1, the ultimate pressure of the vacuum pump should meet the working pressure of the process. The pump pressure is usually selected to be lower than the process requirements of about an order of magnitude. 2, each pump has a certain range of working pressure, therefore, the pump operating point should be selected within this range, but not allow it to work long hours outside the work pressure. 3, the vacuum pump under its working pressure, should be able to drain away all the gas generated in the process of vacuum equipment. 4, select the vacuum unit: (1) When using a pump can not meet the requirements of suction and vacuum, the need for several pumps combined with each other to meet the process requirements. (2) some vacuum pumps can not work at atmospheric pressure, the need for pre-vacuum; some vacuum outlet pressure below atmospheric pressure, the need for fore-stage pump, it is necessary to use the pump combination. The combination of vacuum pumps, we call the vacuum pump unit, which allows the vacuum system to get a better degree of vacuum and displacement. We should choose the right combination of vacuum pumps, because different vacuum pumps have different requirements on the evacuated gas. For example, a Roots-Rotary Rotor is not suitable for systems with more condensable gases under normal conditions. 5, when you choose oil seal pump, you should first understand your vacuum system is required for oil pollution. If the equipment is strictly required oil-free, should choose all kinds of non-oil pump, such as: water ring pump, cryogenic pump. If the requirements are not strict, you can choose to have a pump, plus some oil pollution control measures, such as adding cold trap, oil trap, baffle, etc., can achieve clean vacuum requirements. 6, to understand the composition of the gas being drawn, the gas contains no condensable steam, 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 steam, particles, and corrosive gases, consideration should be given to installing auxiliary equipment such as condensers, dust catchers, etc. on the pump air inlet piping. 7, when the choice of oil seal vacuum pump, to consider the vacuum pump out of the oil vapor (fumes) on the environment how. If the environment does not allow pollution, should choose oil-free vacuum pump, or the oil vapor to the outside. 8, the vibration generated when the vacuum pump work on the process and the environment have no effect, if the process does not allow, should choose no vibration pump or take anti-vibration measures. 9, the price of the vacuum pump, operation and maintenance costs. After we take into account a variety of circumstances, we can finally determine a solution to your needs: (1) the minimum investment costs. (2) the smallest production and operation costs. (3) A feasible plan that distributes the first two cases reasonably and evenly. The best working range of the vacuum pump Pump Type Oil Seal Mechanical Pump Steam jet pump Roots pump oil booster pump Oil diffusion pump The best working range (105 ~ 10 105 ~ 102 102 ~ 1 1 ~ 10-1 5 × 10-2 ~ 10-4 Laws and Formulas 1. Roots pumping speed of the Roots pump: 2. Selection of the pumping speed of the roughing pump: S = (0.1-0.2) S = S = Q1 / P S = 2.3Kq · V lg / Pa S / S S - Pump Effective Pumping Rate (L / s) S-Roots Pump Effective Pumping Speed ​​(L / s) Q1 - Vacuum System Leakage Rate Pre-vacuum to be achieved (Torr) V- Volume of the vacuum system (liters) t - Time required to reach P pre-Pa Pa - Atmospheric pressure (Torr) Kq - The correction factor is related to the pressure P at the end of the equipment
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