What is the difference between absolute, Gauge and vacuum pressures?

To answer this question let us know the various types of pressures

1) Atmospheric pressure

2) Absolute pressure

3) Gauge pressure

4) Vacuum pressure

Atmospheric pressure:

The atmospheric pressure exerts a normal pressure upon all surfaces with which it is in contact, and is known as atmospheric pressure.

It varies with altitude and it can be measured by means of a barometer.As such it is also called "Barometric pressure".

Absolute pressure: -

When pressure is measured above absolute zero it is called absolute pressure. All values of absolute pressure are positive. The lowest absolute pressure which can probably exist corresponds to absolute zero or complete vacuum.

Gauge pressure: -

When pressure is measured either above or below atmospheric pressure as a arbitrary datum then it is called as gauge pressure. All pressure gauges read zero when open to atmosphere.
Pressure gauges read only the difference between, pressure of a fluid to which they are connected & atmospheric pressure.

Vacuum pressure:-

If pressure of a fluid is below atmospheric pressure it is designated as vacuum pressure. Its gauge value is the amount by which it is below the atmospheric pressure. A gauge which measures vacuum pressure is vacuum gauge.

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