Axial and centrifugal compressor control is exceptionally challenging due to the extraordinary speed and severity of problems and the extreme consequences in terms of plant safety and performance. The fastest and most dangerous phenomenon is surge. An axial or centrifugal compressor in surge can reverse flow in 0.03 seconds going from a large positive flow to a large negative flow. Often, the negative flow is not measurable by flow meters leaving the actual situation to your imagination.