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Weil-McLain MGB-6 rebuild.

First off I would like to thank Dan Holohan and many of the posters for getting me through my first year with a single pipe system in a 15 unit apartment block. Thanks to you I got the system balanced and working as best it could last winter.

The city inspected the boiler this summer and it failed the static pressure test. I am now tasked with rebuilding the Weil-McLain MGB-6 and finding some way to reduce the amount of fire it produces before the start of the heating season.

Based on the installed radiator load and a conservative pick-up factor I calculate I have 33%-50% more BTU's than I need. This is born out by the fact that it short cycles once up to pressure. Replacement with a new boiler is an absolute last resort because the owners (my wife and son) are way over extended and would not be able to carry the added debit.

The boiler leaks at the seals between the right and left sections and the adjacent intermediate sections at the level of the supply outlets. The seals between the three intermediate sections are fine. After reveiwing the WM erecting instructions and looking at several other manuals I think that the header is plumbed incorrectly.

The header is a single welded 6" diameter unit that attaches to either side of the boiler to the supply outlets. The equilizer is also welded to the the header. All of the documentation that I have seen shows the header attached to only one side of the boiler and the equilizer attached to the other. In addition all the documention shows headers and equilizers built out of NPT sections not welded.

1. Has this contributed to the leaking between the sections? And if I do go through with rebuilding how should the header be plumbed?

2. When I take the sections apart what are the likely problems I will face trying to make them seel properly again (assuming one or both end sections are not cracked)?

3. Can cracked sections be repaired?

4. Can I turn the MGB-6 into a 5?

5. Can I reduce the number of burners or down fire them (assuming that I can keep the flue gases with in spec.)?

6. What else could be contributing to the short cycling? I understand that the oversized burner will reach cutoff in about 1.5-2 min. but the pressure drops just as fast.

7. Are vent dampers worth the investment?

Thank you for your time and for bending your ears.

Sincerely

Richard Burchill
4583176 MB Ltd.
Winnipeg, MB, Canada

Comments

  • Steamhead
    Steamhead Member Posts: 14,834
    Richard, I'll try

    to answer your questions one by one.

    1. Welded headers can definitely cause this kind of leak. They don't "give" as the boiler expands and contracts like threaded headers will. But since cutting and threading 6-inch pipe is time-consuming and not everyone has the tools to do it, we see a lot of welded headers.

    If you can get suitable pre-cut pipe nipples and build a "drop header", like that shown in the photo, it will go together much easier.

    To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"
    All Steamed Up, Inc.
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    Oil & Gas Burner Service
    Consulting
  • Mark Woll_2
    Mark Woll_2 Member Posts: 67
    I just threw out an MGB5 and am putting in a new LGB4

    Richard, interestingly enough I am in the last phases of replacing a two pipe steam MGB5 with a brand new LGB4. I'm fininshing the electric and minor piping, all the major piping is in. Some interesting points in relation to your posting:

    A.--a solid welded header usually doesn't allow proper thermal expansion and may tend to pull apart or distort the sections. The old MGB we scrapped had a similar problem with the near boiler piping. It seems these Weil-McClain units tend to be susceptible to section leaks with non-perfectly installed headers perhaps due sealing rings not having the same strength as steel nipples. A solution is to use offsets to the header and threaded pipe. Our new LGB4 near boiler piping, for example, was fastidiously and laboriously installed using 4 inch steel pipe, offsets and all cast fitting and new flanges. It cost a small fortune just in special ordered fittings.

    B. The old boiler will not be difficult to take apart and new sealing rings could be obtained from the manufacturer I suppose. The rings themselves are very easy to install. The weight is the main issue. I worked on ours entirely solo, so I erected a moveable gantry with a hoist to manage the sections. I also constructed a stage, made out of wood which extended the firebox sideways, allowing me to gently lay down the old sections and then pickup and walk into the place the new ones. The MGB sections are a bit larger than the new LGB and far more unbalanced owing to the large opening being both on one end. The end sections are particularly heavy.

    C. Our MGB5 was also cracked and corroded, above the water line on an end section, from I believe being about 30-50% oversized and having inadequate clearance to the bottom of the steam header. I attempted to weld it with very expensive special welding rods for cast iron, but the further I got into it, the more corrosion was encountered and the welding became impractical. I have the rods if you want them a good price!

    D. Our new LGB cost me $2800 from the supply house delivered. The fittings were about the same. Though we, like you intended to repair the old boiler, it was obvious that once the old one was unbuttoned, all controls removed, the sections separated and a whole new header/equalizer constructed, etc., the economics did not support keeping an old boiler in the basement.

