillyO . Got it here when dial and private lines came in In 1946...

STEAM DOCTOR

> @Jamie Hall said:
> Your discovery that no water came out of the return side would be expected if the return is pitched to the boiler -- there's no condensate to get into it.
>
> The rotary phone on my desk still works, @BillyO . Got it here when dial and private lines came in In 1946...

There should be water in the return side of the loop. The return itself shouldn't have any water but the vertical leg of the loop should have water. Maybe I am misunderstanding what happened.

Jamie Hall

There would be water on the return side -- certainly should be! -- but if the steam side leg was totally clogged there might not be, if the return is pitched to the boiler Either way it's good to get it open again!

STEAM DOCTOR

@Jamie Hall. Agreed. We are on the same page

superheathermo

Update...Yes Mom's rotary phones still work, she will not modernize. You still get a busy signal if she is talking while you call.
Still clearing the muck from the loop, little by little. I discovered that there is petrified rust on the loop going up toward the return line. Thank you all for your ideas.

wam525

STEAM DOCTOR said:

It's also possible that the return is not properly pitched. The results will be water buildup in the return which will block the main vents from operating. It's very possible that a water buildup in the return is what caused it to corrode and leak in the first place.

So, I thought that it wasn't so necessary to have the return lines sloped back to the boiler. Shouldn't the 1/2 lb of pressure from the steam line push it back? I have a 100 y/o system, and the long returns (≈50 - 60 ft are mostly level or even very slightly uphill in spots. Near the end of the lines there is one of those down loops connecting the steam and return lines. I get intermittent water hammer on the radiators near the end of the line, so I'm wondering if (like superhero's system) there is blockage in that loop. But it's still not clear why the loop at the very end is needed at all, since condensate comes from thee individual radiator return pipes.

Jamie Hall

Wet returns don't have to slope towards the boiler -- or, for that matter, away from it or even consistently. Dry returns and steam line extension must slope towards either the boiler or a drip to a wet return. No exceptions.

Those loops must be deep enough to prevent steam from blowing over into the return, and that is related to the pressure. They must be at a minimum 28 inches deep for every pound of pressure the boiler creates. Anything less and you will get steam in the returns and assorted havoc.

If the steam line slopes away from the boiler, there must be such a loop at the very end, to allow condensate in the steam line to drain. Not all the condensate comes from the radiators! Some comes from the main itself, even if it is very well insulated. Now if that loop at the very end is blocked (which is unlikely, but could happen) condensate will pool in the steam main and, most likely, will hammer.