Undersized steam supply causes carryover, right? Right??

ethicalpaul · December 23

We have heard, read, believed, and advised others that an undersized steam supply causes water to get "sucked up" into the pipes along with the steam. I was a party to this thinking and advocacy myself. It seemed logical. But then several months ago I started thinking maybe not…and decided to find out. Watch, enjoy, and discuss!

https://www.youtube.com/watch?v=xKWln-odoMg

109A_5 · December 23

Your boiler may simply be too small to see the drama you crave. I'm happy it heats your home well.

Try the flex line into a bucket, flex line not connected to the header.

https://youtu.be/8Me67D6a1-A
https://youtu.be/tI3tWuSsX7c

ethicalpaul · December 23

were those industrial boilers in those videos piped with undersized steam supplies?

109A_5 · December 23

I have no idea (I hope they are piped correctly), they are having fun with them like you are.

Try the flex pipe into the bucket, that may increase the steam velocity exiting the boiler. Wear some PPE.

Not sure what you are trying to prove. That it can't happen with any boiler or just yours.

ethicalpaul · December 23

I’m seeing if an undersized steam supply causes any ill effects. I thought I was pretty clear about that in my original post and in the video, but I may have been mistaken. Was that clearer?

Putting the flex pipe into a bucket wouldn’t affect anything, there already isn’t any significant resistance to the travel of steam from my system, especially at startup when the main vent is open.

109A_5 · December 23

Yes you said that but it is a sample of one and it is or close to the smallest boiler on the market. What about this boiler below as an example? One riser many more burners. I mean if you want to experiment try a 1/2" pipe. At what point do things get bad if ever ? I thinking ratios like boiler BTUs to pipe size.

I found it interesting when you opened and closed the valve on the other riser the pressure changed and the amount of liquid in the sight glass changed, one would think same basic heat dissipation in the corrugated pipe the same amount of condensate would be generated, but the liquid went away.

ethicalpaul · December 23

the liquid drained out of the supply sight glass because the velocity in there dropped to the point where it couldn’t hold up the small amount of condensate anymore.

Additionally much less steam was traveling in that pipe with them both open so there would be less condensate formed.

I would bet that boiler above does fine if the water is decent, There’s nothing to make it carry over other than water quality.

I’d love to have a larger boiler to do more kinds of tests but it is what it is.

I mean if you want to experiment try a 1/2" pipe.

People always want to minimize my experiences as if my boiler can violate the laws of physics due to its size so of course I already thought of this. Give me a minute.

Jamie Hall · December 23

Your experiments are fascinating and entertaining… but, forgive me if I look at it from the standpoint of an engineer… you have too many variables involved to draw general conclusions, since your are not varying some of the more important ones.

As I have said, residential and small commercial heating steam systems are incredibly forgiving. Arrangements work just fine which seemingly have no business working at all, and which violate many guidelines. In fact, there aren't that many guidelines which really are all that critical.

That said, the guidelines and general rules of practice are of value, as coming reasonably close to them almost guarantees the system will work, at least "well enough".

ethicalpaul · December 23

thank you, that’s about all I’m saying. We see this same boiler piped with two 2.5” supplies, it may not be necessary 😅

Let me know which variables you’d like me to test to disprove my statement “I see nothing about the size of the steam supply that would cause water to get sucked out of the boiler”

We keep telling homeowners to repipe their supplies and headers with an even greater lack of evidence.

Eastman · December 23

@ethicalpaul

I really enjoy your videos. Is it practical to replace the bushing coming out of the boiler so that the supply starts out immediately reduced down? That would bring the higher velocity down closer to the steam chest.

ethicalpaul · December 23

https://forum.heatinghelp.com/discussion/comment/1878735#Comment_1878735

Thank you! A friend of mine asked the same thing. I should have something for you in the next video

Eastman · December 23

Have you seen these SpiraxSarco videos that show the inside of a steam boiler?

https://www.youtube.com/playlist?list=PLxm4edL_KbsWPkV7NhXPUIKyn0ee9f58_

I thought they were pretty interesting.

Edit: Looks like @109A_5 already posted one of these videos.

ethicalpaul · December 23

Yes I have seen those, but those are boilers of a different design and higher pressure than residential boilers, the focus of my video.

