Vacuum pumps and their types. Oil-free rotary vane vacuum pumps. Types of vacuum pumps depending on the design

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

• double action
• single acting

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 only in this way it is possible to achieve the desired level of performance. If we talk about the differences between the two categories of vane pumps, then they are 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 acts 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 have time to complete two cycles at once in one revolution of the shaft.

In such a device, there is also a certain zone in which the gap between the stator and the rotor is simply minimal. In this section of the system, certain power 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 quality of the system.

But this is far from the limit, so the rotation of the stator is only the beginning, after which a similar procedure will be done 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 is made using a distribution disk, which, by the way, does its job quite well.

After the volume of the working 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.

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

Single acting vane pumps

In this system, the movement of the plates has certain limitations, 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 well 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 conventional installations. But, despite this, the very working process of this unit is fundamentally different from what we often see in conventional installations.

So before buying it is worth considering what kind of unit you need, and what is the key purpose of buying such equipment. Thinking through 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 usual version of the pump. The main advantage of such an installation is the possibility of its operation in ultra-high vacuum conditions, which is currently very much appreciated in the modern market.

Now we will look at 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 vacuum vane pumps:

• Possibility of formation of ultrahigh vacuum
• High performance
• Wider range of applications
• Ability to run multiple processes at the same time

Disadvantages of vacuum vane pumps:

• Too large dimensions that can not always fit in the right place
• High noise and vibration levels 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 productive unit, then a vacuum vane pump is simply the best option, which is actually worth overpaying.

Rotary vane pumps

Rotary vane pumps are now in great demand on the market, and many manufacturers of various products are willing 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 installations and more budget ones in it.

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

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

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

Scope of application of rotary vane pumps:

• Radio engineering industry
• Chemical industry
• Oil production

Each of these industries is currently 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 pumps that have found their greatest 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, as most users are used to trusting proven designs.

Now dry pumps are gaining more and more popularity, but still, not everyone is ready to overpay, while knowing that they are buying equipment that has not yet been fully tested. As for oil plants, they have long established themselves in the market and proved that they are able to work in a wide variety of conditions, giving consistently high performance indicators.

At the same time, users are also confident that such equipment, due 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 allows it to minimize the risk of overheating that can occur due to 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 operation, which does not require constant lubrication or the addition of any liquid.

All that is required from the user is to turn on the vacuum pump, after which it will be able to work without any interruption. But still, do not forget that this is a technique and you need to constantly look after it. 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 still give the same high performance.

Plunger (piston) vacuum pumps. Bypass devices. harmful space

A plunger vacuum pump is a type of mechanical vacuum pump that is capable of compressing gases to atmospheric pressure. Such an apparatus has a device similar to a double-acting reciprocating compressor. The main difference is that the plunger vacuum pump has a higher compression ratio.

Left - initial stage, 2 positions in the center - intermediate stage, right - final stage

The plunger includes a cylindrical part that encloses the eccentric and a hollow rectangular part that moves freely in the hinge slot. When the flat part of the plunger rotates, the pivot also rotates freely in the seat of the pump housing. This plunger is equipped with a channel through which gas enters the pumping chamber from the pumped-out cavity. The ingress of the oncoming gas flow into the inlet of the pump is limited by the preliminary closing of the inlet when the spool moves. There is also the possibility of reducing the harmful space. The tightness of the contact of the rotor with the cylinder in pumps is ensured by the fact that a thick layer of oil is formed in the wedge between the rotor and the cylinder.

Mechanical vacuum pumps carry out pumping of the volume, starting from the level of atmospheric pressure. Due to the fact that the pumped gas is released into the atmosphere, relative to mechanical vacuum pumps, such characteristics as the highest working pressure, as well as the highest starting and exhaust pressure, are not used. The key features of oil sealed mechanical vacuum pumps are:

• ultimate residual pressure;
• speed of action.

