How are vacuums typically created in a boiler or pressure vessel?

A vacuum in a boiler or pressure vessel is typically created when steam within a closed system cools down. As steam condenses back into water, it leaves behind a space that was previously occupied by steam, resulting in a decrease in pressure within the vessel. This reduction in pressure creates a vacuum condition because the pressure inside the vessel is now lower than the atmospheric pressure outside.

The process of cooling steam leads to the formation of a vacuum because the steam’s conversion back to water not only reduces the amount of vapor present but also lowers the absolute pressure. Understanding this principle is critical for those working with boilers and pressure vessels, as it directly affects operations and safety protocols.