Today in 1888, US Patent 385981 A was issued, an invention of Robert Wellens, for his “Beer Pump.” There’s no Abstract, although in the description it includes this summary:

The object of my invention is to provide an improved pump for forcing air into reservoirs for holding beer or other liquids, so as to supply means for discharging the liquid from the reservoir, which pump shall be automatic in its action and shall keep the air-pressure in the reservoir always the same.

My improvements consist,principally,in the mechanism, hereinafter described, by which the water employed to drive the pump is prevented from entering the chamber containing the compressed air and all danger of its entering the reservoir with said air obviated; also in devices by which the pressure of the compressed air in the reservoir is automatically regulated, and, generally, in various details of the apparatus, which I will now describe.