pressure in 1 pipe steam

thfurnitureguy_4

Yes, an old topic but...
If you think well vented but oversized boiler, (approx. double the needed output for the EDR), the system spends much of its time cycling on pressure until the thermostat is satisfied.
If the pressure is raised at the boiler it will run longer and cycle less. The boiler builds pressure but the higher pressure steam is also hotter, so the steam that replaces condensed steam in the radiator is hotter. Hotter steam increases the EDR of the radiators heating the room faster, which should decrease the total run time of the boiler. If my interest is to save money on the gas bill, why is some pressure bad?

AnthraciteEnergetics

Ultimately the energy delivered will be the same. The lower the steam temp, the more efficient the boiler will be. But the difference between 0 psig and 1 psig is like 3 degrees.

Problems with pressure are mostly related to air vents spitting/not closing and condensate return (condensate "stacking up" too high in the drip legs).

The best system would deliver heat at the sane rate your building needs it. If you have an oversize boiler, you could wire a second pressuretrol or vaporstat between the ignition module and gas valve (youre not tripping the safety circuit or turning off the pilot, only cutting off the main burner to maintain the 0.5-1.5 psi control band). Or wire a timer module the same way to reduce the burner duty cycle with more cycles on your gas valve. Or downfire the burners ( this can be done to a limited extent, maybe down to 60%)

thfurnitureguy_4

Thank you for the response. I understand on the pressure concerns.
Can you go further with the gas control? "you could wire a second pressuretrol or vaporstat between the ignition module and gas valve...only cutting off the main burner to maintain the 0.5-1.5 psi control band)." What would this do? Burner would fire at 0.5-1.5 psi while in the pressure condition?
I have a Honeywell gas Ultraviolet flame controller.

MilanD

Some boilers can be 2-staged. There are threads here where the pros mention doing this. Depending on what boiler you have, you could install a 2-stage gas valve and an additional vaporstat, and this would downfire the boiler, in essence reducing your oversized boiler down to about 60% of the full btu input.

So, the boiler fires on full flame, starts boiling and building pressure, then at certain pressure it reduces down to 60% or so of the full burn rate.

Jamie Hall

Whoa. This has been gone over... and over...

Let's start with the radiation. There is a very definite quantity of steam which the radiation can condense per unit of time. While it is true that steam at a higher pressure is at a slightly higher temperature, the difference -- in the pressure ranges about which we are speaking -- is very small, and so therefore is the rate at which it can be condensed. OK so far? Now if the pressure at the boiler is sufficient to continue to deliver steam to the radiation, all the boiler needs to do is to supply that amount of steam. That pressure, for most residential systems, is rarely if ever over 0.5 psi.

OK. Now if the boiler has reached a pressure of around 0.5 psi, then it is delivering to the system all the steam that the system can condense. If we turn off the burner at this point and let the pressure drop to, say 4 ounces instead of 8 ounces, steam is still being delivered to the radiation and the radiation is still delivering all the heat it possibly can to the space -- but we aren't burning any fuel. When the pressure drops to that 4 ounces, we cycle the boiler back on again, let the pressure get back up to 8 ounces, and cut off. And so on. But. Let us suppose instead that we keep the burner merrily firing away until the pressure rises to 1.5 psi and then cut it off. What, exactly, have we accomplished with our extra fuel? Nothing. Except burning some money. The radiation is still pumping out the same amount of heat. The extra fuel has gone into compressing the steam, rather than delivering more heat to the radiation. The off time will be nearly the same (it may be a smidge longer, granted, depending on the differential) as the condensation rate is fixed.

This assumes an on/off burner. If you should be so fortunate as to have a two stage burner, and assuming that both stages have the same efficiency, then yes you will be better off -- a little -- by going to low fire instead of completely off. In many systems, depending on firing rate and radiation, low fire may even be enough to supply the radiation, particularly on warmer days, so you don't cycle off at all.

I might mention that the extra pressure increases the wear and tear on things like traps, but that is actually pretty minor.