In the one they talk about "increasing steam demand" which is not something that really comes into play in residential systems. These are boilers that build up pressure in order to provide steam later to new loads that come online.

ChrisJ · December 23

https://forum.heatinghelp.com/discussion/comment/1878750#Comment_1878750

Might be possible with zone valves.

But even so, going from 1 PSI to 1/4 PSI probably isn't what they're looking at.

Jamie Hall · December 23

Well, one critical variable is the actual evaporative surface area and the geometry and dimensions of the vapour space above the water surface leading to the steam outlets — and related, of course, the firing rate of the heat source(s). Then there's the geometry and areas of the firebox and combustion gas passes within the boiler.

for starters…

Eastman · December 23

I don't know of any videos inside a residential. I just thought the Spirax videos were interesting because you can see directly how different conditions effect the boil. But yeah it is a totally different industrial context.

ethicalpaul · December 23

I agree those are important variables @Jamie Hall but my feeling is those are rather made moot because as boilers increase in capacity, burners are added, sections are added, and number and size of specified supplies is added.

This is why I think my boiler, even though a single unit and the smallest of the Peerless boilers, makes a pretty good experimental platform, as would any other size. All the variables are increased together according to the engineers of the boiler manufacturers.

In this video, I went down two pipe sizes from a single 2" supply to a single 1-1/4" supply. That is a very significant constriction from the manufacturer specification and there is no carryover at all observed even with my water line higher than recommended.

I hope I have at least shown that it's possible that we have been focusing a little too heavily on near boiler piping as a cause of carryover.

Jamie Hall · December 23

And I rather tend to agree with your last paragraph above, @ethicalpaul . To which I might add — I'm not sure but what people tend to place too much blame on "carryover" when the problem may be something else entirely — like inadequate pitch or sags, or poorly place of missing drips, or…

Carryover — or any other condition allowing liquid water droplets in the gas stream — is a serious problem in power boilers (last thing you want is water in a cylinder, or droplets hitting your turbine blades). But in residential use? I'm not convinced.

Eastman · December 23

Focus more on water quality?

ChrisJ · December 23

https://forum.heatinghelp.com/discussion/comment/1878763#Comment_1878763

I believe that's exactly his point, right now.

ethicalpaul · December 23

https://forum.heatinghelp.com/discussion/comment/1878760#Comment_1878760

Thanks Jamie!

Please consider that when we see the water level suddenly dive to the bottom of the gauge glass, that’s what I’m calling bad surging/carryover and it’s all too common in residential boilers. Even in my short non-career I’ve seen it in person at 4 people’s houses, plus mine years ago when I was much more ignorant than today.

see this 2 minute video from very early in my history with steam:

https://youtu.be/WSRvvNQ5WLc?si=Eo-qPsfdzkpt-LEM

I consider this the most serious problem for a homeowner. What are they supposed to do when brown water starts shooting out their vents and their LWCO overfills the boiler? They come here, and too often I fear we send them down a long expensive road of boiler repiping. Thanks again for the discussion!

PS: I don’t call this common phenomenon wet steam or water droplets in steam. In my eyes these are a non-issue in residential steam. This is gallons of boiler water carried to the main

Jamie Hall · December 23

Agreed.. If you have a situation where gallons of water (or even a few pints!) get burped into the mains, which can and does happen, that's not carryover. At least not in my book. I don't think we have a good term for indigestion in the boiler (hmm… ) but that's what it is. A good slick of oil… uncommonly bad sludge or scale build up… high suspended (not dissolve) solids…

And I don't think normal piping makes much difference (though perhaps side outlet boilers may be a little more sensitive) — unless you have a giant economy size header, more like a steam drum , to catch the burp.

ethicalpaul · December 23

Hmm, if that's not carryover then I don't know what is, but OK I hear you, thanks again

ChrisJ · December 23

I believe any materials that leave a boiler besides pure steam is considered carry over. It's stuff being carried over by the gas.

Jamie Hall · December 23

I think there's a subtlety there which we need to be mindful of, @ethicalpaul . True, any liquid carried over is… well, carryover. However, it's a matter of degree. Some carryover, by that broad definition, is quite tolerable (heresy!!!) in a residential system. The less the merrier, but so long as the pipe slopes are adequate and the drips are there, it will be difficult to separate it from normal condensation. Larger amounts — burp! — will cause problems.

