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HX thumping in Seton when fired?

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by Pat53, Dec 2, 2010.

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  1. Pat53

    Pat53 Minister of Fire

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    Hi, just fired up the Seton today and after charging storage up to about 155F the HX in the Seton is doing a bit of thumping and banging, not real bad but can't figure out why. As soon as the draft door closes ( had it set at 165F) and the fire dies the banging stops.

    Pressure is good at about 18 PSI. Pump is moving water quickly thru the system. Never heard a thing last year, any thoughts?

    thx, Pat

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  2. webbie

    webbie Seasoned Moderator Staff Member

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    First thought is that it is making instant steam of sorts.....or some air in there, etc.
    Do you have a temp probe on the water coming directly out of the HE?
  3. Pat53

    Pat53 Minister of Fire

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    Hi, I don't think its air, everything is circulating well. I have an Azel 777 for my setpoint/differential and it is in sync with my temp/pressure gauge which is directly on top of the HX exit.

    It sounds like flash boiling to me because the banging stops almost instantly once the fire is cut out, and returns soon after the unit fires up again. The noise seems to be coming from the header just below the HX exit pipe.

    Today was my first burn using storage so I started out with 50F water, but I didn't notice any banging until my supply temp got up to about 155F. I don't think I'm overfiring the boiler, I only have about 16 feet of stack and the fire is burning nicely, but I wouldn't call it "ripping". The pump is moving plenty of water, it never cycled off once until temp was up to 165F, where I set it initially.

    Pat
  4. webbie

    webbie Seasoned Moderator Staff Member

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    flash boiling sounds like the right term!

    I had some experiences with low water volume and high HE wood boilers of that (and other) designs...... decades ago. The old Volcano boiler had baffles in it made of stainless steel with water tubes blown into them - like a water pillow. Before that, it had copper tubes, 1", and silver solder was used to braze them into serpentines. The copper ones ended up melting the joints and leaking if the boiler was without water or circulation (power failure) for even a few moments. The stainless ones did the flash-boil thing and if the power went out for even 2 minutes, there would be a steam filled basement. Moral of that story is to make certain you pipe the PR valves to a place where they are not going to hit you if and when they go off.

    In the case of the Seton design I would speculate that, for some reason, there is too much heat hitting those tubes......that is, there is not a balance between the heat and the heat exchange. Strangely enough, this could be due to the water moving too fast or too slow...water moving too fast might not pick up all the heat transfer.......

    The other thing I mentioned - air - does not mean you actually have air in your system. But water has air in it, an unless this water has been in the system and heated up many times, the water will continue to give off oxygen for awhile until it turns to "black water" which we commonly see in closed loop boilers.

    Others may know more about that particular design. It may be that it would fit itself when the water gives off most of the initial oxygen. It might be that slightly slowing down the passage of water through the boiler or even raising the boiler temp (nothing wrong with 185 degree water!) might solve it.
  5. sparke

    sparke Minister of Fire

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    When my unit does that it is steam. In my case steam is caused by trapped air...
  6. Pat53

    Pat53 Minister of Fire

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    Craig, you may be right about the oxygen in the water being the cause. I filled the 500 gallon propane tank with my garden hose and the water was splashing around while filling, so there would definitely be a bit of dissolved oxygen in the water. I'll keep the fires relatively small for a while and see if the flash boiling subsides.

    I did run the temp up to 185F last night but the boiling was still there whenever there was a good burn going. As soon as the burn dies down or the draft door closes it stops. Hopefully your correct about the oxygen, I'd like to get this thing ripping once and see how it performs.

    thx, Pat
  7. trailhound68

    trailhound68 New Member

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    Mine will do this too. You're making a little bit of steam at the hottest spot in your hx'er.
    Some molecules are going from liquid to gas and back in your pipes.
    Be thankfull your NOT making a lot of steam.
    It stops when damper closes. When it cools.
    Your on that fine line.
  8. b_board

    b_board New Member

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    I had the same problem last year and it drove me nuts. long story short the wood was to dry which made a very hot burn, when I worked my way to less dryer wood the problem went away....
  9. Pat53

    Pat53 Minister of Fire

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    Yes, I think my problem might be that I'm not moving the water fast enough. I have a Taco 0014 VDT pump but one of the sensors is shot (right out of the box ) and so I had to change a setting on the pump just to get it to work, but it doesn't seem like its running full power. I bought the pump last spring new, but I wish i had bought the new "Setpoint" circulator from Taco, sounds like it would work well for my application.

