Do I Need a Vaporstat?

dlipter

My cutin is 0.5 psi ( 8oz) and my cutout is 1.15 psi (18.4oz).

These numbers seem pretty good to me.

What would a Vaporstat buy me?

Thanks

Jamie Hall

If this is a plain vanilla one pipe or two pipe system, then -- nothing much. Not worth the cost. On the other hand, if it is a vapour system, then it will get you much better operation. If it is two pipe, and you can't really tell, post a picture of one of the radiator valves and a picture of one of the radiator outlets and we can advise.

dlipter

Its a one pipe system.

Jamie Hall

Then you don't need a vapourstat. You're fine as you are.

gfrbrookline

Lets flip the question around, if I have a vaporstat set to 12 oz. cut out and 4 oz cut in and it cycles on pressure with two 15 min cycles which allows the radiator vents to open and close throughout the cycle as the steam condenses isn't that better than having a pressurtrol set to run between 1.5 psi and 8 oz and risk locking up the radiator vents making the boiler just build pressure? I know with steam every system is different.

dlipter

After the cutout pressure is reached on my boiler, the pressure reduces to 0 psi before the pressure starts building again. Does that sound like my radiator vents are locking up?

Jamie Hall

Really the only way to determine what the cutout pressure should be -- and therefore whether you need a vapourstat -- is with a low pressure gauge. If you have one, it's easy. Starting from a cold start, the pressure should be observed to build for a few minutes, and then almost level off (assuming you have adequate main venting -- if it doesn't level off, you don't). And it should stay more or less level -- perhaps rising an ounce or two or three -- until most if not all the radiation is satisfied and, on a one pipe system, most of the vents are closed. Then it will start to rise again -- and that is where, ideally, you want to catch it -- perhaps 20% over that pressure. And, of course, you want to have the cutin below that plateau pressure.

You really don't want the vents to reopen so long as the system is calling for heat. There's no point to it -- the air is already out. So that's not really a problem.

Now you run the experiment, and you find that the ideal cutout is around 12 ounces, let's say just for example -- but the burner runs for an additional 2 minutes to get up to the 1.5 psi cutout. Now we have an economic question: is the cost of those two minutes of running great enough to offset the cost of the vapourstat? Hmm...

And of course talking one pipe systems here. Two pipe, especially orifice controlled or systems like the Hoffman and some others, the maximum pressure is really critical. Hoffman Differential Loop equipped systems, for instance, should never run over 8 ounces.

dlipter

Thanks for the detailed explanation Jamie.

I do have a low pressure guage and I observe my pressure as you outlined.

gfrbrookline

Why wouldn't you want the vent to reopen during the later end of the cycle when the steam begins to condense so the cooled air can escape and more steam can get into the radiator. Since we are not taking about vacuum systems isn't that the whole point of getting vents with the proper drop away pressure? I thought that is what I read in Dan's LAOSH. It has produced wonderful even heat in my building and has eliminated my boiler from short cycling even on the last few teen degree days we have had in Boston.

Jamie Hall

Interesting thought. I'll have to think about this a bit... the dynamics of one pipe systems are really quite different from two pipe...

I think that that would be true, if there were still a significant amount of air in the radiator when the boiler cycled off, and if the pressure in the radiator stayed above atmospheric. When the boiler cycles off, the pressure in the system will drop remarkably rapidly as the steam is condensed. Ideally one would want the boiler to cycle back on before the pressure dropped low enough at the main vents to let them open -- if they were ever closed (in two pipe systems with crossover traps, they should never close)(doesn't happen -- the post purge/delay/pre purge timing for oil burners, at least, is long enough to drop to atmospheric in most cases). But the radiators? Yes, I expect that if there were still air in there, and it was cool enough to let the vent open on temperature, then I suppose...

I'll sleep on it.

gfrbrookline

I just saw in your other post that this is a patched boiler.

You will likely only get another year out of the current boiler so the money would be better spent on a new boiler. Put a vaporstat on the new boiler with a nice drop header.

gfrbrookline

@Jamie Hall it gives me a nice long burn cycle instead of 20min on, from cold, then a long series of 1 minute cycles. It's like the system can breath during the cycle and keeps the running pressure between 2-4 oz.. I only build pressure when the radiators are fully heated and vents are all closed after a long burn.