I might also add -- perhaps it is the KISS in me -- what is the problem with controlling the effective firing rate of the boiler with a vapourstat, set to hold the steam pressure in the desired range, vs. using some other approach -- such as a timer, perhaps -- which does more or less the same thing, but isn't capable of responding to variations in condensing rate, such as might occur if the radiation is in a colder space on a windy day?

Now you do need an additional pressuretrol, set to some higher pressure -- say 3 psi -- as a safety backup. But you should have that anyway.

Bottom line, as I've written before, is that pressure at the boiler is an excellent measure of the match between firing rate and condensing rate. Not perfect, but pretty good -- and I know of no other measurable parameter which is.

thfurnitureguy_4

Got it. Thanks again,
I am going to try a timer on the vaporstat to delay the cycle restart 5 minutes or so. My thinking is it is better to shut down and let the heat soak from the radiators. The boiler is still at a boil while the flame is off for a few minutes and gas is fast to ignite so restarting should not be too inefficient.
The system shuts down on pressure 3 to 4 times before the thermostat is satisfied. If I am right I will save the run time of about 10 minutes, 3 to 4 times per cycle. Current pressurtrol cuts out at 1.5 lbs , new Vaporstat out at 8 oz. It takes about 10 min to build pressure from 8 oz to 1.5 lbs.
I am guessing the fuel burned at low pressure would about equal the fuel burned rebuilding steam back to 8 oz. with no need for valves or gas plumbing.

Fred

How much venting do you have on your Mains? If you vent the mains sufficiently, you may well save that 10 or 20 minutes per heating cycle (or more) by not requiring the steam to have to push the air out of its way so it can do what you want it to do, Heat the radiators.And, that time savings may well satisfy the Thermostat before the short cycling begins.

PMJ

Hitting a pressure stop at all means that you have filled your rads with the maximum amount the system can possibly do. The problem
with this is that you never need that much steam except in the most extreme cold conditions which is basically never. Steam systems have a delay after rads fill to when enough of that heat gets transferred to the room to satisfy the tstat because there are no fans to make it happen faster. This was not a problem in the original design when the boiler was coal fired continuously because rads were continuously partly full and a low fire was producing ultra low pressure steam continuously at a rate much less than the boiler capacity.

I have a very oversized boiler too and my initial solution to this problem was to "pace" the boiler with evenly spaced shorter burns. I do 3 burns an hour evenly spaced. This way there is no pressure ever and rads always only partly full. Much less overshooting, more even heat - even when the system was open vented. The result was that the ongoing condition of the rads(partly full) was much more like the original design.

From the size you describe I'll bet your boiler would not need to run more than 50% of the total time even when it was extremely cold. So if you set a simple control to do 3 -10 minute burns with 10 minutes in between whenever the tstat was calling for heat you would still heat fine on the coldest day yet never have any pressure - and have much more even heat. I ran this way for a number a years before adding additional improvements. Even the pacing alone was a big improvement over a vaporstat control.

Kahooli

For one pipe with no vacuum assist, short burns translate to large jacket and flue losses. System efficiency will suffer.

PMJ

Kahooli said:

For one pipe with no vacuum assist, short burns translate to large jacket and flue losses. System efficiency will suffer.

In residential jacket losses stay in the house in most cases so they aren't really losses. And as long as there is an automatic vent damper there are no flue losses to speak of.

I have seen only continuous efficiency improvement from the moment I began cycling and on into vacuum.

KC_Jones

PMJ said:

Hitting a pressure stop at all means that you have filled your rads with the maximum amount the system can possibly do.

This would be incorrect. It simply means the steam production is exceeding the systems ability to expel the air. If you produce more steam than the amount of air that can be expelled you get pressure, it isn't steam pressure it's air pressure pushing back. A boiler doesn't make pressure the system pushes back on steam production and creates the pressure.

Now on a very cold day when more heat is needed and you indeed get to a point that all the rads are full and the air is gone, then it is indeed steam pressure you are dealing with.

