Which type of regulator is used in series for emergency pressure control in gas piping systems?

The correct answer highlights that a monitoring regulator is specifically designed to maintain and monitor system pressures in gas piping systems. Monitoring regulators can be utilized in series to provide an additional layer of safety and control over the pressure levels within the system.

In the context of emergency pressure control, a monitoring regulator continuously checks the upstream pressure against a set threshold. If the pressure exceeds the predetermined levels, it can trigger a response such as alerting the system or engaging additional safety mechanisms. This functionality is crucial in preventing excessive pressure scenarios that could lead to dangerous conditions or equipment failure.

The other types of regulators serve different functions; for instance, pressure-reducing regulators primarily aim to decrease and maintain pressure at a specified level to meet system demands, while control regulators adjust their output based on the demand to maintain desired pressure or flow rates within a system. Emergency shutoff devices are critical for swiftly stopping the gas flow in emergencies, but they do not actively monitor the pressure continuously in the same manner as a monitoring regulator.