Why can't air be pumped into a Presta valve?

[LaDylan]

Presta valve can't be pumped because the air inlet hole of the valve core is blocked. Solution: unscrew the pressure nut, take out the valve core, remove the valve rubber tube, and use thin iron wire or needle tip to remove the sediment and dirt. Definition of gasoline compound: Fuel additive is a common name for the third generation of gasoline detergent, also known as gasoline detergent or fuel additive. Function of compound: Its purpose is to solve the carbon deposition problem in the fuel system of electronically controlled injection models, quickly restore the engine to its optimal working condition, and compensate for some defects of gasoline in certain properties while giving gasoline some new excellent characteristics, such as improving atomization, reducing wear, protecting the engine, and reducing emissions.

[ElizabethLynn]

Last time I helped my neighbor fix their bike, I ran into the same issue. The core problem with Presta valves not inflating is that the valve core needle isn't being depressed! You need to first loosen the small nut at the top of the valve until you hear a slight hiss of air. The pump head must be pressed straight down firmly - I've seen many people press it at an angle causing leaks. If the inner tube's edge is pinching the valve base, you'll need to push the valve inward slightly. Another possibility is the valve core being clogged with dirt, requiring removal for cleaning. Most crucially, you must use a dedicated high-pressure bicycle pump - car tire compressors lack the pressure to open the needle valve. Always tighten the nut immediately after inflation to lock the air in.

[DeViolet]

Difficulty inflating a Presta valve often stems from incorrect operation. Remember the mantra: Loosen, Press, Lock. First, use your fingers to loosen the silver retaining ring on the valve—a hissing sound indicates the air release channel is open. When attaching the pump, apply firm pressure until you hear a 'click,' confirming proper engagement. Avoid peeking during inflation; keep your left hand firmly pressed on the pump to prevent air leaks. Stop at 80% capacity, then rotate the tire a few turns to allow the inner tube to settle—overinflation risks bulging. I've seen novices strip the valve base threads; replacing it at a repair shop costs around 80 bucks.

[OLorenzo]

After a decade of riding road bikes, I've had enough trouble with Presta valves. If you can't pump air in, it's usually because the valve core is stuck. Use needle-nose pliers to unscrew the core counterclockwise and add a couple of drops of chain oil. Check if the rubber O-ring at the base of the valve is cracked or aged—this tiny ring can cause slow leaks if damaged. Remember to switch your pump head to the Presta valve setting; using the wrong mode is just wasted effort. If you notice air leaking from the side after pumping, it's likely due to sand stuck on the seal—licking the seal can be a quick fix. In sub-zero winter temperatures, rubber hardens, so briefly warm the valve with a lighter before pumping.