Today in 1971, US Patent 3613954 A was issued, an invention of Peter D. Bayne, assigned to Schlitz Brewing Co., for his “Dispensing Apparatus.” Here’s the Abstract:

The invention relates to a dispensing unit for dispensing a beverage containing dissolved carbon dioxide and which utilizes a liquified fluorocarbon gas as a pressurizing medium. The unit includes a closed container containing a beverage having dissolved carbon dioxide. The liquified fluorocarbon gas is contained i a separate reservoir which communicates directly with the headspace of the container above the liquid level. As the beverage is drawn from the container, the volume of the headspace of the container increases, thereby decreasing the pressure in the headspace and resulting in the vaporization of additional quantities of the liquified fluorocarbon gas which act to maintain the desired counterbalancing pressure within the headspace to keep the carbon dioxide in solution in the beverage.