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The last edit to this post was made by LQ198619 on 2017-5-25 at 13:29. V. Operating Performance of Centrifugal Compressors – Performance Curves. A curve that shows the relationship between the pressure ratio (or outlet pressure), power, and efficiency of a compressor (or one of its stages) at different flow rates is called a performance curve. It can be seen from the P-G (exit pressure-flow rate) curve that as the discharge pressure increases, the exhaust volume decreases. This is similar to a centrifugal pump. The N-G curve (power-flow) shows that power increases as the gas flow rate increases. The η-G curve (efficiency-flow rate) has a peak point, and the flow rate, pressure, and power at this point represent the design operating conditions. And the efficiency will decrease when the design conditions are not met. There is a maximum and minimum flow rate on the performance curve. 1. Maximum flow rate: The lower the outlet pressure, the greater the gas flow rate. When the pressure drops to a certain level, the gas flow reaches sonic speeds, and it becomes impossible for the flow rate to increase any further. This maximum flow rate is called the stagnation (blockage) flow rate. 2. Minimum flow rate: As the outlet pressure increases, the volume of gas flowing decreases. When this decrease reaches a certain level, unstable operating conditions occur, a phenomenon known as surge. This is the minimum flow rate that is allowed. 3. The stable operating range of a centrifugal compressor is between the surge flow rate and the stagnation flow rate ； The optimal operating range is around the maximum efficiency ； Operation outside the range is prohibited. The performance curve of a centrifugal compressor includes its most important operating characteristics. Operators must be familiar with how to use this curve in order to understand what consequences will arise under different conditions and to have a clear understanding of the situation.