To overcome boiler pressure, feed water pumps are usually?

Feed water pumps are typically designed to overcome boiler pressure and ensure efficient operation of the boiler system. Positive displacement pumps are particularly effective in this role because they work by trapping a fixed volume of fluid and then forcing it into the discharge line with a specific pressure, regardless of the resistance in the system. This characteristic allows them to maintain a constant flow rate, which is crucial for feeding water into boilers that operate under high-pressure conditions.

In contrast, centrifugal pumps, while commonly used in various pumping applications, rely on rotational energy to move water and may not maintain a consistent flow against varying pressures as effectively as positive displacement pumps do. Rotary and diaphragm pumps may also have their uses, but they do not have the same robustness for handling the high pressures found in boiler systems as positive displacement pumps specifically engineered for this purpose.