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I have a mini pump for my bike - I guess for around 3 years now. It's started to give me trouble recently - it's for a presta valve and it screws on, rather than locks on. For some reason when I screw it onto the valve to full tightness the air starts to come out of the tire through the pump. This never happened before. If I unscrew it to around 3/4 tightness it stops but when I pump the tire like this I am not getting good pressure.

Is it broken? Can I fix it?

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  • It depends on how it's built. As with a lot of questions, we really need a photo or an indication of brand and model.
    – pateksan
    Oct 17, 2022 at 18:19
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    My dad would say you can't make it worse than it is, so you might as well take it apart and have a go at fixing it.
    – pateksan
    Oct 17, 2022 at 18:20
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    The check valve in the pump is leaking. Not screwing the pump all the way on lets the tire valve behave as a (somewhat flaky) check valve. Oct 18, 2022 at 1:34

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I've had minipumps fail while on the bike - vibration from riding seems to back-out any components that are screwed together. Plus they're exposed to rain and road grime.

Take the pump apart, start by untwisting the ring around the metal shaft. Then undo anything that looks threaded.

Check the O rings inside and replace if they are cracked or damaged.

Add a light touch of rubber-safe lubricant, and reassemble. You could use blue (hand tight) threadlocker on any threads that were loose, but sparingly expecially if they're plastic.


Also try this pump on another valve. I've seen presta shafts that were too long and were difficult to pump. Does the same pump work better on the other wheel ?

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    FYI, There is a threadlocker formulation specific for plastic threads.
    – Ted Hohl
    Oct 17, 2022 at 19:58
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    Here are some instructions for Lezyne, which uses a screw-on chuck at the end of a hose. They say just to lightly grease the o-ring and piston (after cleaning the inside, if appropriate). youtube.com/watch?v=iYZ5Smx4FmQ
    – Weiwen Ng
    Oct 18, 2022 at 0:36

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