An air flow rate meter and method for monitoring the flow of air in high-pressure compressed air system includes a low pressure gauge contained within a sealed, high pressure vessel that is connected to the high pressure compressed air line. The low pressure gauge is pneumatically connected to opposite ends of a tube disposed within the meter through which the main air pressure line flows in order to detect the pressure drop across the restricted orifice defined by the tube. The measured pressure drop is then used by the gauge to determined the rate of air flowing through the line. To avoid damage to the meter, the air flow rate meter further includes a pressure regulating valve for regulating the input air flow pressure during startup of the system, and a check valve for closing the flow path through the pressure vessel during shut down.