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Burned blast tube

Dave M
Dave M Member Posts: 36
The attached pic is the end of a Beckett blast tube used on a 3 year old Peerless Pro 03 water boiler. It was purchased as a package unit and no changes have been made from stock. It's an L2 head and a conical end on the blast tube. When I went to clean this boiler boiler a few days I was of course very surprised to see this. What would eat the end of the tube right back like that in such a short time? I'll need to replace the tube and welded-in integrated conical end but that won't fix anything, it will do this again. I'd like to tap the experience of this forum and see what folks make of this. Thanks all.

Comments

  • Paul Fredricks_3
    Paul Fredricks_3 Member Posts: 1,552
    .

    It's obvious that the head and tube have gotten too much heat. That could be caused by an impropper head adjustment, excesive draft, or possibly a loose nozzle. Anything that would put heat on the head is a culprit.

    Is this an AFG burner?
  • Dave M
    Dave M Member Posts: 36
    Yes, AFG

    It's a Beckett AFG with the L2 head. .5 gallon, 60 degree Danfoss per the Peerless specs in the manual. The Z dimension etc. are spot on. Nozzle was not loose. Pump verified at 140. Insulated stainless lined chimney. Smallest of the Peerless Pro series cast iron water boilers, the Pro 03. No other appliances in basement. Is this configuration normally well behaved and clean?
  • STEVEusaPA
    STEVEusaPA Member Posts: 5,323
    I would double check...

    1.  Make sure the boiler is really clean, including combustion chamber.  It's a 3 pass, was it particularly dirty when you opened it up

    2.  Draft.  If it's not correct you'll burn it up (like you see).

    3.  Insertion Depth.  In too far, burns up.  Although I dont think it's adjustable on this set up.

    4.  Flame impingement.  How does the fire look with inspection mirror.

    5.  Combustion air?  Got enough?

    You have the right nozzle, the right pump pressure, what are all the combustion numbers?

    Only other thoughts....Low fire baffle in?......Z dimension w/ conical shroud is 1-3/4".....burner must maintain 4 degree downward pitch..
    steve
  • Dave M
    Dave M Member Posts: 36
    It was dirty

    It was very dirty. Lots of soot and crud. The nozzle had black muck all over it. Nasty. I thought of the insertion depth too and you're right, it isn't adjustable but I will check it. Going from memory but I think it's supposed to be 1/4 inch back from the front wall. The Z dimension is 1-3/4 as you said. Re draft..I believe this is one of those that has positive pressure right at the fire box and I'd have to measure draft slightly downstream in the smoke pipe. There's no over fire hole to stick my draft probe in like boilers with the slide over access door. If this is draft, is it likely too much draft or not enough? There's plenty of make-up air available, it's in an older home (1928) with plenty of leaks in the basement. It does have the factory blast tube with downward slope towards boiler.
  • icesailor
    icesailor Member Posts: 7,265
    Burned Up:

    Looks like a good flame and bad draft. By that I mean, good for the conditions. It must have been some toasty in there. How about debris in the chamber?

    If it was a Pinner, it would have been all sooted up. No place for the soot to stick to.
  • Dave M
    Dave M Member Posts: 36
    Low firing rate baffle

    I'm not at the location of this boiler at the moment but you've got me wondering about a low firing rate baffle. I could check in a minute if were there. Nothing has ever been removed so if it has one it's still there. How can I tell with certainty if this particular application should have one? I don't think that detail is in the installation/maint documentation. This thing has always been very loud when firing. Quite a rocket. I mean you can hear it light off every time even when you are outdoors and all the windows and doors are closed. When visitors are in the house they always ask about it when it's firing because it's loud.
  • R Mannino
    R Mannino Member Posts: 434
    Beckett OEM Guide

    the online one says it needs the LFRB. Nozzle 0.5 x 60 AS. Insertion depth 3-3/4"
  • Steamhead
    Steamhead Member Posts: 14,858
    On some of these 3-pass boilers

    the air tube is supposed to project into the firing zone. Check the specs to be sure.
    All Steamed Up, Inc.
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
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  • Dave M
    Dave M Member Posts: 36
    Insertion depth

