2 pipe system, no traps

sammytorch

Hi there. My house \ office was built in 1901. My 1930's era boiler cracked. It was replaced it with a Burnham IN7. Fired it up yesterday for the first time. I have heat again! Two radiators are not fully heating though. It is a two pipe system with a dry return to the hartford loop. The system T's off to two mains and has two return lines that come back together above the hartford loop. There is one air vent right where the return lines come back together. There do not appear to be any traps at any of the radiators and the return line is almost as hot as the main. There is no steam coming from the air vent - just air. The return side from the two radiators that are not heating well is 65 degrees. About 6 feet away from where these returns would feed into one of the the main returns (going back to the boiler) is hot. All the other radiators get thoroughly hot to about 185-190 degrees. There is no drop in temp from the bottom of the radiator to past the elbow on the return. I really think these returns are filled with steam. Is it possible that the returns are all filing with steam and causing air to get trapped in the return coming from these two radiators and stopping the flow of steam? What should I do?

Jamie Hall

It most certainly is possible that the dry returns are filling with steam. As soon as that happens, steam flow will pretty well stop except for condensation, and if there are radiators which haven't gotten steam -- they won't.

First thing to do is to look at your pressuretrol or, I hope, vapourstat. Chances are that your system is a vapour steam system, controlled by orifices or calibrated radiator valves. This type of system works superbly well -- provided the pressure is kept low.

You need the cutout pressure to be less than half a pound -- 8 ounces per square inch. If what you have is a pressuretrol, you can't do that. You will need to put a vapourstat on there (keep the pressuretrol as a backup) and set it for 8 ounces cutout, 4 ounce differential.

If you already have a vapourstat, make sure it's set for that -- and that the pigtail and boiler opening are free and clear.

Once you get the pressure under control, go around to the radiators. If any of them are getting hot all the way across before others get heat, partially close their valves. What you are shooting for is all the radiators heat, but none of them heat quite all the way across.

mattmia2

Also, make sure that there isn't anything that was under the water line of the old boiler that is no longer under the water line of the new boiler. If the old boiler was a 1930's coal boiler that had been converted, the new boiler likely has a much lower water line.

EBEBRATT-Ed

And post some pictures of the boiler install so we can see how it's piped

Steamhead

EBEBRATT-Ed said:

And post some pictures of the boiler install so we can see how it's piped

Not just the boiler, @sammytorch , but some radiators as well (without covers). This should help us ID your system.

sammytorch

Wow - this really is a popular place. Thank you all for taking a look at this. Here are some photos. Yes, unfortunately I have a pressuretrol installed at 2 psi with a 1.5 diff. Let me post the photos and then I can see the order they post and try to comment on what you are looking at.

sammytorch

The pics are pretty self explanatory except the picture showing the run above that light blue crawl space door. This is a little side main coming off the left main (i.e. from the 2" T above the boiler). This is the main that feeds the two offending radiators. Below is the dry return. My thought is that the steam does not want to travel down that side street until pressure builds in main and the return and by then, it is too late - the pressure is then coming from both sides and trapping air between the radiators and the return.

EBEBRATT-Ed

The boiler is piped wrong but is probably workable the way it is. Looks like you have return lines connected above the boiler water line which will cause all sorts of issues. They should be connected together below the water line I am looking at picture #9

Jamie Hall

Please tell me I didn't read correctly... 2 psi with a 1.5 psi differential...

As i said in my earlier post, that system will run beautifully piped exactly as it is -- on a maximum of about 8 ounces.-- ounces -- per square inch. At that pressure the return problem @EBEBRATT-Ed mentioned is probably correct, not a problem.

Your diagnosis of what happens to those two problem radiators is probably correct -- but, overall, you are getting steam into the dry returns, and that should never happen -- and won't happen if you get the pressure down.

When you get it down, you should also check all the radiators. It's possible that the valve settings have been monkeyed with. The valves should all be set so that, when the system is running at full song, all the radiators get nice and hot, probably all the way across or maybe not the last section -- but not all the way down on the outlet side. If they are too enthusiastic, close the valve a bit and try again.

AMservices

Your pressuretrol is below or at the water line. Its not going to work right or last long with boiling water filling the diaphragm.
It can be mounted on the LWCO you have, but should be on a straight pigtail like this one

Chris_L

Hmm. So pressuretrols won't work below the waterline?

My two boilers have exactly the same setup. That is the way they came from Burnham. And the pressuretrols have worked fine for for 30+ years.

The bigger problem with mounting them that way is that the pigtails tend to get gunked up from the LWCO a lot faster than they would otherwise.

