Today in 1943, US Patent 2321631 A was issued, an invention of Ludvik Sibal, for his “Fluid Pressure Controlling Apparatus.” There’s no Abstract, though it’s described this way in the application:

This invention relates to improvements of fluid pressure controlling apparatuses (gases, liquids,
etc.) and it is the principal object of the invention to provide means for adding gas or liquid pressure to containers from which their contents are being discharged at such a rate that the total pressure head at the point where the fluid flows out of said containers remains practically constant even during the discharge period.

This apparatus is constructed with the special object in view of making it applicable to the so called government tanks in the breweries, from which beer is being drawn to the bottle or can filling machines. In these tanks the beer stands under a gaseous pressure (air or otherwise) the level of which is so chosen as to insure a smooth filling process by the filling machine to which the beer is discharged from the government; tanks. The pressure at the filling machine must be kept constant during the filling process and therefore it is necessary and important that the pressure at the point of flow out of the government tanks likewise be kept constant. The total pressure at the point of discharge from the government tanks is composed of two components: (1) the weight of the beer and (2) the gas pressure within said tanks. As the beer is being drawn from the tanks, the total pressure head causing flow at the point of discharge from the tanks is being decreased due to the decreasing weight of the beer. To make up for this loss in pressure head, gas pressure must be supplied to the tanks until the original desired total pressure head is again reached at the point of discharge. This is usually accomplished by a control man whose duty it is to sight the pressure gauge reading or beer level and to adjust the gas valve accordingly.

The main purpose of this apparatus is to eliminate the human factor of such pressure regulation thus making the regulation as nearly free from all human errors and neglects as is humanly possible. Also my design is such that it is best applicable to breweries and other enterprises where apparatus of this kind must withstand severe mistreatment and where it is necessary to thoroughly wash its interior as well as exterior.

This invention provides an apparatus which, when connected by means of a conduit such as .a pipe or a hose to the point at which the discharge occurs from a tank, throws on or oil? a sensitive snap-action electric (magnetic) mercury switch whenever the pressure head changes slightly in the tank at the point of discharge. This snap action switch is connected by means of electric conduits to a solenoid valve in the gas line leading to the tank, and when contact is made, the solenoid valve is actuated by the electric current so that it opens and admits the gas to flow into the tank thus increasing the total pressure head to the original desired level. As soon as this desired total pressure head is reached, the snap action switch automatically turns off and the gas valve closes.