What holds a turbine's carbon packing rings axially?

The correct answer is spring pressure. In a turbine, the carbon packing rings are designed to provide a seal that prevents steam or gas from escaping while allowing rotational movement. Spring pressure ensures that these packing rings are held firmly against the turbine shaft, thus maintaining a tight seal. The tension provided by the springs compensates for wear and thermal expansion, keeping the packing rings in contact with the shaft to prevent leakage.

The effectiveness of this sealing method is crucial for the efficient operation of the turbine, as leaks can result in energy losses and can affect the overall performance of the system. By using spring pressure, the carbon packing can adapt to slight movements and variations in the turbine’s operation, ensuring consistent sealing throughout various operating conditions.