It's a larger system, running a Burnham V904, I always thought we were oversized but this year, through main and radiator venting, moving a few radiators around to better match the room size and heat loss, and the vaporstat we have been able to dial it in.

dlipter

Why only a year?

The only significant stress on the patch is high temperature.
The patch I used is good to 550 deg F. I measured my flue temp at 500 deg F. which is kind of close, so I looked around for a secondary replacement in case the JB Weld fails and I found a product good to 2300 deg F that is designed for furnaces, flues, exhaust systems and gas turbines.

Jamie Hall

The problem with patching -- with anything -- is the difference in expansion of the patch vs. the base metal. At some point -- unpredictable -- it will crack and fail.

@gfrbrookline -- sounds to me like your running just fine -- if it ain't broke, don't fix it!

gfrbrookline

@Jamie Hall agreed.

@dilpter I was in your position in 2015, had to replace a boiler from 2005 that failed because of a hole in the top between the the last two sections. Patches don't last long because of the dynamics they are subjected to. Plan on a new boiler soon.

Just make sure whoever installs your new boiler either follows the manufacturer's instructions of installs a drop header. Drop header is better, will give you drier steam and a much quieter system. Most importantly make sure it matches your edr and they calculate that based on viewing your connected radiators.

dlipter

I will take all that I learned here and have all my ducks in a row for a new boiler when the time comes.

These patches that you know of that failed, can you elaborate on the material and methods used for these repairs?

dlipter

About my patch........

The material I used has a:
Bond Strength of 1800 psi
Tensile Strength of 3900 psi
Flex SDtrength of 7320 psi

And is impregnated with steel. so it just might expand and contract in a similar fashion to cast iron.

Time will tell!

Fred

@dlipter , trust that those patches will fail and if they don't, new holes will develop. A hole or multiple holes in a boiler block is indicative of other weak spots that will surface. I hope that doesn't happen on the coldest day of the year, but, if it does, at least have all your ducks in a row and know what boiler you need and who you want to do the job and how it should be installed. There is a lot of pride that comes with fixing something that others have said "can't be fixed". Don't let that be your downfall. Be prepared.

Kjmass1

I have a one pipe steam system that has been building a little pressure/noise with these mornings in the teens- I watched my low pressure gauge and it never gets above 8oz that I've seen. When boiler turns off, it drops the pressure in maybe 20 seconds. Could I even use a vaporstat to dial it in or would that just add a ton of cycling?

Jamie Hall

@Kjmass1 -- better to start a new thread. That said, remember that any pressure controller -- vapourstat, pressuretrol, whatever -- has nothing to do with how fast or how much pressure a boiler will build. All it does is turn the boiler off if the pressure is higher than needed. If your boiler never gets much above 8 ounces, a vapourstat isn't going to change anything.

dlipter

Well said Fred!

mikeg2015

If the boiler is sized right you don’t need a pussure control, only a limit.

It’s like having a air conditioner where the outdoor condenser is undersized compared to the compressor size and saying oh, it’s ok, I just turn the compressor on and off when the pressure gets high. Why?

You should only build enough pressure as to overcome pipe resistance in the mains and riser or run outs that’s all. Should only cycle on pressure once all radiators are fully heated. That should take several hours of constant running.

Fix main venting and radiator balance first.

Jamie Hall

Except that it's a very rare installation where you can get the balance between the boiler exactly right. Even then, in one pipe or normal two pipe, it's not too bad -- you can be half a pound high and all it costs is money. In some vapour systems, though, even a few ounces too high can throw the balance way off -- if not stop it from heating altogether. Then, perhaps, a reliable accurate pressure control might be useful... as a control (you might compare it to the throttle on a car?), not as a safety (the safety pressure control, set higher, should be there too).

Fred

mikeg2015 said:

If the boiler is sized right you don’t need a pussure control, only a limit.

It’s like having a air conditioner where the outdoor condenser is undersized compared to the compressor size and saying oh, it’s ok, I just turn the compressor on and off when the pressure gets high. Why?

You should only build enough pressure as to overcome pipe resistance in the mains and riser or run outs that’s all. Should only cycle on pressure once all radiators are fully heated. That should take several hours of constant running.

Fix main venting and radiator balance first.

