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Vertical fire tubes clogging up

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tim smith
tim smith Member Posts: 2,774
As we see more and more of the fire tubes clogging with byproducts of combustion just thinking about best monitoring techniques. I think having having base line pressure drops on high fan speed would really be helpful. Having readings with no flue or comb air pipe connected and with them connected when they are new would be invaluable information for future service. As these boilers are approaching 8-10 yrs we find them quite clogged. Causing excessive heat build up and eventually will cause failure. We pop tops on the boilers pretty much every maintenance. We of course clean combustion chamber and flush tubes. We take a Silvos rod down tubes to see if restricted. We use to be able to get all the way down but appx 7 yrs ago heat x mfr changed dimple pattern to offset every other one which eliminated possibility of getting rod all the way down. This is not every vertical fire tube heat x but the most prevalent amongst the big boys for res/light comm condensing boilers it seems. Just some food for thought.
Not sure what is the best way to get grounds out of tubes, have tried many methods. Not one has proven to be ideal.
Tim

Comments

  • random12345
    random12345 Member Posts: 469
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    Are there any mod-con boilers that are not susceptible to this issue in your experience and if so which ones?
  • tim smith
    tim smith Member Posts: 2,774
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    None in the firetubes we frequent. I would doubt it due to the nature of acidic condensation and high temps in combustion chamber. Seems they will always produce the crystals that we see. Still love firtubes but just trying to figure out best maintenance procedures.
  • GGross
    GGross Member Posts: 1,105
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    Difficult to fix if you are cleaning them annually as good as you can. Viessmann used to tell us that the modern light commercial firetube heat exchangers were too small for the burner they were attached to, of course they are a competitor so take it with a grain of salt. I know their heat exchangers for similar 600k+ btu boilers would be 3-4 times the size of the AIC heat exchanger in every other manufacturers boiler, same goes for their residential firetube the CU3A, that 94k btu heat exchanger is nearly 4ft tall, it is not removable and if there were light inside it you could see clearly through the passages to the bottom. One of the main reasons they use a water tube still on the residential models, you can actually get in there and clean them. The biggest problem is that usually nobody gets in there to clean the things for like 10 years, and by then it may be too late, on the firetube most guys open it up but have no real way to clean them so they don't.

  • tim smith
    tim smith Member Posts: 2,774
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    We have become pretty adept at cleaning them but they still can never be cleared fully and will continue to get harder to clean over # of years. The water tubes are easier to clean but still have not held up as well as the firetubes in most cases. Viessmann's water tube has been the best of the water tubes as far as holding up but they do fail eventually. I always hope that condensing boilers will go 20 +yrs or so but I still guestimate 15-20 when a customer asks. Of course we have all seen the earlier versions of condensing last substantially less than that, especially if not fully maintained. I am still a fan of condensing technology but you have to factor longevity and maintenance into the equation when figuring lifetime cost. Of course the saving of our resources is a totally other equation when using high efficiency equipment.
    Peace
    Tim
    GGross
  • kcopp
    kcopp Member Posts: 4,450
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    Sounds like an opportunity for a tool invention.... :D
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,390
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    Hi @kcopp , Suppose a power washer might make a tiny bit of a mess. :#

    Yours, Larry
  • tim smith
    tim smith Member Posts: 2,774
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    I wish there was a tool to clean these very small firetubes. The only thing thin and stiff enough we have found is silvfos rod. Not ideal but the tubes have to be clear. The problem now is the offset dimpling which does not allow to get all the way through tubes. I have tried several different chemicals that are considered safe for the type of stainless and none seem to break down the crystals. I try them with samples of the debris and put in a bottle with chemicals, agitate them and see if it will soften them, nothing found yet. I am sure there is something that will do it but not found yet. Have to just make sure they won't attack the stainless too.
  • kcopp
    kcopp Member Posts: 4,450
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    Axiom cleaner?
  • tim smith
    tim smith Member Posts: 2,774
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    kcopp, does not even touch it in the tubes.
    kcopp
  • Teemok
    Teemok Member, Email Confirmation Posts: 574
    edited September 2023
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    Well there's the fill and pump over method that works with some fire tube designs. Adapt to the condensate drain port, then to a full port pvc ball valve, then barb to hose into a 5 gallon bucket. Fill the fire tubes up with a light acid (clr) (flow aid), or a solution you think might resolve the build up. Don't be stupid, you're not a witch or a chemical engineer. Well, maybe you are both. The point is be careful. Now let it soak. Fast drain while pumping over with filter catch for bits pre and or post 5 gallon bucket utility pump. I have an irrigation type plastic coarse barrel screen. Refill, wait, drain, pump over, refill. Maybe it is of some value.

    I have imaginations of a h.p. sprayer with a "kisser" on the end that you can spray down individual tubes while staying dry. Ha ha, good luck. Logic tells me the pressure won't hit where it's needed. High volume and high pressure water in burst flow might do some good cleaning after a soak.