We have seen people on here many times talking about cycling on pressure before the rads get any heat. Sometimes this can be fixed with an increase in venting.

PMJ

@KC_Jones,

Boy, I can't imagine building any pressure before rads were basically full and traps closed. Seems to me that anyone trying to run a system that resists expelling air so much as to trip the max pressure on a vaporstat with still empty rads is really doing this the hard way.
Short cycling on pressure with still empty rads? Hmmm.

Jamie Hall

PMJ said:

@KC_Jones,

Boy, I can't imagine building any pressure before rads were basically full and traps closed. Seems to me that anyone trying to run a system that resists expelling air so much as to trip the max pressure on a vaporstat with still empty rads is really doing this the hard way.
Short cycling on pressure with still empty rads? Hmmm.

Amen. Shouldn't happen. That's what vents are for... big enough, and enough of them. Haven't we been here before?

AnthraciteEnergetics

@thfurnitureguy "I have a Honeywell gas Ultraviolet flame controller."

Might not be as easy. Im using an intermittent pilot setup, it only monitors the pilot via rectification probe. The Honeywell controller might drag out your on-off cycles too long.

Try adjusting the manifold pressure on the gas valve you have. It's the only combustion adjustment you can make on these residential gas steamers without changing hardware. If the flame gets ugly (yellow, doesnt cover entire burner tube length) or you have rough ignition, youve gone down too far.

I got rough light-off at around 60% firing rate, where the burners away from the pilot have delayed ignition due to less gas coming out. If any burner tubes fail to light or dont have flame down their entire length its at best a waste of fuel and at worse a safety hazard.

SeymourCates

There is a misunderstanding of what occurs when steam is compressed in a piping system. The boiler starts its cycle at 14.7 psi, and, ideally, never climbs above approx. 14.8 psi. This is the ultimate system. However, some boilers are larger than what the radiation can deliver and they might climb to 3 psig (or 17.7 psi absolute). Effectively, the boiler has used the piping as a reservoir for additional steam. The argument that this is wasted energy would only be valid if this steam is vented to the atmosphere. Since all of this steam is delivered to the rads upon shutdown, it is effectively all recovered. It is similar to an automobile engine that compresses the incoming fuel/air charge by 9:1. The energy required to compress the charge is recovered upon ignition of the mixture. The downsides to operating at elevated pressures include slower steam delivery, potential water level problems, and potential vent damage. But the efficiency is unaffected provided the boiler does not cycle on pressure. At that point, the inefficiencies of starting and stopping the boiler on a very short time interval come into the equation and the potential wear on the equipment becomes a consideration.

Here in Canada, we frequently run oversized boilers at higher than desired pressure without any issues provided the piping heights will allow it. It is preferable than the general consensus of "dialing down the pressure" which will absolutely result in short cycling of the equipment on days that are not even close to the design day.

MilanD

On an oversized boiler you will have a hard time matching venting rate to steam production rate no matter how many vents you put in. Thus, 2 staging can be a good solution for this, in addition to adequate venting of course, if downfiring is not possible. And if you can get into vacuum, even better as you don't have to fight venting AND as rads condense steam they self balance the system.

Dave0176

SeymourCates said:

There is a misunderstanding of what occurs when steam is compressed in a piping system. The boiler starts its cycle at 14.7 psi, and, ideally, never climbs above approx. 14.8 psi. This is the ultimate system. However, some boilers are larger than what the radiation can deliver and they might climb to 3 psig (or 17.7 psi absolute). Effectively, the boiler has used the piping as a reservoir for additional steam. The argument that this is wasted energy would only be valid if this steam is vented to the atmosphere. Since all of this steam is delivered to the rads upon shutdown, it is effectively all recovered. It is similar to an automobile engine that compresses the incoming fuel/air charge by 9:1. The energy required to compress the charge is recovered upon ignition of the mixture. The downsides to operating at elevated pressures include slower steam delivery, potential water level problems, and potential vent damage. But the efficiency is unaffected provided the boiler does not cycle on pressure. At that point, the inefficiencies of starting and stopping the boiler on a very short time interval come into the equation and the potential wear on the equipment becomes a consideration.

