Weitbereich-Turbomolekularpumpen und Membranvorvakuumpumpen als trockene HV- und UHV-Pumpsysteme

The development of new turbomolecular pumps with increased critical backing pressures up to 30 mbar made it possible to use oilfree diaphragm pumps as backing pumps. The combination of a wide-range turbomolecular pump with a diaphragm pump represents an inexpensive, compact and technical dry vacuum pumping system for high and ultrahigh vacuum applications. The interaction of wide-range turbomolecular pumps with diaphragm pumps is discussed in terms of gas throughput, compression ratio, ultimate pressure and power consumption of the turbomolecular pump and selection criteria for the diaphragm backing pump are shown.     

Kenngrößen von Turbo‐Molekularpumpen

Graphs of “high‐vacuum pressure as a function of backing pressure” (“p_HV versus p_VV”) and “compression as a function of backing pressure” (“K versus p_VV”) are presented in this article. The performance of any turbomolecular pump can be fully and reliably evaluated with the aid of these graphs. Until now these graphs have only seldom been shown in catalogs. The catalogs generally lack the so‐called “limit lines” (“Q as a function of p_{VV, Kmax}”). For a prescribed gas throughput Q, the limit line indicates what minimum pressure must be generated by the backing pump at the fore‐line port of the turbomolecular pump so that a stable pressure exists at the high‐vacuum side of the turbomolecular pump. Using the gas‐type‐specific limit line and the corresponding, usually well‐documented pumping‐speed curve, one can already describe the functional proficiency and performance of a selected combination of turbomolecular pump plus backing pump in an approximate manner – but not yet completely. In this article we also indicate analytical functions which excellently describe the pressure dependence of the compression and pumping speed.     

串联分子泵获得10-9 Pa真空的实验研究

介绍了采用两级分子泵串联系统获得10^-9Pa真空度的实验研究。实验证明，通过串联一台分子泵，可以有效地提高系统对氢气的压缩比，显著提高系统的极限压强。     

Characterisation of a turbo-molecular pumps by a minimum of parameters

The design of complex vacuum systems including turbo-molecular pumps requires knowledge of the characteristics of the turbo-molecular pumps. Normally, such characteristics for commercially available turbo-molecular pumps are presented as graphs of pumping speed, compression ratio and so on as a function of inlet or outlet pressure. It is difficult to incorporate such information into a model for designing complex vacuum systems, especially when optimising the number of pumps, their pumping speed and choice of backing pump.Voss [Characteristics of the turbomolecular pumps. Vakuum in Forschung ung Praxis 2002;14(4)] has published fitting formulae for specific pumps as a way of describing pressure, pumping speed and compression at the inlet, by means of a number of parameters which are described in a table for each gas and throughput. These fitting formulae can be used in modelling, but the fitting parameters for an arbitrary pump are not in general available.A new approach is proposed based on ‘true zero-throughput’, which has been defined as the ratio of the probability of a gas molecule travelling from the pump inlet to the outlet to that of its travelling from the outlet to the inlet. This is different from the usually reported ‘zero-throughput’ data which are measured with zero gas injection, but not ‘zero gas load’ at the inlet (due to thermal outgassing of a measuring dome and the pump itself). Parameters in the formulae developed here are no longer simply fitting parameters, but have clear physical meaning. The dependence of the parameters for different gases may be included as a function of mass. The new formulae presented, allow us to model the performance of cascaded turbo-molecular pumps. As an example, the formalism is applied to the differential pumping stages of the KATRIN experiment [KATRIN Collaboration. KATRIN design report 2004. Forschungszentrum Karlsruhe Scientific Report # FZKA 7090, 2005].     

New Turbomolecular Pump with Central Opening for Free Axial Access. Eine neue Turbomolekularpumpe mit zentraler Öffnung für freien axialen Zugang

Standard turbomolecular pumps show typically one annular active intake area on the high vacuum flange side (single‐flow pumps). The central circular part of the inlet of the compressor turbine is blind for pumping. The new design proposes a central opening of a turbomolecular pump all along the axis. This central bore can be used e.g. for mounting of feed throughs, manipulators, windows or for coupling to further vacuum devices, in particular also for enclosing tube‐like vacuum systems. This design allows a multi‐use of a pumping port at a vacuum vessel without reducing there the pumping speed. Moreover, the new design is ideal for axial or radial differential pumping arrangements as e.g. needed for all gas jet like set‐ups or other pressure reduction stages.     

Membranpumpen mit hoher Kompression durch tangentiale Membraneinspannung

Diaphragm pumps dominate the field of rough vacuum (down to 1 mbar) in modern industry and science. Their construction is quite simple and therefore warrants great reliability. Diaphragm pumps are oil‐free, maintenance free, have a low noise level and a long lifetime. Up to now, problems occurred in generating lower vacuum pressure. With a completely new tangential diaphragm insertion as well as with improvements of the gas flow, and the form and position of the valves, the of a Puchheim pump company now solved this problem: The tangential diaphragm pumps reach an ultimate pressure of 20 mbar (single‐stage) and less than 1 mbar (double‐stage). A pump head provides a pumping speed of 36 l/min at atmospheric pressure.     