Danny Scully

Forgive me if this has already been said, but I think this is an “Adsco” system. It’s in the lost art. Hand valves have orifice in them. It should be operating in ounces. Additionally, as has been said, the boiler needs a repipe. 

AMservices

@Chris_L is your pressuretrol mounted on a straight siphon tube or angled?
When was the last time you checked its calibration?
If a steam boiler sized right and running right, the pressuretrol is more or less a fixture. The system satisfies the thermostat before it makes pressure. Obviously a lot of variables change how each steam system operates.
I know I read somewhere what the recommended height of the pressuretrol should sit above the water line. I don't remember the exact measurement, because the article mentioned as long as its above the boiler jacket its (relatively) safe.
I would say on average when I'm testing the calibration of a pressuretrol, 2 out of 10 are on the money.
I see how sensitive these controls are and when I install them, I want to protect them from rusty boiler water and make them as easy as possible to clean.

This is a special type of vapor system. 2 pipe system without traps. For this system to run perfectly it needs a few things.
Keeping the pressure low, clean water and way better venting would be a start. But the next most important thing to do (if not as important) is to make sure the orifice valves are working and set properly.
2 pipe vapor systems without traps heavily rely on these valves to keep steam out of the return and to balance the flow through the system.
Steam, like everything in nature, takes the path of least resistance. With the 2 returns connecting above the water and only 1 vent, steam fills half the system, closes the vent and air locks the other half.
With working orifice valves you can fire up the system, walk around and feel what radiators are heating first and turn them down.
The name of the game is "Don't let the steam touch the last section".
@sammytorch if any of your radiator valves are leaking or not turning, they need to be replaced with another orifice valve.
Packless orifice radiator valves are pricey $ but think of all the money your saving not having to deal with steam traps.

Jamie Hall

"Steam, like everything in nature, takes the path of least resistance. With the 2 returns connecting above the water and only 1 vent, steam fills half the system, closes the vent and air locks the other half."

Not in a properly functioning system. Steam never, ever (well, hardly ever!) gets into the returns. If it does, there is something amiss -- in an Adsco, like this one, one or more of the radiator valves is too far open, or has been replaced with a standard valve and no orifice.

These things are actually MEANT to have the returns join above the water line!

EBEBRATT-Ed

@Jamie Hall
I understand what you are saying about the returns above the water lines. But is there any harm tying them together below the water line? Seems to me it would avoid potential issues

Jamie Hall

EBEBRATT-Ed said:

@Jamie Hall
I understand what you are saying about the returns above the water lines. But is there any harm tying them together below the water line? Seems to me it would avoid potential issues

No, there isn't -- usually. But if the system still has one of the various pressure differential limiting whizbangs on it (Hoffman Differential Loop etc.) that will defeat it.

AMservices

@EBEBRATT-Ed
The main problem is steam shouldn't even get into the return.
Even if the returns drop below the water line and are vented separately, there's still the chance for steam to short cycle through the closest radiator to the vent, closing it and air locking the radiators furtdown the line.
Most vapor systems only work with 1 vent but can rely on steam traps to stop the steam from crossing over.
With no traps, orifice valves are the only controls for balancing this system.

EBEBRATT-Ed

@AMservices & @Jamie Hall
Thanks, got it

Chris_L

@AMservices, the primary pressuretrols on my boilers were mounted just as shown on this photo from the manual:



Not sure why they did it that way with an extra fitting except perhaps to keep it farther away from the boiler jacket.

In any case, street elbow at the top of the LWCO is where the pigtail would start to clog up. I never noticed gunk reaching the diaphragm of the pressuretrol.

I agree, higher is better. I removed the elbow and changed these pigtails to brass, straight-through ones a few years ago when I added a union beneath the pressuretrol.

But as for calibration, the pressuretrols are often off right out of the box. I have calibrated all four of mine, and didn't notice any difference between those that sat above or below the waterline. And they've all stayed in calibration.
(My boilers are both millivolt systems and have a secondary auxilliary pressurtrol mounted well above the waterline.)

SteamCoffee

Search for “Steam Sizing for Orafices” or something similar on this site. There is a chart floating around that will get you squared away. Pressure over a few ounces is killing your system. The correct boiler pressure and orafice sizing (assuming the boiler size is correct) will change your world, your original system was a gem. Simple, quite and efficient.....

Jamie Hall

I might add... a pressuretrol just isn't going to do it for this sytem. You have to have a vapourstat -- and an accurate low pressure gauge to check the vapourstat -- to control it. 6 to 8 ounces per square inch cutout, 4 ounce (subtractive) differential.