Vacuum system?

Well, yes. It does lokk as though it had been a Webster system — but it has also most likely been … um… modified?

Someone else will probably shriek, so I will first — the near boiler piping is not good. It may work — steam is remarkably forgiving — but it ain't right and should be redone the way the boiler manufacturer (and us) want. It will work a lot better.

In the meantime, the Webster — and similar systems — could and did drop into a vacuum at times, but that isn't the most important characteristic. They are called vapour steam systems, and were meant to work on very small pressure differences between the steam main supply lines and the returns, and 2 psig is about 4 times the maximum which they will run reliably on. If you have an ordinary pressuretrol, though, that can't be doen, and so they should have a vapourstat instead, set to a cutout of 8 OUNCES per square inch, with a 4 OUNCE differential. That's an easy right off the bat fix.

Then for your next project — actually two. Get a copy of The Lost Art of Steam Heating (Amazon or the store on this web site) and study it and learn how vapour steam systems in general are supposed to work. Then, taking that knowledge with you go through the entire system and familiarise yourself with all the piping and other devices, particularly the inlet valves on the radiators and any traps and vents — and then figure out what they were supposed to do, what they might be doing now — and what is missing or otherwise "modified". Take your time.

@EdTheHeaterMan I say you are the control electrical an helpful image guy too.

@service_fitter502 Even if it was a Vacuum system how does the air get out ? My guess it it would be considered a Vapor system. Many systems can develop vacuum, they just don't retain it very well.

If the air can't get out the steam is not going to move very far. This valve seems closed.

Notice the check valve at the top.

From:

https://heatinghelp.com/systems-help-center/webster-systems-of-steam-heating/

https://heatinghelp.com/assets/documents/85.pdf

dunham busch isn't the same as warren webster although pretty much all vapor systems work by controlling the amount of steam entering a radiator through a metering valve with a controlled, very low pressure.

here are 2 warren webster catalogs, there are some diagrams although they aren't the full design guide:

the catalog during wwii has some steel and iron substitutions of things that would normally be brass

there is some mention of webster systems in tlaosh but it doesn't seem to quite be the systems i have seen people post here.

if you keep the pressure controlled with a vaporstat, the return trap and single vent are less important.

it looks like it is a type r system. it could go in to vacuum with a check valve on the vent outlet but it wasn't like some other warren webster systems that used a mechanical or educator vacuum pump and smaller returns so it needs vacuum to vent properly.

it looks like the parts are there at the boiler,

the boiler return trap:

and the vent:

can we see what is at the radiators?

@EBEBRATT-Ed makes a good point " The air all has to come out through the vent trap. " the existing Hoffman vent may help vent the steam main, but how does the air in the radiators get let out of the system so the radiators can fill with steam ?

As @mattmia2 mentioned " the outlet of the vent should have a main vent on it. " This may make a huge improvement.

These may help, not inexpensive.

76, 1/2" x 3/4" Straight Main Steam Vacuum Valve
Brand: Hoffman

https://www.supplyhouse.com/Hoffman-401432-76-1-2-x-3-4-Straight-Main-Steam-Vacuum-Valve-11742000-p

Hoffman's opinion;

If it was my system and I had to unwillingly abandon vacuum I would put a Barnes & Jones Big Mouth on top of that Webster vent trap for maximum venting. I would remove the valve or use a full port ball valve, probably won't see much steam.

A few folks on this site are enjoying the benefits of natural vacuum.

Sounds like your intent is to rebuild the near boiler piping. I'd wash off the production oil from at least the inside of the new piping. May save you a bunch of time Skimming the boiler later on.

That vent is so slow as to be almost unusable in a system like this.

This naturally-induced vacuum technique worked great in the Coal Era, but not so well on oil or gas. The problem is that often you get vacuum before all the air is out, which can cause the remaining air to expand and block steam circulation. I tried it once, never again.

The vent to use on that Vent Trap is the Gorton #2, which is at least four times faster than that Hoffman:

https://www.supplyhouse.com/Gorton-G2-Gorton-No-2-Straight-Air-Eliminator-3524000-p

And get rid of that red-handled valve.

What model boiler is that?

Well I think @PMJ with his Mouat system proved vacuum works very well. Although his system is not a Warren Webster Vapor system.

It seems to me if there is less air to push out with each cycle the more efficient the system will be. If the air is not let back in you simply don't have to push it out again (burning fuel to do so). So the vent rate is not terribly important. The trick is keeping the vacuum also no excessive pressure differential between the supply and return.

If you can't maintain the system's integrity as far as keeping the vacuum in you have to go with ample venting. Presently it appears this system has neither, maintained vacuum or ample venting.

The "general" rule that natural vacuum won't work with intermittent fire at least in the case of Mouat piping is completely false. Been doing it 20 years plus and it is a big improvement in comfort and certainly more efficient not less. When you don't let the air back in there is shockingly little venting to do and it makes little difference where that one vent is.

Two thoughts here, since we seem to have wandered off from the character of vapour steam systems to thoughts about vacuum systems — which are not the same thing at all.

Coal fired steam heating systems were encouraged to drop into a vacuum. Hence the existence of vacuum vents. But we need to ask why. it was not to avoid "pushing air out on every cycle" because they didn't cycle. The advantage was that they could and did continue to heat with a low temperature banked fire. This allowed a thermostat (or homeowner…) to maintain a comfort level in the space simply by controlling the draught over the fire. Since they could run under sub-atmospheric pressure, the radiator output would be varied since condensation occurs at a lower temperature at lower pressures. As a little noticed aside, later vapour systems (with vents rather than open returns) could also run at higher internal absolute pressures and hence higher outputs, provided the differential pressure between the mains and returns stayed within design limits (there is no magic reason for a supply pressure of, say, 0.4 psig, by the way. The correct control parameter is that differential pressure — unfortunately our modern widgets are all psig controlled, not differential controlled…)

Hence all later vapour systems had some sort of contraption of varying complexity which controlled that differential pressure (the Hoffman Differential Loop is the simplest one I've seen; some of them are truly wonders of complexity!) Again, on coal systems, some of them also had a device to control the draught in response to differential pressure — usually in tandem with the thermostat control

Now there is no theoretical reason why a similar operating strategy couldn't be implemented with oil or gas firing; the key is modulation, and both oil and gas firing can be modulated over a wide range with little difficulty, and with little loss in efficiency (if any at all). There are several tradeoffs, however. One of the more significant has little to do with thermodynamics but a lot to do with aesthetics: oil burners are most easily modulated by pulse modulation; that is, the burner is on for a certain time, and off for a certain time; the modulation from full power is simply the ratio of on time to total cycle time. Provided the off time of the cycle is short enough that the boiler never goes below a simmer (and this is an argument for systems which can hold a vacuum) there is almost no hit to efficiency; the most common limitation on this is the post-purge and pre-purge delays needed for clean operation. Gas firing can be modulated the same way or, if the burner design is meant for it by limiting the gas pressure to the burner (air flow must be limited at the same time, of course)(this, for you automotive geeks, is how a carburetted engine varies its power output, by the way, except the control is on air flow rather than fuel flow)(fuel injection engines and diesels are technically pulse modulated, by the way).

Is the complexity worth the effort? Maybe. Maybe not. One needs to balance personal preferences, control complexity, maintenance and repair, and efficiency — and everyone will come up with different responses.

Again to look briefly in closing at the automotive world — a current generation gas engine is significantly more efficient than one from, say, the mid 60s (though not as much as one might be led to believe), but maintenance and repair costs and complexity are vastly different.