I don't know how you'd pass inspection without a Pressuretrol. I mean a limit switch would shut the boiler down when you reach that limit but you also need something to tell the burner it's ok to fire again, so a low limit would also be required unless you are going to manually reset it again. If you are going to do both, just install the Pressuretrol and be done with it. Besides that, a Pressuretrol is intended to be a "Safety" to really shut the boiler down on pressure, not only during normal operations but to control it under abnormal/unusual circumstances.

In terms of Priority, system safeties will always come before vents and balancing. IMHO

ethicalpaul

Fred said:

Besides that, a Pressuretrol is intended to be a "Safety" to really shut the boiler down on pressure, not only during normal operations but to control it under abnormal/unusual circumstances.

I don't question this @Fred, the pressuretrol would make a nasty operating control...but what's the alternative? I don't think I've seen a non-pressuretrol way to operate a typical oversized boiler to maintain correct low pressure during a long call for heat (or even a medium call for heat).

Jamie Hall

ethicalpaul said:

Fred said:

Besides that, a Pressuretrol is intended to be a "Safety" to really shut the boiler down on pressure, not only during normal operations but to control it under abnormal/unusual circumstances.

I don't question this @Fred, the pressuretrol would make a nasty operating control...but what's the alternative? I don't think I've seen a non-pressuretrol way to operate a typical oversized boiler to maintain correct low pressure during a long call for heat (or even a medium call for heat).

They existed, back in the bad old days of coal. A variety of nifty gadgets which worked to vary the draught on the coal fire depending on the pressure in the steam system Really only on vapour systems, where pressure is much more critical. Needless to say, the efficiency was horrendous, and the CO levels in the stack gas were truly alarming (no pun intended?). As I have commented before, though, since we do not have modulating burners for most steam systems (not that they couldn't be made -- but a truly modulating rather than step modulating gas burner is a little hard to get right across the range, and a truly modulating oil burner is really hard to get right) we have to do it another way: pulse modulation. Now there is nothing wrong with pulse modulation, provided only that the off interval is relatively short and that the equipment is designed for more frequent starts. The point about more frequent starts really isn't an issue -- something else is going to wear out or need replacing anyway, before the motor and ignitor transformer need work -- but the off interval length is very much related to efficiency. The shorter it is, the less the loss in efficiency, since that loss is related to reestablishing a stable flame. If the firebox is already up to temperature, the loss is negligible. Now -- how do we accomplish pulse modulation? Simple. A pressure control -- pressuretrol for conventional two pipe or one pipe, vapourstat for vapour systems -- with the cutout set correctly for the system (it varies by system) and the cutin also correctly set. Neither setting is rocket science -- it can be done in a short afternoon with a low pressure gauge handy. The result will be a system which automatically modulates boiler output, averaged over time, to system heat demand. All off the shelf components, all simple to set up and maintain.

Now. In addition to the pressuretrol or vapourstat which is acting as a control device, there must be another pressuretrol which is acting as a safety device. This one should be set at some reasonable pressure -- high enough to be well clear of the control range established as above, but low enough to protect the rest of the system, mechanically 5 psi is a nice round number. If you are really a belt and braces type of guy -- like me -- there will be yet another one, set even higher -- say 7 psi -- but that one will be a mechanical reset device. The idea there being that if that one trips, someone had better go and talk to the boiler and find out why the other two didn't do their thing.

Think about it -- a thermostat is also a pulse modulation control device, and no one seems to worry about that...

ethicalpaul

Thanks, @Jamie Hall that was a great writeup. I'm going to seriously adding a pressuretrol to be my "control pressuretrol" like you describe. But I probably won't add two (in fact on further thought, maybe I'll just add the manual reset one to back up the "modulating" one)

I don't worry about the thermostat I guess because I have the pressuretrol behind it. When they are both modulating, it makes me feel nervous, so your solution makes me feel better, thanks again! And sorry for the hijack.

