Generic term for limiting or monitoring device as in "speed governor" or air pressure governor, more often the latter. Pressure governors are used to monitor the rise or fall of air pressure to operate systems or give warnings. Compressor governors are used to automatically control compressors running between predefined air pressure settings to ensure air supplies are maintained. A brake pipe governor may be used to switch off power control automatically if the brake pipe is discharged, initiating an emergency brake application. Speed governors perform the usual functions in a diesel engine control system.