What equipment is typically used to position the feedwater valve in a three element control system?

In a three-element control system, the feedwater valve is positioned using a computing relay. The role of the computing relay is crucial in controlling the operation of the feedwater flow based on three inputs: the drum level, the steam flow, and the feedwater flow.

The computing relay processes this data to determine the precise position for the feedwater valve to maintain the desired drum level, ensuring balance between the steam production and the water input. This level of control is necessary for optimizing boiler performance and efficiency, preventing issues such as low water levels that can lead to serious operational problems.

While other equipment, such as a drum level transmitter and a water flow transmitter, provides valuable feedback, they merely measure parameters rather than position the valve. Similarly, a steam pressure regulator is focused on managing the pressure of the steam, which is not the primary function needed for valve positioning in this specific control system. Therefore, utilizing a computing relay effectively integrates the various inputs to control the feedwater valve accurately and maintain the proper steam generation process.