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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.

  1. mole

    mole Member

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    Hi Pat,
    Do you think you might have a partial air lock in your loop somehere that's causing low flow? I don't think the air lock needs to be in the boiler tubes to cause the problem. When you filled up your system, if you formed an air pocket at a high point, the air may still be trapped up there, which could cause the low flow. Without an air eliminator at the high spot, the air would have no way to get out. Yes, the oxygen will be "consumed" but wouldn't the nitrogen, (which is about 3/4 of the air) remain?
    I've had instances where I drained my system, then I believe (no proof!) I had low flow until the major air pockets worked out of the system. I have three air eliminators, one in each of my three high spots. After refilling the system, I can hear the traps purging periodically for a few days before the air is completely removed. I'd swear I've heard the sound of the pump change as an air pocket is expelled. It quiets down. Your observation about the 30degF delta T with a lame fire sounds like low flow as does the localized boiling.

    My two cents.
    JR

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  2. bigburner

    bigburner Feeling the Heat

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    I didn't think it was O2, I would treat it anyway. Low flow sounds like it maybe be the cause, you could lower the delta-T by more GPM. Curious about the noise, if you don't have laminar flow the turbulence could allow a hot spot. Stick a flow meter or a circuit in the discharge so you can prove GPM. You could lower the split to a few degrees with good flow, not that you would what, but that it is just what is possible. I am not sure why you wouldn't keep the pressure @ 12 psi or above. Most have a 12 psi auto fill that gets you 2.5 stories in to the air, as temp goes up so does the pressure - but it will also compress any air bubbles - with out spending money. I would let it cool off a little and pressure bleed the whole system -- Mole may be correct that low flow is cause by a problem down stream. If you know the P drop across the HX it would be pretty easy to figure what flow you should have.
  3. Pat53

    Pat53 Minister of Fire

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    Hi Mole, well, the delta T is about 25 degrees on a hot burn (400+ stack temp). I'm not sure how that compares to others with Setons or GW's, maybe its too high. I am running a Grundfos 26-99 on high speed. I have only a 40 foot run from boiler to storage and only a few 45's and 2 - 90's in the piping, which is all 1 1/4" black pipe. Now last year I had no storage and was running a Taco 0011, which is about the same pump as the Grundfos 26-99, and I had no problems even with very hot burns, altho they were shorter in duration. And last year I had about a 100' run with only 1" piping and it actually choked down to 3/4" at the propane boiler inlet and outlet. So I would think I had much more head pressure last year and consequently less flow rate than this year, but never once had any kettling or flash boiling. Stack height is the same as last year too.

    As far as air, I have air purgers in several places in the system. I have one right near the HX outlet and another at the top of the storage tank, plus several inside on the zones. When I first pressurized the system I could hear them all venting air. They are all new also, I replaced all the older ones in the house zones also. I never hear any noise from the boiler pump at all when its circulating, no caviatation or anything that sounds like air going thru the impeller.

    If I'm drawing water directly off the bottom of the storage tank, I don't see any way there could be air in that water. And the other strange thing is that the boiler only makes noise when the actual flames from the fire are high and hitting the HX, like after I throw a new piece of wood in. I can be running over 400F on the stack with a good hot fire, but as long as the flames are not licking the HX it will not make any noise. Once the flames flare up I can watch the stack temp climb and then start to hear the water making like "trickling" sounds in the HX and then the kettling will soon follow.

    I'm beginning to think I am just not moving the water fast enough thru the system? What is your approximate delta T in your HX on a hot burn?

    thx, Pat
  4. Pat53

    Pat53 Minister of Fire

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    I'm not sure what the delta T should be accross the HX, altho 25 degrees sounds a bit high I guess. If I were to try and keep the pressure above 12 PSI at the Seton I would get to over 30 PSI at 190F in the basement propane boiler. The pressure difference between indoors (downstairs) and the Seton (outdoors, and about 10 feet higher) is about 6-7 lbs pressure according to the gauges. When I am full storage temp (185-190) my pressure reads about 21 PSI on the Seton and about 26-27 PSI downstairs on the propane boiler, so I'm pushing the limit as is. I have a 44 gallon expansion tank in the system, plus another small one near the propane boiler. I have no idea what the P is accross the HX?