Mechanical vacuum pumps

A mechanical vacuum pump is a gas removal unit that is used to obtain / maintain a pressure below atmospheric pressure in tanks, from which the working fluid is pumped out at certain intervals at a certain composition and size of the gas flow.

The operation of such a pumping unit is based on the fact that the gas moves as a result of the mechanical movement of the working parts of the pump, thereby performing a pumping action. The volume, which is filled with gas, is cut off from the inlet and moves to the outlet. The gas is systematically moved to the outlet of the pumping unit as a result of the momentum of movement, which is transmitted to the gas molecules.

In accordance with the design features and method of operation of this type of pump, seven types of pumps are distinguished (screw / diaphragm / piston / rotary vane / spool / roots / spiral). In accordance with the type of working fluid, mechanical pumps can be molecular (they function due to the flow of molecules of the substance) and volumetric (they function due to the laminar flow of the substance). Mechanical vacuum pumps are differentiated according to the level of vacuum concentration (high, low, medium). In addition, this type of pump is divided into those that can operate without lubricant and with lubricant.

This type of pumping units is used in various industries: chemistry, metallurgy, electronics, food industry, medicine, aerospace. Mechanical vacuum pumps are also used in a wide variety of industrial installations, as well as in technical processes (for example, remelting of metals, deposition of thin films, simulation of space conditions, etc.).

Due to the growing demand for pumping units, mechanical vacuum pumps are continuously improved and developed, pumping units with improved performance are being developed.

The speed of operation of such pumps does not depend on the type of pumped gas. The residual pressure depends on the design of the pumping unit and the properties of the working fluid. The working fluid, as a rule, is oil, which has a list of necessary characteristics:

• low acidity;
• viscosity;
• good lubricating properties;
• low saturated vapor pressure in the operating temperature range of the pump;
• low absorption of gases and vapors;
• viscosity stability with temperature changes;
• high strength of a thin (0.05-0.10 mm) oil film capable of withstanding a pressure difference in the gap equal to atmospheric pressure.

The stability of the characteristics of mechanical vacuum pumps depends on the size of the gaps between the surfaces, the number of these gaps, as well as the quality of the oil that lubricates the rubbing surfaces.

The plunger vacuum pump can be equipped with a bypass device to increase efficiency. Bypass devices may differ structurally. Their function is to equalize the pressure on both sides of the piston at the end of the piston stroke.

In the absence of these channels, the residual compressed gas from the harmful space expands as the piston moves from left to right. In this case, the rest of the compressed gas has a pressure level p2. Curve ea 1 up to suction pressure p1 and p1 and λ 0 \u003d V 1 / V. In a vacuum pump, at the extreme left position of the piston, the rest of the gas moves to the right cavity of the cylinder, where the pressure is equal to p1. The pressure in the harmful space drops from p2 before p in, and the rest of the gas expands along the curve fa. Suction begins at the very beginning of the piston stroke ( λ 0 \u003d (V "1 / V)> λ 0). A similar process occurs when the piston moves in the opposite direction (from right to left). As a result, the volumetric efficiency increases from 0.8 to 0.9 λ 0 .

Presence of harmful space is the reason why a piston vacuum pump is not able to create an absolute vacuum and has a theoretical limit of this value, which corresponds to a certain residual pressure p pr. Value p pr more in the absence of bypass than in the presence of it.

If the vacuum pump operates continuously, then the volume of sucked gas is equal to the volume of process gases emitted into the atmosphere and the volumes that are sucked in from the outside through leaky areas do not change with time. The power indicator on the shaft of the vacuum pump is also not subject to change. It should be noted that this parameter is many times higher for machines equipped with a bypass, because the work of expanding the bypassed amount of compressed gas is lost.

