I was using my bike pump today to fill a pneumatic launcher, and finally I just got fed up with the leaking around the pump base. On every stroke, the first 3/4 of air would be leaked out of the base, and it would only compress the remaining 1/4 of air remaining, and that would only compress if you pushed down very hard, and quickly, otherwise it all leaked out. And no matter what pressure the launcher was pressureized to, the pump handle/piston would slide down slowly, getting pushed down under it's own weight, meaning that there was almost no resistance to it. I think the leak is occuring where the tube meets the pump base, and you can feel air rush out with your legs as you pump. I'm pretty sure there is a one way valve in the gauge portion of the pump, which connects to the base with a hose, and the filling hose is coming out of it, which is allowing me to compress at least a little air before the rest leaks out. I disassembled the pump, starting with the base. Turns out, the leak was from an oring on the tube which was not tightened down enough by a screw on ring around the base of the tube. Put it back together, and voila, pushing my finger against the schrader valve connector and pushing down on the pump handle created pressure against my finger and no leaking. As soon as I hooked it up to my launcher, i realized something was up, I could pump down once, but the pump handle just got pushed upwards as soon as i let go. This is what I can't figure out how to fix. It seems the one way valve in the gauge portion is locked in the open position. Anybody know how to fix this? EDIT: Okay I took pictures of the pieces. I now cannot figure out if the valve is in the base, or the gauge portion, so i have included pics of both. Hopefully someone can help me figure this out. EDIT 2: Turns out the valve is in the base, and the ball just fell out when i first disassembled it, i have now found the ball and it is working fine.