    Pat
  5. mole

    mole Member

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    [/quote]
    Hi Mole, well, the delta T is about 25 degrees on a hot burn (400+ stack temp). I'm not sure how that compares to others with Setons or GW's, maybe its too high. I am running a Grundfos 26-99 on high speed. I have only a 40 foot run from boiler to storage and only a few 45's and 2 - 90's in the piping, which is all 1 1/4" black pipe. Now last year I had no storage and was running a Taco 0011, which is about the same pump as the Grundfos 26-99, and I had no problems even with very hot burns, altho they were shorter in duration. And last year I had about a 100' run with only 1" piping and it actually choked down to 3/4" at the propane boiler inlet and outlet. So I would think I had much more head pressure last year and consequently less flow rate than this year, but never once had any kettling or flash boiling. Stack height is the same as last year too.

    As far as air, I have air purgers in several places in the system. I have one right near the HX outlet and another at the top of the storage tank, plus several inside on the zones. When I first pressurized the system I could hear them all venting air. They are all new also, I replaced all the older ones in the house zones also. I never hear any noise from the boiler pump at all when its circulating, no caviatation or anything that sounds like air going thru the impeller.

    If I'm drawing water directly off the bottom of the storage tank, I don't see any way there could be air in that water. And the other strange thing is that the boiler only makes noise when the actual flames from the fire are high and hitting the HX, like after I throw a new piece of wood in. I can be running over 400F on the stack with a good hot fire, but as long as the flames are not licking the HX it will not make any noise. Once the flames flare up I can watch the stack temp climb and then start to hear the water making like "trickling" sounds in the HX and then the kettling will soon follow.

    I'm beginning to think I am just not moving the water fast enough thru the system? What is your approximate delta T in your HX on a hot burn?

    thx, Pat[/quote]


    Pat, Sorry, I guess I misunderstood. I got the impression you had no vents. So much for the easy answer.

    My storage is likley a bit different from yours. I have 1-1/4" pipes as well with about 75' round trip to the tank and back with maybe a dozen elbows. Inside my non-pressure tank I branch out to three parallel 3/4" copper heat exchangers about 120' long. I have a three stage pump system that increases flow as the water temperature rises. At the moment, I'm also running 25F delta T on two 007's in series. I'm likely about 15gpm and my exhaust is running 578F. (That's about 187,000btu/hr?). That's after taking the back off and cleaning the rear tubes spotless a week ago and "dusting" the ash off the overhead tubes right before starting the fire this evening. I've also made some modifications to help the heat extraction a bit. Bottom line is I have a wicked hot fire running at .095" draft. If I were to run at 400F, I'd be looking at about 12deg dT.

    Where is your circulation pump located in your loop?
  6. Pat53

    Pat53 Minister of Fire

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    My circulator is on the return just before the boiler. Well, I'm not even close to a 12 degree delta T at 400F. If you are moving 15 GPM and having no problems, my flow rate must be a lot less than that. I tried taking one foot off my stack height this evening but that didn't do anything. Still getting well over 400F stack temp. I'm wondering now if my baffle pipe in the storage tank is not allowing enough flow. I have a 2" port on the storage supply line. I welded an 1 1/2" piece of pipe about 5 feet long onto the inside of the 2" port. I put about 30 1/2" holes in that pipe and a plug on the end with a 1/2" hole in it. I would think that should allow for easy diffusion into the storage tank with very little back pressure. Other than that I don't have a clue as to why my flow isn't higher. I have a built in sieve screen in my shutoff that is on the return from storage that I check every week for debris, but it has been pretty clean so far, only a few small pieces of junk on it when I check it. My shut-offs are all 1 1/4" full port valves also. I'll trey running it tomorrow without the screen and see if it makes any difference. I also removed the check valve from the pump and that made no difference.

