Most industrial steam systems are closed systems. When water vaporizes to become steam in the boiler, the expansion pressurizes the system. Steam is forced out of the boiler by its own pressure and is carried by piping to whatever devices are to be employed for heating or processing. The pressure changes within the system provide transportation for the steam and also affect its physical properties. To learn more about how these properties are affected by pressure and how various properties of steam are related to other properties, click on the selections in the left sidebar. The following measurements are expressed as imperial values. To view these pages in SI metric units, click here.