Roots vacuum pumps

The Ministry of Science and Higher Education of the Russian Federation 
Kazan National Research Technological University 
ROOTS VACUUM PUMPS
Tutorial 
Kazan 
KNRTU Press 
2023 

621.521(075) 
Published by the decision of the Editorial Review Board  
of the Kazan National Research Technological University 
Reviewers: 
PhD in Physics and Mathematics P. Osipov 
PhD in Technical Sciences K. Moiseev 
Burmistrov A. 
Roots vacuum pumps : tutorial / A. Burmistrov, A. Raykov, S. Salikeev, 
A. Isaev; The Ministry of Education and Science of the Russian Federation,
Kazan National Research Technological University. – Kazan : KNRTU
Press, 2023. – 84 p.
ISBN 978-5-7882-3339-0 
The tutorial highlights the operating principle, structural modifications, general 
and individual solutions applied for Roots vacuum pumps, as well as advantages and 
disadvantages of the latter. Pumping characteristics of the pumps and units by major 
producers of Roots machines are provided. 
It is intended for use by bachelor`s degree students of the course 15.04.02 “Technological machines and equipment”, specialization “Vacuum and compressor equipment of physical machines”, and master`s degree students of the curricula “Designing 
and operation of vacuum processing equipment” and “Vacuum engineering and technology”. The book will be useful for professors, Ph.D. fellows and students engaged 
in the training programs “Technological machines and equipment”, “Applied physics”, 
“Nuclear engineering and thermal physics”, “Nanoengineering”.  
The tutorial is prepared at the Department of “Vacuum and compressor equipment 
of physical machines”.  
621.521(075) 
ISBN 978-5-7882-3339-0 
© A. Burmistrov, А. Raykov, S. Salikeev, 
A. Isaev, 2023
© Kazan National Research Technological 
University, 2023 
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C O N T E N T
Explanation of symbols and terms 
....................................................................................................... 4 
Introduction 
.......................................................................................................................................... 5 
1. HISTORICAL NOTE ...................................................................................................................... 7 
2. ADVANTAGES AND DISADVANTAGES OF ROOTS VACUUM PUMPS 
........................... 11 
3. OPERATING PRINCIPLE OF ROOTS VACUUM PUMPS. OPERATION WITHIN
THE UNIT ......................................................................................................................................... 13 
4. ROOTS VACUUM PUMPS OF NVD SERIES BY VAKUUMMASH ...................................... 24 
5. BASIC CIRCUITS OF ROOTS VACUUM PUMP WORKING MECHANISMS, AND
GENERAL STRUCTURAL SOLUTIONS ...................................................................................... 31 
6. INDIVIDUAL STRUCTURAL AND TECHNOLOGICAL SOLUTIONS OF ROOTS
VACUUM PUMPS 
............................................................................................................................ 38 
7. MULTI-STAGE ROOTS VACUUM PUMPS 
.............................................................................. 71 
8. SPECIFIC CHARACTERISTICS OF ROOTS VACUUM PUMPS 
............................................ 74 
9. TESTING OF ROOTS VACUUM PUMPS 
.................................................................................. 76 
Conclusion ......................................................................................................................................... 81 
Literature 
............................................................................................................................................ 83 
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E x p l a n a t i o n  o f  s y m b o l s  a n d  t e r m s
NVD (DVN) – Roots vacuum pump 
VP – vacuum pump 
SVP – scroll vacuum pump 
CVP – claw vacuum pump 
RVP – rotary vane pump 
RPVP – rotary plunger vacuum pump 
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I N T R O D U C T I O N
This tutorial continues a set of works studying non-contact oil-free 
vacuum pumps written by vacuum engineers of Kazan. It would not be an exaggeration to say that in the XXI century, Kazan with allocated therein Vakuummash being a major plant of vacuum technology, and specialist Department of “Vacuum and compressor equipment of physical machines” at the 
Kazan National Research Technological University has become a center 
of oil-free vacuum in Russia. 
It stands to mention that some years ago, Russia did not produce oilfree pumps serially. The production was reduced to two “small” Roots vacuum pumps – NVD-200 and NVD-600 manufactured by Vakuummash (Kazan), and singular test specimens of CVP and Roots vacuum pumps. All demand for oil-free vacuum was provided by foreign equipment.   
But in 2016, Vakuummash, in collaboration with KNRTU Department 
of “Vacuum and compressor equipment of physical machines”, began 
the production of “dry” scroll vacuum pumps. There appeared a range of 
scroll vacuum pumps (SVP) with pumping speed of 4, 12, 35 m3/h. Since 
2019, the series was extended by “large” SVP with pumping speed of 
60 m3/h. Currently, series of Roots vacuum pumps and screw vacuum pumps 
are de-signed and exposed to staging. Since 2023, Roots vacuum pumps with 
pumping speed from 1000 to 2100 m3/h and screw vacuum pumps with 
pumping speed of 630 m3/h will be put to serial production. Therefore, Russia will soon produce practically all types of mechanical oil-free pumps, except for claw vacuum pumps. 
For designing and operating such super-complex non-contact oil-free 
machines, as well as building up hi-tech production, there are required highqualified personnel having a good understanding of structural features of any 
construction and being familiar with a variety of engineering solutions. 
This is exactly the goal of the present set of tutorials.     
By content, the tutorial is intended for a wide readership. Primarily, 
for bachelor`s degree students of the course 15.03.02 “Technological machines and equipment” and master`s degree students of the curricula 15.04.02 
“Designing and operation of vacuum processing equipment” and “Vacuum 
engineering and technology”, as well as engineers of vacuum technology. 
However, this material might be useful for constructors, technologists, designers and maintenance engineers working on industrial and laboratory 