Here in Canada, we frequently run oversized boilers at higher than desired pressure without any issues provided the piping heights will allow it. It is preferable than the general consensus of "dialing down the pressure" which will absolutely result in short cycling of the equipment on days that are not even close to the design day.

But that’s just it the steam don’t ever go to the rads, once the burner shuts down no more can be produced, the remaining steam in the system condenses due to no more pressure and it immediately creates a vacuum in the space sucking all the air vents open, it’s a cycle that goes over and over and over. Dan explains this in detail in the LAOSH. So go ahead and crank that pressure-troll up maybe 8 PSI will get heat to the rads, I sure as heck wouldn’t want to pay your fuel bill though.

I’ve set boilers up here that heat with 4-8 oz of steam pressure and they heat good and quietly at 0 degrees too.

SeymourCates

Where did the energy go when the steam condensed after boiler shutdown?

The steam condensed and released the 970 BTU/lb to where?

Was it released to the atmosphere or to the building?

MilanD

> @SeymourCates said:
> Where did the energy go when the steam condensed after boiler shutdown?
>
> The steam condensed and released the 970 BTU/lb to where?
>
> Was it released to the atmosphere or to the building?

If steam is not in the rad, condensing in the riser or the main will heat the riser and the main. Sure, it stayed in the building, just not in the space you want to heat, but the wall cavity or your basement.

Fred

SeymourCates said:

Where did the energy go when the steam condensed after boiler shutdown?

The steam condensed and released the 970 BTU/lb to where?

Was it released to the atmosphere or to the building?

A good portion of it was probably condensed to an unfinished basement or in a crawl space. True it's still in the building just not where it does anybody much good, at least not nearly as good as getting it to the rooms you want heated and comfortable.

SeymourCates

Of course you are correct. The condensing steam stays in the building. The situation is not vastly different from a properly running system that operates at 14.8 psi. When the boiler shuts down, all the steam in the risers and in the mains condenses and is not in the space that you want to heat. In the case of the oversized boiler where you run at 17.8 psi (to avoid short cycling), you are condensing slightly more steam in those risers but the effect is somewhat insignificant as compared to cycling on pressure (when operating at 15.8 psi absolute) where you might condense 15X per hour in the risers if the boiler cycles on pressure.

Which do you believe is more efficient? Cycling at a rate of 15X per hour while maintaining 15.7 psi or not cycling whatsoever if operating at 17.7 psi (the limit for most vents)?

Fred

You asked where the energy went,not which of those two options was more efficient. I happen to have a steam boiler that is about 33% oversized (above and beyond the pick-up factor) and I have a lot of main venting so that I minimize the amount of time my boiler spends pushing air out of the system and building pressure and I run on a Vaporstat set at 12 ounces Cut-out. My boiler runs virtually every cycle at 2 ounces of pressure or less. I can recall twice last winter when it did hit the 12 ounce cut-out, once on each of two cycles. Of course, I set the thermostat and leave it set for the season. Those who think they need to adjust the tstat every time they pass by it or who think they are saving money with set-backs when they are not home or when they go to bed are kidding themselves, unless they actually have a boiler that is very, very well sized.

EBEBRATT-Ed

@SeymourCates , I strongly disagree.

Drive a car up against a tree and step on the gas pedal. You will burn a lot of fuel and not go anywhere.

If you run a boiler against pressure you are wasting fuel. This compressed steam doesn't make it to the radiators. Your burning energy to compress steam when you should be burning fuel to make and deliver steam.

Higher heat loss from the boiler jacket, higher heat loss from the steam lines, longer run time that wastes fuel and yes, a higher stack temperature.

You will succeed in making the basement warmer and maybe some of that heat is conducted up through the floor so on a two story house you will create an imbalance

Jamie Hall

I give up.

PMJ

Oh my.

