What is vacuum?
According to the dictionary, vacuum is "a space entirely devoid gas or matter", or "a state of nothingness". In scientific terms, a space literally void of matter is known as a "perfect vacuum". However, this state is currently unexplored, and a "perfect vacuum" is more of a theoretical concept. On this point, in the minds of our predecessors, vacuum was simply a pressure lower than atmospheric pressure (i.e. not 1 atm)". Currently, under the JIS definition, vacuum is defined to be "a specific state of a space filled with a gas that is at a pressure below atmospheric pressure". Accordingly, when we breath, the pressure inside our our lungs when they are expanded is below atmospheric pressure, and therefore there is a vacuum inside our lungs. Come to think of it, a kiss also makes use of vacuum. (^_^;)
What kind of state is vacuum?
Vacuum is not a thing; it is a state. A state of vacuum represents pressure. The unit of pressure is the Pascal (Pa). In order to make the condition of a vacuum easy to understand, let's consider the relationships between elevation/altitude and a state of vacuum.
|Elevation/Altitude||Degree of Vacuum||Equiv. Vapor|
|0m||0kPa||Atmosphere at Sea Level|
|333m||4kPa||Atmospheric pressure at ORION Machinery (Suzaka City, Nagano Pref.)|
|3776m||38kPa||Atmospheric pressure at the peak of Mt. Fuji|
|6000m||54kPa||Continuous degree of vacuum of a KRF04A Dry Pump|
|7000m||60kPa||Continuous degree of vacuum of a KRF70 Dry Pump|
|10000m||75kPa||Continuous degree of vacuum of a KRF15 Dry
Pump Airspace around a commercial jetliner
Ultimate pressure of a KHA Series Dry Pump
Ultimate pressure of a KCP Oil-Free Pump
Continuous degree of vacuum of a KHH Dry Pump
Ultimate vacuum of a KCM Oil-Free Pump
|Airspace around a man-made satellite|
※ Note that the written degrees of vacuum show both the atmospheric pressure standard and the absolute pressure standard, using the same units.
For example, the flying altitude of a jetliner is approx. 10,000 m. The vacuum conditions in this airspace is 75 kPa, so if someone uses a KRF15 dry pump, he is producing the same amount of vacuum that occurs in the airspace of a jetliner.