Method for Operating a Vacuum Pump, as well as a Vacuum Pump Designed for this Purpose with Two Inlets and One Outlet, its Use and Vacuum Packaging Machines Equipped Therewith

Description

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a method for operating a vacuum pump, in particular a rotary vane vacuum pump for applications, for example, in the plastic, ceramic and/or packaging industry, and a vacuum pump designed for this purpose, in particular a rotary vane vacuum pump which has two inlets and one outlet. Thanks to the special configuration of this rotary vane vacuum pump, an arrangement of two pumps can be replaced and the same vacuum chamber can be evacuated consecutively, or two different vacuum chambers can be evacuated simultaneously or partially overlapping in time. The new possibility of perfectly adapting the pump design to the application of the pump increases the sustainability and efficiency of vacuum packaging machines, for example, which are equipped with the rotary vane vacuum pump according to the invention, as the pump-down times are shorter than with a single, larger pump known from the prior art with only one inlet and only one outlet. A further advantage is savings in investment, operation and maintenance compared to the solution with two pumps or a two-stage pump. Therefore, a further object of the invention is a vacuum packaging machine comprising a rotary vane vacuum pump designed in this way.

STATE OF THE ART

Vacuum pumps, especially rotary vane vacuum pumps, belong to the group of single-rotor positive displacement pumps, and can be used universally in different vacuum applications. In general, rotary vane vacuum pumps comprise a cylinder in which an eccentrically mounted and slotted rotor is arranged in a cylindrical interior, in whose slots arranged vanes are pressed outwards by centrifugal and possibly spring forces when the rotor rotates. In general, the rotary vane vacuum pump comprises an inlet opening and an outlet opening for the medium to be pumped, in particular gas, between which there is a pumping chamber in the interior of the cylinder. The medium to be conveyed is sucked in through the inlet opening, compressed by the changing chamber volumes of the chambers divided by the slide valves and discharged from the conveying chamber via the outlet opening or via an outlet valve, which may be overlaid with oil.

In order to achieve low final pressures and a high pumping speed in a fine vacuum range, several pumps arranged in series or multi-stage pumps are often used. (Example: DE 3 603 809 A1: Two-stage rotary vane pump, consisting of housings with a cylindrical interior in which rotors are arranged eccentrically, which guide radially movable vanes in slots, which form working chambers in the cylinder, the rotors being non-rotatably connected to a horizontally arranged shaft, inlet and outlet ducts open axially horizontally into the working chambers, and that, due to the cylinders rotated towards each other, the working chambers of adjacent stages are arranged in such a way that the outlet duct of the first stage opens directly into the inlet duct of the second stage and thus the shortest possible gas paths are achieved.)

Multi-stage pumps with a common housing are hardly known. From DE 43 25 286 A1 a rotary vane vacuum pump with a high-pressure vacuum stage and a fore-vacuum stage is known, comprising a rotor which has bearing and armature sections of the same diameter and is accommodated in a pot-shaped housing which encloses the pumping chambers. Both armature sections of the rotor, which are equipped with slide slots, are arranged on the end face, with the only bearing section being located between these armature sections.

Furthermore, so-called split-flow vacuum pumps are known for the simultaneous evacuation of several vacuum chambers. This type of vacuum pump makes it possible to dispense with a pump system consisting of several individual pumps and to carry out the evacuation of several vacuum chambers with a single pump. Known from DE 43 31 589 A1 is turbomolecular pump, which has several suction connections, each of which is connected to one of the vacuum chambers of a device. The suction connections feed gas to various axially spaced positions of the rotor, whereby several rotor-stator packs are arranged along the rotor axis, each of which compresses gas. Here, the inlet is connected to the first vacuum chamber and the outlet is connected to the inlet of the next rotor-stator pack. In addition, the area between two rotor-stator packs is connected to a second vacuum chamber. This allows a plurality of vacuum chambers to be evacuated to different pressures, with a rotor-stator package being assigned to each suction connection. In contrast, in the rotary vane vacuum pump according to the invention, two suction connections are only assigned to one “rotor-stator package”.

