Which of the following does NOT have to be done when using two gas pressure regulators in series?

The correct answer indicates that it is not required to install a manual shutoff valve at the second regulator when using two gas pressure regulators in series. In a typical gas system where regulators are installed in series, the first regulator's primary function is to reduce the high supply pressure to a lower pressure suitable for the appliances being served. The second regulator then further reduces this pressure to the exact level needed for safe and efficient operation of specific appliances.

While it is essential to have a manual shutoff valve installed at the first regulator to allow for easy maintenance and service, the requirement for a shutoff at the second regulator is not mandated by safety codes. The focus is more on controlling the flow and pressure to the appliances rather than providing a shutoff capability at every stage.

Moreover, ensuring the accessibility of the first regulator and proper installation of both regulators are critical for safe operation and maintenance of the overall gas system. Proper installation practices and accessibility allow for any necessary adjustments or repairs to be conducted safely and efficiently, playing crucial roles in safety and compliance in gas installations.