Differences and relationships between gauge pressure, negative pressure, absolute pressure, and static pressure

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Definition of gauge pressure (CG): The difference between the absolute static pressure of a fluid and the atmospheric pressure at the point of measurement. 1. The value by which the total absolute pressure exceeds the surrounding atmospheric pressure. 　　 2. The portion of pressure at a certain point in a liquid that is higher than atmospheric pressure. 　　 3. The pressure indicated by a fluid relative to atmospheric pressure, which can be measured with a pressure gauge, is called gauge pressure; that is: absolute pressure – atmospheric pressure = gauge pressure. 　　 4. In the vacuum industry, “gauge pressure” refers specifically to the relative pressure of a gas as measured by a conventional vacuum gauge (a relative pressure gauge); it is expressed as a negative value and represents the difference between the pressure of the gas in question and atmospheric pressure. It is also called negative pressure. Definition of negative pressure: When the absolute pressure of the airflow is lower than the atmospheric pressure at the same elevation outside the well or duct, its relative pressure is negative, and this is referred to as negative pressure. Simply put, “negative pressure” is a gas pressure condition that is lower than normal pressure (i.e., one atmosphere). That is what we commonly refer to as “vacuum”. 1. Pressure lower than the existing atmospheric pressure (taken as the reference zero). 2. Low density below atmospheric pressure. In mines with extractive ventilation, the absolute pressure of the airflow is lower than the absolute pressure at the same elevation outside the mine or outside the air ducts; its relative pressure is negative, and this is referred to as negative pressure. In industry, this concept is often relevant when selecting micro pumps – such as micro vacuum pumps, micro air pumps, micro gas sampling pumps, micro gas circulation pumps, and micro vacuum pumps. Definition of gauge pressure (CA): It refers to absolute pressure, which is the total pressure present in the space where the medium (liquid, gas, or vapor) is located. Absolute pressure is the pressure relative to zero pressure. Correspondingly, gauge pressure (relative pressure): if the difference between absolute pressure and atmospheric pressure is a positive value, then this positive value is the gauge pressure; that is, gauge pressure = absolute pressure – atmospheric pressure > 0. If it is a negative value, it is referred to as vacuum level. Definition of static pressure (HP): the local pressure of a moving fluid. Pressure in a medium in the presence of sound waves. In fluid mechanics, it refers to: 1. The pressure generated by a fluid when it is at rest. 　　 2. The pressure generated by a fluid in motion, perpendicular to the direction of its flow. 　　 3. The gauge pressure value measured in a fluid, unaffected by the flow velocity. Definition of differential pressure (CD): The difference obtained by subtracting the pressure measured at the high-pressure side from that measured at the low-pressure side of a differential pressure transmitter is called differential pressure. Simply put: Definition of pressure: The concept of pressure here actually refers to the physical quantity of pressure, that is, the amount of force per unit area. Absolute pressure: Pressure measured with respect to the absolute pressure zero point, being higher than that zero point. Positive pressure: Pressure that is higher than atmospheric pressure, measured with atmospheric pressure as a reference. Negative pressure (vacuum): A pressure that is below atmospheric pressure, measured with atmospheric pressure as the reference. Differential pressure: The difference between two pressures. Gauge pressure: Pressure that is greater than or less than atmospheric pressure, measured with atmospheric pressure as a reference. Gauge: A device that uses atmospheric pressure as a reference to measure pressures that are either lower or higher than atmospheric pressure. Conversion formula: Relative vacuum level = Standard atmospheric pressure – Vacuum level. For example, if the vacuum level is 80 KPa, then the relative vacuum level is approximately 100 – 80 = 20 KPa; thus, it will be displayed as -0.02 MPa on a relative vacuum gauge. Appendix: Pressure unit conversions: 1 Pa = 1.02×10-5 Kgf/cm2 = 1×10-5 bar = 0.01 mbar = 9.87×10-6 atm = 7.5×10-3 torr = 4.01×10-3 inH2O = 7.5×10-3 mmHg = 1.45×10-4 PSI