What is prohibited from being installed on return piping?

The placement of valves on return piping is typically prohibited in mechanical systems to ensure proper water flow and maintain system efficiency. When valves are installed on return lines, they can create potential points of restriction or blockage that can adversely affect the overall performance of the system. The flow of air or water significantly depends on maintaining a continuous and unobstructed path through the piping system.

In addition to affecting flow, having valves on return lines can create challenges with air trapping and prevent the proper circulation of the fluid. This can lead to issues such as reduced heating or cooling capacity, increased energy consumption, and potential damage to components due to inadequate flow.

Other components, such as filters or fittings, may be allowed in return piping because they serve specific purposes without hindering overall system performance when properly installed. Check valves can also be installed under certain conditions but must be used correctly to ensure they do not interfere with the system functions.

Therefore, the prohibition of valves on return piping aligns with promoting reliable, efficient, and safe operation of mechanical systems.