    I had cleaned all my tubes before the season and they look good still, just a little build-up on them. Anyway, it certainly sounds like low flow could be the problem. I hate to think I need to go with a bigger pump, the Grundfos 26-99 should have plenty of power to move 15 GPM thru my system?

    thx, Pat
  7. bigburner

    bigburner Feeling the Heat

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    In another life I dealt with HX a lot in process water cooling condensers for any thing refrigerated. These things will plug up. I don't remember the age of your equipment -- that doesn't always matter poor water quality in a small tube being heated lends it self to fouling. What I am saying is your HX could be plugged some what.

    where I live the water is a little hard. "rock well" not a lot of iron. A new gas tank type water heater will run about two years before it's starts kettling, and that's build up on the tank from the water being heated - it also cuts down on the economy "longer run times" In your case higher TD.

    using a 30 PSI relief valve with a 12 pound fill you can run well in to the 230F range & if you can't, something else is wrong -- weak relief, faulty gauge, faulty thermometer etc.
  8. Pat53

    Pat53 Minister of Fire

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    I suppose that is a possibility, but this is only my second season with this boiler, its hard to imagine the HX could be that plugged up. My well water is only slightly hard with a small iron content also, but basically pretty good water. My propane water heater has been running for 11 years and it never makes any noise and works great.

    If for some reason the HX is plugged, there would no way to clean it, it would have to be replaced I would think?

    Pat
  9. bigburner

    bigburner Feeling the Heat

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    This is why if a solution doesn't show it's ugly head here soon. That I think a flow checker would be my next step. I bought my circuit setters on eBay. Or what ever you can find that has a " know CV " and it's a simple pressure drop calculation after that.

    As far as cleaning it's fairly simple also, you probably don't have it prepared for this but a couple ball valves on in/out line with Tee's and a couple 1/2 inch ball valves. Just so you can isolate the HX and run a cleaning solution threw there with " what the industry it called an acid pump" just hook it up and let it run in and out of a 5 gallon pail.

    I agree that it should not be plugged already. Trouble shooting is about eliminating the simple things first, but then it gets more involved, you my have arrived here!!
  10. Pat53

    Pat53 Minister of Fire

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    Well, If the HX is plugged up for some reason I'll just have to get by with it for this season. i'm not going to start tearing stuff apart in the middle of winter. The system is actually working quite well. I'm using very little wood this year. If I have to keep smaller fires going I can live with that. I would probably just take the HX out next spring and have my buddy who did the welding on the stove build just cut out the end of the header and examine the inside of the HX. If the tubes need to be reamed out that will make it easy to do, and then he can just weld the end back on again, pressure test it and it should be good to go. The one thing I did just remember is that I made some changes to my plumbing in the off season and I had to drain the HX. I'm sure there was moisture left in it, so it is possible that some rust may have formed inside the HX, but I wouldn't think it would be enough to plug the tubes up, but you never know. based on what my HX delta T is, I think the problem is low flow rate.

    thx, Pat
  11. 2.beans

    2.beans Minister of Fire

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    i think its flow also. ive since added a second pump in line to act as a two speed. with the second pump running it makes the boiler quieter but doesnt completely get rid of the kettling. its a small pump when i find a cheaper bigger one ill give that a try.
  12. Pat53

    Pat53 Minister of Fire

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    Do you know what your Delta T is accross the HX and what your approximate flow rate is? Also, what size pumps are you running?

    I tried running it this afternoon without the sieve screen but it made no difference. The screen is on the suction side of the pump so if it was causing a problem I probably would have heard the pump cavitating anyway. The only 2 things it can be is the diffuser pipe in the tank or the HX. The pump should be plenty big to move the water, and is essentially the same pump I had last year and didn't have any problem with kettling. If I could find a used Taco 0013 or something equivalent, I'd like to give it a try and see what happens just for the heck of it.

    Pat
  13. bigburner

    bigburner Feeling the Heat

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    I think a Taco 011 would be a good choice, it will handle the flow and I head if needed. I sure don't think it's the tank diffuser, unless its plugged some how. In one of the other responses, you mentioned not tearing it down in season, IMO this is when you need to trouble shoot, make changes. My gear sets there all summer, hard to get motivated. There is just no way the flow isn't the issue. got any pic's
  14. Pat53

    Pat53 Minister of Fire

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    I'm going to do a flow test on the HX next week. I can disconnect my supply line to storage and then just attatch a pipe from the HX outflow and then open the valve and turn on the pump and see what kind of flow is coming thru the HX. I've got a few 5 gallon pails and I'll see how long it takes to fill them. Kind of a crude way to check the flow, but it might give me a ballpark figure of approximately what my flow rate is. I may only be able to get a few pails before I draw the pressure down too low, but its worth a try. I don't think its the diffuser either, but I do have a way I could bypass it with minimal work and go directly into the tank.

