What component in the three-element feedwater control system develops a pneumatic output signal proportional to the difference between its outputs?

In a three-element feedwater control system, the steam flow/feed flow differential relay plays a crucial role by developing a pneumatic output signal that is proportional to the difference between the outputs of steam flow and feedwater flow. This component effectively measures the imbalance between the steam being produced and the amount of feedwater being supplied to the boiler.

When steam is generated in the boiler, it creates a demand for feedwater that must be met to ensure optimal performance and prevent issues like water carryover or boiler damage. The differential relay continuously compares these two flows, calculating the difference and adjusting the signal accordingly to maintain the necessary balance. This precise control is vital for boiler stability and efficiency, allowing the system to react dynamically to changes in demand or operating conditions.

The other components, while important in the feedwater control system, do not specifically develop a pneumatic output signal based on the difference between outputs as described in the question. For instance, the boiler drum level controller primarily focuses on maintaining the appropriate water level in the drum rather than comparing flows, while the feedwater pump controller regulates or controls the speed of feedwater pumps based on other parameters. The temperature controller is concerned with maintaining temperature conditions and doesn’t perform the specific function of comparing flow rates as designed in the