So the solution to too frequent cycles on pressure is to raise the pressure even higher and pack even more steam in an already full system. In this way you can lower the number of cycles per hour.

Hopefully without offending anyone I will continue to recommend heading in the opposite direction all the way down into vacuum as much of the time as possible for both comfort and efficiency.

thfurnitureguy_4

WOWSERS! Thanks to all! This is why I love the Wall and admire the passion for the industry that it has helped to keep alive.
When we started with this system we were told to remove it and install forced air or splits, at the time money forced us to keep what we had and improve it to the extent we could. In retrospect, if I were to give advise on what saved money, 3 things come to mind.
1-Relocating the thermostat into a heated room (LOL), why they sold the building.
2-Changing from oil to gas, cut the bill by 50%.
Having said that, the rest of the changes; venting, pipe insulation, lower pressure, pitch of mains, water stop added to the returns, all needed to be done but made no noticeable change in cost but big gains in comfort.
3-New windows and building insulation would be the next capital investment to yield real savings.

So at this point I am splitting hairs trying to maximize comfort, cut the bill further and to be honest it is fun messing with this stuff.

Two posts that I found intriguing concerned vacuum and cycle timing.
Vacuum:
It does make sense if you never suck air back into the radiators you will have less noise and less air to get rid of between cycles. My massive array of Gorton #2s do not relive vacuum before the radiators start to suck air. Does any one make radiator vents that do not suck? (sorry)
Cycle timing:
I get the correlation between the oversized boiler running at diminished capacity and the original coal fired boiler. With 2 staged gas valves, additional timers, sensors or a PLC this can be done. However, running a boiler at low fuel pressure is not efficient unless it is designed for this use, mine is not. Running for equal timed intervals is also based on observation and average conditions and does not make use of the maximum available output from the radiation. I believe it could be more comfortable and some what of a fuel saver though. Neat idea.

My thinking is that a Vaportrol acts as a sensor for when the radiators are full or the room is warm (TRVs). So the Vaportrol insures that with minimum pressure, maximum radiation is being used to heat as quickly as possible during the cycle. This should result in the shortest possible run time which should minimize the fuel cost. The timer spaces the cycle apart allowing the heat to soak into the room. This is to overcome the mismatch of the boiler to the radiation. Unfortunately the timer is only a guess on heat loss of the room or how much the heat the radiator is putting out.

A second thermostat placed near a radiator could act like a sensor for when the radiator output has diminished to where it needs more steam. Set it to close at 100 degrees or so. This could work in conjunction with or instead of the timer. Basically you would delay the restart of the boiler until the output of the radiator dropped below 100 degrees or so.
What do you think?

Again thanks to all!

PMJ

@thfurnitureguy,


What you said here - "maximum radiation is being used to heat as quickly as possible during the cycle" - I think is what you don't want.
What you want is a continuous radiation amount that very closely matches the heat loss. The only time you ever need or want to take advantage of the maximum radiation is in extreme design day cold conditions. Doing maximum radiation on average days only causes overshooting.

You see the original coal systems had very sophisticated pressure sensing devices that controlled a damper on the fire. When it got colder outside that demand condensed steam from the rads at a greater rate, the pressure dropped a small amount, and the damper opened a small amount and provided more steam. The end result was partially filled radiators all the time. In this way the fire was modulated to maintain the same very small pressure (single digit ounces) at all times. The size of the fire was directly related to the heat loss.

Somehow when the fire went to oil and gas and on/off control everyone went to hurry hurry fill the rads and then wait wait wait wait and do it all over again. Controlled that way rads typically went from burning hot to room temp in every full cycle. Many here on this site do far better than that I know with conventional controls, but no one will claim to be as steady state as coal was.

My cycling system combined with vacuum in between gets very close to rads partially warm all the time. A single call for heat typically goes on for 2-4 hours. The heat is many times more even and comfortable than when it was on a vaporstat even at very low pressures. I do the opposite of hurry hurry. I spread out the steam production evenly and then let vacuum take it where it is most needed (which is not the same places at all as where positive pressure and venting would take it).

thfurnitureguy_4

Inspiring post, thank you for sharing. What do you use for radiator vents to prevent loss of vacuum?