    The insertion depth is fixed, it's a welded flange. The distance from the flange to the end of the conical shroud on the end of the air tube is 4 inches. The distance through the front of the iron door and front ceramic wall is 3 inches so that leaves a full inch inside the chamber. Apparently that's the way this is supposed to be. Note that the picture shows the blast tube only, the conical shroud was off when I took that pic. The shroud must be stainless or of another metal type as it is in perfect condition even though it lives in the fire box. The plain steel blast tube is supposed to be protected by this shroud.

    I also checked the low firing rate baffle is in place. 

    I found the air tubes are not readily available, I will have to order one and it will take several days. 

    A couple of further questions...this boiler does not have a slide over inspection door. What is the proper method to adjust the draft on this? I can stick my probe in the smoke pipe right at the boiler outlet. There's a 3/4-inch threaded pipe plug in the front but I would think that would not work well for an over fire draft measurement in this particular boiler. No? And I understand these are positive pressure right in the chamber.

    Lastly, how can you see the flame with a mirror when there's no access?
  • blast tube.

    Hi, I read all the other posts and all had some great advice on what to check. I am wondering what primary control is on this Becket burner. If it is a positive pressure appliance, it should have a post-purge, or what we now call "motor off delay" capable primary control. I have seen this heat damage on a balanced flue unit that had the primary replaced, but with no post purge. I also would check for sufficient make-up air. If there isn't, and if there is a downdraft condition, that would cause the heat damage as well. The look of the porclins, nozzle assy, nozzle, and if the motor coupling is heat damaged as well, would lead me to look for a "tight home" condition. Hope this helps, Wayne
  • Dave M
    Dave M Member Posts: 36
    Does have pre and post purge

    It does have an R7184P controller with a valve on delay and long post purge (I think it's set for 2 minutes). I wish this were a "tight home" but there's plenty of make up air available in this 1928 basement.

    I looked at the IO&M manual again and Peerless says the over fire draft should be +.03 to +.06 depending on the model (# of sections) so it is a positive pressure combustion chamber. In that case I am assuming I'd take out the 3/4-inch pipe plug right over the burner and insert my draft gauge there. There's no other access to the chamber.

    Does anyone know if there is a sight glass that can be screwed into that port either temporarily or permanently to observe the combustion without affecting the draft (like happens when the plug is out). Crown makes some but I'm not sure if those are just for fluid monitoring or they can withstand combustion temps.
  • Dave M
    Dave M Member Posts: 36
    I replaced the air tube

    Alright, I replaced the blast tube with a new Beckett replacement. Doublechecked Z dimension, pump pressure, installed new specified nozzle, etc. It's running again but I want to prevent a recurrence of the burned tube. The blast tube is supposed to project into the chamber on the Pro03, it's a welded flange. The conical end cone is not shown in the pic but it was not harmed at all, it looks new.

    I was able to get greater than 13% CO2 and no smoke. I increased the burner air slightly to get about 12.5%, 4.2% O2. My analyzer says 23% excess air.

    The stack temp seems higher than I would expect on a small 3 pass. I thought it would be 350 to 400 but it kept rising as it came up to temp and settled at 500 degrees. The internal baffles are in place. The over fire draft is supposed to be approximately +.03 according to Peerless IO&M manual. I read +.02 .  The breech draft gets higher as the chimney warms, it was -.03 to -.04 when everything was up to temp. The Field RC damper is installed horizontal and the weight is set all the way towards the lowest draft, -.02. It's an insulated 6-inch stainless liner in a masonry chimney approximately 17 feet tall. Is this as good as this gets or should I try to reduce the chimney draft? That might lower the stack temp. I find it hard to believe I need a second draft damper.?? Thanks all for your expertise.
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