How Beer Pumps Work. Beer pumps themselves are powered by high-pressure gas or compressed air that does not come into contact with the beer. Most retailers power their beer pumps with CO2 ; in these cases, the pump exhaust CO2 gas must be vented outside the cooler or building to avoid CO2 buildup and asphyxiation.
The yeast will transform the sugar into two elements: alcohol and CO2. During this process, the CO2 is release via an airlock valve leaving only alcohol in the beer. The yeast activity is one way to add gas inside the beer.