Today in 1978, US Patent 4070133 A was issued, an invention of Homer McCormick, for his “Pump Compressor Unit for Use with Pumping Draft Beer.” Here’s the Abstract:

An air supply unit provides high pressure moisture-free air in the dispensing of beverages. Components are housed in a portable cabinet and include a compressor and an automatic air pressure switch to switch on the compressor and begin air flow when system pressure falls below a pre-set level. A check valve is located in the high pressure line adjacent the compressor to maintain line pressure when the compressor is off. A small air bleed opening is located between the check valve and the compressor to allow compressed air to move through the air line yet bleed residual pressurized air to prevent stalling of the compressor which could occur if high pressure air was present in the compressor when it is restarted. The high pressure air discharge line includes a dump-check valve to permit high pressure air to be manually bled from the system before the air lines are disconnected and to prevent back flow of fluid into the air supply unit.