The selection of vacuum pumps cannot be separated from the calculation formula of vacuum pump selection. A series of data is calculated based on the formula as the judgment basis for enterprise pump selection. How to choose an imported vacuum pump? This requires basic knowledge of vacuum pumps. Today, we will explain in detail some of the knowledge in the calculation formula for selecting imported vacuum pumps:
1, The concept of vacuum
The word "vacuum" comes from the Latin word "vacuum", which originally means "void" or "empty". Vacuum refers to a gas state in a given space that is lower than the atmospheric pressure of the environment, that is, the density of gas molecules in that space is lower than the density of gas molecules in that area's atmospheric pressure, and is not a space without matter. Water ring vacuum pump is applied in the field of low vacuum (105-103 Pa).
The necessity of understanding the concept of vacuum: It helps to understand the application range of vacuum degree when selecting a pump.
2, The measurement unit of vacuum
In vacuum technology, the quantity that represents the degree of gas thinness in a vacuum state is called vacuum degree, which can be characterized by pressure, molecular number density, average free path, and time constant for forming a single-molecule layer, but is usually represented by the pressure (residual pressure) value of the gas. The lower the gas pressure, the higher the vacuum degree; On the contrary, the higher the pressure, the lower the vacuum degree.
The legal unit of measurement for pressure is Pa [Pascal], with the symbol Pa
1Pa=1N. m-2. In addition, the percentage of vacuum degree can also be used as the measurement unit.
δ-- Vacuum degree percentage (%) P - absolute pressure (Pa) Pb P represents the reading of the vacuum pressure gauge, and the gauge pressure (represented by Pe) is the percentage of vacuum degree δ (%) and pressure P comparison table.
※ The necessity of understanding the measurement units of vacuum: It helps to understand the units in the calculation formula for vacuum pump selection and strengthen understanding when selecting a pump.
3, Unit conversion
1atm (standard atmospheric pressure)=1013.25hPa (hPa)
1mm Hg (mmHg)=1Torr (Torr)=1.333 hPa (hPa)
1 bar=1000 hPa
1mbar=1 hPa
1 inHg (inches of mercury)=25.4mmHg (millimeters of mercury)=33.8 hPa (hPa)
※ Understanding the necessity of unit conversion: It helps to better convert the units in the calculation formula for vacuum pump selection when selecting a pump.
4, Related terms
Gas volume - The gas volume of a water ring vacuum pump refers to the volume of gas, in m3/min or m3/h, that passes through the pump at a given vacuum degree at the inlet and an atmospheric pressure of 1013.25hPa at the outlet per unit time.
Maximum gas volume - The maximum gas volume of a water ring vacuum pump refers to the maximum gas volume on the gas volume curve, in m3/min or m3/h.
Vacuum degree (also known as pressure) - The vacuum pump of a water ring vacuum pump refers to the degree of gas thinness at the inlet in a vacuum state, expressed in absolute pressure, Pa, hPa, kPa.
Extreme Vacuum Degree (also known as Extreme Pressure) - The ultimate vacuum degree of a water ring vacuum pump refers to the vacuum degree, Pa, hPa, kPa, when the air flow at the inlet is zero.
Compression ratio - the ratio of gas volume under suction pressure to compressed gas volume
Saturated vapor pressure - the vapor pressure of a substance at a given temperature at which it condenses and coexists in a phase equilibrium state.
The necessity of understanding the relevant terms above: It helps to select the pump that best meets the customer's operating requirements from numerous vacuum pump models when selecting a pump.