From DE 39 13 414 A1 a rotary vane pump is known to supply a user with needs for different pressures and quantities. In the area of an expanding chamber, the rotary vane pump has a suction opening for supplying a pressure medium and, in an adjoining compression area, a plurality of discharge channels leading to different supply circuits. Accordingly, the compression area is divided into at least two discharge zones with separate discharge channels, whereby the compression area is able to be divided by means of a movable gate.

Known from GB 881 221 A is a rotary vane motor with two inlets, each with a non-return valve and an outlet for hydraulic transmission systems.

SUMMARY OF INVENTION

Proceeding from the state of the art, the present invention has as its object to design a method for the multi-stage evacuation of one or more vacuum chambers i, j, k, . . . , in particular in vacuum packaging machines, in such a way that it provides two suction capacities adapted to the application and two final pressures adapted to the application, as well as a vacuum pump suitable for this purpose, in particular a rotary vane vacuum pump, which ideally has a compact design.

These objects are achieved by means of a method according to one or more of the claims 1 to 6 and a rotary vane vacuum pump suitable therefor according to one or more of the claims 7 to 11. Preferred embodiments emerge from the dependent claims and from the description.

The pressures p_xy(z) achieved with the method are indicated as follows:

• • x stands for the evacuation state of the vacuum chamber:
  • 0=Before pump-down=initial pressure of the vacuum chamber,
  • 1=after pump-down=final pressure of the vacuum chamber.
  • y stands for the inlet of the pump (or for the first and second pump in the two-pump solution from the state of the art and for the first and second stage in the two-stage pump) to which the vacuum chamber is connected:
  • 1=first inlet (inlet 1)/high vacuum pump 21/high vacuum stage 31;
  • 2=second inlet (inlet 2)/fore-vacuum pump 22/fore-vacuum stage 32.
  • z stands for the vacuum chamber: i, j, k, . . .

In the method according to the invention, the vacuum chambers are either evacuated from an initial pressure p_02(z), which corresponds for example to atmospheric pressure, first via the second inlet to a final pressure p_12(z) and then starting from the final pressure p_12(z), which is now the initial pressure p_01(z) at the first inlet, via the first inlet to a final pressure p_11(z), or they are evacuated starting from an initial pressure p_01(z) via the first inlet to a final pressure p_11(z). This means that the initial pressure of the chamber to be evacuated at the first inlet is always lower than the initial pressure of the chamber to be evacuated at the second inlet.

The method according to the invention for evacuating at least two vacuum chambers i and j with a vacuum pump, in particular a rotary vane vacuum pump, hereby has the following steps:

• • a) Providing at least two vacuum chambers i and j with initial pressures p_02(i) and p_01(j) with p_02(i)≥p_01(j);
  • b) Connecting the second inlet to the vacuum chamber i and the first inlet to the vacuum chamber j; (this corresponds to the valve position 41 shown in FIG. 3)
  • c) Evacuating the vacuum chamber i from the initial pressure p_02(i) to a final pressure p_12(i) via the second inlet during an evacuation time t_p2(i) and simultaneously evacuating the vacuum chamber j via the first inlet from the initial pressure p_01(j) to a final pressure p_11(j) during an evacuation time t_p1(i);
    • wherein for the final pressure p_12(i) of the vacuum chamber i and the initial pressure p_01(j) of the vacuum chamber this applies: p_01(j)>p_11(j) and p_02(i)>p_12(i);
  • d) Closing and separating the vacuum chamber i from the second inlet and the vacuum chamber j from the first inlet.

Preferably, the evacuation times t_p2(i) and t_p1(j) in step c) are as equally long as possible. Preferably, the evacuation times t_p2(i) und t_p1(j) in step c) therefore only deviate from one another by a maximum of 25%, preferably by a maximum of 15%, particularly preferably by a maximum of 10%, very particularly preferably by a maximum of 5%.

