Originally Posted by
2 wheeler
Hmmm... I've been using presta valves for about 38 years and can't ever recall any pump head or adapter that "unseats the presta valve stem automatically". I always have to depress the valve to break it's seal before pumping up a tire. Any depressing of the valve stem, that you mention, would have to be automatic and momentary, or air wouldn't stay in the tube.
Could you enlighten me?
Giyo GF-12 pump has a universal Presta/Schrader head that depresses the valve stem automatically for Presta the same way it would for Schrader valves. A bit annoying since it leaks air until you lock the head on, but handy for getting the exact pressure you want and no worries about sticky stems.