pumping equipment. 
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The tutorial provides operating principle, advantages and disadvantages of Roots vacuum pumps, basic diagrams of working gears, general 
and individual structural concepts, specific characteristics of Roots vacuum 
pumps and units by the world`s major manufacturers. 
The book generalizes experience gained by the project performers 
in progress. Writing staff is represented by KNRTU Department of “Vacuum 
and compressor equipment of physical machines”: A. Burmistrov – Doctor 
in Technical Sciences, Professor; S. Salikeev – Ph.D. in Technical Sciences, 
Associate professor; A. Raykov – Ph.D. in Technical Sciences, Associate 
professor, and A. Isaev – Ph.D. student at KNRTU and the head of the mechanical vacuum pumps section of Vakuummash. 
The authors are grateful to their colleagues for instructive discussion, 
provision of separate materials and help of various kinds when editing 
the manuscript. Readers` criticism and suggestions are welcome and will be 
accepted with thanks.  
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.  H I S T O R I C A L  N O T E
Roots vacuum pump is a mechanical rotary vacuum pump of external 
compression, its working chamber being formed by the casing and profile 
straight-toothed rotors rotating in synchronism, in opposite directions with 
minimum clearances. Roots vacuum pump is also called a booster vacuum 
pump. Most papers on Roots-type pumps classify them as volume displacement machines. This makes sense because pumping is realized on account 
of rotors` transport of cut-off volumes. 
However, one should not be surprised that a Roots vacuum pump 
is classified as a volume displacement-velocity pumping facility, since along 
with direct rotors` transfer of cut-off volumes, backflow takes place via slot 
channels from outlet to inlet. Since channel walls are movable, the process 
therein is similar to the one in high-speed (kinetic) pumps. 
Hence, the most appropriate definition of a Roots vacuum pump allowing to construct sufficient mathematical model of pumping process is as 
follows: Roots vacuum pump is a non-contact volume displacement-velocity 
pumping machine, the operating process therein including direct volume 
pumping (due to rotors` gas transfer in cut-off volumes from inlet to outlet) 
and velocity gas backflow via channels of rotary mechanism (from outlet 
to inlet).  
Like many other machines, Roots vacuum pump came to vacuum 
technology from compressor sector where it was used as a rotary blower. 
A Roots blower got its name after American inventors – brothers Philander 
and Francis Marion Roots who founded the Roots Blower Company in Connersville, Indiana, USA. In 1860, the brothers patented principal design 
of the external compression blower intended for operation in blast furnaces 
and other production sectors.  
In 1869, they took out a patent from UK Patent office acknowledging 
the invention of “improved rotary blower machines”. In 1875, the blower 
was shown at the exhibition in St. Petersburg.   
Initially, the main advantage of a Roots blower was its high performance. But in the middle of XX century, vacuum engineers also appreciated the absence of oil in the machine working volumes. This privilege 
considered to be precious at the time of development of semiconductor 
technologies and overall directions applying thin films, as well as food and 
medical technologies. 
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Figure 1.1. Inventors of the first Roots-type machine – Philander 
and Francis Marion Roots 
For most high-vacuum technology equipment, e.g. production lines 
of microcircuits and surface analysis instruments, oil vapour flow 
to the pumped volume is utterly intolerable. Thereby, backflow increases 
sharply when the pump input pressure turns lower than 1–10 Pa. Under such 
pressures, in pipelines there establishes collision-free flow mode, and oil vapour molecules flow toward the pumped gas stream without hindrance.    
Backflow measurement in a mechanical oil-sealed pump gives about 
0.5 mg/h to 1 cm2 of cross-sectional area of inlet nozzle. This corresponds 
to occurring every second an oil film monolayer formed on the surface 
in the vicinity of inlet nozzle. In most cases, this situation naturally causes 
irreplaceable outcome for technology process and is intolerable, therefore. 
To form low, medium and high vacuum, producers of oil-sealed vacuum 
pumps offer to install various traps intended for preventing oil flow 
to the pumped volume, but this solution significantly decreases pumping speed, 
moreover, it does not totally protect the vacuum volume from working fluid 
vapour. 
It is notable how installation of a Roots pump influences oil vapour 
backflow. As seen from Fig. 1.2, rotation of Roots pump rotors makes up 
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a dynamic “trap” for vapours, and backflow even without traps decreases 
several-fold. However, oil-sealed vacuum pumps equipped with such a trap 
fail to prevent oil vapour leak completely. This was the reason to construct 
mechanical oil-free (“dry”) pumping machines of low and medium vacuum. 
Main requirement for a “dry” forevacuum pump is provision of ultimate pressure not exceeding 1 Pa. In this case, a Roots vacuum pump is a fair substitution of an oil-sealed vacuum pump. The requirement is satisfied in the following “dry” vacuum pumps: scroll, screw, multistage claw and multistage 
Roots vacuum pumps. 
 
Figure 1.2. Density of backflow and rate of oil film formation in the input 
nozzle zone for rough pumping system of various structures: 
1 – mechanical pump; 2 – Roots vacuum pump – mechanical pump; 
3 – mechanical pump with a trap; 4 – unit “trap – Roots vacuum 
pump – mechanical pump” 
But for technologies requiring great pumping speed at medium vacuum, Roots vacuum pumps are irreplaceable. Their pumping speed is up 
to 40000 m3/h and they can be combined with both oil-sealed pumps and “dry” 
pumps. In combination with “dry” pumping means, one can obtain an oil-free 
unit characterized by high pumping speed and low ultimate pressure. 
Roots vacuum pumps are well integrated to modern high-duty vacuum 
system, thus, these pumps are manufactured by all major producers 
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