Ideally, the final pressure p_12(i) of vacuum chamber i and the initial pressure p_01(j) of vacuum chamber j in step c) deviate from each other by a maximum of 25%, preferably by a maximum of 15%, particularly preferably by a maximum of 10%, especially preferably by a maximum of 5%, and are most preferably the same.

The pump-down process can then be repeated with further vacuum chambers i and j starting from the pressures p_02(i) and p_01(j) or with other vacuum chambers k and l with corresponding initial pressures p_02(k)=p_02(i) and p_01(l)=p_01(j).

In a preferred embodiment, the method according to the invention is used in particular for evacuating packages, in particular packages of foodstuffs. This means that the vacuum chambers i and j contain packages, in particular packages of foodstuffs. In principle, two different types of arrangement of the vacuum chambers are thereby conceivable, in particular for packaging foodstuffs: In a first preferred embodiment, the vacuum chambers are arranged in a rotary vacuum packaging machine. In this case, the volumes of the vacuum chambers to be evacuated are the same within the manufacturing tolerances. In a second preferred embodiment, the vacuum chambers are arranged in two parallel queues, whereby the vacuum chambers of the first queue are successively connected to the first inlet of the rotary vane vacuum pump and the vacuum chambers of the second queue are successively connected to the second inlet of the rotary vane vacuum pump and evacuated. This means that the volumes of the vacuum chambers to be evacuated in the first queue are the same within the manufacturing tolerances. Similarly, the volumes of the vacuum chambers to be evacuated in the second queue are the same within the manufacturing tolerances. However, the volumes of the vacuum chambers in the first queue may differ from the volumes of the vacuum chambers in the second queue. In this arrangement, however, the final pressure of the vacuum chamber after evacuation via the second inlet preferably does not deviate by more than 25%, particularly preferably not more than 15%, most preferably not more than 10%, most preferably not more than 5%, from the initial pressure of the respective vacuum chamber connected to the first inlet.

If two vacuum chambers i and j are evacuated with the initial pressures p_02(i) and p_02(j) with p_02(i)=p_02(j), whereby the initial pressures p_02(i) and p_02(j) preferably both correspond to atmospheric pressure, the following steps are carried out before step a):

• • a.i) Connecting the second inlet to the vacuum chamber j;
  • a.ii) Evacuating the vacuum chamber j from the initial pressure p_02(j) to a final pressure p_12(j) via the second inlet during an evacuation time t_p2(j) with p_12(j)=p_01(j);
  • a.iii) Closing and separating the vacuum chamber j from the second inlet.
    The final pressure p_12(j) corresponds then to the initial pressure p_01(j) of the vacuum chamber j, when it is evacuated to the end pressure p_11(j) via the first inlet during an evacuation time t_p1(j).
    The steps a.i) to a.ii) or respectively a.i) to a.iii) are carried out, for example, when the process is started.

Since the final pressure p_12(i) of the vacuum chamber i corresponds to the initial pressure p_01(j) of the vacuum chamber j, it is possible, provided that the vacuum chambers i and j are the same size within the manufacturing tolerance, that the vacuum chamber i is connected to the first inlet after the first pump-down process and is further evacuated to the final pressure p_11(i) during an evacuation time t_p1(i). However, it is necessary for another vacuum chamber k with the initial pressure p_02(k) to be connected to the second inlet at the same time, which is then evacuated to the final pressure p_12(k) during the evacuation time t_p2(k). This process of transferring a vacuum chamber (here the vacuum chamber i) from the second inlet to the first inlet is used, for example, in the case of the application in a rotary vacuum packaging machine.

