The three-element feedwater regulating system uses three measured variables: steam flow, feedwater flow, and water level. Which option lists exactly those three?

The three-element feedwater regulating system uses three measured variables: steam flow, feedwater flow, and water level. Which option lists exactly those three?

• A. steam flow, feedwater flow, and water level
• B. steam pressure, feedwater pressure, and water level
• C. fuel flow, air flow, and flame temperature
• D. temperature, pressure, and humidity

Answer: (A)

In a three-element feedwater regulating system, the control relies on the relationship between boiler load, water level, and the feedwater input. The steam flow signal represents the boiler load—when more steam is demanded, the system must feed more water to maintain level. The water level measurement is the actual process variable the system aims to keep at the setpoint. The feedwater flow is the manipulated variable the regulator adjusts to respond to the load and level changes. So the trio that truly defines this control scheme is steam flow, feedwater flow, and water level. The other options list parameters that aren’t part of this three-element configuration, such as pressure-related or combustion-related variables, which don’t directly drive the feedwater regulation in this setup.

In a three-element feedwater regulating system, the control relies on the relationship between boiler load, water level, and the feedwater input. The steam flow signal represents the boiler load—when more steam is demanded, the system must feed more water to maintain level. The water level measurement is the actual process variable the system aims to keep at the setpoint. The feedwater flow is the manipulated variable the regulator adjusts to respond to the load and level changes. So the trio that truly defines this control scheme is steam flow, feedwater flow, and water level. The other options list parameters that aren’t part of this three-element configuration, such as pressure-related or combustion-related variables, which don’t directly drive the feedwater regulation in this setup.