译文：
一、泵的抽速定义为在一定的吸入压力下，单位时间通过泵口被抽除的气体的体积。一个完正的真空系统，不论是为了何种应用，都应有一个需要抽成真空的容器或室体，一套真空机组，也可能是一台真空泵，还有连接管道、阀门、冷阱等。而管道、阀门、冷阱等作为组成真空系统的部件，对气体的流动都有一定的阻碍作用。反过来说它们对气体的流动都有一定的通导能力，这种能力称之为流导。这在气体的流动中是一个很重要的概念，它的定义为单位压差下的流量。气体的自然流动总是从高压流向低压，上述任一部件，当两端的压力分别为P1、P2时，而流过的气体量为Q，则该部件流导 U=Q/(P1-P2) 不同的真空系统部件的流导可以通过计算、模拟、测量等方法确定，它除了与几何形状有关外，还与气体的流动状态有关。不同部件的流导是可以进行串并联的。 真空泵是为了抽除真空容器内的气体，但往往泵的抽气口不能直接与被抽容器相连接，由于工艺上的需要或是降低有油蒸汽污染的真空机组的污染程度，必须通过冷阱、阀门、管道才能与被抽气容器连接，由于每种真空部件都有确定的流导，所以可以说泵必须通过一定的流导才能与被抽容器连接，如图所示，泵与真空室之间的连接管道可以包括冷阱和阀门等。假定泵与真空室之间的流导为U，则泵必须通过流导U才能对真空室抽气，其抽气能力要受到限制，此时对容器的抽气作用真正有意义的应是真空室抽气口处的有效抽速S0。 上式称之为真空基本方程，它是真空系统设计中所依据的基本规律。 根据真空基本方程，可从数学上得到两个极端的结果，即当流导U非常大时，真空室的有效抽速S0可以近似等于泵的抽速S；当泵的抽速S非常大时，或者流导U非常小时，真空室的有效抽速S0近似等于流导U。上述结果从物理上可能更易理解，从真空室抽气口抽除的气体必须经过流导U（即管道、阀门等）才能被真空泵抽除，只不过被抽除的气体从真空室抽气口向泵口运动过程是从高压向低压的流动，而从泵口被抽除是从低压向高压的基于某种抽气原理的强制流动。如流导U非常大，即通过它的气体量不受限制，那么泵的抽气能力就决定于自身的抽速大小，这与泵口直接与真空室相连接是一样的。但如果泵的抽速非常大，这也就是相对于泵的抽速流导U非常小，此时泵的实际抽气能力并不决定于它的抽速大小而决定于气体通过流导U的能力，流导的数值恰为泵的有效抽速S0。 为了尽量发挥泵的抽气能力，{zd0}限度的加大流导U是xxx的方法，但往往难于实现。而一味增大泵的抽速更不切实际。所以采用昼量大的流导和选用昼量大的抽速的泵就非常值得权衡。从真空基本方程可以知道，有效抽速S0随S或U都是单调递增的函数。真空基本方程描述的内容并不深奥，但也没有浅显到可以作为每个人的常识，所以在不少的应用领域，用户往往忽略流导对泵抽速的限制，而造成真空技术应用的效果大受影响。 二、对于一个没有漏气，也没有放气的真空系统如真空室体积为V，真空室有效抽速为S0，则随着抽气的过程，真空室内压力随时间遵从如下的变化规律 以上规律揭示，每经过约的时间，真空室内压力降低一个数量级，显然t越小，压力下降越快，当V一定时，有效抽速S0越大，才能越小。 然而没有一个真空系统是不漏气，不放气的，即使真的不漏气，放气总是存在的，实际上（3）式反映的是泵在抽除真空室内空间气体的过程中压力的变化规律。当压力较高时，系统的漏气量和放气量相对空间的气体量较小时，其影响可以忽略，可以认为近似满足不漏气和不放气的条件，也就是（3）的规律能近似成立。当压力较低时，系统的漏气量和放气量不可忽略甚至成为主要的气体负载时，（3）的规律就要发生偏离，表现在压力下降变为缓慢，一般发生这一转变的压力在0.5Pa左右，因此一个真空系统典型的抽气过程先是压力下降很快，到某一压力开始变慢。由于一个合格的真空系统对其漏率有严格的要求，所以放气是影响系统压力降低的主要因素，而放气是一个缓慢的过程，即使采用烘烤等强化措施，要达到某一预定的压力，往往要经过很长的时间。 任何真空系统都希望尽量缩短抽气的时间，这关系到提高效率和降低能耗，但并不是所有的真空应用都具有缩短抽气时间的条件。可以把不同的真空应用分为两大类：一类是不改虑系统内的放气量，而只有真空度的要求；另一类是要求真空室内充分的放气，即放气率要降到某一临界值。这两类不同的应用对泵配置的要求是不一样的。对于前一类应用，如真空度要求在0.5pa以上，只要时间常数足够的小，便可昼量缩短抽气的时间。但如真空度要求在0.5Pa以下，就必须改虑放气对压力变化的影响。放气量随时间的变化缓慢。特别是在无烘烤的情况下。要在预定较短的时间内达到较高的真空度，就必须以较大的抽速抽除较大的放气量。也就是说如放气量为Q，泵的有效抽速为S0，则可达到平衡压力P=Q/S0。如平衡压力确定，则达到的时间越短，要求泵的有效抽速就越大。蒸发镀膜就是典型的这类的应用，由于蒸镀的速度快，时间短，所以不考虑放气量的影响（即活性气体的影响）。但蒸发粒子的能量低，要求绝大部分粒子无碰撞地沉积到工件上，以保证结合力及减少散射，这就要求真空室内的平均自由程不小于蒸发源到工件的距离，与此相应的压力约在1×10-2Pa，这便是蒸发镀膜对真空度的要求。 如何在尽量短的时间内达到这一压力，就对泵的有效抽速提出了要求，原则是时间越短，由于放气量越大，有效抽速就要求越大。所以蒸发镀膜一般配置抽速强大的油扩散泵机组，功率有数十千瓦，几分钟至十几分钟内便可达到工作真空度，但该系统对工件造成的油蒸汽污染是难以避免的，特别是塑料金属化膜层易发黄。目前涡轮分子泵抽速满足不了大型蒸发镀的需要。而大抽速的低温泵又是工业化规模镀膜所承受不了的。根据被抽空间气体负载的特性，利用分子增压泵抽除{yj}性气体，结合低温冷凝水捕集泵抽除水蒸汽，有望实现大抽速获得清洁真空的全新抽气工艺。真空室内压力在0.5Pa以上时，主要气体成份是{yj}性气体，而0.5Pa以下的主要气体成份是水蒸汽（90%）。由于分子增压泵具有超强的中真空抽气能力，从100Pa到0.5Pa抽气时间极短，而在0.1Pa以后启用低温冷凝水捕集泵，可在较短时间内使室内压力降低1个数量级，达到1×10-2Pa。对于3-5m3的大型蒸发镀膜设备，配置3-4台1000升/秒的分子增压泵和一台功率5kw的低温冷凝水捕集泵便能实现上述的抽气工艺，这无疑具有开创性。对于后一类应用，由于放气量变化依赖于温度和时间，而与气相空间的压力关系不大，只要压力低于现存吸附量所对应的平衡压力即可，一般在抽气过程中均满足此条件。因此，用强劲的抽速即使在很短的时间内把空间压力降至很低，依然不能明显减少真空室内的放气量，而必须配置合适的抽速，在合理的烘烤温度下，在合理的时间内使放气量达到工艺要求的水准，这一般要历经数十分钟的时间。这类应用较为典型的有钛金行业的溅射镀膜和离子镀膜,稀土永磁材料熔炼等。其中，过量的活性气体会影响膜层的品质和材料的质量，因此工艺中均有一段较长时间的精抽过程。 对于镀膜室为1m3左右的溅射或离子镀膜设备，一般配置4000升/秒抽速的真空机组，为了促使真空室和工件更快地放气，往往烘烤到300℃的温度。值得强调的是，在钛金镀膜中，泵的抽速大小，泵的特性、抽气工艺及所需的沉积压力之间表现出的辩正关系。在一个镀膜周期中，真空机组的抽气可以分为三个阶段，即精抽阶段，辉光轰击和溅射沉积阶段。精抽的目的是为了减少真空室内的放气量,其结果主要决定于烘烤温度和抽气时间,与空间压力关系不大,特别是压力在同数量级内。因此，主泵的抽速在适当的差异内，精抽的效果是一样的，真空室内的放气率都可降低到相同的水平，尽管所对应的极限真空不同。具体地讲1000升/秒分子增压泵和1500升/秒的涡轮分子泵在这一阶段抽气的效果是相同的。辉光轰击阶段，由于此时放电压力在2Pa左右，一般来讲主泵的抽气能力受到影响，传统地均采用节流的方法以牺牲抽速来换取泵的稳定工作，扩散泵和涡轮分子泵都是如此，尤其是扩散泵抽速损失更大，相应地放电的氩气流量也明显减少。