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Filling Steel Compression Tank

mjstraw
mjstraw Member Posts: 30
edited October 11 in THE MAIN WALL
This is the drain/fill valve on my rafter-mounted steel compression tank.  I assume the plug (with super fine threads) connects to a "dip tube" that allows air into/out of the tank during drain/fill.

About 15 years ago when I last drained the tank, I let it totally drain then replaced the plug and refilled.  So the entire volume of the tank in air was compressed to 12psi.

Today I needed to drain it again (15years, not bad).  While draining, I quit once the dip tube stopped gurgling.  I then started the fill and replaced the plug once water started coming out.  Finished filling.  So a smaller volume of air is compressed to 12psi.

In both instances, boiler and system water were at ambient temperature.

So, any thoughts as to which method was/is correct?


Mark
Indiana PA

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 16,514
    The first one will give better and longer results.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 9,616
    I agree wit @Jamie Hall

    Your drained it so the dip tube was not submerged but you don't know the water level in the tank. Better to drain it all and then refill

    For easier service a valve between the boiler and the tank (if you don't have one) and replace the drain/vent plug with a nipple and a ball valve
  • mjstraw
    mjstraw Member Posts: 30
    Already have a valve between the boiler and tank.

    Plug is like 1/4in with some of the finest threads I've ever seen.  Nipple/valve rather impractical.
    Mark
    Indiana PA

  • neilc
    neilc Member Posts: 1,337
    Close the valve that's not shown,
    put a hose on that bib end to a drain,
    open the hose bib,
    then that lil plug let's air in,
    til its all drained down,
  • STEVEusaPA
    STEVEusaPA Member Posts: 5,176
    Doesn’t that valve do double duty? When you open the valve it closes between boiler and tank and drains tank at the same time?
    steve
  • mjstraw
    mjstraw Member Posts: 30
    @STEVEusaPA, I think you're right.  But I shut off the nice ball valve in the boiler-to-tank line just in case.
    Mark
    Indiana PA

  • PolychromeUganda
    PolychromeUganda Member Posts: 14
    The whole dip tube theory is elegant, but there may be no dip tube at all and the plug may be there to use as an air vent as the system is filled. The larger the air cushion the less the system pressure rises when the water expands as it heats up, The maximum cushion is achieved by filling the tank with air at the system’s auto fill pressure. If there’s a Schraeder valve on top somewhere…
  • retiredguy
    retiredguy Member Posts: 461
    The biggest problem with that kind of drain fitting was that after many years the vent tube would sometimes rust, plug, or break off and not allow the vent to work properly. The fix was to replace it. I used to buy them from the B&G pump distributor. Just match the vent tube to the diameter of the tank you are using. That plug with the fine threads is a standard brass 1/8" pipe plug. Some of those drain fittings would close off the supply piping but most did not. If the expansion tank had a sight glass, some did but most did not, I would remove the bottom drain valve on the sight glass and pump air from a compressor into the tank to correct the air/water level. Hope this helps.
  • mjstraw
    mjstraw Member Posts: 30
    No Schrader valve, no site glass.

    "Pumping Away" pgs 52-56 describe filling a tank equipped with a B&G Airtrol Tank Fitting which also has a copper dip tube.  Procedure matches my most recent one.  Also talks about having 2/3 water and 1/3 air on startup which the dip tube helps establish.
    Mark
    Indiana PA

  • leonz
    leonz Member Posts: 415
    mjstraw said:

    No Schrader valve, no site glass.

    "Pumping Away" pgs 52-56 describe filling a tank equipped with a B&G Airtrol Tank Fitting which also has a copper dip tube.  Procedure matches my most recent one.  Also talks about having 2/3 water and 1/3 air on startup which the dip tube helps establish.

    =================================================================


    Yes, you want 1/3 air 2/3 water in the steel compression tank exactly as mine is.
    I have a B+G/ WESSEX 15 gallon steel compression tank with the glass tube water level gauge, a B+G Internal Air Separator feeding the hot water with air bubbles to an 3/4" airtrol valve in the base of the steel saddle hung compression tank.