A turbomolecular pump (TMP) refers to special pumps that allow creating and maintaining a deep vacuum for a long time, on the order of 10 -2 to 10 -8 Pa. Of interest is the etymological meaning of the name of the pump. The prefix "turbo-" is an abbreviated version introduced into the technical lexicon since 1900, the term "turbine". These two words come from the French. "turbine" - "turbine", and earlier from lat. "turbo", meaning "disorder, disturb, whirlwind, 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 following term “pump” is originally ours, Slavic, as it was transformed from the Old Orthodox words “suck, ssati, ss”, meaning “suck breast milk”, “suck on the brain bones”, “pull 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 turbopump;
• turbopump price;
• disadvantages of turbopumps;
• 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 Gaede 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 gap of 0.1 mm between the rotor rotating at a speed of about 8000 rpm and the fixed stator. The rarefaction of the gas up to 10 -4 mm Hg was obtained. The new pump even began to be produced by the German company Leybold's Nachfolgers, but was not widely used. Firstly, there was no urgent need for it, and secondly, technological difficulties with the manufacture of such small gaps interfered. The ingress of macroscopic solid particles (pebbles, chips, glass) into the pump together with the gas caused the rotor to 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 resumed 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 principle of operation of TMN pumps continued to be improved, such designs as the Agilent TV 81M turbomolecular pump and the latest (2015) high-vacuum turbomolecular pump Twistorr 84 FS by the Italian company Agilent Technologies, the TG 350F hybrid turbomolecular pump by the Japanese company Osaka Vacuum and others appeared. In this case, often the nodes of these devices are interchangeable. For example, a power supply unit for 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 gaseous medium is pumped out due to the communication of mechanical energy impulses to the substance molecules from the solid, liquid, gaseous surfaces of the pump moving at high speed. At the same time, in a molecular pump, the directions of movement of working surfaces and gas molecules coincide, and in a turbomolecular pump, the directions of movement of working elements and molecules are mutually perpendicular.

Cutaway image of a molecular pump

Molecular pumps according to the principle of operation are divided into:

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

For example, the high vacuum molecular pump MDP 5011 is a device with mechanical working elements. The movement of gas molecules to the outlet pipe of the pump provides a solid surface of the rotor-glass, which makes 27,000 rpm. This model MDP 5011 is the bestseller among turbopumps. Clearly, you are interested in the price of the MDP5011 molecular pump. Please contact us with questions such as call or email. We will advise and help.

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

Appearance of turbopumps

1. Turbopumps for pumping liquids.
2. Turbopumps for pumping suspensions.
3. Turbopumps for pumping gases.

The disadvantages of turbopumps include the complexity of the design, long downtime when repairing a pump or turbine, and high cost. Therefore, if you need to buy an oil turbo pump ТМН-6/20, naturally, the question arises, what is the price of a turbo pump. If it does not suit you in other firms, come to us.

Turbomolecular pumps (TMP) are made in the form of multi-stage 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 arranged mirror to each other, makes it possible to effectively pump out gas molecules due to the different probability of passing molecules through channels located at an angle in the direction of pumping and supply. TMPs are fixed on a massive base through shock absorbers, which reduces vibration during pumping.

Appearance of the turbomolecular vacuum pump ТМН-500

The principle of operation of the turbomolecular pump is as follows. The energy of the turbine blades rotating at high frequency 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 moving gas particles. Chaotic motion of molecules turns into accelerated motion in a given direction of pumping. Such effective rotor action is possible only in the molecular gas flow mode, which is created by an additional low pressure fore vacuum pump.

A good impression is made by domestic double-flow oil-free pumps: a turbomolecular vacuum pump TMN-500 and a pump TMN-200 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, non-failure operation and sufficient durability.

A dry vacuum pump (oil-free) works in the same way as an oil pump. But in a dry type pump, oil is not used to lubricate the rubbing parts, and there are no sealing devices. Therefore, not metal, but a graphite composite material is used as the 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 dry vacuum pump

Advantages of the vacuum oil-free pump:

• absence of oil vapors at the exit of air from the pump, the workplace becomes clean, the environment ecology improves;
• no need to purchase and fill in expensive oil, monitor its level and pollution;
• lower cost.

