How does a phosphate feeder function in a boiler system?

A phosphate feeder plays a crucial role in boiler systems by adding chemicals that produce a protective film on the internal surfaces of the boiler. This film serves to prevent mineral deposition or scale buildup, which can adversely affect the efficiency and safe operation of the boiler. When water is heated, it tends to precipitate minerals like calcium and magnesium, which can accumulate and create scale.

By utilizing phosphates, the phosphate feeder ensures that these minerals remain suspended in the water rather than settling on surfaces where they can cause problems. This process helps maintain the efficiency of heat transfer and reduces the need for frequent maintenance or cleaning tasks associated with scale removal.

In contrast, the other options do not reflect the primary function of a phosphate feeder. While softening the water supply is an important aspect of water treatment, it is not the direct role of a phosphate feeder. Enhancing the boiler's heating capacity and cleaning out old scale and rust are also not functions attributed to the phosphate feeder; other technologies or processes are typically employed for those needs.