然而这一阶段只有大的有效抽速，大的氩气流量才能获得更好的轰击清洗的效果。在这一点上分子增压泵是有明显的优势。在{zh1}的溅射沉积阶段典型的工作压力为0.5Pa，扩散泵和涡轮分子泵仍需节流，且不说在该种情况下，沉积的压力难于稳定，减小的抽气速率势必要让精抽过程中所达到的活性气体（放气）的分压明显地回升。在放气量一定的情况下，活性气体的分压高低决定了对沉积膜层质量的影响。能以满抽速稳定抽气的分子增压泵，在此又一次显示了它的优越性。 三、不同的真空系统要求的真空度不同。因此往往必须由一套真空机组来完成。即由工作在不同压力范围的真空泵串接起来，高真空一侧的真空泵能达到系统要求的真空度，而低真空一侧的真空泵是直排大气的。显然最简单的真空机组就是一台直排大气的真空泵。但高真空系统一般需要三级机组，中真空一般需要二级机组。一台高真空泵和一台低真空泵难于组成有效的高真空机组。 这有几方面的原因。流量的连续性就是其中之一。高真空泵都有前级耐压的限制，即前级高于某一压力，泵就不能正常工作。而当前级泵达到这一临界压力时，往往抽速会减小，这样前级泵的排气流量可能会小于主泵的排气流量，这种流量的不一致破坏了流量连续性的要求，必然会引起真空机组不能正常工作。但如在高低真空泵之间再连接一台中真空泵，便可起到承上启下的作用，流量连续，而且各泵皆可工作在{zj0}状态。罗茨泵能工作在中真空范围，是最适合的，故又称罗茨增压泵，由于其压缩比不高，正好可连接几Pa至几百Pa的范围。当三级高真空机组进入较高的真空度时，由于主泵的排气流量明显减少，此时仅靠一台较小的前级泵便可维持抽气的连续性，在实际运用中这是经常采用的方法，这样可减少机组的能耗。高真空机组往往需要三级机组的另一个原因归结于高真空泵的吸入压力的限制。泵都有起始工作压强，传统的高真空泵都在几Pa的范围。因此前级泵必须预抽到这一压力主泵才能开始工作。但直排大气的前级泵抽至这一压力往往需要较长的时间，因为随着压力降低泵的抽速在减小，特别是对于周期性抽气的真空机组，对达到工作真空度的时间是有要求的，预抽时间越长，进入工作真空度的时间也越长，故增加一台中真空泵与前级低真空泵配合，可在较短的时间达到主泵可以工作的压力，这样可以使系统尽快地进入工作压力，保证了设备的使用效率。 罗茨泵和油增压泵都可以作为中真空泵，分子增压泵有极高的压缩比，这除了使它能获得清洁真空外还具有优异的高真空性能，同时在中真空范围也有超强的抽气能力。这就使分子增压泵成为目前{wy}兼有中高真空性能的真空泵，所以只需要与低真空泵配合便能组成性能堪比三级机组的高真空机组。具体地讲由于分子增压泵耐压高，所以可使前级泵易于处于高流量状态；而分子增压泵吸入压力高，减缓了前级泵的预抽负担。分子增压泵可以在100-50Pa工作，前级泵从大气到这一压力，基本遵从每经过时间压力降低一个数量级的规律，因此，机组可以具有很高的抽气效率。简化高真空机组，取消罗茨泵是分子增压泵的又一个优势。对于较大型的高真空应用设备，也可适当加强前级泵的预抽能力，进一步缩短抽气时间，由于预抽时间与整个排气过程相比很短，所以前级泵的使用时间也很短，因此可以兼作多套设备的预抽作用，而这往往是非常现实的。这就使规模化应用的真空机组得到大大的简化。在某些中真空应用中，需要进入10-1Pa范围，这对罗茨泵的二级机组往往难于实现，而使用二级罗茨泵串接的三级机组可使真空度提高一个数量级而进入10-1Pa，所以中真空应用也常用三级机组。由于分子增压泵在10-1Pa可以满抽速，所以亦可以在三级中真空机组中取代两级罗茨泵。一般地讲，长时间工作在中真空的低端压力范围的罗茨泵，分子增压泵可以xx取代。而长时间工作在中真空xx压力范围的罗茨泵相对而言应该较少，因为这一压力范围前级泵往往还具有强劲的抽速。这从宏观上预测了分子增压泵取代罗茨泵的前景。

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原文：
1, the pump pumping speed is defined as a certain suction pressure in unit time through the pump port is the volume of gas extraction. Is a complete vacuum system, whether it is for what application, should have a need to pump into a vacuum container or chamber body, a vacuum unit, it may be a vacuum pump, as well as connecting piping, valves, cold trap and so on. The pipes, valves, cold trap vacuum system such as the composition of the components of the gas flow has a baffling effect. On the other hand they have a certain flow of gas through conduction capacity, this ability is called conductance. This gas flow is a very important concept, which is defined as a unit under pressure flow. Always the natural flow of the gas flow from the high pressure low pressure, one of these components, when both ends of the pressure is P1, P2, and that the amount of gas flowing through Q, then the parts flow conductance U = Q / (P1-P2) Different parts of the flow conductance vacuum system by calculation, simulation, measurement and other methods to determine which in addition to the shape and geometry, but also with the state of the gas flow. Different parts of the flow conductance can be series and parallel. Vacuum pump to vacuum extraction of gases within the container, but often the pump exhaust port can not be directly connected with the vessel have been drawn, as technology reduces the need or vapor contaminated with oil pollution of the vacuum unit, to through the cold trap, valve, exhaust pipe to the container and being connected, because each component has a set of vacuum flow guide, so