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I've been trying to use a small hand pump to put air back into my flat tire with a presta valve. I've read the instructions from the pump manufacturer on how to change the pump to be able to pump air into presta valves and I've watched a bunch of videos on pumping air Ito presta valves but I still can't seem to get air in. I've unscrewed the top piece and the tire is completely flat so when I push the valve in with the screw undone nothing is going to come out. So when I'm trying to pump in air is the piece coming out of the valve supposed to stay out or does it get pushed back in when the pump goes over top and locks onto it?

thanks!
 

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sounds like you have a flat, like in need a new tube. unless there is something i am not getting from your post.
 

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After you unscrew the valve push it in for a moment to unstick it.

Make sure the pump head is well seated on the valve. If there's air coming out between the pump head and the valve the head is not seated.

On heads with levers often the lock position is up, not down. To tell which way is locked, look at the presta hole in the head while operating the lever. The lock position will squeeze the rubber around the hole so the head can hold on to the valve.

Last, if it's a combo presta/schrader head with two holes make sure you're using the right one.
 

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Have you broken the valve? Try using your floor pump to check you can actually inflate it period. Small pumps, especially direct fit, can be tricky. Try using the hand pump to inflate a spare unbroken unmounted tube to see if it is just user issues (BTDT). I despised my direct fit pump so I bought a flex hose lezyne pump after side of the road frustrations.
 

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I'm not really understanding the question or problem, but just to ditto some of what's been said and add my own experience:

To start, you should "burp" the presta valve. Open it up, depress it to unstick the seal and let a little air escape. This - for me - was a cause of not being able to inflate the tires, now I do it routinely.

Make sure you understand how your pump works. Make sure you know how to seat it on the valve. Make sure you understand the difference between the lock and unlock position on the little lever. If it's a multi-valve pump, make sure you have the right configuration of the inner rubber gasket that grips the valve (large opening for Shraeder valve, small opening for Presta valve).

Make sure your getting it seated and locked properly before you pump.
If you feel air escaping around the valve stem and the pump fitting, either it isn't seated or you've broken the valve.
If it just won't pump air in (hard resistance to pumping), it needs to be burped or re-seated.
If you pump air in, and it just seems to escape, the tube's probably bad.

Pumping with a mini pump can be difficult. It takes some finesse and thought to get it on properly, and to hold the pump and wheel so it doesn't move around a lot and damage the valve while you're pumping. It takes some patience to pump slowly and completely every stroke to get the air in a tiny bit per pump. Worth practicing in the garage before the flat tire event on the road.
 

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Pumping with a mini pump can be difficult. It takes some finesse and thought to get it on properly, and to hold the pump and wheel so it doesn't move around a lot and damage the valve while you're pumping. It takes some patience to pump slowly and completely every stroke to get the air in a tiny bit per pump. Worth practicing in the garage before the flat tire event on the road.
I carry a mini-pump just in case but this sounds like a good reason to use CO2. I need to do some dry runs with both before I get the inevitable flat.
 

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I started carrying co2 for the first time after my first (and only) flat early in the season. Last year I got a flat and one of my friends let me inflate with the co2 and it was really nice! I can get the mini pump to work just fine and can get 85 or 90 pounds in it OK (which is all I really need), but am really looking forward to using the co2.

I still keep the mini pump on the frame though. Old habits die hard.
 

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I use my full sized frame pump for most of the pumping of my tires. I did pick up a mini-pump somewhere, and may try to mount it if I put a second water bottle back on.

It sounds like most people do the same thing. Unscrew the valve. Momentarily push the valve in to get it unstuck. Put your pump on and start pumping. If you have a pump with a fixed head, always hold the pump head and tire to avoid breaking anything as you're pumping.

With the Schrader valves, the pump physically depresses the valve. With the presta valves, the pump does not depress the valve, and the tire valve works as a one-way valve as you inflate your tire.
 

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A presta valve is different from the schrader valve which is found on a car. When you pump a schrader valve, the pump has to mash down the little pin in the middle of the valve for air to get into the car tire or bicycle tube. See this picture:


The presta valve is different. Instead of a spring which closes the valve, it simply relies on the higher pressure inside the tube to push the valve closed against the lower air pressure outside the tube. When the little nut on the top is screwed down, that is just like extra insurance to keep the valve closed because the pressure inside the tube should already be pushing the valve up keeping it closed. To pump air through the presta valve into the tube, you push on your pump which increases the outside pressure (in the pump hose of a floor pump or in the barrel of a minipump itself) to a higher pressure than what's inside the tube, and that pushes the presta valve open. Typically the pressure in the tube and in the pump hose will then be equalized. When you disconnect your pump, then you're releasing the pressure on the outside of the presta valve and the high pressure in the tube pushes the valve shut.

So what does all this mean? First, you have to have the little nut at the top of the presta valve loosened so the valve can open and close. When the nut is tight, the valve is closed tight so air cannot pass through the valve. Secondly, you don't need to mash down the pin in the middle of the presta valve during pumping because the pump pressure is enough to push air through the valve. People recommened quickly "burping" the valve before attaching the pump head simply because the valve can be a little "sticky", so "burping" it quickly makes sure it moves freely when you try to pump it. Thirdly, it's important that your pump head seals decently to the outer part of the valve stem because you need enough of a seal for the pump to increase the pressure going through the pump hose higher than the pressure already inside the tube. If the pump head leaks at a lower pressure than the pressure you want to pump the tube up to, the air from the pump will leak out from between the pump head and the valve stem instead of going through the presta valve into the tube.
 

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Nice explanation.

I've ridden on sewups with busted screw things on the presta valves. They work just fine without the top being screwed down. However, I generally am careful not to brake the tops off of the valves (and thus like to keep a cap or schrader adapter over the valves when not pumping them up.
 

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A presta valve is different from the schrader valve which is found on a car. When you pump a schrader valve, the pump has to mash down the little pin in the middle of the valve for air to get into the car tire or bicycle tube. See this picture:


The presta valve is different. Instead of a spring which closes the valve, it simply relies on the higher pressure inside the tube to push the valve closed against the lower air pressure outside the tube. When the little nut on the top is screwed down, that is just like extra insurance to keep the valve closed because the pressure inside the tube should already be pushing the valve up keeping it closed. To pump air through the presta valve into the tube, you push on your pump which increases the outside pressure (in the pump hose of a floor pump or in the barrel of a minipump itself) to a higher pressure than what's inside the tube, and that pushes the presta valve open. Typically the pressure in the tube and in the pump hose will then be equalized. When you disconnect your pump, then you're releasing the pressure on the outside of the presta valve and the high pressure in the tube pushes the valve shut.

So what does all this mean? First, you have to have the little nut at the top of the presta valve loosened so the valve can open and close. When the nut is tight, the valve is closed tight so air cannot pass through the valve. Secondly, you don't need to mash down the pin in the middle of the presta valve during pumping because the pump pressure is enough to push air through the valve. People recommened quickly "burping" the valve before attaching the pump head simply because the valve can be a little "sticky", so "burping" it quickly makes sure it moves freely when you try to pump it. Thirdly, it's important that your pump head seals decently to the outer part of the valve stem because you need enough of a seal for the pump to increase the pressure going through the pump hose higher than the pressure already inside the tube. If the pump head leaks at a lower pressure than the pressure you want to pump the tube up to, the air from the pump will leak out from between the pump head and the valve stem instead of going through the presta valve into the tube.
This is an excellent explanation, clearly written and concise! Thanks.
 
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