From this, there results the following method according to the invention for evacuating any number of vacuum chambers, at least three, vacuum chambers i, j und k with the initial pressures p_02(i)=p_02(k)= . . . and p_01(j), possibly in the rotation system, i.e. in a rotary vacuum packaging machine, which has the following steps:

• • a) Providing at least three vacuum chambers i, j and k with the initial pressures p_02(i)>p_01(j) and p_02(i)=p₀₂(k), that is a vacuum chamber i with an initial pressure p_02(i), a vacuum chamber j with an initial pressure p_01(j), and a vacuum chamber k with an initial pressure p_02(k),
  • b) Connecting the second inlet to the vacuum chamber i and the first inlet to the vacuum chamber j (that corresponds to the valve position 41 shown in FIG. 3);
  • c) Evacuating the vacuum chamber i from the initial pressure p_02(i) to a final pressure p_12(i) via the second inlet during an evacuation time t_p2(i) and simultaneously evacuating the vacuum chamber j via the first inlet from the initial pressure p_01(j) to a final pressure p_11(j) during an evacuation time t_p1(j), where p_02(i)>p_12(i) and p_01(j)>p_11(j);
  • d) Closing and separating the vacuum chamber i from the second inlet and the vacuum chamber j from the first inlet;
  • e) Connecting the second inlet to the vacuum chamber k and connecting the first inlet to the vacuum chamber i (that corresponds to the valve position 42 shown in FIG. 3);
  • f) Evacuating the vacuum chamber k from the initial pressure p_02(k) to the final pressure p_12(k) via the second inlet during an evacuation time t_p2(k) and simultaneously evacuating the vacuum chamber i from the initial pressure p_12(i) to the final pressure p_11(i) during an evacuation time t_p1(i), where p_02(k)>p_12(k) and p_12(i)>p_11(i);
  • g) Closing and separating the vacuum chamber k from the second inlet and the vacuum chamber i from the first inlet.
    With this method any number of vacuum chambers i, j, k, . . . can be evacuated successively, overlapped in time, when arranged in a rotating way, as often as desired. This means that the cycle can start from the beginning with step b). Hence the method according to the invention has optionally the following step:
  • h) Optionally repeating steps b) to g).

According to the invention, a vacuum pump, in particular a rotary vane vacuum pump, is used in the inventive method. The rotary vane vacuum pump for evacuating at least two vacuum chambers comprises a cylinder and a rotor arranged inside the cylinder in a way eccentric to its center axis, so that this rotor forms with the cylindrical inner wall a, preferably lunate, conveying chamber. The cylinder has an outlet as well as a first and a second inlet, both inlets being connectable to the vacuum chambers. The rotor has slots, in which at least two vanes are borne in a movable way. With rotation of the rotor, the vanes are pressed outwardly against the cylindrical inner wall and form therewith sealing points, and thus divide the, preferably lunate, conveying space into individual conveying chambers, in which the suctioned gas is conveyed from the first inlet to the second inlet and from the second inlet to the outlet of the rotary vane vacuum pump, and is compressed. Thus, according to the invention, a second inlet is provided on the rotary vane vacuum pump, which second inlet is arranged offset at an angle to the first inlet in the conveying direction and can be controllable by means of a valve device. The angle and thus the relationship between the pumping speed of the two inlets is determined during the design process depending on the boundary conditions and given by the application.

In principle, rotary vane vacuum pumps can be used universally in the entire rough and fine vacuum range, i.e. up to a final pressure of 10⁻³ mbar and a pumping speed in the range from 3 to 1600 m³/h, whereby a single-stage or a two-stage pump is used depending on the pressure range.

The method according to the invention or respectively the rotary vane vacuum pump according to the invention is used in particular for evacuation of foodstuff packaging, so that therefore the vacuum chambers contain packages for foodstuff.