you can say pumps must be guided by a certain stream and have been drawn to connect the container, as shown, the pump and the vacuum chamber the connection between the pipes and valves may include cold trap so. Assume that the pump and the flow conductance between the vacuum chamber for the U, the pump must flow guide U to exhaust the vacuum chamber, the pumping capacity to be limited, at this time on the role of container extraction should be a truly meaningful vacuum Room exhaust mouth of the effective pumping speed S0. The type known as the basic equation of vacuum, vacuum system design is based on the basic rules. According to the basic equation of the vacuum can be obtained from the mathematical results of the two extremes, that is when the flow conductance U is very large, the effective pumping speed vacuum chamber can be approximately equal to S0 pump pumping speed S; when the pump is very large pumping speed S , or the flow conductance U very hour, the vacuum chamber is approximately equal to the effective pumping speed S0 Conductance U. These results may be easier to understand physically, from the mouth extraction chamber exhaust gas must flow conductance U (ie pipes, valves, etc.) can be vacuum extraction, but is extraction of gas from the exhaust port to the vacuum chamber pump mouth movement is the movement from high pressure to low pressure, but I was extraction from the pump low pressure to high pressure from the exhaust based on a principle of coercive mobility. Such as the flow conductance U is very large, that is unrestricted by the amount of its gas, then pump pumping capacity decided on the size of its pumping speed, which pump port directly connected with the vacuum chamber is the same. However, if the pump pumping speed is very large, it is relative to the pump's pumping speed flow conductance U is very small, the actual pumping capacity of the pump at this time is not determined by the size of its pumping speed depends on gas flow conductance through the U of ability, conductance values appropriate for the pump's effective pumping speed S0. In order to maximize the pump's pumping ability, to increase the maximum conductance U is the most effective method, but often difficult to achieve. Increasing the pump by simply pumping speed is more realistic. Therefore, the flow volume by day day guide and selection of large pumping speed of the pump is very worthwhile trade-off. From the vacuum can know the basic equation, the effective pumping speed S0 with S or U are monotone increasing function. The basic equation to describe the contents of the vacuum is not profound, but not as simple and obvious to everyone's common sense, so in many applications, users tend to ignore the flow conductance of the pumping speed restrictions caused by the effect of a large vacuum technology affected. 