There are 4 Main Types of Pressure:

1. Absolute pressure.

2. Atmospheric pressure.

3. Differential pressure.

4.Overpressure (gauge pressure)

Explanation:

1.Absolute pressure:

The clearest reference pressure is the 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. For the required differentiation from other types of pressure, it is denoted with the index “abs”, which is derived from the Latin “absolutus”, meaning detached, independent.

2.Atmospheric pressure:

The atmospheric pressure is subject to weather-dependent fluctuations, as is only too well known from the daily weather report. At sea level, pamb averages 1,013.25 hectopascal (hpa), corresponding to 1,013.25 millibar (mbar). With “cyclones” and “anticyclones this pressure varies by about 5 %.

3.Differential pressure:

The difference between two pressures, p1 and p2, is known as the pressure differential, Δp = p1 - p2. In cases where the difference between two pressures itself represents the measured variable, one refers to the differential pressure, p1,2.

Accordingly, in order to measure differential pressure, at first two different pressures are captured in a measuring instrument.

4.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.

A positive overpressure is referred to when the absolute pressure is greater than the atmospheric pressure. In the opposite case, one speaks of negative overpressure.

The indices of the formula symbols “abs”, “amb” and “e” clearly define the reference point of the respective pressure. They are only attached to the formula letter p, and not to the unit symbols.

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