What must be installed between two shut-off valves in a propane system?

In a propane system, the installation of a hydrostatic relief valve between two shut-off valves is important for safety and regulatory compliance. This valve plays a critical role in managing pressure within the system. In the event of an overpressure condition, the hydrostatic relief valve will activate to release excess pressure, preventing potential ruptures or explosions in the gas line.

By situating this valve between the shut-off valves, it ensures that the system can be isolated for maintenance or safety reasons while still having a mechanism in place to protect against pressure buildup in the adjacent piping. This proactive measure is essential in maintaining the integrity of the propane system and enhancing overall safety.

The other options, while relevant components in some contexts, do not serve the same function as a hydrostatic relief valve in this specific scenario. For instance, a pressure sensor is used for monitoring and does not mitigate pressure risks directly. A shut-off switch is for controlling the flow but does not provide safety against overpressure. An inline filter is designed to remove contaminants from the gas, but it does not address pressure regulation or relief. Therefore, installing a hydrostatic relief valve is the necessary and appropriate choice in a propane system configuration between shut-off valves.