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Take a look at the bottom graphic. To work with schrader valves, for most Blackburn pumps, you take off the cap that holds the pump head together, then reverse the guts. Take the rubber gasket and the plastic doodad under it out, separate them, then insert the plastic doodad back in, with the shrader pin sticking up; reverse the rubber gasket so the presta side is down, facing the doodad; then screw the cap back on. Then the gasket is wide enough to fit over the valve, and the pin depresses the valve when you plunk it on the valve stem. The lever compresses the gasket to make a tight seal.