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Have tried a number of times to inflate mountain bike tires with schrader valves using a pump but it never inflates. Tires already inflated but feel a little low on air, so I go to pump them and the valves are not accepting air, just feels like I'm compressing the air in the pump. It doesn't appear that the valve is blocked or anything because when I first put the pump on the valve it lets air out.

What is going wrong?

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  • Pump not far enough over the valve? Pump has some handle which needs to be closed but isn't closed? Hard to tell.. Can you post a picture perhaps (valve with and without pump or so)? – stijn Aug 28 '17 at 19:22
  • Most likely the pump's chuck is not far enough onto the tube's stem. – Daniel R Hicks Aug 29 '17 at 2:03
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You may simply not pushing the pump onto the value body enough, and the internal valve is not being opened.

Most pumps have a plastic insert behind the valve hole that is reversible for Schrader or Presta value use.

enter image description here

[Schrader left Presta right.]

This insert may be the wrong way around, or (as has often happened to me) the small peg that opens the Schrader valve has been bent so it no longer pushes on the valve.

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