What is a key characteristic of high pressure feedwater heaters?

High-pressure feedwater heaters are designed to operate at significant pressures that can be found in modern steam systems. As a result, a key characteristic of these heaters is their ability to withstand the feed pump discharge pressure. This is crucial because high-pressure feedwater heaters must effectively handle the high pressures generated by the feed water pump to ensure safe and efficient operation.

These heaters work by preheating the feedwater before it enters the boiler, improving the overall efficiency of the system. The ability to withstand these pressures also indicates that the materials and construction of the heaters are robust enough to handle the stresses imposed by these operating conditions.

In contrast, other options don't align with the fundamental function and characteristics of high-pressure feedwater heaters. For instance, operating at ambient pressure would not suffice for high-pressure systems, and being located upstream of the pump does not accurately represent their typical placement or function within the system. Additionally, while they do enhance efficiency, they do not eliminate the need for boiler feedwater; rather, they optimize its temperature before it enters the boiler.