Surging - what are the physics and is "skim it" the answer?

copperred

This is my first post here but I've benefited a lot from reading the forum of the years and I'm glad to finally be a part. I hope my question isn't too much of a repeat (I've searched a lot). Here goes:

TL;DR: new boiler on previously balanced system is surging, knocking, and flooding the garage

I recently had my boiler replaced. Before the replacement, I spent a lot of time balancing the system (adjusting vent sizes) and I was happy with the outcome (aside from the ailing boiler that needed replacement). My point is that the system is decently balanced and all rads heat up.

I had the old boiler replaced with essentially the same thing. Since then, the system suffers from rapid drops in the water level (surging?), lots of knocking, and it has been pushing water back up the return and out a vent in the garage. Yikes! My plumber has repeatedly (3x) drained the water, refilled, and added some "treatment" to clean things out.

Everything I've read has led to "skim the boiler" as a solution. But I'm having a hard time understanding what is actually happening inside, assuming there's something oily in there that needs to be skimmed.

It seems like there's a rapid pressure build up that both rushes up towards the radiators and forces water down the return. When I watch the gauge glass, shortly after the boiler is fired (from a warm condition), the water level plunges to slightly below the bottom of the glass. Sometimes the LWCO trips and sometimes it does not. When it trips, the water usually rises back up within 10 seconds or so, which keeps the feeder from adding water. Water is being added too often but not every day, based on the meter.

How does oil contribute to the water level being pushed down (and back up the return) ? I read that "bubbles have a hard time breaking the surface" but I can't picture how this causes all of my issues. The rapid drop in water level confuses me. Wouldn't trapped bubbles slow down the boiling process? Or do bubbles build up and get "released" all at once when the surface breaks and rush to push through the mains and can't escape fast enough? But wouldn't accumulation of bubbles under the surface push the water level UP, not DOWN? And push it down slowly as the bubbles accumulate? Maybe the gauge is not exactly matching what is happening inside??

I can also hear the radiator vents very noisily when the "steam is coming" as if there's a rapid purge of air (previously they barely made a sound for a couple seconds as the steam approached). It gives me the impression that things are moving more quickly which I again makes me think of higher pressure inside the boiler. And obviously the water backing out of the vent in the garage is a major concern and means that water is pushed back up the wet return. But the pressure limit is set to 1.5-2PSI and doesn't seem to be unhappy.

Studying the pipe, one thing I see is that the equalizer "T" on the H-loop is a bit high. It seems to be at the same height as the prior boiler install though, which had none of these issues.

Any insights would be wonderfully appreciated.

JUGHNE

One shortcoming in your boiler piping it the reducing 90 at the end of the header. It should point down to drain the header back into the equalizer.
As it is now the header retains a good inch of water that is not draining over the concentric fitting.

The plug in the boiler just to lower left of gauge would be a good skimming port. An 8 point socket may remove it before it is steam welded in place.

nicholas bonham-carter

Yes to skimming through that front plug. Drain out the treatment as soon as you can.
Was the new boiler sized to the measured radiator EDR, or just duplicates the size of the old boiler?
What pressure is the boiler running at?--NBC

JUGHNE

The oils float on the top of the water.
Draining the water off the bottom will let the oils cling to the sides inside the boiler.....think of the ring around the tub when it is drained.
Refill of the boiler put the oils back into the "floater" mode.

The skim done slowly will let the floaters come off of the top of the water. It may have to be done several times. New boiler and piping contain a fair amount of oils.

Jamie Hall

On the physics of surging -- really not a mystery. What happens is that in a new boiler -- or even with extensive new piping -- there is a good deal of casting and cutting oil. Can't help it. That oil forms a film -- sometimes a rather impressive one -- on the surface of the water. When a steam bubble comes up, it can't break through that smoothly until it gets much bigger -- and then it breaks through violently. This throws a good deal of straight out plain vanilla hot water up into the risers and, often, even into the mains. Presto. Boiler surges.

The solution is skimming, in which you release water slowly -- so as not to disturb things -- from the surface. That way, that film of oil is drawn off and you can dispose of it. If you just drain the boiler, that film of oil is simply redeposited on all the surfaces inside, and when you refill it is picked up and you are right back where you started.

There are detergent additives which, if the surfaces are fully underwater (they aren't, in a steam boiler) and the water with additive is thoroughly circulated (it can't be, in a steam boiler) can also remove the oils -- provided they are fully circulated and flushed -- and rinse and repeat a couple of times -- and then thoroughly flushed out. Used in a steam boiler, they may actually make things worse if they permit or cause foam to form. So... don't use them. If they have been used, you will need to drain the boiler, refill, and drain again, and then refill with clean water and skim.

As @JUGHNE noted, that reducing elbow at the end of the header is a catastrophe. Until that is fixed, you have guaranteed problems.

mattmia2

The water does not get pushed in to the return, it is being carried in to the steam mains by the steam. i am not positive of the physics of it, but I think it is basically when it builds more pressure to break the tension of the film of oil a larger pocket of water turn in to steam and that carries more water with it which is more than the near boiler piping can remove and a fair bit of it get carried in to the steam main.

Oil has to be removed by draining water off of the top of the boiler by adding water slowly from below the water line. If you drain it from the bottom, it will simply cling to the inside of the boiler as you drain it and the new water will pick it up from inside the boiler.

With all that new piping and whoever installed it not knowing what skimming does or having installed a skim port, it is very likely your issue is oil from the new piping trapped in the boiler.

Steamhead

JUGHNE said:

One shortcoming in your boiler piping it the reducing 90 at the end of the header. It should point down to drain the header back into the equalizer.
As it is now the header retains a good inch of water that is not draining over the concentric fitting.