2 for a no leak, no gas-vacuum system, such as vacuum chamber volume V, the effective pumping speed vacuum chamber for the S0, then with the extraction process, vacuum chamber pressure with time to comply with the following variation Above the law reveals that after about every time, vacuum pressure in one order of magnitude, the smaller t is clear, the faster the pressure drops, when V is constant, the greater the effective pumping speed S0 can be smaller. However, there is no vacuum system is not leak, tightly gas, even if no leakage, deflation is always there, in fact (3) style reflects the vacuum pump in the extraction process of interior space gas pressure variation. When the pressure is high, the system of gas leakage and the amount of gas is relatively small space of the gases, their impact can be ignored, that the approximation does not satisfy the conditions of gas leakage and tightly, that is, (3) the establishment of the law can approximate . When the pressure is low, the system of gas leakage and the amount of gas can not be ignored or even become a major gas loads, and (3) the law should deviate, and in the pressure drop into a slow change in the pressure of this generally occurs in 0.5 Pa around, so a typical extraction process of the vacuum system pressure drops rapidly at first, to a certain pressure to a slower start. As a qualified vacuum system leak rate to its strict requirements, so deflated that affect the main factor reducing the system pressure, while deflation is a slow process, even with baking and other strengthening measures, to achieve a predetermined pressure, often after a very long time. Any vacuum pumping systems hope to shorten the time it relates to increasing efficiency and reducing energy consumption, but not all applications have reduced exhaust vacuum conditions of the time. Can be applied in different vacuum into two categories: one is not changed within the system put gas into account, and only vacuum requirements; those requiring full deflation vacuum chamber that deflation rate should be reduced to a critical value. Two different types of applications the requirements on the pump configuration is not the same. For the former type applications, such as vacuum requires more than 0.5pa, as long as the time constant small enough, can reduce the exhaust volume time of day. However, if the vacuum requires 0.5Pa the following, we must consider deflation pressure to change the impact of changes. Amount of gas changes with time slowly. Especially in the case without baking. Scheduled to be in a relatively short period of time to achieve high vacuum, it must be larger than the larger pumping speed up pumping gas. In other words, such as amount of gas for the Q, the effective pumping speed for the pump S0, can balance the pressure P = Q/S0. Such as the equilibrium pressure determined, then the shorter the time to require the pump the greater the effective pumping speed. Evaporation is a typical kind of application, due to evaporation speed, time is short, so I do not consider the impact of gas release (ie, the impact of active gas). But the evaporation of low energy particles require no impact to most of the particles deposited on the workpiece to ensure adhesion and reduce the scattering, which requires a vacuum chamber is not less than the mean free path to the workpiece from the evaporation source, and the corresponding the pressure of about 1 × 10-2Pa, which is the vacuum evaporation coating on request. How short a time as possible to achieve this pressure, the effective pumping speed of the pump set forth requirements, the principle is the shorter the time, due to the greater amount of gas, the effective pumping speed requires