Active systems must have a visual or audio system failure indicator, such as the one shown in Figure. 6-1.
Criteria for System Failure Indicators
Must provide a clear warning of system failure
Visual or audible
Must be easily interpreted
Example: U-Tube Manometer
Typically, active systems will have a manometer similar to the one shown in Figure. 6-1. A simple U-tube manometer is mounted to the system vent pipe. The manometer measures the operation of the system fan.
When the liquid levels in the legs of the manometer are uneven, a pressure differential exists, indicating correct operation of the fan and system.
Conversely, if the manometer liquid levels are even, the fan or system is not operating properly and needs repair