Where's the line? Dunno…

ethicalpaul · December 24

OK, but have you seen any of the many of my videos that show my boiler running normally where there is not a single visible drop of liquid water above the top of the boiler? It is very very easy to make this very so-called "dry steam" (a term I don't agree with). You can do it without a drop header, and without a header at all. And now I have shown you can also do it with an undersized steam supply too. All you need is clean water.

EBEBRATT-Ed · December 24

IMHO you have to keep in mind the load connected to the boiler as well.

I know for a fact that one job we did in a school that we had issues with. An HB SMITh model 28 boiler brand new 2 of them in fact with 1 5" supply from each boiler piped exactly how the MFG shows in their manual.

I know no one will believe this story.

We did not size the boiler. We just installed what the "engineer " picked and he wasn't an engineer.

We removed two old boilers much larger than what was installed.

On a cold start with both boilers beginning to steam you could not keep water in the boiler. The gauge glass went berserk with the water level jumping up and down violently. tripping low water and bringing on the feed pumps.

This is what I think was happening. And yes the boilers had been skimmed several times.

When the boilers fired and began making steam slowly (large elementary school with a mile of 6" main)

steam started making its way into the system. But there was so much cold 6" pipe and the boilers (I believe undersized) the steam condensed putting a vacuum in the main as the steam collapsed. (2 pipe steam with traps). Now in the instance of a cold start all the water in the boiler has to be at 212 before making steam. Pull a vacuum on the boiler and water happens to the water in the boiler?. It starts to flash and the water level goes nuts You actually for a short time condensing the steam as fast or faster than the boiler(s) can produce it.

They had a steam pressure transducer mounted to the main with a pressure read out and it showed a vacuum. As the boilers cycled on low water, they finally started to gain ground. As soon as the pressure transducer went to +.2psi positive everything ran normal.

Another condition a competitor of mine went through was a boiler with unstable water line. He had the boiler mfg look at it. His condensate was too hot due to traps blowing through.

Condensate was like 200 deg. MFG had the boiler rated at 160 condensate so if you fired the boiler at max normal rating for 160 condensate when the condensate was 200 your overfired..

Btus in the boiler was over what it should have been.

Complicated business.

This is why steam trap MFGs say to size traps at 2-3 times the actual condensate load for warm up load.

The steam a boiler produces isn't just the nameplate rating. Its the nameplate rating at certain conditions.

When the conditions change the output can change.

Risers and the header have to be able to take cold start

Eastman · December 24

@ethicalpaul

Is it practical to try vacuum conditions?

Jamie Hall · December 24

our school story is delightful — and I rather think you are right. With, perhaps, an additional twist — as the pressure dropped, there would have been intensified boiling in the boiler — possibly not at or near the surface. Just a thought…

And yo bring to my mind an observation from the power boiler side of things — on a really big power boiler (think medium size and up ship, for instance) one needs to be careful to bring the firing rate up slowly, over several hours or perhaps even a day or more, partly so expansion can take place eveny, but also to avoid localized boiling.

ethicalpaul · December 24

https://forum.heatinghelp.com/discussion/comment/1878836#Comment_1878836

No, I don't think so.

I believe your story @EBEBRATT-Ed — and to add to what Jamie said, it reminds me of that (in)famous Weil-McLain glass tube boiler demo. They run the pressure up to 5 or 10 psi (which also raises the temperature of the boiler water), then they throw open a valve to open the pipes to atmosphere.

This instantaneous reduction in pressure also lowers the boiling point, causing the boiler to violently boil and blow its guts all over the parking lot as I'm sure you've seen. I can see a relationship between this and what you saw at that school.

109A_5 · December 24

Steaming boiler and a Shop-Vac, what could go wrong…

mattmia2 · December 24

https://forum.heatinghelp.com/discussion/comment/1878836#Comment_1878836

https://www.supplyhouse.com/Ridgid-62703-RT1200-12-Gallon-NXT-Wet-and-Dry-Vacuum

Undersized steam supply causes carryover, right? Right??

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