Which system is employed to control steam pressure in boilers?

The correct answer is the automatic pressure control systems. These systems are designed to continuously monitor the steam pressure within a boiler and make real-time adjustments to maintain the pressure at a set point, ensuring the safe and efficient operation of the boiler. They utilize control loops that can automatically activate or deactivate burners, adjust feedwater supply, and manage combustion air to keep steam pressure consistent, which is crucial for the reliable performance of steam systems.

In contrast, manual pressure control systems require operators to make adjustments, which can lead to delays and human error, particularly during dynamic operational conditions. Hybrid pressure control systems combine elements of both manual and automatic controls but are less common and do not provide the same level of responsiveness as fully automatic systems. Emergency pressure control systems are generally designed for situations where pressure exceeds safety limits and involve safety measures rather than routine operation, thus they do not serve the primary function of maintaining normal pressure levels. Automatic pressure control systems are essential in modern boiler operations for their efficiency and safety features.