I have a tube with a Schrader valve, previously repaired (twice). I needed to use it, so I inflated it by hand until it ballooned to 2x the size, search for leakages in water (valve too) and let it all night to check for slow leakages, but none were found. Later, I put it inside the tire, inflated it by hand (~15 psi) again, put a little soap in the valve, and went to check my email. Ten minutes later, it was totally flat. I repeat the whole procedure twice and it was the same story: the tire showed no leakage outside the tire but lost all pressure when inside the tire. (Finally, it blew out while outside the tire). Why is this happening? I'm just curious ...
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Your tire tube is still subject to the basic laws of physics and logic on this Earth. If air is leaking out of it, then there is a leak somewhere and it is perforated.
There is probably something in your tire causing the damage, especially if this continues to happen. It's also possible that the leak was close to the valve, and whenever the valve was up against the rim of your wheel, it was bent just so to allow the leak.
Try putting the tire in water with a bit of dish soap. The soap will make the bubbles a bit more apparent. Adding a bit more pressure and trying to articulate the area around the valve may help identify the source of the leak. Keep an eye out for tiny air bubbles forming on the surface of the tube while you hold it under water. Also, be careful to check around existing patches.
After checking the tube thoroughly, check the inside of the rim for any sharp ridges or places where the rim tape maybe has been worn too much and may let a sharp edge protrude under pressure.
Then check the tire itself for any items which may be lodged in it. Glass and metal shards can hide within the rubber of the tire, and when under load or pressure, the fragment can puncture your tube. They may not always be visibly apparent. Slowly feel around the inner surfaces of your tire (lining up the label on the tire with the valve stem can help you identify where to look if you find a hole in the tube). Sometimes I try and work slowly around the tire and bend the tire so that any gaps in the inside of the tire would open slightly and expose the fragment.
Well, I think it is not the fact that it is inside the tyre, but you are probably inflating it to much larger pressure when inside the tyre. At larger pressure tube starts to leak.