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How to Clean Out Glass Gauge

nycpa Member Posts: 108
I have a Weil McCain Steam Boiler. How to I take out the glass gauge that lets you see how much water there is and clean it.  I can barely see the water. 

Also, besides draining the water, what else can I do as part of the yearly maintenance for my steam heating system. 

Thanks for the help. 


  • BobC
    BobC Member Posts: 5,470
    clean / replace gauge glass

    To clean out the gauge glass you have to remove it and before doing that you want to have a pair of Gauge Glass Washers on hand and probably a new Gauge glass as well. the process of removing the glass will destroy the gauge glass washers and you may damage the glass while taking it out.

    Once you have the washers and a spare gauge glass you can take the old one out but first shut the boiler down and let it cool a bit..

    First close the valve above and below the glass to isolate it. Next loosen the hex bonnet nuts that hold the glass in place and slide them towards the middle of the glass. Now you should be able to lift the glass out, it is longer than the open space you have so you have to slide it down into the lower valve so you can tilt the top clear of the top valve. You will see remnants of the old washers on the glass and stuck inside the bonnet nuts. It usually takes a knife or screwdriver to scare the residue out of the bonnet nuts. Clean the glass with some soap and a bottle brush, or just use a new one and clean up the old one as a spare.

    To put things back you have to slide a washer onto one end of the glass and then slide both bonnet nuts on; the slide the washer onto the other end of the glass. now you have to put the bottom of this assembly into the lower valve and then tilt the top of the glass to get it into the top valve. Now hold the glass so it is centered in between the two valves and tighten one of the nuts so it engages a couple of valve threads. then tighten the other nut to engage the other valve. Tighten both nuts hand tight and then use a wrench to tighten them another turn or so.

    Now open the valves above and below the glass and fire up the boiler. As it comes up to steam you may see some weeping from one of the valve/glass ends, just tighten up that nut enough to shop the weeping. Over the next few days you may have to tighten the bonnet nuts a bit more.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Rod
    Rod Posts: 2,067
    Marking the Boiler Waterline.

    One of the pros, I believe it was Norm Harvey, came up with a neat trick and that was to put an extra O ring on the outside of the glass and then adjust it to where you want the boiler waterline marked.

    - Rod
  • FJL
    FJL Member Posts: 354
    Washers and Spare Sight Glass

    Where do you get a spare sight glass and extra glass gauge washers?
  • BobC
    BobC Member Posts: 5,470
    Where to buy

    You can get both at a local supply house, in the old days the local hardware store carried them but those days are gone. You have to know the diameter and the length you need.

    Because the glass fits into both valves the measured length between the nuts is not right, you have to round it up; the measured distance between my tightened bonnet nuts is just under 5" so I needed a 6" gauge glass.

    The rubber washers are about 5/16" high, as you tighten the bonnet nuts they compress and seal against the glass.

    The gauge glass washers can be had at McMaster Carr - http://www.mcmaster.com/#gauge-glass-washers/=acibyj  They sell gauge glass as well - http://www.mcmaster.com/#gauge-glass/=acicxg from 8" long on up. If you need a 6" length you have to buy a longer length and then cut it to size.

    8" and 12" seem to be common lengths, my Burnham boiler uses a 6" X 5/8" gauge glass and i bought a cut piece from a guy on Ebay (because i didn't want to buy a gauge glass cutter that I would use every 5-10 years).

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • j a_2
    j a_2 Member Posts: 1,801
    one more way

    I have had good luck cleaning them in two ways....First one is to simply close off the top and bottom valves undo both nuts, remove glass and clean it, never had a problem,just never over tighten anything that has an o ring or washer,once they are compressed that is it.....Secondly, remove the drip nut on the bottom valve and fill the boiler till water streams down from the top,,this does a good job providing your boiler water is clean...close off the drip and drain boiler to the manufactures normal water line..  good luck   j a
  • Big-Al_2
    Big-Al_2 Member Posts: 263
    edited January 2011
    From the Bottom

    I can't see your fittings clearly in the photo, but they look like the ones on my boiler.  On mine, there was a plug directly below the sight glass.  I removed it (and I might have had to remove the valve stem on the bottom too.)  Once those were out of the way I was able to use a long skinny screwdriver to work a strip of cloth up into the glass and clean it out without further disassembly.  The whole thing took me about fifteen minutes.  The glass wasn't perfectly clean when I was done, but it was close enough.
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