Today in 1877, US Patent 194010 A was issued, an invention of Edward Stewart, for his “Improvement in Beer Pumps.” There’s no Abstract, although in the description it includes these claims:

My invention relates to an improvement in beer-pumps, the object being to provide a beer pump of such construction that the vacuum formed within a barrel or keg of beer or other liquid as the same is drawn therefrom maybe supplied with air, and any desired pressure maintained within the keg, thereby preventing the escape of the contained gases and rendering the beer pleasant to the taste.

My invention consists in the combination, with an air-pump, the upper end of which is provided with a flexible tube to connect with a barrel or keg, of a pivoted platform, one end of which rests in contact with the lower head of the bellows or piston, While the opposite or free end of the platform projects outwardly to allow the party engaged in drawing the beer to stand on the treadle and operate the pump by his weight to force air into the keg as the beer is being drawn therefrom, whereby the hands of the operator are entirely free to hold the glass or other vessel into which the beer is to be drawn, and also to regulate the faucet and accurately govern the flow of beer, the weight of the operator on the movable platform serving to force a sufficient quantity of air into the barrel or cask to effect the desired object.