greater. Therefore, the general configuration pumping speed evaporation coating of oil diffusion pump power unit, there are tens of kilowatts of power, can be reached within a few minutes to ten minutes of working pressure, but caused the system to the workpiece is difficult to avoid the pollution of oil vapor, in particular, metallized plastic film is easy to yellow. Currently turbo molecular pump pumping speed can not meet the needs of large-scale evaporation deposition. The high pumping speed of cryopump is coated by an industrial scale can not afford. Was pumping gas space under the load of the characteristics of a permanent molecular gas booster extraction, combined with low temperature condensate pump trap water vapor extraction is expected to achieve high pumping speed of access to clean and vacuum the new pumping technology. Vacuum chamber pressure 0.5Pa above, the main gas component is a permanent gas, and 0.5Pa following major gas component is water vapor (90%). As the molecule has a powerful vacuum booster pumping capacity, pumping from 100Pa to 0.5Pa very short time, after the opening in the 0.1Pa cold trap condensate pump can reduce pressure in a short time to make a orders of magnitude, reaching 1 × 10-2Pa. For the 3-5m3 of large vapor deposition equipment, configuration, 3-4 sets 1000 l / s molecular booster pump and a power 5kw low temperature condensate pump can trap the exhaust process to achieve the above, this undoubtedly create sex. For the latter application, because changes in discharge volume depends on the temperature and time, pressure and gas space has little to do, as long as the pressure is lower than the existing corresponding adsorption equilibrium pressure can, usually in the exhaust process are to meet this conditions. Thus, the strong pumping speed even in a very short space of time the pressure dropped very low, it was not significantly reduce the amount of gas the vacuum chamber, which must configure the appropriate pumping speed, at a reasonable baking temperatures, in the reasonable period, the amount of gas required to achieve the standards process, which generally after several minutes. Typical of such applications are titanium industry sputtering and ion plating, smelting and other rare earth permanent magnet materials. Where excessive activity of gas will affect the film quality and the quality of the material, so have a longer time to process the fine pumping process. Coating around the room for 1m3 sputtering or ion plating equipment, general configuration 4000 l / s pumping speed of the vacuum unit, vacuum chamber and the workpiece in order to promote faster deflation, often baking temperature to 300 ℃. It is worth emphasizing that in the titanium coating, the pump's pumping speed size, pump characteristics, the exhaust pressure of the deposition process and the required performance out of the debate is between the relations. In a deposition cycle, the vacuum unit's exhaust can be divided into three stages, namely precision pumping stage, glow bombardment and sputtering deposition stage. Finish drawing is intended to reduce the amount of gas the vacuum chamber, the results mainly on the baking temperature and extraction time, pressure has little to do with the space, especially within the