    Then there's the PAS idea (pressurized aggregate slurry). Oh ah.... I'll pass on that. Fill the combustion chamber with yet to be chosen high viscosity fluid that contains some undetermined level and type of small aggregate. The gel barely naturally drains down the tubes. Non problem tubes could be plugged up as they clean up. Now... plate off the top and bolting it down. Inject high pressure air into the top plate air fitting forcing gel rapidly by all the undesired deposits. Collect the gel at the drain and refill to the top chamber port.

    While in total spit ball fantasy mode, a vacuum/pressure rapid reversal cycle might be good. 1 time unit pressure (down) 80% vac. time (up) to keep flow heading down but get some up down scrubbing action going. Rinse well when done. Haven't found a boiler in need that's worth anything like that level of effort.... yet. The 15 year old L.P. carbon-ed up residential Triangle Tube can meet the recycler's teeth.
  • hot_rod
    hot_rod Member Posts: 22,491
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    Id like to try one if these pressure washer kits for the coil type mod cons. Maybe one is available for fire tube type?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • HomerJSmith
    HomerJSmith Member Posts: 2,511
    edited September 2023
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    Do you find that Nat gas or Propane is a worse culprit? When I was a mere lad, I use to sell vapour injectors for cars. After a while, the carbon in the cylinders and spark plug would clean up. Pistons would sparkle. Injecting water vapour into the fire tube as the blower is running may prevent the formation of deposits to begin with. I would inject it into the sys between the gas valve and blower I would think. Maybe before the gas valve. Probably throw off the CO readings and lean out the incoming gases, hmmm
    Notice how cars ran much better in thunder storms with a high water vapour content in the air?
  • Teemok
    Teemok Member, Email Confirmation Posts: 574
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    I've had a high pressure sprayer Giannoni HX cleaning kit Idea since my first munchkin cleaning way back. Plate with center sliding push pull wand and dual rubber tipped spinner sprayers on arms close to the tube gaps. I've never had enough HX cleaning services lined up to warrant the development. Working for another company, my son is currently in the process of cleaning 32 units one after another. Yuck! I would have built it for that project. The idea of sending any tool down one of those little fire tubes seems risky and futile. I've heard of techs making slightly restricted tubes completely blocked with silver braze rods while attempting to clear them. I find condensing LP is the worst, non-condensing Nat. the best.
  • tim smith
    tim smith Member Posts: 2,774
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    These are all natural gas. Have tried using restricted tip nozzles to blast down them, uh, that's not so great spraying all over the place. Nope! I think the best solution but in final outcome would probably not be worth it would be to pull heat x when they are starting to get bad and put them in an ultrasonic bath with Citric acid. The tube are so restrictive as you pass down them that no specific tool goes down. Ultrasonic would loosen the grounds that are down in the lower half of tubes, at the constricted points where the dimples are. They become very hard and adhere to each other. Then we can't even get a silvfos flat brazing rod down through them after soaking in CLR or one of the Fernox or Axiom cleaners. I am going to stop racking my brain over this as retirement is just around the corner.
  • tim smith
    tim smith Member Posts: 2,774
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    Teemok there is no option when they have already become 30, 50 or 75% blocked. And no you don't compact any more, they are already there. The risk is only that you cant leave them blocked so either it's time for new heat x or you clear them well enough to operate. We always warn in advance that the heat x may have to be replaced when they are like this. Sometimes after clearing the grounds they will leak, rarely but has happened and client knows this in advance. None of these smaller vertical firetubes are exempt from this, it will happen. Some of the higher temp systems have less of an issue with grounds build up but it is unusually random even with those.
    Tim
  • Teemok
    Teemok Member, Email Confirmation Posts: 574
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    I get its a last ditch effort and the notifications. That's good policy. The randomness of grounds lines up with the old Munchkins experiences. Two boilers on either end of a building under similar loads, fuel, tuning, age and environmental conditions and one doesn't have many grounds while the other is loaded with them. Much speculation about materials consistency, pseudo science and finger pointing. I haven't seen that with fire tubes but I know you are correct when you say it has and will happen more. I had the idea of a thin brushed cable loop. If it could be fished down the tube and caught through the flue opening at the base and maybe a pull up brush loop could be made. At lease a long down and back up pull is possible. The different sizes and turbulator designs makes it hard to standardize a mechanical cleaning approach. I've thought this is an area a manufacture could stand apart. If there was a removable turbulator in the tubes, cleaning becomes possible and we might have a long service HX. I know that's not in their interests necessarily but hopeful the arch of engineering bends towards the good.
  • tim smith
    tim smith Member Posts: 2,774
    edited September 2023
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    Thats funny, I have been thinking about removable turbulators also. Then it would be a no brainer for cleaning, yank turbulators, flush out and put back in. The offset dimple pattern that the heatx mfr AIC has went to has made it impossible to pass through the small oval tubes to drain pan. It prevents us from clearing the tubes all the way. Oh well! The spiral water tube heat x we had down on cleaning except when we cleared grounds they some times like to give a shower in final outcome. 12-15 yrs on them seems to be their longevity. Sometimes less sometimes bit more.
    Tim