Pressure compounding in turbines

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Pressure compounding is a method where steam pressure is lowered in several steps across multiple stages instead of all at once in one nozzle. It is used in Rateau and Zoelly turbines. The arrangement has a series of simple impulse turbines on one shaft, with the exit from each stage feeding the next nozzle.

Each stage has its own nozzle ring and moving blades. Steam from the boiler first passes through the initial nozzle ring, where its pressure drops and its velocity increases. The high-velocity jet transfers most of its velocity to the first set of moving blades while the pressure stays nearly the same. The steam then goes to the next nozzle ring, where its pressure drops again and its velocity rises again, followed by another moving-blade stage absorbing that velocity. This continues through all stages until the full pressure drop is achieved. The total pressure drop is shared among all nozzle rings, which lowers the velocity of steam entering each blade and helps improve overall performance.