A rotary vane vacuum pump of this type enables a flexibly configurable pumping speed and therefore universal application possibilities for diverse applications. The flexible adaptability of the pumping speed is achieved without a significantly larger installation space and/or a more complex design of the rotary vane vacuum pump. In particular, it is not necessary to provide separate pumping stages in the form of a plurality of rotary vane vacuum pumps to evacuate one or more vacuum chambers. Since the adjustment of the pumping speed and/or the final pressure p_12(i)/p_12(k) or the initial pressure p_01(j) can be achieved without changing the rotor speed, the dynamic properties of the rotor only change to a small extent, so that, for example, the bearings and elements of known constructions can also be used to a large extent. This means that costs can be limited.

The above-mentioned advantages are achieved in particular by the fact that volume flows {dot over (V)}₁ and {dot over (V)}₂ can be introduced via the first inlet and the second inlet and can be set as a function of each other. For example, a first volume flow {dot over (V)}₁ can be set via the first inlet, which is arranged upstream of the second inlet, and a second volume flow {dot over (V)}₂ which is dependent on this, can be set via the second inlet. The size of the volume flows {dot over (V)}₁ or respectively {dot over (V)}₂ is determined during the design. The volume flows to be designed are defined by the customer's specification of the volume of the vacuum chamber to be evacuated, including tubing/piping, the pump-down time and the working pressure.

In a preferred embodiment, the ratio of the volume flows {dot over (V)}₁ und {dot over (V)}₂ is in a range from 0.8:1 to 1.1:1, particularly preferably in a range from 0.9:1 to 1.0:1.

The nominal pumping speed of a rotary vane vacuum pump is determined by the following parameters: the diameter and axial length of the cylindrical interior of the cylinder, the rotor diameter, dimensions and arrangement or respectively orientation of the vanes as well as a rotational speed of the rotor, the number of vanes accommodated in the vane slots, which limit variable chamber volumes between adjacent vanes as well as the closing angles of the inlets and the opening angles of the second inlet and of the outlet. The number of vanes can be either even or odd. With three vanes in a largely even radial distribution on the rotor, there are three 120° conveying chambers for the pumped medium, with 6 vanes there are six 60° conveying chambers and with 9 vanes there are nine 40° conveying chambers (9, 9′, 9″, . . . ).

In particular in the rotary vane vacuum pump according to the invention with a first inlet and a second inlet, the nominal pumping speed at the first inlet and at the second inlet can be achieved by a number of vanes greater than three. The vanes are preferably arranged in a rotationally symmetrical manner.

The optimal number of vanes depends, among other things, on how many vanes should be between the two inlets. The optimal number also depends on the size of the pump. For example, in a preferred embodiment, there should be at least one vane between the first and second inlets. For a given pump, the optimal number of vanes is then in the range of 3-17.

With other materials and geometries, more than 17 vanes can also be present.

In addition to the number of vanes, the position of the inlets and their length also have an influence on the ratio of the pumping speeds for the first and second inlets. These parameters are therefore selected during the design, depending on the application, and are all coordinated with each other:

The greater the number of vanes, the higher the pumping speed up to the optimal number of vanes; beyond that, it drops again. The smaller the angle between the first and second inlet, the greater the pumping speed. The longer the first inlet, the better the flow into the conveying chamber. The longer the second inlet, the better the flow into the conveying chamber and the lower the geometric compression. All variables are coordinated when designing the rotary vane vacuum pump.

A further parameter to be selected is therefore the arrangement of the first inlet relative to the second inlet. This applies both when the first inlet and the second inlet are designed as radial inlets and when they are designed as axial inlets. By selecting the angle which is included between the first inlet and the second inlet, influence can be exerted on the ratio of the first pumping speed at the first inlet and the second pumping speed at the second inlet. The position of the first inlet relative to the second inlet can be selected depending on the application, i.e. depending on the evacuation task in the evacuation of two vacuum chambers. In one embodiment of the present invention, the first inlet can be provided in a range of approximately 10° to 120° and the second inlet offset in a range of approximately 175° to 220°, relative to the axis of rotation of the cylinder or respectively the axis through the center points of the cylinder, rotor and dead center. Thus, the ratio of the first nominal pumping speed to the second nominal pumping speed can vary in a range from 0.5:1 to 5:1, preferably in a range from 0.5:1 to 2.0:1.