This!!!!! I thought that was a nicely installed header before I saw that reducing ell. It is definitely a big part of your problem.

copperred

JUGHNE said:

One shortcoming in your boiler piping it the reducing 90 at the end of the header. It should point down to drain the header back into the equalizer.
As it is now the header retains a good inch of water that is not draining over the concentric fitting.

The plug in the boiler just to lower left of gauge would be a good skimming port. An 8 point socket may remove it before it is steam welded in place.

Thank you! Yes I see your point now about water pooling in the header. I just went down there for a "cycle" and heard some banging and could definitely tell that it was coming from that horizontal equalizer section. Ugh. The old setup had the drop down at an angle off the header and it appears the new setup was routed horizontal with a 90 to leave room for the auto-filler piping.

I'd love to skim this sucker if I could get that plug out. I'll have to find a huge socket. It's a big square shape. Of course, I'll ask the installer about it too.

nicholas bonham-carter said:

What pressure is the boiler running at?--NBC

I don't see anything registered on the gauge.

JUGHNE

Find the install book for your boiler model. It would have come with the boiler....might be 50-60 pages.
It will have piping diagrams that point out having the reducing fitting on the vertical drop.
It will also state if your size boiler requires 2 boiler risers and the size of them.

Also may point out the skim tapping and perhaps how to use it.
With this document you have a basis to pressure the installer to follow the directions.
He did fairly well considered some installs we see here.

copperred

nicholas bonham-carter said:

Was the new boiler sized to the measured radiator EDR, or just duplicates the size of the old boiler?

The new boiler was almost a 1:1 replacement of what was there previously.

copperred

mattmia2 said:

With all that new piping and whoever installed it not knowing what skimming does or having installed a skim port, it is very likely your issue is oil from the new piping trapped in the boiler.

Thank you for the feedback. The installer asked me if I wanted copper or black pipe and I chose black. There's no excuse either way but maybe he's used to using copper... The previous system had copper from the reducing elbow down.

copperred

mattmia2 said:

The water does not get pushed in to the return, it is being carried in to the steam mains by the steam.

I'm not really sure but I have water pouring out sometimes. This is at the end of a long return that goes all the way around the house below the water line, then goes up. These vents are about 6 1/2' above the floor. There are other branches off this line before this point that could be a pressure source. It could be pressure coming around from the mains pushing water in the last leg of the return maybe? (Ignore that low voltage wire I have hanging there - not connected to anything )

Video
https://drive.google.com/file/d/1X7MAqNLnNow4Nr0Wi5ql6gEHeKCny567/view?usp=sharing

mattmia2

It should always be black iron on the steam supply side, that isn't a good sign that whoever is working on it really understands steam.

What is most likely happening is the boiler is making wet steam both because of that improper fitting holding water in the header and because it hasn't been skimmed and the returns can't handle the amount of water in the mains and it is backing up out of the vent.

If that boiler requires 2 risers when set up for steam in that capacity that would also contribute to making wet steam.

The old boiler might have been downfired as well, you don't know how well the boiler matches the load if someone didn't measure the edr of the radiation before choosing the boiler.

ethicalpaul

Here is what it looks like. 

https://youtu.be/jvt8qxBaRJU

copperred

JUGHNE said:

Find the install book for your boiler model. It would have come with the boiler....might be 50-60 pages.
It will have piping diagrams that point out having the reducing fitting on the vertical drop.
It will also state if your size boiler requires 2 boiler risers and the size of them.

Also may point out the skim tapping and perhaps how to use it.
With this document you have a basis to pressure the installer to follow the directions.
He did fairly well considered some installs we see here.

I have all the paperwork and will raise the issue with the installer. The instructions have a bit of a mixed message on the piping...

mattmia2

Is youre system parallel flow, are the returns only at the far ends of the mains?

copperred

ethicalpaul said:

Here is what it looks like. 

https://youtu.be/jvt8qxBaRJU

Okay that totally destroys my mental model! Amazing setup and much appreciated Paul!

ethicalpaul

I'm glad you liked it

Note that my boiler has a drop header and water was STILL getting up to the riser, almost to the main (or maybe even to it).

If yours had similar frothing/wet steam, it would be sending a lot of water into your main.

You're going to have good piping once that equalizer pipe is heading downhill and the skimming should clear up any surging you might be having.

copperred

mattmia2 said:

Is youre system parallel flow, are the returns only at the far ends of the mains?

There are multiple connections that drop down to the return. Here's an approximation as far as I can tell:

Jamie Hall

So long as the drops actually drop to a wet return, and the wet return is solidly below the water level of the boiler, you should be fine.

On the slightly ambiguous wording you circled, the story is simple: the piping diagram shown as recommended is the minimum piping which the boiler manufacturer wants to see. The 24 inch dimension shown is a minimum, and more is better. The pipe sizes shown are minima, and -- within reason -- bigger is better, particularly for the horizontal pipe labelled "H". The 2" dimension is pretty exact -- you want to get as close to that as you can.

If your system has counterflow mains -- the mains slope back to the boiler, rather than away from it -- then there should be a drip from the main down to the wet return very close to the boiler.

copperred

ethicalpaul said:

I'm glad you liked it

Note that my boiler has a drop header and water was STILL getting up to the riser, almost to the main (or maybe even to it).

If yours had similar frothing/wet steam, it would be sending a lot of water into your main.

You're going to have good piping once that equalizer pipe is heading downhill and the skimming should clear up any surging you might be having.

How does one open the port? Something like this maybe?