    Pat
  10. RobC

    RobC Minister of Fire

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    When you added the storage to the Seaton could that be causing much colder water to return to boiler ? Would it be possible that you need return boiler protection mixing valve like the gassers have ? Do others have storage hooked to Seatons ?
    Totally different animal but I started to burn Pine in my Tarm this past month. I got banging down low on bottom of boiler. My controller didn't start to circulate Tarm water until boiler hit 160. So I changed my boiler circulator start to 150. The banging stopped. Even though the return water was coming through the protection valve, the fire ( Pine instead of Oak ) was heating so fast that the circulator couldn't keep the excessive heat off the walls of the firebox. ( That's my theory anyway )
    I know that the Seaton runs a big, hot refractory could it be that the water differential is so cold that it's causing the HX to drop so much that's the problem ? Would you possibly need a protection valve on the storage side of HX to keep the large drawdown of temp ?
    I know I'm not comparing apples to apples but thought I would share a similar experience and solution.
  11. Pat53

    Pat53 Minister of Fire

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    I don't think it is a problem of cold return water. I tried firing back up today after letting the storage temp get down to only 160F on the return line and as soon as the fire got cranking the boiling started. Even as return water was getting up to about 170F it was still boiling anytime a hot fire was going. As soon as the fire died down or the air was cut off the banging stops almost immediately. Whenever the stack temp gets above 350F or so it starts thumping. And I noticed that I am getting a big Delta T in the HX. Supply is coming out about 25-30 degrees hotter than incoming water.

    It is possible that there could be still some O2 in the water, but I'm starting to think I need more pump speed. My lines are all 1 1/4" black pipe and only a 40' run from boiler to storage tank. I'm hoping Taco can tell me how to get this pump to run full speed until I can get a new sensor, hopefully it will work then.

    Pat
  12. 2.beans

    2.beans Minister of Fire

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    i think its called kettling, google it.fred seton told me this was due to to hot of a fire and not enough circulation. i also didnt have this noise until i added storage. and i havent been able to make it stop. i havent tried that hard to get rid of it yet either.
  13. Pat53

    Pat53 Minister of Fire

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    Well I sure hope the problem is just low pump speed. That sounds like what it must be because it only starts making the noise when the stack temp gets to about 350F. Last year , without storage, I would get a hot fire going for sometimes 20 minutes before the draft shut down and never had any "kettling" at all. The stack temp was over 400F . The thing i don't understand is that it doesn't matter what the water temp is coming out of the boiler, it will still make noise. Fired up this afternoon and my return water was on 143F. As soon as the stack temp hit 350F or so the kettling started and the water coming out of the boiler was only 160F ? How can 160F water boil?

    What size pump do you have on your system? Last year I had a Taco 0012 and had no problem. Now I have a Taco 0014 VDT variable speed pump but one of the sensors is bad, and I know the pump is not running full speed. I'm going to call Taco Monday and see if there is any way to over-ride the system and get the pump to just run full speed until I can get another sensor. Hopefully it will operate like its supposed to with a new sensor.

    Pat
  14. ISeeDeadBTUs

    ISeeDeadBTUs Guest

    Can you find a boiler guy that will let you borrow a bigger pump? From all the talk, it sounds like this would be my first most likely 'fix'.
  15. Pat53

    Pat53 Minister of Fire

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    Allready have one ordered, I needed a back-up pump anyway. Even tho the Taco VDT is brand new, they can fail without warning at any time I guess.

    Pat
  16. Willman

    Willman Minister of Fire

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    I wonder about having the backup circ piped in ready to go in case of failure of original circ.At the very least make sure you can isolate it and purge it. Do you have a dump zone ready for the inevitable ?? What are you running for O2 elimination ? Takes awhile to remove O2 from 500 gals.
    Will
  17. Pat53

    Pat53 Minister of Fire

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    Hi Will, If my primary pump were to fail, it would take me about 15 minutes to replace it. I do isolator valves on both ends of the pump. For overtemp I have an 2000 watt inverter that will keep the circ going.

