Vacuum pumps types and characteristics. Turbomolecular pump: history of creation, analysis of molecular and turbo pumps, operation of TMN pumps and dry vacuum pumps

Catalog section for screw dry vacuum pumps DRYVAC from Leybold GmbH (Germany)

Screw vacuum pump DRYVAC from Leybold GmbH (Germany)

The principle of operation, based on the rotation of the screws, allows for the evacuation of gas without the presence of oil in the area of compression. The DRYVAC screw vacuum pump has a compression cavity formed by the surface of the housing, as well as two rotors that rotate synchronously. Due to the fact that the rotors rotate in opposite directions, there is a gradual movement of the compression cavity from the suction side towards the exhaust side, which ultimately provides the necessary pumping effect.

Despite the fact that the process of internal compression of the gas occurs in the considered design, the "particle path" in the internal space of the pump is minimal. This feature greatly simplifies maintenance, and also reduces the need for service work to the possible minimum.

The DRYVAC range is a new series of oil-free screw vacuum pumps. The configuration, which can be different, must be selected taking into account the field of application, as well as other individual criteria.

During the development of the series, the actual needs of the processes were taken into account, in which the requirements for vacuum pumping systems are quite high. The considered devices are used, in particular, in the manufacture of screens, photovoltaic elements, as well as for a number of other industrial applications.

Each version of the pump from the DRYVAC line is equipped with water cooling, which makes it a compact design and the ability to be relatively easy to install even in complex systems in parallel with the reliable RUVAC pumping units of the WH, WS and WA series.

The DRYVAC range of screw vacuum pumps includes:

model DV 450
model DV 450S
model DV 650
model DV 650-r
model DV 650 S
model DV 650 S-i
model DV 650 C
model DV 650 C-r
model DV 1200
model DV 1200 S-i
model DV 5000 C-i

Turbomolecular pump (TMN) refers to special pumps that allow you to create and maintain a deep vacuum for a long time, of the order of 10 -2 to 10 -8 Pa. The etymological meaning of the name of the pump is of interest. The prefix “turbo-” is an abbreviated version of the term “turbine” introduced into the technical lexicon since 1900. Both of these words came from the French. "Turbine" - "turbine", and earlier from lat. "Turbo", meaning "to make a mess, to disturb, a whirlwind, a spinning top." The second part of the first word “- molecular” comes from lat. "Molecula" - "part, particle", as a diminutive of "moles" - "mass, lump, bulk". The next term “pump” is originally ours, Slavic, as it was transformed from the Old Orthodox words “suck, suck, suck”, meaning “to suck breast milk”, “suck on the brain bones”, “draw out liquid”.

In this article we will look at:

pfeiffer turbomolecular pump;
agilent tv81m turbomolecular pump;
high-vacuum turbomolecular pump twistorr 84 fs;
turbomolecular pump tg350f;
power supply unit for turbomolecular pumps type bp 267;
turbomolecular pump working principle;
molecular vacuum pump;
molecular pump mdp 5011 price;
buy a turbo pump;
turbo pump price;
disadvantages of turbo pumps;
turbomolecular pump tmn 500;
pump tmn 200;
dry pump;
oil-free vacuum pump;
oil-free foreline pumps;
dry type vacuum pump;
oil-free rotary vane vacuum pump;
vacuum piston oil-free pump;
foreline pump 2nvr 5dm.

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In 1913, the German scientist Wolfgang Gede published in the journal "Annalen der Physik" a description of a new vacuum pump, for which the laws of the molecular kinetic theory of gas movement were used. For the purpose of experimental verification, he manufactured the first vacuum molecular pump with a minimum clearance of 0.1 mm between a rotor rotating at a speed of about 8000 rpm and a stationary stator. The gas was rarefied to 10 -4 mm Hg. The new pump even began to be produced by the German company "Leybold's Nachfolgers", but did not receive wide distribution. Firstly, there was no urgent need for it, and secondly, technological difficulties with the manufacture of such small gaps interfered. If macroscopic solid particles (pebbles, chips, glass) enter the pump together with the gas, the rotor will jam.

In the late 1950s, interest in molecular pumps resumed.

