Threaded joints in medical gas and medical-surgical vacuum systems shall be permitted for all of the following except?

The certification standards for medical gas and medical-surgical vacuum systems are designed to ensure safety and reliability. Threaded joints are often used in various components of these systems; however, certain applications are more critical than others.

In this context, check valves serve to prevent backflow and are essential for maintaining the integrity of gas supply systems. When check valves are installed in the main line, the potential for leakage or failure can compromise the entire system, leading to hazardous situations. Thus, using threaded joints in this critical application may not provide the necessary level of security and leak-proof capability required for mainline applications, hence why it is not permitted.

In comparison, components such as alarm pressure switches, check valves on source equipment, and gauges do not bear the same level of risk when connected via threaded joints. These parts either measure or indicate system statuses without directly carrying or managing the gas flow in a high-pressure mainline context, which makes the use of threaded joints acceptable in those instances.