Neue Vorvakuumpumpe: Schnelles Evakuieren dank Membran‐ Stabilisierungssystem. New roughing pump: Fast Evacuation thanks to Diaphragm Stabilization System

Diaphragm pumps are used at turbomolecular pumps to generate rough vacuum. They are characterized by high suction speed, which however deteriorate when the working pressure decreases. This is caused by the difference between the working pressure of the pump and the ambient pressure. The larger the pressure difference, the more the elastic diaphragm bulges, lowering the effective input volume of the pump. This problem is alleviated by a newly developed diaphragm stabilization system. Diaphragm roughing pumps equipped with this system pump down faster than pumps without the system. Due to the enhanced suction speed, they also ensure greater process reliability. The first application of the diaphragm stabilization system (patent applied for) is in a newly developed diaphragm roughing pump. This pump is driven by a compact, brushless DC motor with very great efficiency. The pump is available in 24‐volt DC and 90‐ to 264‐volt, 50/60‐Hz AC versions. OEM and portable versions are available.     

Fragen zu Vakuum‐Molekularpumpen

Questions about vacuum molecular pumps For experiments about gas friction we used a turbomolecular pump with magnetic bearings. The blade system was replaced by a cylinder of carbon fiber materal. lt rotates in a stationary aluminium cylinder at a distance of 0. 8 and 0. 4 millimeters at a rotating speed up to 48000 rpm. We got a linear dependance of the reciprocal values of pressure and viscosity in good agreement with other experiments in that field. Preparing experiments showed us our apparatus is working like a pump too. We saw differential pressures in dependance of flow and gas pressures. In our sytem pumping works against the flow resistance. The pumping range is limited by a graph showing the compensation of pumping and resistance. Here we have no flow through the system but only in tangential direction by the rotation The experiments showed graphs with 2 arms showing the compensaion of pumping and flow resistance. In the range between the arms the pressure difference reaches the highbest negativ numbers. That is the point of best pumping. The position of this point decreases to lower rotation frequencies with rising gas pressure and flow. The question is: what are the reasons for this behavior? Possibly the molecular pump developped by Siegbahn uses this effect. It makes higher compression rates by lowering the friction speed. The molecular pump of the Holweck type has at a constant rotation speed an optimal pumping effect at a certain nitrogen gas pressure and flow. At this optimum the pump makes high compression rates for additional hydrogen or helium.     

Überlastgrenzen bei Hochvakuumpumpen

High-vacuum pumps have a limited inlet pressure above which they cannot function. Recognizing and dealing with the approaching overload conditions is an important aspect of vacuum system operation. This paper outlines the basic considerations for selecting the pressure at which the high vacuum pumps are started, emphasizing the importance of mass flow (throughput) limits rather than the pressure as such. Some basic parameters, such as the ratio of pumping speeds of the roughing pump and the high vacuum pump are associated with the choice of the cross-over pressure. Practical engineering recommendations are offered for system design and operation. Adverse system effects (e.g., backstreaming and oil loss) resulting from pump overload are noted for momentum transfer pumps (diffusion pumps and turbomolecular pumps) and capture pumps (sputter-ion pumps and cryogenic pumps). To prevent any adverse effect, normally, the transient pressure rise during switching should not be longer than a few seconds.     

罗茨真空泵试验方法的研究

罗茨泵的抽气速率和极限压力是泵的主要性能,但它在很大程度上要依赖于前级泵的型式和性能,因此它并不是罗茨泵本身特有的性能。能代表罗茨泵特征性能,而又与前级泵无关的是零流量压缩比、最大允许压差与溢流阀压差、漏率和噪声,它们与罗茨泵的真空状态、抽气性能和运行质量有着极其密切的关系。文中对特征性能的试验方法和装置进行了分析和研究,提出了有异于国内外现行标准的,更精粹、独特的见解。     

Engineering aspects of turbomolecular pump design

The development of modern (thin-bladed) turbomolecular high-vacuum pumps began in 1957 with the demonstration of the possibility of obtaining high compression ratios with axial flow compressors in the molecular flow regime. Thirty years later, such pumps had become the major method for high vacuum pumping. It had been apparent from the beginning that pneumatic compressors can be useful at any pressure provided a proper number of suitable impellers were used. However, theoretical studies, initially by Prof. A. Shapiro's group at MIT (Massachusetts Institute of Technology) dealt primarily with the pumping mechanism in molecular flow rather than with an optimum practical pump design. Some observations in such studies were misunderstood and the first pump designs were not optimized. Later, compound or hybrid pumps were introduced, which incorporated molecular drag pumping stages. In more recent years, pumps have been made which can exhaust directly to the atmosphere by means of added centrifugal-regenerative impellers. The use of different impeller types provides freedom to the designer to create pumps that match any reasonable desired performance.This paper will attempt to explore some of the engineering aspects of design, especially relationships of volume and mass flows, permissible pressure ratios in various density domains, and their relevance to power consumption.     