Only at the end of the 50s of the last century, interest in molecular pumps was renewed when the German engineer W. Becker invented the Pfeiffer turbomolecular vacuum pump with a large number of vane disks on the shaft and with increased clearances, of the order of 1 mm. This pump was patented in 1957 by Pfeiffer Vacuum. Further, the device and the principle of operation of TMN pumps continued to improve, such designs as the Agilent TV 81M turbomolecular pump and the newest (2015) Twistorr 84 FS high-vacuum turbomolecular pump of the Italian company Agilent Technologies, the TG 350F hybrid turbomolecular pump of the Japanese company Osaka Vacuum and others. In this case, the nodes of these devices are often interchangeable. For example, the power supply unit of a turbomolecular pump of the BP-267 type can be used for pumps of the NVT-340, NVT-950, 01AB-450, 01AB-1500 models.

In a molecular pump, the evacuation of the gaseous medium is carried out by imparting mechanical impulses of energy to the molecules of the substance from the solid, liquid, gaseous surfaces of the pump moving at high speed. In this case, in a molecular pump, the direction of movement of the working surfaces and gas molecules coincide, and in a turbomolecular pump, the directions of movement of the working elements and molecules are mutually perpendicular.

Sectional view of a molecular pump

Molecular pumps, according to the principle of operation, are subdivided into:

mechanical (rotary and turbine);
ejector;
steam jet;
gas jet;
water jet;
diffusion.

For example, the MDP 5011 high vacuum molecular pump is a device with mechanical working elements. The movement of gas molecules to the pump outlet is provided by the solid surface of the rotor-cup, which makes 27000 rpm. This MDP 5011 model is the best-selling turbo pump. It is clear that you are interested in the price of the MDP5011 molecular pump. Please contact us on such questions, call, write by e-mail. We will advise and help.

A turbo pump is a pumping device driven by a turbine, the units and parts of which are included in the design of the pump. There are the following types of turbo pumps depending on the type of pumped working medium.

The appearance of the turbo pumps

Turbopumps for pumping liquids.
Turbopumps for pumping suspensions.
Turbo pumps for pumping gases.

The disadvantages of turbo pumps include design complexity, long downtime during pump or turbine repair, and high cost. Therefore, if it is necessary to buy an TMN-6/20 oil turbo pump, of course, the question arises, what is the price of the turbo pump. If it does not suit you in other firms, come to us.

Turbomolecular pumps (tmn) are made in the form of multistage axial turbines, which ensure the achievement of medium, high and ultra-high vacuum. The special design of the rotor and stator stages of the turbine, in which inclined channels are made, placed in a mirror to each other, makes it possible to efficiently pump out gas molecules due to the different probability of molecules passing through the channels located at an angle in the direction of pumping and supply. ТМН are fixed on a massive base through shock absorbers, which reduces vibration during pumping.

External view of the TMN-500 turbomolecular vacuum pump

The principle of operation of a turbomolecular pump is as follows. The energy of the high-frequency turbine blades is transferred to the gas molecules. The latter collide with the surfaces of the blades, move together for a fraction of a second and fly off tangentially to the rotating turbine. There is a summation of the kinetic energy of the blades with the thermal energy of the moving gas particles. The chaotic movement of molecules turns into an accelerated movement in a given pumping direction. Such an effective rotor action is possible only with a molecular gas flow mode, which is created by an additional low pressure foreline pump.

A good impression is made by domestic two-flow oil-free pumps: the TMN-500 turbomolecular vacuum pump and the TMN-200 pump with a capacity of 500 and 200 l / s, respectively. Of course, in terms of build quality and design, they are inferior to foreign counterparts. But at a low cost, they are characterized by reliability in operation, reliability and sufficient durability.

A dry vacuum pump (oil-free) works in the same way as an oil pump. But the dry type pump does not use oil to lubricate the rubbing parts, and there are no sealing devices. Therefore, not metal, but a graphite composite material is used as a material for the blades of dry pumps. Graphite blades are cheaper than metal blades made of titanium, aluminum, stainless steel, they are characterized by a lower coefficient of friction and reliably seal the pump chamber.

