Put a little lubricant , Vasaline, I use lithium grease,etc, on a swab and wipe it lightly inside the pump to lube the "O" ring or whatever they use for a seal. Add a very small amount to the presta stem and the pump head goes on an off slick as a goose ( this lesson and recomendation from my lbs after I had snapped a Presta) OLE it works and fixed a pump I was ready to throw away because I was having to push and pull the head on the valve. It is now better than new.