Today in 1975, US Patent 3908871 A was issued, an invention of Antonin Gottwald, for his “Keg Closure and Coupler Assembly.” Here’s the Abstract:

The assembly includes a keg connector body having first and second passages communicating with the interior of the keg and a dispensing line connector body having first and second passages communicating with a dispensing line and a source of compressed gas. Lower and upper separable plates having registering bores are disposed between the two bodies. Relative movement between the plates and the bodies enables closing off of both the interior of the keg and the dispensing line and source of compressed gas, the plates then being separable with the respective closures still in effect.