Appearance of a dry vacuum pump

Advantages of the oil-free vacuum pump:

absence of oil vapors when air leaves the pump, the workplace becomes clean, the ecology of the environment is improved;
no need to purchase and fill in expensive oil, monitor its level and pollution;
lower cost.

Disadvantages of a dry pump:

the depth of the created vacuum is lower than that of oil-sealed pumps;
the durability of graphite blades is much less than that of metal;
wear products in the form of pulverized graphite are released into the atmosphere.

However, experts believe that the future belongs to oil-free vacuum pumps. And they are already trying to buy an oil-free rotary vane vacuum pump, an oil-free piston vacuum pump, an oil-free foreline pump, regardless of their price. Since the simpler and cheaper operation of a dry pump will pay off all the initial costs.

The foreline pump is a device for creating an initial rarefaction of the gaseous medium - forevacuum (from German "vor" - "before, in front" of the vacuum and Latin "vacuus" - "empty"). The principle of operation is that the foreline pump is installed as the first stage in a system of pumps that create high and ultra-high vacuum. Provides energy savings and improves the operating capability of the next high stage pump.

The most suitable for this is the domestic rotary vane foreline pump 2NVR-5DM, designed both for creating low and medium vacuum independently and as an auxiliary pump.

External view of the foreline pump 2NVR-5DM

If you are interested in the described turbomolecular and backing pumps from the range of our company, you can get more detailed information from our consultants. Our highly qualified specialists will help in choosing the optimal pump option, explain the conditions of purchase, operation and service, and justify prices. They will assist you in the selection of spare parts and auxiliary materials, such as blades for Becker oil-free pumps, oil for the foreline pump and others. Call our phones or contact us by E-mail. We will be happy to help you.

Basic principle of any type of vacuum pump Is repression. It is the same for all vacuum pumps of every size and every application. In other words, operating principle of the vacuum pump is reduced to the removal of the gas mixture, steam, air from the working chamber. During the displacement process, the pressure changes and the gas molecules flow in the desired direction.

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Two important conditions that the pump must fulfill is to create a vacuum of a certain depth by pumping out the gaseous medium from the required space and to do this within a given time. If any of these conditions are not met, then you have to connect an additional vacuum pump. So, if the required pressure is not provided, but for the required period of time, the foreline pump is connected. It further reduces the pressure to meet all the necessary conditions. This operating principle of a vacuum pump is similar to a series connection. Conversely, if the pumping speed is not ensured, but the desired vacuum is achieved, then another pump will be required to help achieve the required vacuum faster. This principle of operation of a vacuum pump is similar to a parallel connection.

Note. The depth of the vacuum created by the vacuum pump depends on the tightness of the working space, which is created by the pump elements.

To create a good tightness of the working space, a special oil is used. It seals the gaps and bridges them completely. A vacuum pump with such a device and operating principle is called an oil pump. If the principle of a vacuum pump does not involve the use of oil, then it is called dry. Dry vacuum pumps have the advantage of using them, since they do not require maintenance with oil changes and so on.

In addition to industrial vacuum pumps, small pumps that can be used at home are widely used. These include a hand-held vacuum pump for pumping water from wells, reservoirs, pools and more. The principle of operation of a manual vacuum pump is different, it all depends on its type. The following types of manual vacuum pumps are distinguished:

Piston.
Rod.
Wing-type.
Membrane.
Deep.
Hydraulic.

Piston vacuum pump works due to the movement of the piston inside it with valves in the middle of the body. As a result, the pressure decreases and water rises through the bottom valve while the piston handle moves down.

Rod vacuum pump It is similar in principle to a piston, only a very elongated rod plays the role of a piston in the body.

Vane vacuum pump has a completely different principle of operation. The pressure in the working chamber of the pump is created by the movement of the impeller with blades (impeller). In this case, the water rises along the wall of the chamber, this increases the pressure and, the water splashes out.

A more complex design is rotary vacuum pump... But this complexity is compensated by the fact that the pump is capable of pumping not only water, but also heavier oil liquids. The pressure in the pump is created by a rotor with thin plates that rotate and, with the help of centrifugal force, draw the liquid into the container, and then by physical force pushes it out.

