How is this venting?

Zipper13

I'm slowly reading what I can bout how these systems work, so forgive me if this is a dumb thing to be asking about.

I'm trying to figure out how my system vents - and it appears to be doing so just fine.

I thought that vents for systems like mine should be at the end of the main to expedite the steam filling it by evacuating air in its way.

The only vent I have is atop the hoffman loop.
I see three routes to the vent:
-in pictures 1 & 2 from the right of the vent, at the far upstream end of the dry return. there's a tee to the hoffman loop
-in picture 1 & 2 from the right of the vent, the same tee noted above, except coming up from the wet return.
-in picture 1 & 2 from the left of the vent, there's an equalizer pipe (I think) coming from the header, going around to the other side of the Hoffman loop

None of these appear to have a direct path to evacuate air from the main, right?

Al I can think is that the air in the main is forced into the dry return through the trap in pictures 5 and 6 (at the downstream ends of the return and the main) and pushed upstream all the way back around the dry return to the the vent. If true, I suspect this would explain why I have not lost any water all season since any steam forced back into the dry return would have to circle all the way back around - and condense along the way - meaning there's no steam vented.

does that sound reasonable or is something else going on?

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gerry gill

That should be the only vent on the system for it to work as designed. The boiler piping that someone put in later is somewhat questionable i must say.

Jamie Hall

Hoffman Vapour system. They are fabulous (ask the man who owns one).

Here's what happens: air is vented out of the mains by the crossover traps which you have pointed out. When steam hits those traps, they close. The air goes into the dry returns and returns that way, as you have noted, to the vent on top of the Hoffman Differential Loop. Any condensate from the steam mains is taken care of by the drips to the wet returns. Air and condensate are vented from the radiators into the dry returns. Condensate is taken care of by drips, and all the air returns to and is vented by that vent at the Hoffman Differential Loop.

No steam should ever get into the dry returns under normal operation; if some does, you have a bad trap -- under normal operation.

Normally that vent should never close -- I'll get to that in a minute.

Now. Here's where it gets interesting and ingenious. If the differential in pressure between the steam mains and the dry returns rises higher than approximately 8 OUNCES per square inch, the Differential Loop will "trip" and allow steam into the dry returns at the top of the loop. This will close that vent, and the pressure will equalize between the steam mains and the dry returns, until the steam in the dry returns condenses. This protects all your traps from overpressure and, not incidentally, also protects you from having water back out of the boiler into the dry returns (hence the trademark "Watchman of the water line").

I said above that the vent at the loop should never close. The above is the one situation where it will.

However... the original system was not designed with modern high power small boilers in mind, so to make it perform at its best, you need more venting at the loop. I would suggest that you create an antler there, with the existing vent on it plus one or two additional Gorton #2s. This will reduce the tendency for the system pressure to get too high in the early stages of firing.

You also need a vapourstat. The system really truly does not like pressures over 8 ounces per square inch (indeed, 7 is better). A low pressure gauge is also handy, to see just what pressure the system is running at.

Oh -- and one more thing. There must be no other vents of any kind anywhere else on the system, other than the cluster/antler right at the loop.

Zipper13

@gerry gill There's a decent amount of banging at start up. I suspected it migh be due to the poor piping. I'm having someone come in the next couple weeks to do maintenance on the boiler ( I don't think the old owners ever did) and to see what he thinks of the boiler piping.

@Jamie Hall thanks so much for explaining and clarifying all this. I'm so glad to have everyone here so generous with their knowledge. I had my new neighbor over the other day (who replaced his steam with hot water baseboards 15 years ago) and he was trying to give me tips that were just garbage.

I'll look into the vapourstat in the near term
And then maybe repiping the header this summer before I insulate the main.

Zipper13

@Jamie Hall For the vaporstat: I'm reasonably handy and figure I can save a few bucks on labor and parts markup if I install myself. Is this a fairly straightforward swap out? Or is it more complex than it looks and therefore worth paying a pro
I am eyeing this 0-16oz job at supplyhouse where I got my replacement flue damper recently. It looks identical, save for the pressure scale, to my current pressuretrol

Honeywell Vaporstat Controller (Steam), 0 to 16 oz/in2
SKU: L408J1009

Jamie Hall

Yup. That's the one. It does look the same, but the internal diaphragm is quite different. It is a straightforward swapout, so far as that goes -- just make sure to note where the wires went on the old one and get them the same. And do it with the power off..

Zipper13

@Jamie Hall Another question for you (and anyone else who wants to weigh in):

So I have this original Hoffman #11 vent...I have to believe that it's failed stuck open after 100 years so I think I should really remove and replace it rather than just add additional vents. Do you know if the threads of the #11 match those of the Gorton #2?

Do you know how the venting rate compares? I'm thinking of using two #2's on a wye but not sure if that's an improved vent rate vs the existing #11 or not.

Thanks

Danny Scully

The # 11 is 3/4” I believe, while the gorton # 2 is 1/2”. You would need (2) gorton #2 to match (slightly exceed) the #11 venting capacity.

Fred

Hoffman #11 is 1 CFM at 1 ounce of pressure. Gorton #2 is 1.1 CFM at 1 ounce of pressure. A single Gorton #2 has slightly more venting capacity than the Hoffman.

ethicalpaul

Weird, why didn't Gorton make the #2 have the same nice dual 1/2 and 3/4 threads that the #1 has??

Jamie Hall

The Hoffmann 11 was a vapour vacuum vent -- now obsolete. It's venting capacity is about the same as a Gorton #2. I have no idea whether the threads match, but you can always use bushing or adapters of one sort or another.

If you're sure the 11 is dead, then I'd probably use two #2s in its place -- not on a wye (they must be vertical -- they have floats in them) but on an arrangement of a T a couple of elbows and 4 nipples.

Make sure the Hoffmann is dead first -- you should be able to blow through it, but not such through it.

Zipper13

Thanks for the comments and guidance again, guys!

Zipper13

100 year old Hoffman vent is still alive! I'm blown away that this hasn't failed yet. Plumber came to clean the boiler and it closed up tight when he tried to drain.

1Matthias

They built stuff to last back then.