I have an Avenir floor pump that I've been using with my presta valve-equipped bikes for probably over 10 years now. It's got a Silca head on it with a brand new seal. Earlier today I successfully inflated a road tire, the proceeded to attempt inflation the tires on a cruiser for my wife (it has presta valves too) to no avail. I then tried pumping up the tires on three different bikes, but no dice. I'd put it on a tire and pump, and the pressure gauge would go up then go back down. If I let go of the handle, it'd shoot up to a higher position like the pump was holding pressure but none was going into the tire. I could not hear any leaks from the pump. When I put my thumb over the hole on the head and pumped, I could feel air coming through. At first I thought this was just due to old presta valves on some of my tires, but I moved around to different bikes and newer valves and had the same problem. And yes, I did loosen/push down on each presta valve before attempting inflation. Is my pump hosed? The behavior strikes me as kind of odd.