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Old McDonnell Miller Round Port Model 47-2 maintenance

PrecaudPrecaud Member Posts: 307
My steam boiler has a M&M 47-2 LWCO with auto-feeder. I'm doing annual maintenance. The feeder is the older version with the round port. It works fine and has been a very reliable combo.

Removing and cleaning the strainer was obvious, and am now trying to remove the cartridge for cleaning. The manual instructs to use a 13/16" socket, but that apparently applies to the newer cartridges; the nut inside this unit is smaller than that and doesn't look like the manual's drawing. Before forcing the issue and removing it I thought it wise to check; is the cartridge on the older version removable for cleaning? Or should I just leave it alone?
1950's Bryant boiler in a 1-pipe steam system at 7,000 ft in northern NM, where basements are rare.


  • JUGHNEJUGHNE Member Posts: 6,797
    Round port indicates built before 1995.
    M&M recommends replacement every 10 years.

    You can replace the water feed cartridge assembly with new version. But by the time you spend with that and you should also crack the bowl open and look inside.

    Repair parts add up to a new one pretty quickly.
  • PrecaudPrecaud Member Posts: 307
    Thanks but the question is not about replacement. The unit works fine, I'm just doing seasonal maintenance.
    1950's Bryant boiler in a 1-pipe steam system at 7,000 ft in northern NM, where basements are rare.
  • JUGHNEJUGHNE Member Posts: 6,797
    Maintenance should include opening the bowl to clean it and the float inside.
  • PrecaudPrecaud Member Posts: 307
    Understood, but that is not what my question is about. It is SPECIFICALLY about if the cartridge on the older models are removable for cleaning.

    Anyone have experience with this?
    1950's Bryant boiler in a 1-pipe steam system at 7,000 ft in northern NM, where basements are rare.
  • retiredguyretiredguy Member Posts: 214
    I repaired many of these but I do not know what you are calling the cartridge. I used to carry parts in my truck many years ago to completely rebuild both the #47 and the $51. I never had to disassemble anything that required a 13/16 socket. So I am going to say no . You sometimes have to replace the cam for the #2 switch, the strainer, and on rare occasions the float. If you have to replace anything else, it may be better to replace the whole control.
  • PrecaudPrecaud Member Posts: 307
    Perfect, thank you, @retiredguy . I think it's good to go, then. The manual for the old version doesn't say anything about the cartridge, but it mentions cleaning the strainer only in passing in the troubleshooting section. The manual for the new version is more explicit about maintenance.
    1950's Bryant boiler in a 1-pipe steam system at 7,000 ft in northern NM, where basements are rare.
  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 6,947
    edited May 2
    Nobody usually fools with cartridge they just replace the whole valve and strainer assembly.

    A homeowner has all the time in the world to fool with things and that's fine if you have the time I have no issue with that. M/M parts are $$$

    Most contractors can't take the time to rebuild a control unless it's a simple repair the labor cost will exceeds the value of the control especially with a 1995 control. You get a call back and your screwed

    And if a contractor rebuilds a 25 year old control which the MFG gives a 10 year life and if fails and cooks the boiler guess who looses.

    @Precaud not putting down what your doing, just explaining why many won't know about some of the internals
  • PrecaudPrecaud Member Posts: 307
    Thanks for the explanation, @EBEBRATT-Ed , it makes sense. If I were doing this for hire, I wouldn't screw around with it, either, for the reason(s) you said.

    That said, on the newer (post-1995) 47-2, this maintenance (along with cleaning the screen filter) is pretty easy to do.
    1950's Bryant boiler in a 1-pipe steam system at 7,000 ft in northern NM, where basements are rare.
  • mattmia2mattmia2 Member Posts: 1,205
    I suspect since the boiler is leaking a little you want to put as little in to the controls as safely possible.
  • PrecaudPrecaud Member Posts: 307
    That. And, if it ain't broke...
    1950's Bryant boiler in a 1-pipe steam system at 7,000 ft in northern NM, where basements are rare.
  • dopey27177dopey27177 Member Posts: 286
    Here is a cautionary note.

    I got involved with a dry fire on a brand new 350 horsepower boiler.

    The boiler was equipt with a McDonnell Miller 150 MD LWCF and pump controller and Model series 63 LWCF.

    Some time during the first heating season (1 month old) the boiler dry fired and 50 tubes melted.

    When an inspection was done by Hartford boiler and McDonnell and Miller it was found that some one had taken the the 150 MD apart and did some kind of service on the control. Additionally the series 63 control was not wired correctly, it did not shut down the boiler.

    Fortunately there was a log book in the boiler room where a service tech from the boiler installer company came on a no heat call. He found a problem with the auto feeder. He found the float ball was stuck in the up position which prevented the pump from filling the boiler with water.

    What was strange was the inspectors claimed the 63 cutoff was wired incorrectly. I say this because when the tech came on the no heat call the shut down on low water, there fore there was no wiring problem with the control.

    Fortunately my customer had me come to the building to meet with the inspectors.

    I had a discussion with them about the wiring of the 63 LWCF.

    Since I am no control person or electrician I asked them this question. When there was a heat complaint how come the was out on low water. Additionally the tech tested the 150MD and the 63 LWCF for operation and he noted in the log book the pump control and lwcf combo and the 63 LWCF worked as intended.

    Here are two lessons.
    1. Have your customer keep a log book in the boiler room and have your techs make the service entries.
    2. Question insurance inspectors on their findings, people make mistakes.

    I only put this comment in this discussion because when you fix a LWCF you take the responsibility of he boiler on your head.
    Hopefully you have liability insurance and an error of omission and commission policy to cover you if you screw up on a repair of a safety for a boiler.

  • retiredguyretiredguy Member Posts: 214
    edited May 3
    This is my experience with a low water control being miss wired similar to what @dopey27177 wrote about. The company I worked for discovered a situation with a MM #157 LWCO as the primary control and a back up secondary MM #63 on an H B Smith Boiler where the limit feed for the #63 LWCO boiler control and the control "out" wires were switched. Both controls utilized the alarm terminal to announce that a low water condition existed. Either control would shut down the boiler when operated by itself when "testing" (blowing down) but when both controls operated under normal operating parameters, the primary control would shut the boiler down safely. Then, if the water level continued to fall due to the boiler still producing steam, the secondary control, the MM #63, would also open the limit circuit. Due to the miss wire the result was that the alarm circuit on the second control would then put power back into the limit circuit and allow the boiler to fire normally. The result of course was a dry fire and boiler melt down. This happened when both controls were wired utilizing the alarm terminal. The fix was to never wire the secondary LWCO utilizing the alarm terminals. . The melt down was caused by a service tech switching those 2 wires in the course of normal LWCO maintenance. Switching the limit circuit in and out wires caused a major catastrophe. However removing the alarm terminal wire corrected this potential problem. My employer was charged with this mistake and resulted in an insurance claim.
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