How is a vacuum defined in terms of atmospheric pressure?

A vacuum is defined as any pressure that is less than atmospheric pressure. Atmospheric pressure at sea level is typically defined as 14.7 psi (pounds per square inch). When the pressure in a given environment drops below this level, a vacuum is created, resulting in a pressure that is lower than the pressure exerted by the surrounding atmosphere.

Understanding this concept is crucial in refrigeration systems, as maintaining proper vacuum levels can significantly affect the performance and efficiency of the system. Additionally, this knowledge helps in processes like evacuation prior to charging a refrigeration system, where it’s important to remove moisture and non-condensable gases by creating a vacuum.

In contrast, pressures that are equal to atmospheric pressure, any pressures above it, or those defined only as less than 14.7 psi do not accurately capture the definition of a vacuum according to the field's standard definitions.