Systems using positive-displacement compressors containing more than how many pounds of refrigerant must have stop valves?

The requirement for systems using positive-displacement compressors to have stop valves is determined by the amount of refrigerant contained in the system. In this context, the threshold is set at 6.6 pounds of refrigerant. This requirement is part of safety and operational standards designed to ensure that systems are equipped with appropriate control measures, especially as the amount of refrigerant increases. Having stop valves in systems with refrigerant amounts exceeding this threshold allows for safer maintenance, repair, and potential emergency situations by enabling isolation of the refrigerant in the system.

Stop valves are essential for controlling the flow of refrigerant within a system and for providing a means to isolate sections of the system, thereby minimizing the risk of refrigerant leakage during service or in case of a malfunction. Meeting this guideline helps enhance safety and compliance with established mechanical codes, reflecting best practices in mechanical system design and operation.

The other amounts listed in the options do not align with this specific requirement, as 6.6 pounds is the established limit in relevant mechanical codes for the necessity of incorporating stop valves. Understanding and adhering to these values is critical for compliance and ensuring the safety and efficiency of refrigeration systems.