A balloon inflation device for use with a keyed balloon weight associated with a balloon to be filled with gas includes a source of pressurized gas sending gas through gas lines and multiple valves associated with an inflation block, wherein each valve is opened by properly manipulating elements of the inflation block. A key weight valve is opened by placing a key weight into a key weight receptacle in the inflation block, and a clamp valve is opened by manipulating a clamp mechanism. The key weight is associated with a balloon having a open neck that is placed over an inflation nozzle of the inflation block, before placing the key weight into the key weight receptacle. The clamp mechanism clamps the neck of the balloon to the inflation nozzle as it opens the clamp valve. With both valves open, gas may flow to the inflation nozzle to fill the balloon.