Abstract: A bottle cap assembly it is described which includes a hollow cylindrical body adapted to be fastened to the neck of a soda water bottle to seal the top opening thereof, a valve seat having valves to seal an outlet hole on the hollow cylindrical body, a division plate to hold said valve seat in place, a cap retained on said hollow cylindrical body and a bellows within said body retained by the cap. The device functions when the cap is pressed which causes outside air to be compressed and fed into the soda water container to pressurize the same. A release of the cap causes an expansion of the bellows which readmits outside air into the bellows without releasing the contents of the soda water bottle.