The position of the two inlets is selected here so that the flow chambers connected to these inlets are separated from each other by at least one vane, preferably by at least two vanes. The number of vanes is therefore selected such that there is at least one sealing point between the first inlet and the second inlet, preferably two sealing points between the first inlet and the second inlet. This results in increased internal leak-tightness, as the conveying chamber between the two inlets serves as a buffer between them. As a result, the backflow losses are lower, which leads to a better final pressure. This means that the pumping speed is better and the pump-down times are shorter than they would be without this buffer.

The position and length of the two inlets, as well as the number of vanes, can therefore be used to define the ratio of pumping speeds for the first inlet and the second inlet. Depending on the planned application of the rotary vane vacuum pump, these parameters are therefore selected when designing the rotary vane vacuum pump.

When designing the system, it must be taken into account that the full pumping speed is not available at the second inlet, the fore-vacuum inlet, but is reduced by the pressure-dependent volume flow, i.e. by the gas volume of the first inlet, the high-vacuum inlet, conveyed at a certain pressure. This reduction can be compensated for by a correspondingly larger design pumping speed at the second inlet.

All inlets, in particular the first and/or second inlet, can in principle be designed as radial and/or axial inlets. For example, it may be advantageous for the first inlet and the second inlet to be radial. In principle, an inlet can also have a plurality of inlet openings.

Due to the arrangement and design of the first inlet in relation to the second inlet or in relation to the first final pressure to be reached and the second final pressure to be reached, the evacuation times can also differ. For example, in one embodiment of the rotary vane vacuum pump according to the invention, the evacuation time via the first inlet for a pressure reduction from 100 mbar to 10 mbar is approximately 20 to 50% longer than the evacuation time via the second inlet for evacuation from 1000 mbar to approximately 100 mbar. The pumping speeds of the two inlets can be matched to each other during the design in such a way that as much as possible the same pump-down time, i.e. evacuation time, is achieved for both inlets. This means that the evacuation times t_p1 and t_p2 are as equal as possible (depending on chamber volume, final pressure, etc.). This is the most preferred embodiment. In another embodiment of the method according to the invention, the evacuation times deviate from each other in particular by a maximum of 25%, preferably by a maximum of 15%, particularly preferably by a maximum of 10%, very particularly preferably by a maximum of 5%.

The invention is shown by way of example on a rotary vane vacuum pump with one pumping stage, but can also be implemented in rotary vane vacuum pumps with two or more pumping stages. In rotary vane vacuum pumps with more than two pumping stages, two inlets and one outlet can be provided in only one pumping stage as well as in a plurality of or in all pumping stages.

The installation space required for the rotary vane vacuum pump according to the invention is comparable to that of a single single-stage rotary vane vacuum pump and smaller than that of a two-stage rotary vane vacuum pump. The maintenance effort for the rotary vane vacuum pump according to the invention is reduced compared to two individual single-stage rotary vane vacuum pumps. In addition, the rotary vane vacuum pump according to the invention has lower procurement costs and a reduced energy requirement, i.e. also lower operating costs of approximately 10-20%.

Further details of the invention are apparent from the following description of the preferred embodiments of the device according to the invention, which are shown by way of example in the accompanying drawings. Further advantages of the present invention can be gleaned from the description, as well as suggestions and proposals as to how the subject matter of the invention can be modified or further developed within the scope of what is claimed.