Improvements in the performance of turbomolecular pumps

A new range of turbomolecular pumps, nEXT, has been developed. This incorporates a new damping mechanism and pumping stage options. A new Siegbahn drag stage in combination with a regenerative mechanism are described in their combination with pure turbomolecular stages. Consequent increased backing pressures, high compression ratios and the facilitation of a boost port being used to create additional pumping capacity in the viscous flow regime will be described.     

Die Membranpumpe - Entwicklung und technischer Stand

The modern diaphragm pump has become a proven device for generating coarse and fine vacuum. The article describes disigns and functions of various construction types as well as state-of-the art development and manufacturing. Physical and technical demands have resulted in diaphragm pumps with typical ultimate pressures of 70 to 0,1 mbar and a pumping speed of several m³/h. As an almost chemically resistant pump, the diaphragm pump is used in the chemical laboratory. Combining a diaphragm pump with an oil-free, not against atmosphere compressing pump, a contamination-free pump assembly for (ultra-)high vacuum is obtained which is well suited for coating technology, vacuum metallurgy and semiconductor industry due to its oilfree operation.     

如何选择和使用涡轮分子泵

本文首先介绍了涡轮分子泵的工作原理,结构型式及其优缺点。为了利用涡轮分子泵,获得清洁真空,国外多利用干式机械泵作其前级泵,构成无油的真空系统。然而,目前国内涡轮分子泵多以油封机械泵为其前级泵,构成了有油真空系统,如果操作不当,很难避免油蒸汽返流,对真空系统的污染。利用有油系统获得清洁真空,国内外都有一些有效防止返流的措施和成功的操作经验。这些对用户正确选择和使用涡轮分子泵有油系统获得清洁真空,有一定的参考价值。     

Konstruktion und Eigenschaften von turbinenartigen Hochvakuumpumpen

Turbomolecular pumps are essentially axial-flow compressors designed for pumping rarefied gases. Original designers adapted more or less traditional axial-flow compressor stage arrangements using mathematical modeling based on studying molecular trajectories inside alternating rotating and stationary blade rows. Recent designs trends lean toward hybrid stage arrangements, which incorporate turbomolecular and turbodrag stages within the same body and mounted on the same shaft. The new pumps achieve much higher compression ratios (10 to 100 times) permitting higher discharge pressures and allowing the use of oil-free backing pumps. At the present time, there are four types of turbine pumps: multistaged axial-flow turbomolecular pumps, molecular drag pumps (usually of the Holweck type), hybrid pumps with modified downstream stages but the same number of rotors, and compound pumps which combine the axial stages with additional drag pumps in the same body. Turbine-type high-vacuum pumps, unlike vapor-jet pumps and cryopumps, permit relatively simple engineering solutions for increasing their pressure regime to an almost arbitrarily high level, including the possibility of discharging directly to atmosphere. This provides opportunities for further improvements.     

Performance increase in turbomolecular pumps with curved type blades

Mostly, flat-type blades are used in the turbomolecular pumps in both rotor and stator sections. In this study, performance characteristics of the turbomolecular pumps consist of one rotor or rotor-stator pair with flat-type blades is calculated in different flow regimes. Next, the same calculations are realized for the curved-type blades in dissimilar geometries. Following, these performance characteristics are compared to find out which combination is the most efficient in terms of maximum pumping speed and maximum compression ratio. In case of turbomolecular pump consists of only one rotor, flat blades give the best performance. However in rotor-stator pairs, the performance of the flat-type only blades is surpassed by a combination of rotor with flat-type blades and stator with curved-type blades. Consequently, it is concluded that curved-type blades should also be considered in stator sections in addition to the flat-type blades in order to increase the performance of the multi-stage turbomolecular pumps.     