Dry pump disadvantages:

• the depth of the created vacuum is lower than that of oil-sealed pumps;
• the durability of graphite blades is much less than metal ones;
• wear products in the form of powdered graphite enter the atmosphere.

However, experts believe that oil-free vacuum pumps are the future. And now they are trying to buy oil-free rotary vane vacuum pump, oil-free piston vacuum pump, 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.

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

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

Appearance 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 the consultants. Our highly qualified specialists will help in choosing the best option for pumps, explain the terms 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 by E-mail. We will be glad to help you.

In various spheres of human activity, the creation of a vacuum is required. This term characterizes the state of the gas phase, the pressure of which is below atmospheric. It is measured in millimeters of mercury or pascals. Dilution of gases occurs when a substance is forced to be removed from devices that have a limited volume. A technical device designed for this purpose is called a vacuum pump. It can be used on its own or be part of more complex systems.

Vacuum is widely used in various technical devices. It allows you to lower the boiling point for water or chemical liquids, to remove gases from materials that require increased homogeneity of the composition, to create sterile conditions for processing and storage. With small dimensions and economical energy consumption, modern vacuum pumps allow you to quickly reach a deep degree of vacuum. They are used in a wide variety of processes and areas of activity:

• in the oil refining and chemical industries to maintain the necessary conditions for the course of reactions and separation of the resulting mixtures;
• when degassing metals and other materials to create parts with a homogeneous structure and the absence of pores;
• in the pharmaceutical and textile industries for quick drying of products without raising the temperature;
• in the food industry when packaging milk, juices, meat and fish products;
• in the process of evacuation of refrigeration and other equipment with increased requirements for the absence of moisture;
• for the normal functioning of automatic conveyor lines using vacuum suction cups as grippers;
• when equipping production and research laboratories;
• in medicine during the operation of breathing apparatus and dental surgeries;
• in polygraphy for fixing thermal films.

The principle of operation of vacuum pumps

A vacuum is created when a substance is mechanically removed from a closed space. Technically, this is implemented in various ways. Principle of operation jet type vacuum pump is based on the entrainment of gas molecules by a stream of water or steam flying out of the ejector nozzle at high speed. Its scheme provides for the connection of a side pipe, in which a vacuum is created.

The advantage of this design is the absence of moving parts, and the disadvantage is the mixing of substances and low efficiency.

In technology, the most common mechanical units. The operation of a vacuum pump with a rotating or reciprocating main part consists in periodically creating an expanding space inside the housing, filling it with gas from the inlet pipe, and then pushing it out through the outlet. The design of the vacuum pump in this case can be very diverse.

The main types of vacuum pumps

In the manufacture of devices for creating a vacuum, metal and plastic materials are used that are resistant to the chemical effects of the pumped medium and have sufficient mechanical strength. Much attention is paid to the accuracy of the fitting of the nodes and the tightness of the contact of the surfaces, which excludes the reverse slip of gases. Here is a list of the main types of vacuum pumps, which differ in design and principle of operation.

Water ring

A water ring vacuum pump is one of the options for liquid ring units, using to create a vacuum clean water circulation. It has the form of a cylinder with a rotor equipped with blades, rotating on an off-center shaft. Before starting work, it is filled with liquid.

When starting the engine, the impeller accelerates water along the inner walls of the housing. A crescent-shaped vacuum region is formed between it and the rotor. Gas rushes into it from the inlet pipe of the pump. Moving vanes move it along the shaft and eject it through the outlet. Units of this type are often used also for partial gas treatment due to its intense contact with water.

The use of liquid as a working body provides many advantages.

1. Water rotating in the space between the rotor and the pump casing eliminates the possibility of gas backlash, replacing seals and reducing the requirements for precision in the manufacture of parts.
2. All rotating parts of the pump are constantly flushed with liquid, which reduces friction and improves heat removal.
3. Such devices rarely require repair, have a long service life and consume a minimum of electricity.
4. Working with gases containing water drops and small mechanical impurities does not adversely affect the technical condition of the equipment.

