Theory bites are a collection of basic hydraulic theory and will touch upon pump design and other areas of pump industry knowledge.
Absolute pressure: The clearest reference pressure is pressure zero, which exists in the air-free space of the universe. A pressure which is related to this reference pressure is known as absolute pressure.
Overpressure (gauge pressure): The most frequently measured pressure in the technological field is the atmospheric pressure differential, Pe (e=excedens = exceeding). It is the difference between an absolute pressure, Pabs, and the relevant (absolute) atmospheric pressure (Pe = Pabs – Pamb) and is known, in short, as the overpressure or gauge pressure.
Atmospheric pressure: The probably most important pressure for life on earth is the atmospheric pressure, Pamb. It is created by the weight of the atmosphere which surrounds the earth up to a height of approx. 500 km. Up to this altitude, its magnitude decreases continuously.
Source: WIKA & ScienceStruck
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