What is the primary function of a vacuum pump in a boiler system?

The primary function of a vacuum pump in a boiler system is to draw condensate back from the system. When steam is generated and used, it condenses into water, known as condensate, which needs to be efficiently returned to the boiler to maintain system efficiency and performance. The vacuum pump creates a negative pressure environment that facilitates the movement of condensate from the system back to the boiler.

This process is crucial as it helps in maintaining the system's water level, aids in preventing water hammer, and enhances the overall efficiency of the boiler system. By ensuring the condensate is returned promptly, the boiler can generate steam more effectively and reduces the amount of fresh water needed to replace the steam that has been used.

The other options focus on functions that do not accurately describe the role of a vacuum pump. For instance, increasing pressure is typically a function of a feedwater pump or the boiler itself, circulating water is within the realm of circulation pumps, and removing air from water lines, while important, is not the primary function of a vacuum pump in a boiler system.