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I had my back wheel out during winter because the bike was on the trainer and it of course lost some air. When I put the bike together for outside riding recently, I noticed that I'm having a hard time inflating it back, again.

The nut was indeed unscrewed and pressing in with my thumb made it open but it didn't really work with the track pump, air goes mostly by, after many tries, I got it back to full pressure when I finally got the snap sound indicating the valve opens under pressure.

In the end, I was annoyed and just replaced the tube so that I get air in on the road easily if I ever have to.

When being pumped up, the tube/valve were holding air just fine, any idea what the problem could have been and how to fix that next time, like taking off the full cap and cleaning the channel with a needle or something like that?

Cheers, Florian

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    Clean, grease with light oil or WD40, check for corrosion, it can be anything.
    – Vladimir F Героям слава
    May 5 at 9:19
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    Nit pick on the previous comment: WD-40 is not a grease or lubricant, it's a penetrating oil and is probably not appropriate for this application unless it's part of the first "clean" step. You should never lubricate any part of your bicycle with WD-40, it may flush the dirt out but then you'll be left lubricant free and friction will be increased from what it otherwise would have been.
    – Sam Whited
    May 5 at 12:05
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    @SamWhited That's not correct. WD-40 is, in fact, a light lubricant. About 35% of it is a petroleum based oil, according to their MSDS. It's true that the lubricant is too light to be suitable for most parts on a bike, but unsticking a valve stem is a fairly ideal application since they don't require much lube anyway. I wrote a whole answer about using WD-40 on bikes a couple years back.
    – jimchristie ♦
    May 5 at 12:54
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    Yes, but it's small enough that it's generally not worth mentioning. I suspect trying to make such fine distinctions will confuse more than it will help, but that's just me. Generally speaking: if the part moves, don't use WD-40, if it doesn't, it depends. This doesn't seem worth being pedantic about though; "use a lube" is easier, more generally applicable advice.
    – Sam Whited
    May 5 at 16:40
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    Nit pick on the previous comments: What WD40 product are you talking about? They have everything in their range from the general fix-it-all-lubricant over degreasers to even road-bike-specific dry chain lubes. I got the tube out of the bin and got the valve apart for a little clean job, it seems that it now works... tried without a tube and too much pressure w/o casing, so I saved one spare. If that doesn't work, I guess there's not much to be lost using WD40 lubricant or a small drop of chain lube on a tube that cost 4 bucks and has a problem, anyway.
    – DoNuT
    May 8 at 5:46

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In the end, as suggested in the comments, I took the valve apart, cleaned it (cotton swab, blowing out dust), put it back together and it seems pop open, again.

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