Diaphragm vacuum pump does not have any rubbing parts, therefore it can be used for pumping very dirty mixtures. A vacuum is created using an internal pendulum and a membrane, which moves the liquid through the housing to the desired location. To prevent the body from jamming from accidentally lingering debris, the pump is equipped with special valves that clean the pump.

Deep well vacuum pump able to lift water from very great depths (up to 30m). Its principle of operation is the same as that of a piston, but with a very long rod.

Hydraulic vacuum pump it pumps viscous substances well, but it has not received widespread use. We will consider in more detail the principle of operation and the device of vacuum pumps in its individual types.

The principle of operation of liquid ring vacuum pumps

One of the types of vacuum pumps is a liquid ring vacuum pump, its principle of operation is based on the creation of a tightness of the working volume with the help of a liquid, namely water.

Let's consider in detail the liquid ring vacuum pump and its principle of operation. Inside the body of the liquid ring pump there is a rotor, which is offset from the center slightly upward. The rotor has an impeller with blades rotating during operation. Water is pumped into the housing. When the wheel moves, the blades capture water and throw it towards the body by centrifugal force. Since the rotation speed is high enough, the result is a water ring around the circumference of the body. In the middle of the case, a free space is obtained, which will be the so-called working chamber.

Note. The tightness of the working chamber is ensured by the surrounding water ring. Therefore, these pumps are called liquid ring vacuum pumps.

The working chamber is crescent-shaped, and it is divided by the blades of the wheel into cells. These cells are obtained in different sizes. During movement, the gas moves alternately through all the cells, heading in the direction of decreasing volume and at the same time contracting. This happens a large number of times, the gas is compressed to the required value and exits through the discharge hole. When the gas passes through the working chamber, it is cleaned and comes out already clean. This property is very useful for pumping contaminated media or steam-saturated gaseous media. During operation, the vacuum pump constantly loses a small amount of working fluid, therefore, a reservoir for water is provided in the design of the vacuum system, which then, according to the principle of operation, returns back to the working chamber. This is also necessary because gas molecules, while contracting, give up their energy to water, thereby heating it. And to avoid overheating of the pump, the water is cooled in such a separate tank.

You can see in detail how the liquid ring vacuum pump works and how it works in the video below.

Operation of rotary vane pumps

The rotary vane vacuum pump is one of the oil pumps. In the middle of the body there is a working chamber and a rotor with holes, which is located eccentrically. The rotor has blades that can move along these slots under the influence of springs.

Having considered the device, now we will consider what the principle of operation of rotary vacuum pumps is. The gas mixture enters the working chamber through the inlet and moves through the chamber under the influence of the rotating rotor and blades. The working plate, pushing from the center with the spring, covers the inlet, the volume of the working chamber decreases, and the gas begins to compress.

Note. During gas compression, condensation may occur due to steam saturation.

When the compressed gas is released to the outside, the resulting condensate is released along with it. This condensate can adversely affect the operation of the entire pump, therefore, it is still necessary to provide a gas ballast device in the design of rotary vane pumps. You can schematically see how a rotary vane vacuum pump works, its principle of operation, in the figure below using a Busch R5 pump as an example. As mentioned, a rotary vane pump is an oil pump. Oil is needed to close all gaps and gaps between the blades and the casing, and between the blades and the rotor.

The oil in the working chamber is mixed with the air, compressed and released into the oil container. The lighter air mixture passes into the upper chamber of the separator, where it is finally cleaned of oil. And the oil, the weight of which is greater, settles in the oil container. From the separator, the oil returns to the inlet.

Note. High-quality pumps clean the air very thoroughly, there is practically no oil loss, therefore, it is extremely rare to add oil to such pumps.

The principle of operation of the VVN pump

VVN is a water vacuum pump, the operating principle of which is the same as that of a liquid ring vacuum pump.

The working fluid of the VVN pumps is water. The diagram shows a simple principle of operation of the VVN pump.

