Inflating Presta valves

[whippet65]

Hi all,

I realise this is a ridiculous question, and I feel pretty stupid for asking it, but in attempting to inflate my presta valve, I unscrewed the nut and proceeded to deflate the tyre in about two seconds. I have followed online advice - unscrew the nut as far as it will go and then inflate, but I cannot get the pump to lock onto the valve and air is escaping rather than going into the valve. I have the correct pump. Am I doing something fundamentally wrong?

 

[dhk2]

Most pumps these days have heads that accomodate both presta and schraeder valves. The schraeder option will have a center post which will deflate the presta valve as you mentioned; on presta set up, there's no post since the air pressure is enough to cause the presta valve to open and allow inflation.

On pumps I'm familar with, to change to presta, you have to unscrew the big "packing nut" on the head, remove a rubber grommet and center pin, turn them over and replace the nut. The nut compresses the grommet and controls the fit to the valve stem. Don't tighten it down, or the head won't fully seat on the valve.

OR ,if you've got an experienced cyclist or LBS handy, just ask them to show you.

 

[whippet65]

That was exactly it. Thanks so much

Mark