Selbsttrocknende Membran‐ Vakuumpumpen für feuchte Gase

Diaphragm vacuum pumps have proved their superiority as dry‐running systems over other types of vacuum pumps in many applications, and in particular in the medical, analysis, and process engineering sectors, as well as in the chemical industry. These pumps deliver the media without any contamination of content, have a high gas tightness, and can be designed as chemically resistant with regard to those parts which come in contact with the media. Although they are in principle relatively insensitive towards condensates which may be formed or conveyed with the media, liquids in the vapor or gas flow may be the cause for the prolongation of a vacuum process, which can be considerable and is certainly undesirable. This applies in particular to applications involving multi‐user vacuum systems in chemical laboratories, which under certain circumstances may contain very substantial volumes of condensates, and to the use of pumps in steam sterilizers (autoclaves) and vacuum drying cabinets. These examples of applications will be considered in greater detail hereinafter. The condensates which occur in the pump head of a diaphragm vacuum pump cause interference in that — due to re‐evaporation during the suction cycle — they incur a substantial reduction in the usable suction capacity of the pump. This problem can be resolved by means of a drying system for diaphragm vac uum pump heads. The drying system makes use in this case of the pressure differential which pertains between the pump chamber and the atmosphere outside the pump. The function of the drying system can be described as follows: A solenoid valve vents the pump head in a cyclic manner, with the result that liquid in the pump head will be blown out, while the process vacuum in the process engineering system will continue to be maintained. Diaphragm vacuum pumps equipped with this drying system have provided excellent results, for example in the chem ical laboratory, both in individual diaphragm vacuum pumps as well as in multi‐user vacuum systems. Extremely good experience has also been gained in the evacuation of sterilizer autoclaves and vacuum drying cabinets with the use of diaphragm vacuum pumps fitted with the drying system. When using the drying system on steam sterilizer autoclaves, another favorable effect is also encountered: The vapor fraction in the pumping medium is cooled in the diaphragm pump head to below the evaporation or boiling temperature, with the result that the vapour condenses. This reduces its volume to a fraction of the initial value, which is the equivalent of an additional suction capacity, in the same manner as with a condenser. The condensate which occurs with this process is blown out of the pump heads by the drying system, and, as a result, can no longer cause interference due to re‐evaporation.     

High vacuum side channel pump working against atmosphere

The OnTool™ Booster vacuum pump consists of side channel and Holweck pump stages. This pump achieves 10⁻³ Pa final pressure and exhausts against atmosphere. Research is done on side channel pump stages. It shows the ways to increase the compression and pumping speed while simultaneously reducing size and power consumption.The influences of a backing pump on the power consumption, the form and number of rotor blades on the performance of side channel pump stages have been investigated. It was shown that the power consumption of the pump at final pressure drops from 1150 W to less than 150 W, if a backing pump is used. The properties of double-flow and single-flow side channel stages were compared to each other. It was shown that double-flow stages have a higher pumping speed and a lower compression than single-flow stages.As a result of the investigation the compression and pumping speed of side channel pump stages are increased significantly at reduced power consumption.     

Pumping speed measurement of turbomolecular pumps by a quasistationary pump-down method

The pumping speed of a turbomolecular pump is usually measured by injecting a stationary known gas flow via a standardised test dome into the pump and measuring the equilibrium pressure in the test dome. The ratio of gas throughput and pressure is just the pumping speed. In practice, the pressure can be conveniently and accurately measured, whereas the convenient and accurate throughput measurement is a challenging experimental problem. The present paper reports on a new method for measuring the pumping speed in which the throughput is generated by the pumping down of a vessel via an orifice. From the decrease of vessel pressure with time, and from known vessel volume, the throughput can be directly and accurately derived. Exploring measurements by the new method in fact give high accuracy, systematical error sources are practically negligible.     

Turbomolecular pumps designed for plasma processes industry. Turbomolekularpumpen speziell für die Plasmaindustrie

Plasma processes are a very popular method to produce high‐grade quality thin films on many different substrates. There are a large variety of different coating systems. Such systems go from small‐scale machines (i.e. Optical coating systems for ophthalmic lenses and filters), through mid‐size machines (such as systems for deposition on flexible substrates used in the food, electronics and packaging industry or systems used for producing optical and magnetic data storage media), up to large‐area systems (i.e. used for architectural glass coating or in the flat panel display industry). Even if all of these systems look very different, there are few common specific points that characterize most of these applications. The plasma is normally based on Argon, Oxygen, Nitrogen (and more recently Krypton) mixtures in the mid 10^–3 mbar range. The base pressure is generally over the mid 10^–7 mbar range. The deposition rate is very high and so the demand for gas throughput is high as well. (i.e. a glass coater can ionize more than 2000 sccm of Argon per cathode segment). There is a high probability of debris and particle generation within the process; roughing and venting cycles are fast and sometimes uncontrolled (they can be described as air‐in rushes in some cases). Uptime and reliability are not an option, but a must in industrial production environments. It is therefore difficult to believe that turbo molecular pumps originally designed to reach the 10^–10 mbar range with a high number of pumping stages and very tight clearances, are capable to work reliability in this demanding environment. We are keener to think that if we want a reliable and performing pumping solution the design of the turbomolecular pump must be specific and dedicated to the application. Ideally this development process is done side by side with the ultimate equipment users, matching at best process requirements and turbomolecular pump design know‐how. As Varian Vacuum Technologies, we have followed that process and this article is sharing the results.