What is the function of a vacuum breaker in a steam turbine?

In a steam turbine, the function of a vacuum breaker is primarily to prevent backflow, which can occur when there is a negative pressure in the system. This device is crucial for maintaining the operational efficiency and safety of the turbine by allowing air to enter the system when a vacuum forms. This prevents potential damage to the turbine components and ensures smooth operation.

While the other options address various aspects of turbine function or performance, they do not accurately describe the role of a vacuum breaker. For instance, increasing water pressure and maintaining constant temperature are objectives that might be addressed by different components or systems within the turbine setup, but they are not the primary function of a vacuum breaker. Additionally, achieving a faster coast down cycle is not typically associated with the purpose of a vacuum breaker; instead, it's focused more on the operational dynamics and stability of the steam turbine system. The primary and correct role of the vacuum breaker is indeed to prevent backflow of steam, safeguarding the integrity and performance of the turbine.