Fred

@ethicalpaul , that is my point. I wasn't saying there is a quick, easy way to control an over sized boiler, other than to let the Pressuretrol do its thing as an operating control, especially on an over sized boiler, my point is it needs to be there and has to be given priority over vents and balancing. Nothing bad, other than lost efficiency, will happen if you don't have vents or if the system isn't balanced. Not true if the Pressuretrol is ignored or eliminated. The poster suggested that you don't even need a Pressuretrol if the boiler is properly sized. I take exception to that comment from both current code and the fact that, even with an upper limit switch, you still need something to turn the boiler back on when the pressure falls back into acceptable ranges, which then means a low limit switch as well. That's a Pressuretrol. Why reinvent the wheel or why suggest that the right size boiler would eliminate the need? First, not many of us can just go out and install a new boiler, perfectly sized to our EDR and second, it still needs the safety controls, even if you don't need the operating control.

ethicalpaul

Yes it all makes sense. My question was because I have several times read on HH that "pressuretrol is not an operating control" and yet on so many systems, it is, and I wondered if there was something else I didn't know about that is an operating control.

coelcanth

my boiler is about 30% oversized and was installed with a limit pressuretrol (currently set to 5psi) as well as a control pressuretrol.. but i am struggling to figure how to best set this one up.

when boiler is running the low psi gauge barely flickers.. always hovering between 1.5-2.5oz ..always less than 3oz (0.2psi)

with the control pressure set to cut out just under 2psi and cut in near 0.5psi, i don't think this pressuretrol ever really comes into play. not sure it's possible to dial any lower without going to a vaporstat control...

i do not notice any pressure 'plateau' effect towards the end of a call for heat before the thermostat shuts things down. perhaps i am venting some of the bigger radiators too quickly ?

in practice, the thermostat is the only factor, but i'm not sure if that is best for efficiency

Jamie Hall

You're probably fine. From what you describe the boiler is probably very close to exact -- be happy!

ethicalpaul

Yeah I agree. With that pressure profile I wonder why you think your boiler is oversized

Fred

I agree with @Jamie Hall and @ethicalpaul . What's the problem? It sounds like the system is working fine. It may trip the Pressuretrol when the weather gets much colder but it is what it is. Ideally, The thermostat should be the only control engaged in a heating cycle. Based on what you have said, a Vaporstat will do absolutely nothing for you that the Pressuretrol isn't doing. I am left with the impression that you might be thinking that the boiler is more efficient if it shuts down on pressure. That's not the case, at all.

coelcanth

there's no major problem.. i'm quite happy with the heat.
i am just trying to learn this system and how to set these controls and keep things running ship shape.. hopefully we can save a little gas along the way..

it's a bit confusing when i read about normally setting the cut out right near where the pressure levels off and yet that doesn't seem possible with this setup..

i know the boiler is oversized at 450sqft because i measured my edr to be about 300sqft

ethicalpaul

Hard to tell from here, but my rather limited experience tells me that your system _should_ reach the cut-out during a reasonably long call for heat. In fact, the way you said your pressure never rises above .2 psi, I would suspect a steam leak in the boiler or something weird like that. But my experience is very limited.

You're right that with your pressure never going over .2, your pressuretrol will never see any action, and that's fine, as long as nothing else is amiss (which, as I said, something definitely looks possibly amiss given those EDRs)

Jamie Hall

Looking back over this thread, I think @ethicalpaul may be on to something. That boiler should begin to build pressure eventually. Check around your building while it's running. Do a long enough call so all the radiation is pretty well hot, then go down to the basement and keep an eye on the pressure: once the radiation is full, it should start to build. If it doesn't, you may have a steam leak somewhere -- maybe even into the firebox. Billows of white steam outside?

coelcanth

no, no leaks.. this is a brand new boiler (well on it's second season)
i have it set up to only fill manually and don't really use any makeup water either.

this winter seems fairly mild so far, hovering near freezing temps.. so most calls for heat not much more than 20 minutes running every hour or so. most radiators only heating the first three or four sections.. i can only recall one cold day when they were nearly full. i'll have to try and catch the boiler when the weather cools way down and it does a good long fire.

ethicalpaul

OK sounds good. Or you could do a setback if you leave for a day and observe it when you restore the old setting.

The thermostat doesn’t know how cold it is outside anyway...probably 😅

Fred

LOL, The boiler is running exactly like it should and all seem to be trying to figure out why it's running "exactly like it should"

coelcanth

well i hung out with the boiler to watch it work while recovering from a setback of about 1.5-2 degrees..
we don't normally touch the thermostat. but i had just skimmed for 5 hours so everything was quite cool

it ran for one hour and the max pressure hit was 0.15psi (2.4oz)

all the radiators were nearly full.
temp overshot by one degree.

ethicalpaul

Sounds great! But still a little mysterious