The movement of the VVN pump rotor occurs directly by the engine through the clutch. This provides high revolutions to the rotor, and as a result, the possibility of obtaining a vacuum. True, VVN pumps can create only low vacuum, because of this they are called low pressure pumps. Simple VVN pumps can pump gases saturated with vapors, contaminated media, and at the same time clean them. But the composition must be non-aggressive so that the cast iron parts of the pump are not damaged as a result of reaction with the chemical compositions of the gas. Therefore, there are models of VVN pumps, parts of which are made of titanium alloy or nickel-based alloy. They can pump out any mix without fear of damage. The VVN pump, due to its principle of operation, is performed only in a horizontal version, and the gas enters the chamber from the top along the axis.

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A vane pump is a mechanism that is very unusual in structure, which is why many are afraid to buy this type of device for themselves. Vane pumps are often divided into two main types:

Double acting
Single action

Both options work on the basis of key assemblies consisting of plates and a rotor.

The plates inside the system move exclusively in the radial direction, since this is the only way to achieve the desired performance level. If we talk about the differences between the two categories of vane pumps, then they consist only in the very shape of the stator surface, which is slightly different from each other in terms of its design.

Double-acting vane pumps

The stator in such a mechanism most often protrudes in the form of an oval, which allows the device to work as evenly as possible. This is achieved due to the fact that all the plates inside the system, in one revolution of the shaft, have time to do two cycles at once.

In such a device, there is also a certain area in which the gap between the stator and the rotor is simply minimal. In this section of the system, certain voltage surges can occur, which are handled very well by special sensors that regulate all such issues.

As for the inner plates, they are constantly under pressure and pressed against the inside of the working stator. It is this density that allows you to achieve the highest level of tightness, which is also very important for the high-quality operation of the system.

But this is far from the limit, since the rotation of the stator is only the beginning, after which a similar procedure will be repeated several more times. After the rotation continues, a vacuum is formed inside the system, allowing the work process to continue. During this process, the working chamber of the device is already connected to the suction line, and this connection takes place using a distribution disc, which, by the way, does its job quite well.

After the volume of the cooking chamber reaches its maximum volume, its connection to the suction line is completely interrupted. If the rotor continues to rotate, this means that the device is operating in the correct mode and the volume of the working chamber should gradually decrease. Further, the working fluid of the system flows out of the system through the side slot and is directed towards the pressure line, where a completely new process takes place.

The force of pressing the plates to the rotor also plays a significant role in this entire process. This indicator is determined using the pressure emanating from the internal mechanism. That is why, most often, such installations have two plates operating at the same effective frequency as standard.

Single-acting vane pumps

In this system, the movement of the plates has certain restrictions, which end at the level of the stator, which has a cylindrical surface. The unusual location of the stator in the system allows the internal elements of the system to work much more efficiently.

In this system, as in all others, there is a process of filling the working chamber, which is very similar to what we are used to seeing in ordinary installations. But, despite this, the very workflow of this unit is fundamentally different from what we often see in conventional installations.

So before buying it is worth thinking carefully about what kind of unit you need, and what is the key purpose of buying such equipment. Having thought all this in advance, you can completely protect yourself from a rash purchase.

Vane vacuum pump

The vane vacuum pump is already a more modernized version of this unit, which has a large number of advantages that you simply cannot see in the conventional pump version. The main advantage of such an installation is its ability to operate in an ultra-high vacuum, which is currently very much appreciated in the modern market.

Now we will consider the advantages and disadvantages of vane vacuum pumps, in order to still understand whether it is worth overpaying for work on a vacuum basis.

Advantages of vane vacuum pumps:

Ultra-high vacuum capability
High level of performance
Wider range of applications
The ability to run multiple processes at the same time

Disadvantages of vacuum vane pumps:

Too large dimensions that cannot always fit in the right place
High level of noise and vibration during operation

After reviewing the advantages and disadvantages, we can conclude that there are still more advantages to vacuum vane pumps, and if you still decide to take a more efficient unit, then a vacuum vane pump is simply the best option, which is actually worth overpaying for.

Rotary vane pumps

Rotary vane pumps are now in great demand on the market, and many manufacturers of various products are ready to pay a lot of money to buy such equipment. If we consider the entire range of vane pumps, then you can find both expensive and more budgetary units in it.

Now we will consider the most successful version of a rotary vane pump, which will be the most practical in terms of price and quality.

