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Thermal Exp Tank in Place of Well Pressure Tank


Isn’t a thermal expansion tank and a well pressure tank the same tank just used for different purposes? Consider the following:
I suspect I will not get a straight answer on this because I fear the well industry would like to keep this a secret to control the prices of their equipment, namely, well pressure tanks but here goes nothing...

I was given a brand new thermal expansion tank Amtrol Therm-X-Trol ST210V (86ga) leftover from a job site. In as far as I can tell, it is identical to the Amtrol Well-X-Trol line.

My old galvanized air-over well tanks are rusting and I want to replace them.

Anything I should know before doing so?

Thank you in advance


    JUGHNE Member Posts: 10,561
    Thermal tanks are not protected/coated for fresh water usage, that would be why they are less money. It might last 1-2 years as a well tank.

    Well tanks are protected/coated inside from the corrosion caused by the oxygen introduced with fresh water, that is why they are more money. It might last 5-10 years. BTW the larger the tank, the longer it will last, pay now or pay later.
  • hot_rod
    hot_rod Member Posts: 19,260
    I think the ThermTrol is a domestic HW expansion tank, intended for potable water.

    Possibly the well and ThermTrol tanks may have a different diaphragm material? it has to be a FDA approved product if it contacts drinking water. Maybe not so in hydronic tanks.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    JUGHNE Member Posts: 10,561
    I am wrong :o , Hot Rod is right. I didn't read well. I have had a ST on my domestic water heater for 15+ years.

    However a ST diaphragm does not have to contract & expand as quickly as a well tank would. The change in pressure is less and more gradual. That could be where the money difference is.
    I would guess the FDA rating for drinking water would be there for the ST diaphragm as HW is used by some for cooking, ice making etc.
  • rafjr64
    rafjr64 Member Posts: 5
    the term-x-trol and the well-x-trol both have the same butyl bladder and the same polypropylene liner. Both are rated for drinking water. Assuming that is true, go ahead and use the therm tank?
    JUGHNE Member Posts: 10,561
    They may have the same materials, what I mean is the strength/thickness of the bladder could be less for the thermal tank because it was designed for less rigorous flexing. IMO
  • rafjr64
    rafjr64 Member Posts: 5
    Ok. Gotcha. Thank you. Will call the manufacturer and ask them. Appreciate you taking the time to comment.
  • RobG
    RobG Member Posts: 1,850
    It could also be that a thermal expansion tank may have a smaller inlet as the dump load is minimal. The price difference could also be in the certifications required? I know that ASME tanks cost more than non-ASME although the manufacturing process is the same.
  • rafjr64
    rafjr64 Member Posts: 5
    It's Amtrol. They have all the certs. I am wondering if the inside of the steel tank is lined differently on the ST210V vs. the WX-350. The ST210V has a 1yr warranty and the WX-350 has a 7yr. This is the only difference I have been able to ascertain.
  • Jamie Hall
    Jamie Hall Member Posts: 21,091
    They can be used interchangeably, and that is no secret to anyone -- there's no deep dark conspiracy here. What is also no secret is that the tanks designed to control well pumps (and also used for similar purposes) have different interior linings -- not just the bladder, for bladder type tanks. This is part of why the tanks used for drinking water have a seven year warranty. Will a tank designed to control thermal expansion in a system work as a well pump control tank? Yes. Will it work as long? Probably not -- but you might get lucky.

    Be sure, however, that you are staying within the precharge and acceptance volumes.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • rafjr64
    rafjr64 Member Posts: 5
    Thanks Jamie. Appreciate your input.