pressure in the same order of magnitude. Therefore, the main pump of the pumping speed in the appropriate differences, the essence is the same as the effect of pumping, the vacuum chamber outgassing rate can be reduced to the same level, although the limit corresponding to different vacuum. Specifically, 1000 l / s molecular booster pump and 1500 L / sec turbo-molecular pump exhaust at this stage the effect is the same. Glow bombardment phase, because this time around 2Pa discharge pressure, in general, the main pump pumping ability, the traditional way are used to reduce expenditure at the expense of pumping speed in exchange for the stability of the pump, diffusion pumps and turbo molecular pump is the case, especially the proliferation of a greater loss of pumping speed, the corresponding discharge of argon gas flow rate also decreased. However, this phase only large effective pumping speed, large argon bombardment of traffic to get a better cleaning effect. In this molecule there is a distinct advantage booster pump. In the final stage of a typical sputtering work pressure 0.5Pa, diffusion pumps and turbo molecular pumps still need to cut expenses, not to mention in that case, the deposition pressure difficult to stabilize, reducing the pumping speed is bound to make precision achieved by pumping the process of active gas (discharge gas) partial pressure significantly rebounded. Put gas in certain circumstances, the activity level of the gas partial pressure determines the quality of the deposited film. Full pumping speed and stability can exhaust the molecular booster pump, in which once again shows its superiority. Three different vacuum vacuum system requirements different. Which often must be a vacuum unit to complete. From work in tandem with different pressure range of vacuum pumps up the side of the high vacuum pump to achieve vacuum system requirements, and low vacuum side of the vacuum pump is the vertical atmospheric. Obviously the simplest vacuum unit is a vertical atmospheric vacuum pump. However, the high vacuum system usually takes three units generally require two units of vacuum. A high vacuum pump and a vacuum pump difficult to form an effective low-high vacuum unit. There are several reasons for this. Continuity of flow is one of them. High-pressure pumps are pre-class constraints, that is, a pressure higher than the former level, the pump will not work. The current pump to the critical pressure, often pumping speed will be reduced, so that the exhaust flow before the pump may be smaller than the main pump to the exhaust flow, this flow inconsistencies undermined the flow continuity requirements will inevitably lead to a vacuum unit is not working properly. However, if another connection between the level of a medium vacuum pump, can play a connecting role, continuous flow, and the pump Jieke work in the best condition. Roots vacuum pump can work in the area, is the most suitable, so called Roots Booster, due to its compression ratio is not high, just a few can be connected to hundreds of Pa Pa range. When three high-vacuum unit into a high vacuum, because the main pump to the exhaust flow was significantly reduced, this time only by a small pump can maintain pumping before the continuity, in the practical application