What is prohibited in the return line connected to a burner or pump?

In a fuel system, having a valve or obstruction in the return line connected to a burner or pump is prohibited because it can create several operational issues. The purpose of the return line is to ensure that any excess fuel is safely returned to the tank or reserve from which it came, allowing for a smooth and consistent flow of fuel to and from the burner or pump.

If a valve or obstruction were present, it could lead to a blockage in the return line, potentially causing pressure build-up, overheating, or even fuel leaks. This could compromise system safety and efficiency, and increase the risk of fire or explosion due to fuel accumulating where it shouldn't.

By prohibiting valves or obstructions in the return line, the code ensures that there is always a clear path for fuel flow, maintaining the integrity of the fuel system and promoting safe operational practices. This is particularly important as safe fuel handling and minimizing risks are critical aspects of fueling system design and maintenance.