Pressure less than atmospheric pressure can be referred to by different terms in different contexts. These terms include suction pressure, vacuum pressure, and negative gauge pressure. Let's understand each term in detail.

Suction Pressure:
Suction pressure is the pressure exerted by a fluid when it is being sucked or drawn into a system. It is the difference between the pressure at the inlet of the system and the pressure at the outlet. Suction pressure is usually less than atmospheric pressure.

Vacuum Pressure:
Vacuum pressure is the pressure that is less than atmospheric pressure. It is measured with respect to the absolute vacuum, which is the complete absence of pressure. Vacuum pressure is often used in applications where a fluid must be drawn or sucked into a system.

Negative Gauge Pressure:
Negative gauge pressure is the difference between the pressure at a particular point and the atmospheric pressure. It is usually expressed in negative values. Negative gauge pressure is often used in applications where the pressure at a specific point needs to be measured relative to the atmospheric pressure.

All of these terms refer to pressure less than atmospheric pressure, but they are used in different contexts. Suction pressure is used when a fluid is being drawn into a system, vacuum pressure is used when the pressure is measured with respect to the absolute vacuum, and negative gauge pressure is used when the pressure at a specific point needs to be measured relative to the atmospheric pressure.

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