    Just some thoughts, may or may not help. Mark W. Philadelphia, PA
  • Steamhead
    Steamhead Member Posts: 14,834
    I'd use a threaded-pipe drop header

    like the one in the photo- it handles expansion & contraction much easier than anything else out there. Mad Dog built this one.

    If you really can't afford a whole new boiler, W-M might have some replacement sections. If you go this route, get all new gaskets and follow their instructions for installing them.

    There are several schools of thought on down-firing. Some say it's not a good idea at all, others say don't down-fire more than 25% etc. etc. My own boiler has been down-fired for most of its 20 year life with no apparent ill effects. If you decide to try it, test with a digital combustion analyzer such as a Testo or Bacharach. Stack temp should not be lower than 300 degrees or so to prevent condensation.

    Same with stack dampers- some like them, others don't. I've had good results with mine.

    Keep in mind- the boiler is only one part of the efficiency picture. Problems out in the system can cause uneven heat distribution and short-cycling. Did we calculate how much venting your steam mains need?



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  • Sorry about

    the lack of funds. However, now is the time to talk to your banker.

    That MGB is over 20 years old. Never was a good steamer. They put 850 mbh of gas under 32 gallons of H2O. Too much fire w/ too little water. The sealing rings are still available. But, what is the iron like around the ports and above the water line. Time to cut your losses and buy new.

    Count the radiation and size your new boiler properly. Weil corrected the steaming problem w/ the LGB. The 6 section LGB has a 650 mbh input under 34 gallons of H2O. Works a whole lot better.

    And you already know the FIRST rule of boiler installation. Read and follow the instructions. Wish we were all that smart.

    Good luck.
  • Mark Woll_2
    Mark Woll_2 Member Posts: 67
    here's a photo pf the drop header I put in

    Here's the LGB4 with my new drop header. All new 4 inch threaded pipe with cast fitting into existing six inch header. Should provide nice dry steam hopefully.
  • Richard Burchill
    Richard Burchill Member Posts: 3
    rebuild MGB-6 continued.

    Thank you all for the advice. So far the castings look as thaough they can be used again. But if I do go ahead and rebuild I want to reduce the amount of gas the system uses.

    1. Has any one done or heard of a 2 stage gas valve retro for the MGB?

    2. Is there an approved damper system for the MGB?

    3. If I do have to replace the boiler are all steam boilers built like the MGB/LGB or is there a better way to put the sections together?

    Sincerely

    Richard Burchill
  • Richard Burchill
    Richard Burchill Member Posts: 3
    I need some guidance on how to make a swing joint.

    Everything I have read says to use swing joints to reduce the effects of expansion and contraction on the boiler and the rest of the plumbing. But I have yet to find an objective description of how to make a swing joint nore any rules on sizing. From what I can gather a swing joint is the use of two or three 90 deg ells to create a loop or accordian to allow for pipe movement. Anyone know of a good referance on where to use and how to size swing joints?

    Sincerely

    Richard Burchill
  • Luke Lefever
    Luke Lefever Member Posts: 62
    We're rebuilding an LGB-6 right now...

    Thing dry fired, LWCO didn't function properly. All sections glowing red hot when we arrived. Told them to let it cool and we'd be back the next day. Two sections with holes burned in them.. We provided estimate for all new sections, etc... they said that was too much money and they would have the two obviously damaged sections "welded shut". We said, be our guest, probably won't work. Sort of worked... $3000 later, they would like us to go ahead and order a new section pack and do it right, like we should have done last year. Oh well, live and learn I guess.

    Luke Lefever
    Lefever Plumbing & Heating, Inc.
    Elkhart, Indiana
  • Mark Woll_2
    Mark Woll_2 Member Posts: 67
    picture of LGB6 install

    See picture for new LGB4 with all new 4 inch double drop header into the old 6 inch "sub" header. Yes I could've removed the 6 inch pipe are just plumbed a new 4 inch, but the 6 inch work done in 1929 was still in perfect shape. kinda nice steamfitting.
  • Mark Woll_2
    Mark Woll_2 Member Posts: 67
    pix of LGB4

    Here's a picture of my LGB4 with all new near boiler piping. 4 inch double drop header into existing 6 inch (1929 constructed) "sub" header, all new flanges, etc. All American made cast fitting. Why did I do that? Because the old header was quite low (i.e., close to the floor) the system being a counterflow two-pipe with the low point at the boiler and no wet returns at the main ends.

    Also added a 2nd duplexing boilerfeed pump with "alternator" circuit of my own custom design to equalize run time between pumps and provide for backup running of secondary pump in case of primary failure. Will share wiring diagram if anyone's interested. Interesting use of relays if anyone is inclined to think electrically.
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