Any combination of a (preferred) feature with another (preferred) feature, whether relating to the method, the vacuum pump or the use, is hereby encompassed by the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Shown are:

FIG. 1: a schematic representation of a state-of-the-art system in which two single-stage rotary vane vacuum pumps simultaneously evacuate two different vacuum chambers;

FIG. 2: a schematic representation of a further state of the art, in which the stages of a two-stage rotary vane vacuum pump evacuate two different vacuum chambers simultaneously;

FIG. 3: a schematic representation of the single-stage rotary vane vacuum pump according to the invention with two inlets, via which two different vacuum chambers are evacuated simultaneously;

FIG. 4: a cross section of a stage with six vanes of a rotary vane vacuum pump according to the invention, with the arrow at the top indicating inlet 1, the arrow at the bottom right indicating inlet 2 and the arrow at the bottom left indicating the outlet;

FIG. 5: a cross section of a stage with six vanes of a rotary vane vacuum pump according to the invention, with the arrow at the top indicating inlet 1, the arrow at the bottom right indicating inlet 2 and the arrow at the bottom left indicating the outlet.

DESCRIPTION OF THE STATE OF THE ART

From FIG. 1, an arrangement of the prior art can be seen in which two single-stage rotary vane vacuum pumps simultaneously evacuate two of three different vacuum chambers i/20, j/20′ and k/20″ in a cyclical process. At the same time, the third vacuum chamber, which is not connected to one of the two rotary vane vacuum pumps, is ventilated. The rotary vane vacuum pump 22 is the fore-pump here, while the rotary vane vacuum pump 21 is the high vacuum pump.

In valve position 41, the vacuum chamber i/20 with fore-pump 22 is evacuated from an initial pressure p_02(i) to a final pressure p_12(i) and the vacuum chamber j/20′ with the high vacuum pump 21 is evacuated from an initial pressure p_01(j) to a final pressure p_11(j). The following applies: p_02(i)>p_12(i)≥p_01(j)>p_11(j). In parallel, the vacuum chamber k/20″ is brought to an initial pressure p_02(k).

When the valve is changed from position 41 to position 42, the vacuum chambers are disconnected from the pumps and reconnected as follows: At valve position 42, vacuum chamber k/20″ is evacuated with fore-pump 22 from an initial pressure po2 (k) to a final pressure p12 (k) and vacuum chamber i/20 is evacuated with the high vacuum pump 21 from the initial pressure p_12(i) to the final pressure p_11(i). The following applies: p_02(k)>p_12(k)≥p_12(i)>p_11(i). In parallel, the vacuum chamber j/20′ is brought to an initial pressure p_02(j).

When the valve is changed from position 42 to position 43, the vacuum chambers are disconnected from the pumps and reconnected as follows: At valve position 43, vacuum chamber j/20′ is evacuated with rotary vane vacuum pump 22 from an initial pressure p_02(j) to a final pressure p_12(j) and vacuum chamber k/20″ is evacuated with rotary vane vacuum pump 21 from the initial pressure p_12(k) to the final pressure p_11(k). The following thereby applies: p_02(j)>p_12(j)≥p_12(k)>p_11(k). In parallel, the vacuum chamber i/20 is brought to an initial pressure p_02(i).

The valve position is then changed from position 43 to position 41 and the cycle starts again from the beginning.

This arrangement is significantly more expensive than the rotary vane vacuum pump according to the invention in terms of its purchase and operating costs. In addition, its use in a packaging machine, in particular a rotary vacuum packaging machine, requires more installation space than the rotary vane vacuum pump according to the invention. Another disadvantage of this arrangement is the higher maintenance costs.

FIG. 2 shows a schematic representation of a two-stage rotary vane vacuum pump as is also known from the state of the art. In this case, the two stages evacuate two of three different vacuum chambers i/20, j/20′ and k/20″ simultaneously in a cyclical process. At the same time, the third vacuum chamber, which is not connected to one of the two stages, is ventilated. Stage 32 is the fore-vacuum stage, while stage 31 is the high-vacuum stage.

In valve position 41, the vacuum chamber i/20 is evacuated, with the fore-vacuum stage 32, from an initial pressure p_02(i) to a final pressure p_12(i), and the vacuum chamber j/20′ is evacuated, with the high vacuum stage 31, from an initial pressure p_01(j) to a final pressure p_11(j). The following thereby applies: p_02(i)>p_12(i)≥p_01(j)>p_11(j). In parallel, the vacuum chamber k/20″ is brought to an initial pressure p_02(k).

