Which of the following must NOT be located between a pressure relief device and the container unless a listed PRV manifold is used?

In the context of propane systems, the placement of components in relation to the pressure relief device (PRD) is crucial for safety and proper functioning. The correct answer indicates that shutoff valves must not be located between a pressure relief device and the container unless a listed PRV manifold is used.

The reason for this is that the primary function of a PRD is to relieve excess pressure in the system, thereby preventing potential explosions or ruptures in the container. If a shutoff valve is positioned between the PRD and the container, it could inadvertently block the release of pressure. This blocking could prevent the PRD from functioning effectively during an overpressure situation, posing a significant safety hazard.

In contrast, flow regulators, flexible hoses, and pressure gauges can typically be installed between the PRD and the container without compromising safety, provided they meet regulatory standards. These components can either control flow or provide readings without obstructing the essential function of the PRD.

Thus, the emphasis on avoiding shutoff valves in this particular placement is grounded in the need to maintain an unimpeded safety mechanism.