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expansion tank

FrancisFrancis Member Posts: 2
I have a Slant-Line boiler; w/ a heat exchanger to heat the house w/ forced air; and a seperate water tank thru which a coil runs from the boiler to heat the water. I am noticing (especially at night) banging/ not very loud or prolonged but a sound I did not used to hear. So I am wondering if the expansion tank needs replacement. Last year found it sounding the same on the top & bottom to a tap on the side so we took off the tank & found it full of water so we charged up the air valve & now the top sounds different than the bottom to a tap on the side. It is a: Vol 8, Combu tank, with psi 75, & a stamp for Oct. 1990. Does that sound like it needs replacement? It looks like a gallon size; which don't seem to be locally available. Is Combu still in business? they used to be in Woonsocket R.I.? What is the usualy life expectancy of these tanks? Where can I get a gallon size tank & what should I expect to pay for it?
Thank you, Francis


  • Brad White_26Brad White_26 Member Posts: 35
    Not sure about the brand you mentioned

    but diaphragm expansion tanks are short money. The most common size, a #30, costs about $35-40. Sounds like you only need a small one, but the price should not be much less.

    Taco, Amtrol, Vent-Rite are other brands, all will work. Any heating supply place will have them.

    Not worth losing sleep over.

    I have had one failure in 25 years.

    The banging you hear might be a diaphragm failure, the air or nitrogen that was in the tank is now in the piping, allowing water some momentum in velocity, then it stops at an elbow, thus you hear some, well, unpleasant sounds.

    Good luck!

    BTW: Taco and Amtrol at least are still in RI if that matters. I believe in supporting local economies and Rhode Island is having a simply horrible ski season this year. :)
  • Paul Fredricks_2Paul Fredricks_2 Member Posts: 34

    Are you sure he doesn't mean a water hammer arrester? He does mention 75 PSI.
  • Brad White_26Brad White_26 Member Posts: 35
    You know

    THAT is a very good point! No wonder the tank is so tiny...

    I took the pressure rating as just that, a rating, not working pressure.

    May have to scratch that....
  • FrancisFrancis Member Posts: 2

    I appreciate your thoughts I should look for a "hammer arrestor" [near this tank is some white powery stuff on one of the joints & a single drip mark on the tank, can that leak be mended without taking the joint apart? Would some solder from the outside (once the water is drained) seal that up?] also can that hammering or banging cause a problem? Francis
  • Brad White_9Brad White_9 Member Posts: 2,440
    Watts Company

    among others make water hammer arrestors.

    What you are probably seeing on the joint is corrosion from residual solder (acid based), minerals such as calcium or magnesium from dripping water (think stalactites in Carlsbad Caverns. Charge your neighbors to come look at 'em :) )

    I would not solder a screwed joint. It is screwed for the reason that it was meant to be taken apart at some time.

    Look for a union nearby and in-line, which will enable you to tighten it (after draining of course!) and restore the line to service. You may have to clean and re-dope the threads, in fact, you really should do that.
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