was out on my bike earlier and thought the id top the tyres up when i got in in prep for tomos commute so i blew the front up without a prob ,the rear was blew up(for a short while )when i removed/pulled off the pump head the valve core pinged off in a sudden deflation ,oh well ,new tube required ,just when i read the thread about presta valves being a bit rubbish and thinking to my self "theyve always been ok ime "