Abstract: A manually-operated device for safely inflating automotive vehicle tires. A pressurized gas cylinder is connected to a manual valve for delivery of pressurized gas to a vehicle tire. The gas pressure is safely controlled (regulated) by a stepped piston that is slidably arranged in a vent chamber. A small diameter rod section of the piston is aligned with a valve seat in the main flow passage. Pressure rise on the large diameter section of the piston causes the rod section to temporarily interrupt the main gas flow. Gas is vented around the large diameter section of the piston to enable the rod section to move away from the associated valve seat, thereby permitting gas flow to resume through the main passage.