The latter circumstance is important when using such pumps for pumping air from containers containing moisture. They are used for air conditioners and other refrigeration units when the system is evacuated before filling them with freon.

Lamellar-rotary

Such pumps have a cylindrical body with a carefully polished inner surface and a rotor located inside it. Their axes do not match, so the side clearance has a different value. The rotor contains special moving plates, which are pressed against the body by springs and divide the free space into sectors of variable volume. When the engine is turned on, the gases move in such a way that a vacuum is always created in the intake pipe, and excess pressure is always created in the pressure pipe.

To reduce friction, the plates are made of antifriction materials or special low-viscosity oils are used. Pumps of this type are able to create a sufficiently strong vacuum, but they are sensitive to the purity of the pumped liquid or gas, require regular cleaning and contaminate the product with traces of grease.

Membrane-piston

The working body of pumps of this principle of operation is flexible membrane associated with the lever mechanism. It is made of modern composite materials that are resistant to mechanical stress. Its edges are firmly attached to the housing, and the central part, under the action of an electric or pneumatic drive, bends, alternately reducing and increasing the space of the inner chamber.

The change in volume is accompanied by the suction and expulsion of incoming gases or liquids. When working together in antiphase of the two membranes, a continuous pumping mode is provided. The valve system regulates the correct distribution and direction of flows. The mechanism has no rotating or rubbing parts in contact with the pumped product.

To advantages of such pumps should include:

• no contamination of the product with grease or mechanical impurities;
• complete tightness, excluding leaks;
• high profitability;
• ease of flow control;
• long-term operation in dry mode, which does not harm the structure;
• the ability to use a pneumatic drive to work in an explosive environment.

screw

The operating principle of screw pumps is based on displacement of liquid or gas along a rotating screw. They consist of a drive, one or two helical rotors and a suitably shaped stator. High precision manufacturing of parts does not allow the pumped medium to slip back. As a result, excess pressure is formed at the pump outlet, and vacuum is formed at the intake.

Such equipment is expensive due to high quality requirements. It can not be kept in a "dry" mode for a long time.

The main advantages of such pumps:

• flow uniformity;
• low noise level;
• the ability to pump liquids with mechanical inclusions.

Vortex

Vortex vacuum pumps by their design reminiscent of centrifugal equipment. They also have a vaned impeller that rotates on a central shaft. The fundamental difference lies in the location of the inlet pipe on the outer circumference of the body, and not in the region of the central axis.

The minimum gap between the impeller and the housing ensures the stable movement of the pumped liquid in the required direction. Units of this type are capable of creating a sufficiently high discharge pressure and have a self-priming effect. These pumps are easy to operate, easy to repair and have proven themselves when pumping gas-liquid mixtures, but they have a low efficiency. They are sensitive to the ingress of mechanical impurities that can lead to rapid wear of the impeller.

Self-manufacturing of a vacuum pump

If you are not ready to bear the costs of acquiring factory equipment, try making a vacuum pump yourself. For pumping air from a small volume container, it may fit a medical syringe or a slightly modified hand bicycle pump.

Advice! With frequent use and evacuation of large vessels, it is more convenient to use devices with an electric drive.

Consider the option of manufacturing a vacuum installation from the compressor of an old refrigerator. It is already designed for pumping gas and, with minimal repairs, will be able to create a vacuum. Your actions will be extremely simple:

• at some distance from the compressor, cut with a hacksaw for metal two copper tubes suitable for it;
• dismantle the compressor together with the power supply circuit or replace it, together with the starting relay, with a new one similar to the old one;
• on the copper pipe that came from the condenser, put on a durite hose of a suitable diameter and connect it with the other end to the container being evacuated;
• for tightness of the connection, you can use a regular clamp or use a twist of steel wire;
• connect the vacuum pump to the electrical network and, after starting, by venting air from the second copper pipe, make sure that it works correctly.

