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How to add air to an old steel expansion tank without an air inlet tube

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Tyrell
Tyrell Member Posts: 3
Question related to a gas Boiler with an old steel expansion tank. The tank has one of the inlets attached to the main water line with also a garden hose valve as part of the attachment to enable water drain. No indication of an air inlet tube. The other inlet found on the tank is plugged. If I empty the water from the tank as part of maintenance how to fill the tank with air if no air inlet valve is present? This is the original installation with the other two boilers also with the same setup. Thanks

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  • Jamie Hall
    Jamie Hall Member Posts: 23,433
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    If you can get the water out... the tank will then be full of air. You then reconnect to the heating system, and adjust the pressure in the system the usual way. If the only air removal device on the heating system goes to the compression tank inlet, you're all set.

    Pictures?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    HomerJSmith
  • JUGHNE
    JUGHNE Member Posts: 11,075
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    It is best if, hopefully, you have a valve between the tank and boiler.
    You shut that off and then drain the tank to nothing.

    Close the drain and open the isolation valve and the tank should fill with water about 1/2 to 1/3 full with an air cushion above it.
    PC7060Tyrell
  • leonz
    leonz Member Posts: 1,158
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    Tyrell said:

    Question related to a gas Boiler with an old steel expansion tank. The tank has one of the inlets attached to the main water line with also a garden hose valve as part of the attachment to enable water drain. No indication of an air inlet tube. The other inlet found on the tank is plugged. If I empty the water from the tank as part of maintenance how to fill the tank with air if no air inlet valve is present? This is the original installation with the other two boilers also with the same setup. Thanks

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    You may just have an air vent valve that looks like a boiler drain and not have to do anything to it.
    If you can post a picture of the valve and the valve handle face with the tag all the better.

    Here is a John Wood tank fitting in the attachment. You may not have to do anything unless a water fill valve was left on and you lost the point of no pressure change.






  • Tyrell
    Tyrell Member Posts: 3
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  • Tyrell
    Tyrell Member Posts: 3
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    Thank You for all the comments. Very Helpful!
  • leonz
    leonz Member Posts: 1,158
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    Please remove the sheet rock under the tank so we can see the steel compression tank.
  • jumper
    jumper Member Posts: 2,289
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    If you can get the water out... the tank will then be full of air. You then reconnect to the heating system, and adjust the pressure in the system the usual way. If the only air removal device on the heating system goes to the compression tank inlet, you're all set.

    Pictures?

    I used to spank the tank with my tender hands to get the water going. A venturi eductor comes in handy.