Jamie Hall

@PMJ has some very good thoughts. I still think in terms of simplicity, however. Further, I have a dislike -- from a long history of practical engineering -- of controls which do not have some relationship to what they are controlling. Such as timers.

Therefore... you can accomplish much the same thing as his timer by controlling the thermostat(s) properly. Again, back in the bad old days most thermostats had anticipators; small heating elements which fooled the thermostat into thinking the room was heating faster than it really was, and thus shut down the system a little sooner than would have happened otherwise. This mimicked very accurately -- when they were properly adjusted -- the ability of a steam or cast iron water radiator to keep heating for quite some time after the boiler shut off.

Pity we don't have those any more... but many of the better thermostats do have the ability to do much the same thing electronically. It doesn't work as well as an anticipator, but on the other hand it doesn't take a slightly fiddly adjustment.

Unless you are coming out of a setback, the thermostat should normally shut the system off before it has a chance to cycle -- and before the radiators are full of steam. This seems to have been overlooked in this discussion...

PMJ

Jamie,

I do actually understand your issue with the timing approach. Maybe think of it this way - the same way I recommend anyone start this because it is so simple. All that needs to happen to be assured that the temp will never fall is to have an on/wait schedule where the total on time per hour is enough to heat the place in extreme conditions. You time your system on a cold day and add a little. For me that is 50% with my big boiler. With that knowledge with a simple on/off timer where you can adjust both on and off times independently put in series with the tstat will just spread out the full fire which we all know is never needed constantly anyway. That really is pretty simple. I did it that way a number of years. A little slow on cold starts, but way better when heat was really needed and there are no cold starts.

From there as you know I enhanced the control with a PLC to handle the cold start issue and expanded to 3 different on/off schedules that ramp up based on the length of the call.

And while I really do believe that many of you do not have a short cycle issue with proper venting and pressure controls, there is no way that rads are not more full each time than really required. Is it worth any extra effort at all? Personal choice. I will just say I have been startled by the improvement - mostly by the improved balancing of the vacuum - and will never go back. Mission control here would have my bags on the front stoop in short order if I said I was going back to the original control.

PMJ

thfurnitureguy said:

Inspiring post, thank you for sharing. What do you use for radiator vents to prevent loss of vacuum?

I have a two pipe system so only one vent location on the dry return and there I use an electric solenoid valve.

Steamhead

Hey @thfurnitureguy , good to hear from you! I think the last time I saw you was when we were looking at starting All Steamed Up, Inc. How you been?

Is this the Burnham V9 in your store? What burner is on it?

thfurnitureguy_4

Still the old Burnham. Had a gas burner installed 2 years ago. I think a Beckett. Made a huge difference in the heating bill. Installing a vaportrol this year and playing around with some controls. Some neat ideas being kicked around on the Wall. I like the vacuum idea and the timed run concept. You staying busy?

mikeg2015

I think PMJ nailed it. These systems were designed for very low pressures for constant firing, variable output coal boilers. Piping was oversized accordingly and vacuum vents were normally used.

Here's the think, we are fixated on pressure, but ultimately the only way to generate pressure is either venting rate or resistance in the pipe.

Look at it this was, if you had a wide open 3" pipe coming of your boiler, what is the pressure on the steam chest? Maybe 0.1oz to get out the 3" orifice. SO then why does pressure go up at all? Every elbow and length of header adds resistance, just like in a compressed air, hydronic heating system chilled water, etc.

So if you have more than the amount of pressure needed to push steam to a wide open header at the end, (~1oz per 100') then you need more venting at the radiators. IF that number is more than about 1oz per 100', then your header is undersized.

Low steam pressure means less leaks at valve stems and fittings. I have a gauge glass that looks like it's been leaking like crazy for years. But if I keep pressure low, it barely leaks at all. Just filling the boiler up to the header so I have ~35" of pressure on the gauge glass, causes a steady drop. But when firing, pressure is less than a couple inches of pressure.

