1, the working pressure of the vacuum pump should meet the ultimate vacuum vacuum equipment and work pressure requirements. Such as: vacuum coating requires 1 × 10-5mmHg of vacuum, the vacuum of the vacuum pump used at least 5 × 10-6mmHg. Usually choose the degree of vacuum pump is higher than the degree of vacuum vacuum equipment to an order of magnitude. 2, the correct choice of vacuum pump working point. Each pump has a certain range of working pressure, such as: diffusion pump 10-3 ~ 10-7mmHg, in such a wide range of pressure, pump pumping speed varies with pressure, and its stable working pressure range of 5 × 10 -4 to 5 × 10 -6 mmHg. Therefore, the operating point of the pump should be selected within this range, but can not let it long-term work under 10-8mmHg. Another example of titanium sublimation pump can work under 10-2mmHg, but its working pressure should be less than 1 × 10-5mmHg as well. 3, the vacuum pump in its work pressure, should be able to drain away all the gas generated in the process of vacuum equipment. 4, the correct combination of vacuum pump. Due to the vacuum pump selective suction, therefore, sometimes the choice of a pump can not meet the pumping requirements, the need for several pump combinations, complement each other to meet the pumping requirements. Such as titanium sublimation pump high hydrogen pumping speed, but can not helium, and the triode sputtering ion pump, (or bipolar asymmetric cathode sputtering ion pump) has a certain pumping speed argon, both When combined, the vacuum will get a better degree of vacuum. In addition, some vacuum pumps can not work under atmospheric pressure, requiring pre-vacuum; some vacuum pump outlet pressure below atmospheric pressure, the need for fore-stage pump, it is necessary to use the pump combination. 5, vacuum equipment, oil pollution requirements. If the equipment is strictly required oil-free, should choose a variety of oil-free pumps, such as: water ring pump, molecular sieve adsorption pump, sputtering ion pump, cryogenic pump. If the requirements are not strict, you can choose a pump, plus some anti-oil pollution measures, such as adding cold trap, baffle, oil well, etc., but also to achieve clean vacuum requirements. 6, to understand the composition of the gas being drawn, the gas containing non-condensable vapor, whether the particles of dust, whether or not corrosive. When choosing a vacuum pump, you need to know the gas composition and select the appropriate pump for the purged gas. If the gas contains vapors, particles, and corrosive gases, consideration should be given to installing auxiliary equipment such as condensers, dust catchers, etc. on the pump inlet piping. 7, the vacuum pump out of the oil vapor on the environment how the impact. If the environment does not allow contamination, you can choose oil-free vacuum pump, or the oil vapor to the outside. 8, the vibration generated by the vacuum pump on the process and the environment have no effect. If the process is not allowed, should choose no vibration pump or take anti-vibration measures. 9, the price of the vacuum pump, operation and maintenance costs. [Water ring vacuum pump selection] A pump type to determine the type of pump is mainly required by the work of the gas, vacuum or exhaust pressure may be. Pump work, you need to pay attention to the following two aspects: 1, as far as possible in the high efficiency area, that is, critical vacuum or critical discharge pressure in the region. 2, should be avoided in the maximum vacuum or maximum exhaust pressure near the operation. Operating in this area is not only inefficient but also unstable and prone to vibration and noise. Cavitation occurs frequently in vacuum applications where the vacuum is high, and the obvious hallmark of this phenomenon is noise and vibration in the pump. Cavitation can cause damage to the pump body, impeller and other parts, so that the pump can not work. According to the above principle, when the pump required vacuum or gas pressure is not high, priority can be selected in the single-stage pump. If the vacuum or exhaust pressure is high, the single-stage pump often can not meet, or require the pump at higher vacuum conditions still have a larger amount of air, which requires the performance curve at a higher degree of vacuum is flatter, the choice of two Pump. If the degree of vacuum required in -710mmHg above, the optional water ring - air pump or water ring - Roots vacuum unit as a vacuum device. If only for the vacuum pump, the single-use pump is better. Because the single-action pump is simple in construction, easy to manufacture and maintain, and has good resistance to cavitation under high vacuum conditions. If only for larger compressor use, then the choice of double-acting pump more appropriate. Because the dual-acting pump has the advantages of large gas volume, small size and light weight, the radial force can be automatically balanced, the shaft is not prone to fatigue fracture, and the pump has a longer service life. Second, according to the amount of gas required for the system to select the vacuum pump After the initial selection of the type of pump, the vacuum pump, but also according to the amount of gas required to system selection of pump models.
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