Regaining tension in an old spiral balance

A home owner from Loves Park, IL says:
My Thermalguard windows are 28 years old and just about all of them will no longer stay up (mostly bottom sashes). I took the window apart and measured the spiral tube to be 21" so I am assuming I have the correct spiral balance. .

I purchased the charging tool for tilt windows from you and I am not sure I have enough detailed information in regard to how to charge and regain tension. I read your do it yourself guide on how to charge the balances and need more detail on what I need to do to gain tension. Do you have a detailed description of the internal workings of the spiral tube?

Is there supposed to be a spring inside the spiral tube? and if not how do I know if I need a new spiral tube? Any help you can give would be appreciated . . Thanks Tom
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Paul from SWISCO responded:
Good Morning,

If the spiral balances in your 28 year old windows have not been replaced in the last 28 years they almost definitely need new replacement balances. If you try to use the charging tool and the spiral balance does not regain tension, that is a sign that the balance needs to be replaced. See our guide on how to tension a tilt-window spiral balance. If you decide to replace your spiral balances, make sure you have the correct tube diameter. The Series 900 spiral balance has a smaller tube diameter of 3/8" and the more popular Series 600 spiral balance has a larger tube diameter of 5/8"
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