What is the purpose of a plug in the external bypass part of a two pipe fuel pump?

The purpose of a plug in the external bypass section of a two-pipe fuel pump is primarily to allow oil to return to the tank. In a two-pipe system, one pipe is used to supply fuel to the pump while the other returns excess fuel back to the storage tank. This design helps maintain a balanced system and ensures that the fuel pump operates efficiently, preventing any excess fuel from becoming problematic in the system. By allowing the oil to return to the tank, the plug helps maintain proper pressure levels and flow, which is crucial for the overall operation of the fuel pump system.

While improving efficiency, increasing pressure, and preventing overflow are relevant concepts within fuel pump operation, they do not specifically pertain to the role of a plug in the external bypass. The direct function of allowing oil to return is the key aspect in understanding the operation of two-pipe systems in heating and cooling applications.