    I don't have anything for O2 elimination. I'm not sure if my problem is too slow of flow or O2 that is causing the kettling, but it starts like clockwork at about 360F stack temp and stops by abouit 340F stack temp when its cooling off.

    Last year, before I had storage, I was running a Taco 0011 and had about a 75' run (150' total) with 1" pipe and never had any problem with kettling, even with stack temps above 400F. Now this year with storage, I only about 100' of 1 1/4" black pipe with only a few 45's and 90's. I'm running what I believe is a "crippled" Taco 0014 VDT that is not moving enough water thru the HX to keep it from kettling, but I'm not positive on the flow, so it could be O2 in the water that is the problem. I'm going to get a Grundfos 26-99 3 speed for back up or possibly my main pump depending on if the 0014 will work or not. It sucks keeping small fires going all day to charge the storage for overnite..

    I am estimating about 20 feet of head for 18 GPM?

    Pat
  18. rglazier65

    rglazier65 New Member

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    as b_board says .... how dry is your wood. a little less dry or a mix of some greener i think would settle it down. worth a try.
  19. Pat53

    Pat53 Minister of Fire

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    Well, I've added a bigger pump (Grundfos 26-99) and I am still having the kettling noises. The kettling only happens when I first get a hot fire going. It seems as if as long as the flames are licking the HX, it will make noise. Once the flames die down, I can have a hot fire going with stack temps well over 400F but no kettling.

    When I filled the 500 gallon propane tank I filled it with a garden hose and I know I introduced a lot of oxygen into the water because it was splashing into the tank while filling. It never occurred to me that dissolved oxygen in the water might cause a problem. I do not think actual air in the system is a problem. The zones and pumps in the house are all virtually silent.

    Is there any way to put an additive in the water that will eliminate dissolved oxygen from the system?

    thx, Pat
  20. bigburner

    bigburner Feeling the Heat

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    "Is there any way to put an additive in the water that will eliminate dissolved oxygen from the system?"

    I built myself a shot feeder, an air tank standing on end, welded a two inch coupling on top - put a tee before & after the pump with a couple ball valves and you are in business. used it today to add some chemical that I got from Mike - 920 324 2007. If you don't use much make up water the iron will eventually use up the O2 in the water. should treat it for long term health of the equipment.
  21. Pat53

    Pat53 Minister of Fire

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    Bigburner, can you tell me what the name of the additive is?

    thx, Pat
  22. bigburner

    bigburner Feeling the Heat

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    What he sold me was CLT-200P. I think it's private label stuff. Think it's nitrate based!! Phone call, credit card, 3 days later it's here along with sample bottles for included testing. I talked to some industral chem guys and they didn't even want to talk to me about it, they are looking for a maintenance type contract, not to sell to a guy with a tank in his back yard. Call Mike - he does over 300 of these type units.
  23. Pat53

    Pat53 Minister of Fire

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    Bigburner, I talked with Mike and he did not think it was dissolved oxygen in the water. He said any oxygen that may have been introduced should be used up or vented out by now. He thinks it could be air in the system yet, or a negative pressure point, but my system pressure never falls below 6 PSI when the storage is ready to be charges. Is that pressure too low and possibly letting air in somewhere?

    Actually, when I think about it, there is no way there could be air in the HX inside the boiler. That water is coming from the bottom of the storage tank, not from a dip tube, so I think I can safely rule out air as the problem. The only thing I can imagine is that the fire box is just getting too hot and causing flash boiling in the HX. I suppose I could try a bigger pump, but a Grundfos 26-99 should be plenty big I would think. Or perhaps taking a little off the stack height. I currently have about 17 feet, and stack temps will get over 500F on a good burn. Anyone have any other suggestions?


    thx, Pat
  24. 2.beans

    2.beans Minister of Fire

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    what psi is your auto fill valve set at? is your system adding fresh water when the storage temp gets low?
  25. Pat53

    Pat53 Minister of Fire

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    Its set at 12 PSI, but the autofill is near my propane boiler in my basement. The pressure gauge on that boiler only gets down to about 13-14 PSI when the system is cold (150F). My Seton is outside and about 10 feet higher and the pressure gauge will get down to about 6-8 PSI before I fire it up. I never hear the pump cavitating even at that pressure.

    Any fresh water that may be added is from my well (188 feet down), which shouldn't contain any dissolved oxygen.

    Pat
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