Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit

Replace compression tanks?

Chuck_17 Member Posts: 133
Commercial boiler replacement. Just replacing the boiler and the main pump. The question is whether or not to replace the two (50 year old) 120 gallon compression tanks with a diaphragm type expansion tank.
The original design temperature was 230 deg if that makes a difference.


  • Steamhead
    Steamhead Member Posts: 15,050
    If the original tanks are in good shape I'd leave them there. They don't have any moving parts to fail, as diaphragm tanks do.

    The line to the tanks should be connected to the top of a good air separator. The size of the air separator will depend on the main pipe size leaving the boiler. This setup will direct air from the system up into the tank, maintaining its air cushion. A B&G Airtrol Tank Fitting will help keep air from migrating from the tank to the system- again without any moving parts. I believe Dan covers this in one of his books- maybe "Pumping Away"?

    And speaking of Pumping Away, of course you should.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    aircooled81delta T
  • aircooled81
    aircooled81 Member Posts: 197
    Steamhead is right on the money.
    If the budget is good, replacement of the airtrol's might be a good place to spend, with the addition of the airseperator he mentioned.
    Make sure the piping from the airtrol to the tanks gets a good pitch upward on horizontal runs so the air can head that direction. Don't put anysort of valve in the horizontal that would trap air, like a reduced port model.
    If the budget is even greater, replace the guage glass valves and SG, or rebuild the packing on all.
    Make sure no one has any auto air vents in the system, or if they are there, valve them off. Good for fast/initial fill, not good to stay open during normal circulation on compression tank systems.