The RZ 6 rotary vane pump is a device that has managed to combine not only high technical characteristics, but also assembly quality, stability in operation, low cost and a huge number of important points that should always be remembered.

If we talk about the scope of application of rotary vane pumps, then we can see that they are used in a variety of industries. Now we will consider those areas of industry where at the moment they have become a key element, without which production could not be the same.

Applications of rotary vane pumps:

Radio engineering industry
Chemical industry
Oil production

Each of these industries at the moment is in dire need of the work of rotary vane pumps, which have now become an integral part of the work in all these areas.

Oil pumps

Judging by the type of pump that has found its greater use in most industries, then, of course, we can say that these are oil pumps. It is this category of devices that is currently the most popular, since most users are accustomed to trusting proven designs.

Nowadays, dry pumps are gaining more and more popularity, but still, not everyone is ready to overpay, while knowing that they are buying not yet completely proven equipment. As for oil installations, they have long ago established themselves in the market and proved that they are able to work in a variety of conditions, giving consistently high performance indicators.

At the same time, users are also confident that such a technique, thanks to constant lubrication, is more reliable, and its internal parts will not give in to wear.

Dry Oil Free Vacuum Pump

The dry oil-free vacuum pump is an air-based device that minimizes the risk of overheating that can occur due to a lack of oil in the system. Recently, many have begun to lean towards dry vacuum pumps. The main reason for this is the new technology of work, which does not require constant lubrication or the addition of any fluid.

All that is required from the user is to turn on the vacuum pump, after which it can work without any interruptions. But all the same, do not forget that this is a technique and it must be constantly looked after. By doing all the necessary procedures for this device, you can be sure that it will serve you for many years and during this time its internal parts will remain in perfect order and will produce all the same high performance indicators.

Oil-free (dry) rotary vane vacuum pumps are positive displacement pumps that allow to obtain a vacuum of medium depth with the complete absence of oil exhaust in the discharged air. The depth of the achieved vacuum is from 90 to 400 mbar residual pressure, depending on the model. Which is 9 to 40% of atmospheric pressure.

It is quite difficult to create a good oil-free rotary vane pump, so the number of manufacturers in the world is not so large. Basically, they are made in Europe (, and). And only low-capacity pumps are produced in the USA, China and Taiwan. Among the latter, Taiwanese pumps are in greatest demand.

Operating principle

Dry rotary vane pumps have in general the same principle of operation as. They also use an eccentrically mounted rotor with blades that can slide freely in their slots.
Animation 1: the principle of the rotary vane pump

However, there are some differences. Dry pumps do not use oil to seal the clearance between the blades and the housing, nor to lubricate moving parts, nor to cool. Therefore, the blades of dry pumps are made not of metal, but of a graphite composite. Graphite creates much less friction than metal and therefore does not require much cooling. In addition, the graphite vanes quickly rub against the surface on which they slide, ensuring good sealing of the gaps between the housing and the vanes.

On the one hand, the design of oil-free pumps is simpler: there is no oil separator and no oil channels. On the other hand, the lack of lubrication increases the demands on the quality of the surface finish.

Pros and cons of oil-free rotary vane vacuum pumps (versus oil)

There are two main reasons why you should choose a dry rotary vane pump: relatively clean air at the outlet and the ability to work with a coarse vacuum for a long time. In addition, there is no need to constantly monitor the oil level and worry about dehumidification of the pumped gas.

All the advantages of dry pumps are a mirror image of the disadvantages of oil-lubricated models: if it is preferable for oil to work in a high vacuum support mode, then a dry pump can work for a long time with a coarse vacuum at the inlet. Also, a situation often arises when the evacuated air remains in the same room where people work. Having passed through the oil-lubricated model, the air is inevitably saturated with oil vapors, which not only smell unpleasant, but are not particularly useful for those around them. Exhaust line filters solve this problem to some extent. But there are no perfect filters.

On the other hand, after passing through an oil-free rotary pump, the air, although it does not remain perfectly clean, in this case, instead of oil, particles of graphite dust enter the air. This dust, firstly, is emitted much less than oil. And secondly, graphite does not smell, and it is much easier to filter it out. Therefore, an oil-free pump is a good choice for areas where people work.

