Dunham valve rebuild?

What's it not doing? Unless someone has really been a gorilla, they rarely wear much if at all. That said, if it hasn't been turned in years it may take some careful freeing up…

Being a 2-pipe system the 'main' vent may be elsewhere, not on the actual steam main. It may not need a vent on the steam main when all is working correctly.

That type of valve usually means it is a vapor system. If it is working properly, the pressure at the boiler is controlled to be very low and whatever special parts are at the boiler are correct, it should never get steam to the outlet of the radiator so it should never need the radiator traps. the crossover traps do need to be working.

some vapor systems vent only through the device at the boiler so that it can equalize the mains and returns without filling the returns with steam. yo need to understand this particular system before you can figure out if it can have main vents or if the mains must vent through the returns or the emitters.

you can replace the trap innards if you want, but as long as they are open and the valves are set up correctly you shouldn't need to.

it depends on the specific system. as i said a couple comments ago, some vapor systems need to vent only at a device at the boiler. i assume we determined your system wasn't one of those systems or it had been butchered such that it would never work as intended again.

I'm going to chime in here where I'm probably not wanted. Definitely see some confusion here.

I believe the comment you cited above was to change these vents, not add new vents to the end of the Steam Main. And it looks like you did just that, you change them. This may be the ultimate end of the Steam Main or it may be where the dry return drops down to a wet return, not sure I'm not there.

This is the pitch or slope of the pipes, not the size.

https://forum.heatinghelp.com/discussion/comment/1730609

" I'm curious, how would adding a vent on the main mess things up for the crossovers? "

IMO, Depending on the system and if done correctly it may not mess anything up. However you can only vent so fast, since the steam has to warm up the pipes.

Then it becomes extra equipment that needs to be maintained and the initial cost of the equipment and its installation. If the crossover traps are working correctly and the original venting is sufficient it is kind of a waste of money and time.

I apologize if you took my comment to be snarky. It was not so intended. HOWEVER if you do not know for sure that you have crossover traps, and that they are functional. most of the effort in balancing radiators will be for naught.

Now. How can adding main vents on the mains for a system which was designed for crossover traps cause a problem? Depends on the system. In many vapour systems, which I believer yours to be since you have at least some Dunham equipment, there were — and possibly still are — devices at or near the boiler which prevent the differential pressure between the dry returns and the steam mains from rising above a specific value — usually around 8 to 18 inches of water — thus preventing water from backing out of the boiler (not good) and getting into the dry returns (also not good). Adding main vents — or any vents, for that matter — anywhere else in the system will defeat those devices.

Now in a modern fuel fired system these may not be required — assuming that there is a reliable Vaporstat set at not more than 8 ounces per square inch gauge pressure cutout. If this is the case, there may be no harm to adding main vents here and there on the mains. If the actual main vents on the dry return are working, and the crossover traps are working, there will be no gain either.

Thanks for writing that up @Jamie Hall . i was busy before and didn't have time to write that out. The reason to not add main vents unless you know exactly what system you're dealing with is that you can break the system.

If the main vent is not at that equalizer device (and that device can just be a loop of pipe of a specific height), if it lets steam in to the returns to equalize the differential pressure and the only vent is not at that device, that steam can follow the returns to other vents and cause all the problems associated with steam in the returns like emitters that don't heat because they can't vent and water hammer.

This is why you must make sure there isn't an equalizer device at the boiler(or somewhere else in the system, there is no reason it has to be at the boiler, it just usually is) before you add main vents to a 2 pipe system that did not originally have main vents.

" Regarding my system, those main vents were added by local plumbers and none of the traps were working. Why wasn't breaking the system a concern back then? "

Did they diagnose the system or just add / change the vents at your request ?

You may have answered your own question.

" And before anyone chimes in with "get a pro to do it" we live in a remote new mexico town, there are no pros, just hacks. "

" Regarding my system, those main vents were added by local plumbers and none of the traps were working. Why wasn't breaking the system a concern back then? "

So this is referring to before your ownership ?

And you added the Gorton #2 yourself ?

So you don't know if adding the smaller vents prior to your ownership had any benefit. The systems original (as built) venting may not be functioning properly and the smaller vents were a Band-Aid (got lucky) repair, that helped but was not what should have been the actual repair. And as you said the traps had issues that were not addressed.

" Should I cap off the main vents this season to see what happens? Or is there a reason why my crossovers wouldn't be sufficient? "

No I would not do that. Since all the things that were done in this case all seem to be beneficial.

Crossovers and vents to the atmosphere kind of do different things. The Crossovers help vent the air out of the mains and also keeps steam out of the returns while allowing any condensate in the main to drain.

Vents to the atmosphere let the air out of (and back in) the whole system but won't let the steam out to conserve water.

The situation is, in all the time before your ownership you probably have little information on what was done and what was possibly removed from the original system. So you have to do the best you can with what is left. The whole system may have been vented by equipment that is no longer there, for example where this vent is connected (picture below). This small vent may have been insufficient so the others were added. And those were small also and larger vents improved the venting.

Historically for example some venting went into the chimney to take advantage of the draft.

I would look over your system (if you have not) carefully, thinking how can air exit the system as steam wants to fill the steam part of it. I would also closely compare to your friend's system since the venting there may be more like it was originally intended.

To me with the picture below is seems something else may have been there, the Tee (other equipment connected, now removed) and the galvanized pipe added as a plug. Or that is just what they had handy to add that vent. Those ball valves are not 100 years old.

What was this pipe for ? Probably not for venting but it looks abandoned.