Vacuum pump performance indicators

1. VACUUM The vacuum in a vacuum pump refers to the state of a thinner gas whose absolute pressure is less than atmospheric pressure (negative gauge pressure) or less than the local mass density of gas, that is, the number of gas molecules whose gas molecule density in this space is lower than the atmospheric pressure in the area density. The degree of vacuum indicates the leanness of the gas under a vacuum, that is, the absolute value Pv of the negative gauge pressure. The degree of vacuum in the project generally has the following two methods of expression: (1) The absolute pressure household said that the unit is Pa, kPa, MPa, bar, torr. Magnetic pump, diaphragm pump (2) Relative pressure (absolute value of gauge pressure) Pv said, in units of Pa, kPa, MPa, bar, mmH9. Conversion of two ways of representation: 2. Ultimate vacuum (/ K, said the pump's ultimate pressure) Extreme vacuum refers to the vacuum system (except the pump itself), without leakage and deflated conditions, after a long time to ask after pumping, pump inlet can reach the minimum Stable pressure value. The magnitude of the ultimate vacuum depends on the system's own leak or the working fluid pressure of the pump. Ultimate vacuum determines the pump can effectively use a variety of pumping methods of low pressure range of vacuum limits, is an important indicator of vacuum pump selection. 3. Volume flow (also known as the suction rate or volume flow rate, referred to as pumping speed) Volumetric flow Qv refers to the unit of time, the vacuum pump inlet at a specific pressure and temperature gas volume volume, the unit is m3 / h, m3 / min , In3 / s. 4. Start-up pressure The start-up pressure of the vacuum pump indicates that the pump can start non-destructively and obtain pump inlet pressure for suction. This value for different pumps are quite different. Some pumps start at atmospheric pressure and some require a vacuum to start. 5. The maximum working pressure corresponds to the maximum gas flow inlet pressure. Under this pressure, the pump can work continuously without being damaged. 6. Maximum Exhaust Pressure The maximum exhaust pressure is the allowable exhaust pressure of the vacuum pump for normal operation. When the pump l: 1 pressure exceeds this value, the pump will lose pumping capacity. 7. When asked to ask the vacuum system to reduce the pressure from the atmospheric pressure to a certain pressure when asked. (1) rough vacuum, low vacuum pumping time calculation In the rough vacuum, low vacuum, vacuum equipment, the inner surface of the gas output and the total gas load compared to negligible. Therefore, in rough vacuum, low vacuum calculation of extraction time generally do not need to consider the impact of the gas. Simple exhaust system consists of vacuum chamber, piping and vacuum pump is composed of three parts. Pump pumping speed constant pumping time calculation. Vacuum equipment from pressure P. The pumping time required to descend to the household is: S≈Sp when the conductance is large (U "Sp,), where f is the exhausting time, S; V is the volume of the vacuum equipment, L ; S - Pump effective pumping speed, L / s; Sp - Pump pumping speed, L / s; p - Equipment after pumping pressure at time t, Pa; Pi - Pa; P0 - the ultimate pressure of the vacuum chamber, Pa; U - the conductance of the conduit, the conductance indicates the ability of the vacuum conduit to pass through the gas, and at steady state the conduit conductance equals the conduit flow divided by the conduit 2 End pressure difference, L / s. ② mechanical pump suction time calculation. Mechanical vacuum pump chamber from the atmospheric pressure began to pump, in the low vacuum area, mechanical pump pumping speed with the vacuum drop. The pumping time is calculated using the following formula £ - Pumping time, s; Sp - Pump pumping speed, L / s; V - Vacuum equipment volume, L; p - Pa; P0 - the ultimate pressure of the vacuum device, Pa; Pi - the pressure when the device starts pumping, Pa; Kq - the correction factor, See Table 2-18. Table 2-18 Kq value p / Pa 105 to 104 104 to 103 103 to 102 102 to 10 10 to 1 Kq 1 1.25 1 to 5 2 4 (2) Calculation of evacuation time under high vacuum In the field of high vacuum, the inside of the vacuum equipment Of the outgassing can be ignored, the vacuum chamber of the exhaust time calculation and low vacuum exhaust calculation the same. Due to the high vacuum pump pumping speed, this time is very short. In fact, high vacuum pumping time, mainly depends on the material outlet. attenuation. Calculating the time required to reach a certain pressure is determined by the ratio of the total output to the effective pumping speed of the pump (or unit). Can be used to check the material outlet rate curve and drawing method to calculate.

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