What is the purpose of not allowing valves on return piping?

The purpose of not allowing valves on return piping primarily focuses on ensuring proper fuel circulation. In many mechanical systems, particularly those involving fuel lines, the return piping needs to maintain a consistent flow to effectively bring fuel back to the source for recycling or reuse. Valves in the return line could create points where fuel flow could be restricted or stopped entirely, potentially leading to a buildup of pressure or stagnation of the fuel. This can not only disrupt the efficiency of the system but can also lead to problems with contamination or the proper operation of equipment.

In systems designed for optimal performance, maintaining a straightforward and uninterrupted flow of fuel is critical. Allowing valves could complicate the flow dynamics, which is why their presence in return lines is typically avoided. This consideration safeguards against operational issues and ensures that the fuel can circulate as intended without interruption.