Important! The compressor of the refrigerator is not designed for operation in a humid environment, so care must be taken not to get water on it.

Oil-free (dry) rotary vane vacuum pumps are positive displacement pumps that produce a medium-deep vacuum in the complete absence of oil exhaust in the exhaust air. Depth of the reached vacuum - from 90 to 400 mbar of residual pressure depending on model. What is from 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 pumps of small productivity are produced in the USA, in China and in Taiwan. Among the latter, Taiwanese pumps are in the greatest demand.

Operating principle

Dry rotary vane pumps generally operate on the same principle as . They also use an eccentrically mounted rotor with lamellas that can slide freely in their slots.
Animation 1: principle of operation of a rotary vane pump

However, there are some differences. Dry pumps use no oil to seal the gap between the blades and casing, lubricate moving parts, or provide cooling. Therefore, the blades of dry pumps are not made of metal, but of a graphite composite. Graphite creates much less friction than metal, so it does not require much cooling. In addition, graphite vanes quickly rub against the surface on which they slide, providing good sealing of the gaps between the casing 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 requirements for the quality of surface treatment.

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

There are two main reasons for choosing a dry rotary vane pump: relatively clean air at the outlet and the ability to work with rough vacuum for a long time. In addition, there is no need to constantly monitor the oil level and take care of draining the pumped gas.

All the advantages of dry pumps are a mirror image of the disadvantages of oil-lubricated models: if the oil prefers to work in the mode of maintaining a deep vacuum, then a dry pump can work for a long time with a rough vacuum at the inlet. Also, a situation often arises when the pumped air remains in the same room where people work. After passing through an oil-lubricated model, the air is inevitably saturated with oil vapors, which not only smell bad, but are also not very useful for others. 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, although the air does not remain perfectly clean, in this case, particles of graphite dust enter the air instead of oil. This dust, firstly, is released much less than oil. And secondly, graphite does not smell, and it is much easier to filter it. Therefore, an oil-free pump is a good choice for rooms where people work.

Another significant disadvantage of oil lubricated pumps is the need for constant monitoring of the oil level. This level can both increase, due to the appearance of condensate, and decrease, for example, when working with a rough vacuum or when the temperature is exceeded. Any of these scenarios is detrimental to a vane oil pump: if there is not enough oil, it will overheat and burn out, 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 disadvantages: 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 it is no longer suitable for creating a deeper vacuum. The most advanced models in our catalog can provide only 100 mbar of residual pressure. Another limitation is the service life. Oil-filled models can deliver the same performance for years (only an occasional topping up of oil is required), which is what many laboratories use to maintain 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, its performance will drop. 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 working plates are constantly moving along special slots in the rotor. Flying out under the action of centrifugal force, they fit snugly against the walls of the chamber and divide the free space of the working chamber into several isolated volumes.

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

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

Worn graphite blades (plates) lead to air leaks and a decrease in vacuum depth, as well as pump performance. What is the average blade life of oil-free pumps? Most manufacturers shyly do not indicate this period. However, we do have some information.

The Taiwanese Stairs Vacuum indicate the need to replace the blades after 8,000 to 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 service life of records 10,000 hours. An engineer once came to our office, who had an SB 16 pump from this Italian company. He said that the pump had worked for them for 20,000 hours (albeit 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 longer, but with a decrease in operating parameters.

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

Image 2. Graph of performance degradation of dry rotary vane pumps due to blade wear.

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

The efficiency of oil-free vane pumps is not a fixed value, but depends on the operating point (vacuum depth). At near atmospheric inlet pressure (at rough vacuum) pump efficiency is very low and becomes acceptable (40% and above) 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.

Image 3. Comparison of the efficiency of a dry rotary vane vacuum pump and a 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 2 devices do not compete with each other, but complement each other. In the range of generated 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 blower already works much more efficiently.