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When I patch a tube, does it need to be in a tire to "remain fixed"?

I mean: I understand an empty fixed tube will remain fixed if I keep it folded in a box...

But how about with air inside? does the patch need the pressure against the tire to remain steady?

I have pretty much never patched a tube,... so not really confident about the repair yet... Is it a good idea to ensure the quality of the repair by inflating the fixed tube and leaving it out there for a few days and hope it keeps its pressure?

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It takes an hour or two for the patch cement to fully "set" and attain full strength. Once that time has passed, the patch should be essentially as strong as the rest of the tire and able to withstand pressure outside the tire. If you must "patch and run", however, it's probably best to treat the patch gingerly until installed inside the tire. You should still test-inflate the tube outside the tire, but don't overdo it. (Also note that if you must "patch and run" you should apply talc to the patch area, or roadside dust, or a piece of tissue, to prevent sticking to the inside of the tire.) –  Daniel R Hicks Nov 27 '12 at 16:38
    
Thanks. In my case, I always have a spare tube to fix quickly a flat. And patching is done at home with all the time in the world... It is my first real patching, so would you say that letting the patch dry for ~5 hours, then inflate (mildly but to give full form) the tube and leave it like this for a couple of days is a safe test the patch is well attached? –  tisek Nov 27 '12 at 16:49
    
If the patch has fully cured it's safe to over-inflate the tube a bit, and this will be a better test. –  Daniel R Hicks Nov 27 '12 at 19:12
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1 Answer

up vote 4 down vote accepted

It's not necessary for the tube to have the external pressure of being installed in a tire. If patched correctly the patch will hold just fine if there are days or months before it is used.

My normal habit is to travel with a spare tube. When I flat, I switch the tube out, and carry the old one home where I patch it later. In my garage I have a box of patched tubes that I reuse as spares and the patches always hold.

If you wait a few minutes after patching, you can, as you ask, fill it with air outside of a tire, and the patch should still hold. In fact doing that and then dunking the tube in a basin of water can be a good way to test that the patch was installed correctly before you deflate it and store it for later use.

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Thanks! I recently had a flat and patched it at home, and I was going to inflate it, leave it a couple of days to check it keeps shape and later put it an hour in water to check it is fine. Sorry, first flat repair, still a bit nervous on the subject. Thank you. –  tisek Nov 27 '12 at 14:52
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