When two gas pressure regulators are installed in series, what is required at the second regulator?

When two gas pressure regulators are installed in series, the requirement at the second regulator is that no manual valve shall be required. This configuration is often used to ensure that the pressure is adequately reduced to safe operating levels. In such setups, the second regulator is meant to further stabilize and control the gas pressure, typically relying on the performance of the first regulator and the inherent design of the second regulator for safety and efficiency.

A manual or shutoff valve may not be necessary at the second regulator because the design and operation of the regulators inherently manage pressure without the need for additional manual intervention. This avoids the potential safety risks associated with manual valves, such as improper operation or maintenance issues. Furthermore, the absence of a manual valve can enhance the reliability of the system by preventing human error.

The other options involve valves that may not be required or can complicate the regulator setup, which is contrary to the streamlined operation desired in gas systems. Thus, complying with the guideline that no manual valve is required at the second regulator helps maintain safe and effective gas pressure management.