Another significant drawback of oil-lubricated pumps is the need for constant monitoring of the oil level. This level can both increase, due to the appearance of condensation, and decrease, for example, when working with a coarse vacuum or when the temperature is exceeded. Any of these scenarios is disastrous for a vane oil pump: if there is not enough oil, it will overheat and burn, and if there is a lot of condensate in the oil, the pump will quickly rust. An oil-free pump is initially devoid of these drawbacks: there is no need to constantly monitor it, it is enough to check the thickness of the blades every 2-3 thousand working hours.

In general, for residual pressures above 400 mbar, an oil-free pump is a good choice. But for creating a deeper vacuum, it is no longer suitable. The most advanced models from our catalog can provide only 100 mbar residual pressure. Another limitation is the service life. Oil-filled models can produce the same performance for years (only occasionally adding oil is required), which is what many laboratories use, maintaining a stable vacuum in the laboratory cabinet day and night. A dry rotary vane pump can also operate 24/7, but as the blades wear out, its performance will decrease. Therefore, it is recommended to turn on such a pump exactly when it is needed, and turn it off at the end of the shift.

Wear of working plates

As you can see from the animation above, the plates are constantly moving along special slots in the rotor. Escaping under the action of centrifugal force, they adhere tightly to the walls of the chamber and divide the free space of the working chamber into several isolated volumes.

The rotor of the pump rotates at a high speed (usually 1400-1500 rpm, since 4-pole electric motors are used), therefore, the problem of friction of the plates on the inner surface of the working chamber arises. In pumps with oil lubrication, this problem is not acute, therefore the working plates (blades) can be either composite or more durable metal. However, in dry pumps, only carbon vanes are available. Graphite itself is a good lubricant - graphite plates slide over the working chamber without overheating. But at the same time, graphite wears out relatively quickly. Moreover, not only its length is reduced from friction against the pump casing, but its thickness is also reduced from friction against the rotor.

Image 1. Three types of wear of graphite blades of rotary vane pumps.

The wear of the graphite vanes (plates) leads to air leaks and a decrease in vacuum depth and pump performance. What is the average life of oil-free pump blades? Most manufacturers bashfully do not indicate this term. However, we have some information.

Stairs Vacuum Taiwanese indicate the need to replace the vanes after 8,000 - 10,000 hours. However, they note that the performance of any oil-free rotary vane pump begins to decline after 3,000 hours of operation.

The Italians DVP write about the life of the records of 10,000 hours. Once an engineer came to our office who had an SB 16 pump from this Italian company. He said that the pump had worked for them 20,000 hours (though in compressor mode, but this does not change the essence), after which it stopped working normally (it was about the wear of the blades, and not about the breakdown of the pump). At the same time, the exhaust hoses inside were covered with a thin layer of graphite dust. This example says that the manufacturer indicates the minimum guaranteed service life of the blades, in practice they can work even more, but with a decrease in operating parameters.

The Germans Becker VX, KVX series hold the record for blade service life (alas, for the price of pumps too) - at least 20,000 hours, in practice, from 20,000 to 40,000.

Image 2. A graph of the decrease in performance of dry rotary vane pumps due to wear of the blades.

At what depth of vacuum does the efficiency of rotary vane vacuum pumps become the highest?

The efficiency of oil-free vane pumps is not fixed, but depends on the operating point (vacuum depth). At an inlet pressure close to atmospheric (at rough vacuum), the pump efficiency is very low and becomes acceptable (40% and higher) at a vacuum depth of 300 mbar (700 mbar residual pressure). The efficiency reaches its maximum (almost 60%) at a vacuum of 600-700 mbar (300-400 mbar absolute pressure), and then again begins to decrease to 40% as the vacuum deepens.

Picture 3. Comparison of efficiency of dry rotary vane vacuum pump and vortex single-stage blower.

If we compare, for example, an oil-free rotary vane vacuum pump and a single-stage vortex blower operating in vacuum mode, it turns out that these two devices do not compete with each other, but complement each other. In the range of created pressures from -100 to -300 mbar, the vortex blower shows the best efficiency values, and in the range from -300 to -900 mbar, the rotary vane device already works much more efficiently.