Hoffman 2 pipe steam system

hoss50

Good morning,
I have a client with the above system, I am a contractor in Westchester County NY
I don't usually don't come across these systems and am having a bit of trouble solving this issue.
Original call was for 3 radiators not heating.
Replaced the traps with Hoffman 17C and 1 is still not heating.
Replaced 2 of 3 crossover traps with Barnes & Jones Big Mouth Air Vents, the 3rd was in the ceiling of a finished area and the owner did not want to disturb that area.
Radiator still not getting hot.
Original boiler from around 1932 only thing that I can see that was changed was the vent before the differential loop.
Looks like a Hoffman 75, not sure as its up in the ceiling
Any thoughts?
Thanks

nicholas bonham-carter

Is there any way of checking the output of the third crossover trap, without opening the ceiling. Crossovers are so important for correct operation.
Maybe opening the trap of the non functioning radiator will show if you have steam in the return which is closing that trap.
If you could borrow an IR camera, you may be able to follow the steam visually, and look for a bottleneck.
Quite likely the main vent is a Hoffman 76-vacuum vent.—NBC

hoss50

No way to get at the trap without opening the ceiling.
When you say open the trap do you mean take off the cover or break the union?
I may be able to borrow an IR camera only problem is the risers in the basement ceilings are all plastered.

Jamie Hall

OK. First off, replacing the crossovers with the Big Mouth vents was a serious error. Sorry. You MUST go back and replace those with crossover traps; Hoffman 17Cs will do just fine. Hoffman Equipped systems are designed to have the air vent, or vents, in one place and one place only -- at the Hoffman Differential Loop.

The main vent very likely is a Hoffman 75. It probably is still working, although if the system pressure is too high (I'll get to that in a moment) it may not be. In any event, it may be too small. If it is still working, keep it and build an antler to accommodate a Gorton #2 as well; if it is toast, two Gorton #2s.

Now. Go out in the system. Since the original boiler has not been replaced you are probably OK on the drips from the dry returns and the steam mains to the wet returns at the crossover traps (boiler replacements often lower the water line and dry those out, with very bad results). However, you should check and be sure that all the steam mains and dry returns are pitched correctly for their full length. Sags, particularly in the dry returns, can give rise to problems (such as the no heat radiators). Then check and make sure that all the dry returns tie together at the boiler, before the Hoffman Differential Loop.

Next, back at the boiler, make sure that the Differential Loop is still properly connected -- steam line from the header, dry returns in at the top, line to wet return down.

Next, pressure. The system cutout pressure must not be more than 7 ounces per square inch; the cutin can be perhaps half that.

Run it and see what happens. If that one radiator is still not heating, I know it sounds obvious but make sure that its control valve is open. Then take a very close look at the return from the radiator; it must slope to the dry return. If it's still obstinate, trace the runout from the steam main and see how far along it it gets hot; that may give you some idea of where the trouble is.

While you are playing with that radiator and the system otherwise running, check all the other returns. They may be very warm or even hot -- but not steam hot. If any of them are steam hot, you may have a bad trap on that return.

And please report back on how it goes!

hoss50

I thought I read where the big mouths were what could be used and as far as I know there are not any other issues since we were there 2 weeks ago.
I did eyeball the lines in the garage , didn't put a level on them, they looked fine but I'll make sure and check the other parts of the house.
All dry returns do connect before the differential loop, nothing has been touched since FDR was in office.
As far as the pressure switch it looks like an original L408A mercury switch with a pigtail off the top of the boiler.
Was thinking about backing out the pigtail but was afriad she would break off and the owner was concerned about the asbestos thats covering the boiler.
I didn't try clearing it with a wire and I know thats a pain
Once I can figure out how to get the pictures from my phone I'll post them.
Its an old Burnham and has an odd casting that might be quite interesting
Have to head out, it's a bit cold here today, duty calls
Thanks for your help

Jamie Hall

Did you hook the Big Mouths up as crossover traps? If so, they should be OK -- I may have misunderstood, and, if so, my apologies.

On that mercury vapourstat -- be happy! The only thing to watch with them is they must be very accurately leveled; there is provision for a level on the top of the case. Use a good one! There is another way to tell if you're having pressure problems -- the Differential Loop should not trip. And you can tell quickly if it does -- the dry return at the entrance to the loop will get steam hot and the vent there will close (which is what is supposed to happen -- it's the only time on a Hoffman system that the vent will close). If that happens, the pressure is too high and you'll want to back it off. That usually happens at about 8 ounces, but there is some variation between installations.

On the pigtail. Well... If you don't want to take it off (I would, and not tell anyone about asbestos -- and simply plan to replace it in brass) you could take the vapourstat off it and pour water in it, which should drain out into the boiler freely.

Steamhead

@hoss50 , first thing to do is change the vent. If that system was installed in 1932, and the Differential Loop was the later model, the original vent was a Hoffman #15, which vented way faster than anything Hoffman makes now. The Gorton #2 is a good choice on this system.

BobC

On the leveling of vaporsats - this has to be done when everything is at temperature. make sure the pigtail loop is perpendicular to the face of the vaporstat, if you are looking through the loop of the pigtail when looking at the face of the vaporstat it is oriented wrong.

If it's off a little when cold it usually does not matter.

Bob

nicholas bonham-carter

Have you had any success with this system yet?
I should have been more clear on checking the returns for steam at the cold radiator: you should close the inlet valve for the radiator, and then unscrew the trap lid, and perhaps, remove the capsule, and if there is steam in the return it will come out. Then you can check nearby traps for a failed open condition. Having a helper ready to shut down the boiler at a moments notice would be useful.
If you need to cut into the wall to check the last crossover trap, then an access panel could be installed for the future.—NBC

hoss50

Haven't gone back yet.
Emailed him yesterday to set up a day this week
I'll get back to let you know how it worked out
Thanks for your help

nicholas bonham-carter

I wonder if the original hidden crossover trap is a slower venting trap than the newly replaced big mouth traps. This situation might result in steam arriving more slowly on the old trap line.
If the thermostat anticipator doesn’t run the boiler long enough, then those rads served will be colder.
Maybe you can valve off the radiators on the big mouth sections, and see if the cold radiator gets hot.—NBC

Jamie Hall

Um. Well, maybe, but even a Hoffman 17C -- a not uncommon crossover trap -- has about the same capacity as a Big Mouth.