An inflation stem having an inflation valve combined with a blow-off valve to prevent overinflation. The valves are forced open during inflation when the actuating pin is depressed by the compressor chuck head, opening a fill chamber through which fluid flows into an inflatable object, and also opening a blow-off chamber. A blow-off intake allows lower pressure fluid from the interior of the object to enter the blow-off chamber. The fluid entering the blow-off chamber is isolated from the high pressure fluid coming in from the compressor through the fill chamber by a separation fin and shield joined to the bottom end of the actuating pin. A blow-off gasket is biased upward by a blow-off spring. But as pressure in the object and the blow-off chamber increases, the blow-off gasket is forced down, until at the predetermined pressure it is pushed past a blow-off port, through which fluid then escapes.