Fixed-core versus removable-core valves.
Cleaning a plugged tubeless-tire valve
The valve on the left is a standard UST tubeless valve. If this valve becomes plugged with tire sealant, it's virtually impossible to clear. You'll need to install a replacement valve.
On the right is a valve with a removable core. Once the core is removed, you can clean out hardened sealant, then screw the core back in.
Removing the core.
The sides of the cap threads (the silver part just under the valve knob) are flattened so a
wrench can be used to unscrew the core. Turning counter-clockwise removes
the core from the
stem.
And it's out.
Once the threads are unscrewed, the valve simply slides out of the stem.
Cleanup.
The plug will usually be at the bottom end of the core. Peel or wipe it away.
But here's my "full disclosure:" I bought a bag of 10 valve cores online for next-to-nothing. So when a valve core gets full of crud, I just toss it and insert a brand new one.
Refreshing the sealant in the tire.
If necessary, put fresh sealant into the tire.
Tight, but not too tight.
Insert the valve core, turning clockwise to tighten. (Don't simply finger-tighten. The valve
will become loose during your next ride, causing an air leak.)
If the bead came away from the rim, get the tire back in position.
If the tire's bead has separated from the rim, force the bead back out against the side of
the rim. Using both hands, push your thumbs down in the center of the
tire, while your fingers
drag the sidewall of the tire outward. When it looks like the bead is
sitting on the rim liner
all the way around, you're ready to inflate.
Inflating the tire. If the tire is still stuck to the rim, just pump.
Inflate the tire using a floor pump or a CO2 power inflator. (If the seal on the tire bead
has been broken, a mini-pump doesn't provide enough air pressure to seal
the tire.)
Spreading sealant around.
Work the sealant around the tire's edges, as discussed in the section on setup or repair of
sealed tubeless tires.