    The pump I have now is a Grundfos 26-99 which is about the same as the Taco 0011, so that shouldn't be the problem.

    Pat
  15. 2.beans

    2.beans Minister of Fire

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  16. 2.beans

    2.beans Minister of Fire

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  17. 2.beans

    2.beans Minister of Fire

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    my delta t across the hx is 40-60+*, i run a 011 and the second pump i added is a 007. i have 250' one way run of inch pex into the storage tanks. i dont know what the flow is. im sure theres a way to figure it out. hope that helps.
  18. Pat53

    Pat53 Minister of Fire

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    Well, now I'm really confused ! If you're delta T is 40 degrees , and higher, that is even slower flow than I have. Your HX should be banging like hell I would think. My greatest delta T is about 30 degrees at a stack temp of aout 450F-500F.
  19. 2.beans

    2.beans Minister of Fire

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    mine does bang like hell. its worse the longer into the burn.
  20. Pat53

    Pat53 Minister of Fire

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    I was just out checking the boiler and the stack temp was 425F and the cirulator was on speed 3 (high). The HX was doing its usual thumping and gurgling. Outlet temp was 190F (setpoint is 195F ) and return was about 162F. Just for the hell of it I turned the circulator speed down to speed 1 (low), and much to my surprise the banging stopped and everything was nice and quiet. So I threw in a small split of oak and the stack temp headed up to 450F and the banging started again, but not as bad as before. So now I don't have a clue what the heck is going on. I didn't think it was possible to push the water thru too fast, as long as it wasn't cold retutn water (below 140F or so). But it seems like the slower pump speed has corrected the situation somewhat, weird.

    Does anyone have an idea of what is happening here ! ? LOL

    thx, Pat
  21. 2.beans

    2.beans Minister of Fire

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    not to sound like a jerk is the three setting really high? i dont have any knowledge of that style pump. did the delta t change when you changed pump speed?
  22. Pat53

    Pat53 Minister of Fire

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    Beans, the pump is the Grundfos 26-99. It has 3 speed settings. yes, the delta T definitely goes up a little on speed 1 as oppsosed to speed 2 or 3, but the kettling also stopped. If the problem is supposedly too SLOW of flow, why would the kettling stop on an even slower flow? This doesn't seem to make any sense. The only problem with running a slower flow speed is that it will cause the boiler to go into idle more often.

    When I switched from speed 3 down to speed 1, I thought for sure the kettling would intensify, but it completely stopped in about 30 seconds and everything went quiet. I am completely at a loss as to why that would happen?

    Pat
  23. 2.beans

    2.beans Minister of Fire

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    im at a loss too. i wish mine would stop. ive tried cutting flow back by shutting the ball valve on the supply from the wood boiler and it changes it but its still there. i guess now you have to make it not idle!
  24. Pat53

    Pat53 Minister of Fire

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    At a sustained burn of 400F or so, the boiler is nice and quiet with the circulator on low. As soon as I kick it up to speed 2 it starts to make some noise, and on high speed it makes even more noise. Actually as the stack temp comes down from 450F+ to 400F, the supply water temp starts to actually go down, so the flow is fast enough on low speed to overcome a pretty hot fire. I just can't figure out why the boiler makes more noise the faster the circulator goes. Does anyone have any ideas why this would happen? I'm wondering now if it could possibly be the diffuser pipe in the storage tank. Could it be that the head pressure is increasing too much with the higher circulator speed?

    thx, Pat
  25. Pat53

    Pat53 Minister of Fire

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    For anyone interested, here is a follow up on my debacle from last year.

    After removing the HX this fall and cutting off one end, I reamed out all the tubes with a 3/4" wire brush on a flexible pipe. 2 of the tubes were partially plugged with something. When I pushed the brush thru a light grayish brown powder came out the other end. I had to run the brush in and out about 20 times to get those 2 tubes cleaned well. Welded everything back up, pressure tested and put it back in the Seton.

    Fired it up today and got a good hot fire going after about an hour. Stack temp was well over 500F for a while. Not a sound from the HX !!! Everything smooth and quiet. Heated up my 500 gallon propane storage tank from 63F to 195F in 5 hours. I am quite relieved that all seems well with the system now.

    Pat

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