of this is often the method used, this reduces the unit energy consumption. High-vacuum unit to another often requires three crew attributed the high vacuum pump suction pressure limit. Pressure pumps are starting work, the traditional high-vacuum pumps are in the range of several Pa. Therefore, pre-pumped before the pump to the pressure of the main pump to work. However, the first level of atmospheric vertical pumping to the pressure required a longer time, because with the lower pressure pump pumping speed in the reduced, especially for the periodic pumping of the vacuum unit, vacuum degree on the work achieved time is required, the longer the pre-pumping into the vacuum of time working longer, it increased by a medium vacuum pump with a vacuum pump with a low level can be achieved in a short time the pressure of the main pump can work, this can the system as quickly as possible into the working pressure to ensure the efficient use of equipment. Roots pumps and oil can be used as the vacuum booster pump, booster pump molecules have high compression ratio, which in addition to the vacuum cleaner so that it can obtain high vacuum also has excellent performance, while in the scope of a powerful vacuum exhaust capacity. This makes molecular booster pump as the only performance both in high vacuum pumps, we only need to be able to form with a low vacuum pump with the performance comparable to three units high vacuum unit. Specifically, the high pressure of molecular booster pump, it can easily pre-pump at high flow state; the molecular booster pump suction pressure is high, slowing the pumps before the pre-pumping burden. Molecular booster pump can work in the 100-50Pa, the former-stage pump to the pressure from the atmosphere, the basic time-pressure to comply with every one order of magnitude of the law, so the crew can have a high pumping efficiency. Simplified high-vacuum unit to remove Roots pump is another advantage of molecular booster pump. For larger high-vacuum equipment, may also be appropriate to strengthen the pre-pre-pump pumping capacity, to further reduce the pumping time, as expected time to process compared with the whole exhaust is very short, so use the time before the pump is also short, it can double as many sets of equipment, pre-pumping effect, which can often be very realistic. This makes large-scale application of vacuum unit are greatly simplified. In some applications, in a vacuum, to enter the 10-1Pa range, which is the secondary roots pump unit are often difficult to achieve, while the use of two cascaded three-level Roots pump vacuum unit can raise and enter an order of magnitude 10-1Pa, it is also commonly used in the three units of vacuum applications. As the molecular booster pump can be filled in the 10-1Pa pumping speed, so also in the three units to replace two Roots vacuum pump. Generally speaking, work long hours in the vacuum of low pressure in the range of the Roots pump, booster pump molecules can be completely replaced. The long working hours in high pressure range of Roots vacuum pumps should be relatively small, because the pressure range before the pump is often also has a strong pumping speed. This is predicted from the macro-molecular pump booster pump to replace the prospect of Roots.