Steamhead

thfurnitureguy said:

Still the old Burnham. Had a gas burner installed 2 years ago. I think a Beckett. Made a huge difference in the heating bill. Installing a vaportrol this year and playing around with some controls. Some neat ideas being kicked around on the Wall. I like the vacuum idea and the timed run concept. You staying busy?

Oh yes, we're extremely busy. Going out on a no-heat a bit later today.

Not sure if a Beckett gas burner is upgradable to 2-stage firing, but some PowerFlame burners are. We've done a few with good results.

PMJ

mikeg2015 said:

I think PMJ nailed it. These systems were designed for very low pressures for constant firing, variable output coal boilers. Piping was oversized accordingly and vacuum vents were normally used.
.

Right and thanks for noticing. The original system chugged along with the header just over atmospheric and the rads in and out of slight vacuum.

When you let all the air back in every cycle then on the next call for heat you are in the hurry up mode to vent all that air and start warming the rads again. Just seemed so wasteful to me and unlike the original design so I started closing things up.

With the system closed up and the deepest part of the natural vacuum being in the rads, there is practically nothing to vent. Steam is always moving towards the rads and they are always partially warm.

thfurnitureguy_4

I installed the timer box this weekend. Learned there is a difference between 24V dc and 24v AC transformer when it comes to relays... DUH! after I switched to a DC power supply all worked as planned.
The system thermostat calls and the radiators fill to capacity if they do not shut down first by the stat.
Once the radiators are filled the Vaportrol shuts down at 8 oz, timer latches in, Vaportrol resets when pressure drops but the timer stays locked up until the time is satisfied. Once it times out the system will restart as long as the thermostat is still calling and pressure is below 8 oz.
During the initial run the stat was satisfied during the timer period and the unit did not restart. Normally it would have cycled 2-3 times on pressure before the stat was satisfied, with each burn cycle firing about 15 minutes before pressure returned. It would also continue to heat the room 1 to 2 degrees past the set point after the boiler quit.

More about vacuum. I have one pipe steam and with an absence of radiator valves that do not suck air I have invented a farmer fix.
It turns out using the Maid o mist valves it is relatively easy to make a check valve to prevent them venting back. Using a shell casing pressed over the vent orifice and installing a small flap of copper (bullet gas check modified) under the casing it creates a check valve with little to no cracking pressure, works great at 8 oz of pressure. Unfortunately I need like 25 of these and they are a little time consuming to make. I can not speak to if this will work on a system level, but for now it does eliminate the vacuum sucking noise on the units that I have done so far, it also appears that the rad with the check valve stays warm longer than the one of same size located across the same room from it. Vacuum pulling steam?

JUGHNE

Could we see your prototype?

MilanD

Can you elaborate on this:

"Using a shell casing pressed over the vent orifice and installing a small flap of copper (bullet gas check modified) under the casing it creates a check valve with little to no cracking pressure, works great at 8 oz of pressure."

I've been thinking about this very thing, some kind of a flap over the vent hole, just couldn't figure out the material.

PMJ

@thfurnitureguy ,

You sir are on your way. I doubt very much you will ever look back. Keep us posted.

mikeg2015

I really like your idea to keep the boiler steaming. Just like hte old coal boilers did.

I have a similar issue, where my boiler is sized really nice for pickup, but , like all, exceeds radiation pretty quick. Plus above 3oz the vents get noisy from I assume wet steam (till cleaning things up, have no equalizer).

I could see using a vacuum pump just on the main header only... or take 2 or 3 big mouth valves, and pipe them to a big header with a simple ball check. But it would need a very light ball.

My only concern is that pressure imbalances might occur. Keep us posted.

I might at least take the timer idea. Once I reach the limit on the vaporstat (maybe 3 or 4oz), then have an off delay on break , then enable again if it's still calling for heat. Like yours, vaporstat is on the control side, not the safety circuit. The LWCO's and pressuretrol are on the safety end.