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# Knowledge of vacuum degree

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The density of the gas in the vacuum state is usually represented by 'high vacuum degree' or 'low vacuum degree'. High vacuum degree indicates a 'good' vacuum degree and low vacuum degree indicates a 'poor' vacuum degree.

If the pressure inside the equipment measures lower than the atmospheric pressure, then the measurement of the pressure requires a vacuum gauge. The reading on the vacuum gauge is called the vacuum degree. The value of the vacuum degree indicates to what extent the actual system pressure is lower than the atmospheric pressure, i.e. vacuum degree=(atmospheric pressure - absolute pressure)/pg, wherein: p is liquid density and g is gravitational acceleration. By definition, 'Vacuum degree' is the degree of vacuum. It is the main parameter of such vacuum-pumping equipment as vacuum pumps, mini vacuum pumps, mini air pumps, mini air extracting pumps, mini air extracting and inflating pumps, etc. The so-called 'vacuum' refers to a gas state where the pressure is lower than 101,325 Pascals (a standard atmospheric pressure of about 101KPa) in a given space. In a vacuum state, the density of the gas is usually represented by the pressure value of the gas. It is clear that the smaller the pressure value, the more rarefied the gas.

The first identification method is to use 'absolute pressure' and 'absolute vacuum degree' (how much the gas exceeds the 'theoretical vacuum' in pressure); in reality, the absolute pressure value of a vacuum pump is between 0-101.325KPa. The absolute pressure value needs to be measured by an absolute pressure instrument. The initial value of an instrument for measuring vacuum degree (an absolute vacuum gauge) is 101.325KPa (a standard atmospheric pressure) at 20℃ and an altitude of 0.

The second method is to use 'relative pressure' and 'relative vacuum degree' (how much the gas pressure is lower than the 'atmospheric pressure'). 'Relative vacuum degree' refers to the difference value between the pressure of the measured object and the atmospheric pressure in the measured location. It should be measured by an ordinary vacuum gauge. The initial value of the gauge is zero in a state without vacuum (the atmospheric state). In case of measuring the vacuum, its value is within the range of 0 to -101.325KPa (usually indicated by negative numbers).

'Vacuum degree', commonly used in the international vacuum industry, is also the most scientific term and is identified with absolute pressure; it refers to 'ultimate vacuum, absolute vacuum degree or absolute pressure', but 'relative vacuum degree' (relative pressure, pressure of vacuum gauge, negative pressure) is also widely used because its measurement method is simple and the measuring instrument is common, available and inexpensive.

Common units for vacuum degree are Pa, Kpa, Mpa, atmospheric pressure, kg (Kgf/cm2), mmHg, mbar, bar, PSI and the like. The approximate conversion relationship is as follows:

1MPa=1,000KPa

1KPa=1000Pa

1KPa=1,000Pa

1 atmospheric pressure=100KPa=0.1MPa

1 atmospheric pressure=1 kg (Kgf/cm2)=760mmHg

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