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When I removed the valve core of an MTB tyre that's set up tubeless, it was spotless—so pristine that I figured the tyre must have an inner tube, despite the presence of a stem that looks suspiciously like one for a tubeless tyre (it turned out that my generous LBS threw the feature in without telling me, nor charging me for it).

Shouldn't the valve core of a tyre that's set up tubeless have some goo from the (partially) solidified sealant?

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Not normally in a new install. You might see a small amount of fluid coating the core.

It normally takes some months of use to see evidence of clotting in the valve. You’ll start to find it harder to inflate the tires and at that point you might be able to use a pick or small blade to unblock the core or just install new ones. They cost about $1/€1 and a 5 pack should last you a few years depending on your tolerance for pumping difficulty.

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  • Ok, it makes sense, kind of. The sealant solidifies into a sheet inside the tyre. When I pull the valve core out, it separates cleanly from the sealant's rubber-like-sheet inside on account of that sheet's cohesion. But why does that change for an older install? So now when I inflate the tyre, the air enters between the rubber sheet and the tyre, rather than into the vast chamber. To avoid that, I need to remove the valve core and puncture (say with a toothpick) the rubber sheet. Now the sealant will make contact again with the valve core and leave a trace on it. Am I close?
    – Sam7919
    Dec 3, 2023 at 0:12
  • The sealant remains fluid in the tire until a puncture causes the latex in suspension to coagulate in the puncture. This answer explains better. bicycles.stackexchange.com/questions/59714/… Dec 3, 2023 at 8:40

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