A two-element boiler feedwater regulator is controlled by which two signals?

• A. Steam Flow and Drum Water Level
• B. Steam Flow and Boiler Pressure
• C. Drum Water Level and Feedwater Temperature
• D. Boiler Pressure and Water Level

Answer: (A)

Two signals are used to balance the water being fed with the water that’s being turned into steam. Steam flow tells the regulator how much water is being vaporized and thus how much feedwater is needed to replace it. Drum water level provides direct inventory feedback, showing whether the boiler is under-filled or over-filled and by how much. By using both together, the feedwater regulator can raise or lower the feedwater flow to keep the drum level within a safe, efficient range while responding to changes in steam demand.

This combination specifically captures both the load (how much steam is being produced) and the current water inventory (drum level). A two-element setup doesn’t rely on boiler pressure, which would be more characteristic of a three-element control that adds an additional signal to improve performance under varying loads. Using drum level with feedwater temperature, for example, would miss the immediate steam-demand signal, so it wouldn’t respond properly to changes in how much steam is being generated.