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Solvent to clean LWCO internals? McDonnell Miller 67

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Motorapido
Motorapido Member Posts: 307
Upon removing a McDonnell Miller 67 low water cut off (float type, not probe) for cleaning, I was pleased to see just a modest amount of gunky rusty residue on the cast iron housing's internal walls and on the brass float. The float appears to travel through its entire range of motion smoothly, without any notchiness and without hanging up on any goobers of contamination. I would prefer not to separate the gasket that holds the bellows and float to remove the float for separate cleaning, and instead I would like to clean it out from the bottom, where I have removed the cast housing that holds the ball valve, opening the bottom for easy inspection. Is there a cleaning method recommended? I don't want to push a bottle brush or anything up inside for fear of damaging the linkage on the float. Is there a recommended solvent? White vinegar? Diluted rust-eating solution? I want to clean as gently as possible while still cleaning as much as I can without doing damage by over-aggressiveness.

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  • Fred
    Fred Member Posts: 8,542
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    Do it right. Buy a new gasket and take the float out and scrape the inside of the housing out. I'm not sure what effect solvents/chemicals will have on those gaskets or the brass float.
    STEVEusaPA
  • ChrisJ
    ChrisJ Member Posts: 15,701
    edited August 2018
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    Fred said:

    Do it right. Buy a new gasket and take the float out and scrape the inside of the housing out. I'm not sure what effect solvents/chemicals will have on those gaskets or the brass float.

    I didn't even go that far....

    I pulled one apart, cleaned it all out and then used black RTV instead of a gasket.

    It never leaked.

    Either way I'd be pulling it apart and cleaning it out. Even if the RTV did fail at one point, I'd rather a dripping LWCO than a non-functional one.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • ch4man
    ch4man Member Posts: 296
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    i use a liberal amount of dihydrousmonoxide sprayed vigourously around. second choice will be R718
  • ChrisJ
    ChrisJ Member Posts: 15,701
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    ch4man said:

    i use a liberal amount of dihydrousmonoxide sprayed vigourously around. second choice will be R718


    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
    ch4mandelta T
  • Motorapido
    Motorapido Member Posts: 307
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    > @ch4man said:
    > i use a liberal amount of dihydrousmonoxide sprayed vigourously around. second choice will be R718

    I hope I don't throw that poor old lwco into a state of hyponatremia. But if so, that's better than hyponatremia of the boiler jacket.
  • Koan
    Koan Member Posts: 439
    edited August 2018
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    +1 on removing float, this also allows for better inspection of the bellows. The bellows on mine leaked so the float would sink triggering a cutoff. The valve to blow down was so full of rust and gunk it would not work correctly. This gave me a chance to remove the original valve and replace with a quarter turn blow down valve.
    Once apart scrape the inside until no more scale comes loose. You will be glad you did so you can better determine what is coming out of the boiler. In fact - there was no way to get mine really clean without removing the float, the blow down valve, and the plugs and scraping off the rust with screwdrivers and brushes.
  • Koan
    Koan Member Posts: 439
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  • Motorapido
    Motorapido Member Posts: 307
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    > @Koan said:
    > +1 on removing float, this also allows for better inspection of the bellows. The bellows on mine leaked so the float would sink triggering a cutoff.

    I've removed it the float now. You're right. Removing it revealed lots more gunk to clean out in the body. What is the material of the bellows? My float terminates in a spring and I wondered how all that is sealed from the switch:actuatng mechanism. I see a spring but no bellows or diaphragm.
  • Fred
    Fred Member Posts: 8,542
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    The float is what trips the switch. There are no bellows or diaphragm. There is a gasket that seals the water away from the electrical components.
  • JUGHNE
    JUGHNE Member Posts: 11,062
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    Fred, doesn't the float have to move?
  • Fred
    Fred Member Posts: 8,542
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    JUGHNE said:

    Fred, doesn't the float have to move?

    The float actually pivots on an arm that makes or breaks contact with the switch. If my memory serves me right, it's like an accordian type neck on the float that flexes up or down, depending on the water level.
  • Koan
    Koan Member Posts: 439
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    @Fred is correct. The float has a bellows that allows movement. If you look at the pic above you can see it between the float and the flange. The float must move and does pivot to trip the switch, but the flange holds the float in place so the "accordion" at the base of the float allows movement. The annular rings at the base of the float are the "bellows' to which I am referring.

    @Motorapido - the float is brass and the bellows at its base are part of the float. Removing the float (item 4) and the LWCO valve (Item 8) prior to cleaning will help a lot. You can then get a screwdriver in there, break up the scale, and keep rinsing until clear.
  • gerry gill
    gerry gill Member Posts: 3,078
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    i clean 67's with a long curved scraper (similar to a bent screwdriver) and a toothbrush for the float bellows. I shoot water into the housing as i clean it with a giant medical syringe
    gwgillplumbingandheating.com
    Serving Cleveland's eastern suburbs from Cleveland Heights down to Cuyahoga Falls.

  • gerry gill
    gerry gill Member Posts: 3,078
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    i clean 67's with a long curved scraper (similar to a bent screwdriver) and a toothbrush for the float bellows. I shoot water into the housing as i clean it with a giant medical sryringe
    gwgillplumbingandheating.com
    Serving Cleveland's eastern suburbs from Cleveland Heights down to Cuyahoga Falls.

  • rickster359
    rickster359 Member Posts: 3
    edited October 2021
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    After cleaning add surgex to prevent any priming.Great for steam boilers.
  • delcrossv
    delcrossv Member Posts: 742
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    What's the recommended disassembly and cleaning interval for these? I have the type 61 (round one)
    Trying to squeeze the best out of a Weil-McLain JB-5 running a 1912 1 pipe system.
  • Chris_L
    Chris_L Member Posts: 336
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    I agree it is best to take the float out. I've had problems with the switch not closing after flushing the LWCO because the gunk at the top of the housing prevents the float from rising enough. It is hard to clean the top of the housing without removing the float.

    It has been some years since I've done this. Can anyone tell me if by removing the two long screws at the end of the switch assembly, can you separate the switch assembly (5-6-7 in the illustration) from the float assembly? I'd rather avoid disconnecting all the wires if possible.