When charging a refrigeration plant, the King valve should be what?

When charging a refrigeration plant, the King valve should be closed to ensure that the refrigerant is contained within the system. The primary function of the King valve is to act as a service valve that regulates the flow of refrigerant into and out of the system. By keeping this valve closed during the charging process, it prevents any refrigerant from escaping and allows for accurate measurement and control of the refrigerant being added. This practice ensures the proper functioning and efficiency of the refrigeration system, minimizing the risk of leaks and potential safety hazards associated with uncontrolled refrigerant release.

Opening the King valve at this stage could result in an improper charge and disrupt the system balance, which is why it is critical to keep it closed until the system is adequately charged and prepared for operation.