In a multi-stage centrifugal compressor, the volumes of the stages are typically which of the following?

• A. The stages increase in volume with each stage
• B. The stages decrease in volume with each stage
• C. The stages are identical in volume
• D. The stages vary widely and unpredictably

Answer: (C)

In a multi-stage centrifugal compressor, the same mass of gas passes through every stage in sequence, so making each stage the same size and volume helps ensure each stage contributes a similar amount of work and a similar pressure rise. Identical stage volumes mean the flow area, diffuser geometry, and velocity are matched across stages, giving a predictable, uniform head per stage and a clean overall pressure increase when the stage heads multiply. If stages varied in volume, some stages would take more or less energy, creating uneven loading, reduced efficiency, and control challenges as the gas wouldn’t raise pressure evenly through the stack. Extreme variation or unpredictable stage sizes would disrupt flow matching and could lead to instability or surge. Therefore, identical stage volumes are the standard design approach.