Which gauge is used to measure both positive pressure and vacuum in fire protection systems?

The correct choice is the Master Pump Intake Pressure Gauge, which is designed to measure both positive pressure and vacuum conditions within fire protection systems. This gauge plays a critical role in monitoring the system's performance during pump operations, allowing operators to assess the intake pressure while also detecting the presence of vacuum that may occur under certain conditions, such as when the pump is drawing water from a substantial lift.

Master Pump Intake Pressure Gauges are specifically calibrated to handle the varying pressures associated with fire protection systems and provide valuable feedback on the system's operational readiness and efficiency. This is essential for ensuring that water supply and flow rates are maintained at adequate levels, which directly impacts firefighting effectiveness.

Although a vacuum gauge is used primarily for measuring vacuum pressure, it does not measure positive pressure; hence it would not be suitable for the dual role required in this context. The other options, such as the pressure relief gauge and flow meter, have specific functions that do not encompass the measurement of both positive pressure and vacuum simultaneously as required in this scenario.