Abstract: The present invention utilizes measurements of the characteristic standing pressure wave frequencies in normally liquid-filled pipes to detect the presence of gas bubbles or gas pockets within the pipes. Because gases, for example air, are more compressible than liquids, gas in a pipe causes the natural frequencies of standing waves to be shifted from their values with no gas. The characteristic standing wave frequencies are determined from a Fourier transform of pressure fluctuations within the pipe. The pressure fluctuations, measured using a hydrophone or other pressure transducer, are due to either background flow noise (passive technique) or a deliberately induced pressure transient (active technique). The technique is sufficiently sensitive to detect relatively small gas bubbles as well as complete gas blockage. The apparatus required depends somewhat on whether the particular application requires use of the active or passive technique.

Abstract: The present invention utilizes measurements of the characteristic standing pressure wave frequencies in normally liquid-filled pipes to detect the presence of gas bubbles or gas pockets within the pipes. Because gases, for example air, are more compressible than liquids, gas in a pipe causes the natural frequencies of standing waves to be shifted from their values with no gas. The characteristic standing wave frequencies are determined from a Fourier transform of pressure fluctuations within the pipe. The pressure fluctuations, measured using a hydrophone or other pressure transducer, are due to either background flow noise (passive technique) or a deliberately induced pressure transient (active technique). The technique is sufficiently sensitive to detect relatively small gas bubbles as well as complete gas blockage. The apparatus required depends somewhat on whether the particular application requires use of the active or passive technique.