What is the primary function of the dry pipe in the steam drum?

The primary function of the dry pipe in the steam drum is to enable the final separation of steam and moisture. In a steam drum, water and steam coexist, and the dry pipe plays a crucial role in ensuring that only dry steam is delivered to the superheater or downstream equipment.

As steam rises within the drum, it may carry some moisture with it due to the natural process of evaporation and phase separation. The dry pipe is designed to extend down into the water section of the drum, allowing only steam to pass through while keeping any moisture behind. This process helps to improve the efficiency and performance of the steam system, as dry steam provides better thermal properties for heating and power generation.

The other options, while they are relevant functions in different contexts, do not accurately describe the specific role of the dry pipe. For instance, maintaining constant steam pressure is generally managed by control systems and valves throughout the steam generation process rather than solely by the dry pipe. As for filtering impurities or adding water to the steam system, these tasks are performed by other components such as steam purifiers and feedwater systems.