In a three-element feedwater control system, which component develops a pneumatic signal proportional to the actual boiler water level?

The drum level transmitter is responsible for developing a pneumatic signal that is proportional to the actual boiler water level in a three-element feedwater control system. This device continuously monitors the water level within the boiler drum and converts that measurement into a pneumatic signal, which is then used to control the feedwater flow.

The accuracy of the drum level transmitter is crucial for maintaining the appropriate water level, which helps to prevent issues such as carryover of water into the steam system or boiler damage due to low water levels. By ensuring that the pneumatic signal reflects the exact water level, the system can effectively manage the amount of feedwater being supplied to the boiler, enhancing overall efficiency and safety.

In contrast, the feedwater pump is responsible for delivering water to the boiler but does not measure or provide feedback on the boiler level. The control valve regulates the flow of water into the boiler but relies on the signals generated by the drum level transmitter to do so. The safety valve serves a distinct purpose of releasing excess pressure to protect the system from overpressure conditions and is not involved in level measurement.