When the valve is changed from position 41 to position 42, the vacuum chambers are disconnected from stages 31 and 32 of the pump and reconnected as follows: At valve position 42, the vacuum chamber k/20″ with the fore-vacuum stage 32 is evacuated from an initial pressure p_02(k) to a final pressure p_12(k) and the vacuum chamber i/20 with the high vacuum stage 31 is evacuated from an initial pressure p_01(i) to a final pressure p_11(i). The following thereby applies: p_02(k)>p_12(k)≥p_01(i)>p_11(i). In parallel, the vacuum chamber j/20′ is brought to an initial pressure p_02(j).

When the valve is changed from position 42 to position 43, the vacuum chambers are disconnected from the pump stages and reconnected as follows: At valve position 43, the vacuum chamber j/20′ with the fore-vacuum stage 32 is evacuated from an initial pressure p_02(j) to a final pressure p_12(j) and the vacuum chamber k/20″ with the high vacuum stage 31 is evacuated from an initial pressure p_01(k) to a final pressure p_11(k). The following thereby applies: p_02(j)>p_12(j)≥p_01(k)>p_11(k). In parallel, the vacuum chamber i/20 is brought to an initial pressure p_02(i).

The valve position is then changed from position 43 to position 41 and the cycle starts again from the beginning.

Here too the procurement costs are higher than with the rotary vane vacuum pump according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS ACCORDING TO THE INVENTION

FIG. 3 shows a schematic representation of the single-stage rotary vane vacuum pump 10 according to the invention with two inlets 1, 2, via whose two inlets 1, 2 two of three vacuum chambers i/20, j/20′, k/20″ are evacuated simultaneously. At the same time, the third vacuum chamber, which is not connected to one of the two inlets, is ventilated. Inlet 1 is the high vacuum inlet and inlet 2 is the fore-vacuum inlet: Inlets 1, 2 are each connected in turn to vacuum chambers i/20, j/20′, k/20″.

In the first valve position 41, the vacuum chamber i/20 is connected to the fore-vacuum inlet 2 and the vacuum chamber j/20′ is connected to the high vacuum inlet 1. The vacuum chamber i/20 is evacuated there in an evacuation time t_p2(i) from an initial pressure p_02(i) to a final pressure p_12(i), while, preferably simultaneously (t_p2(i)=t_p1(j)), the vacuum chamber j/20′ is evacuated in an evacuation time t_p1(j) from an initial pressure p_01(j) to a final pressure p_11(j). In this case, p_02(i)>p_12(i)≥p_01(j)>p_11(j) applies. Ideally, p_12(i) and p_01(j) are the same, i.e. their values preferably deviate from each other by a maximum of 25%, particularly preferably by a maximum of 15%, especially preferably by a maximum of 10%, most preferably by a maximum of 5%. The vacuum chamber k/20″ is not connected to any of the inlets and is brought to an initial pressure p_02(k) in parallel.

The valve position is then changed from valve position 41 to valve position 42. During the change, none of the vacuum chambers i/20, j/20′ and k/20″ is connected to an inlet of the pump.

In the second valve position 42, the vacuum chamber k/20″ is connected to the fore-vacuum inlet 2 and the vacuum chamber i/20 is connected to the high vacuum inlet 1. The vacuum chamber k/20″ is evacuated from an initial pressure p_02(k) to a final pressure p_12(k) in an evacuation time t_p2(k), while, preferably simultaneously (t_p2(k)=t_p1(i)), the vacuum chamber i/20 is evacuated from the initial pressure p_01(i) to the final pressure p_11(i) in an evacuation time t_p1(i). In this case, p_02(k)>p_12(k)≥p_01(i)>p_11(i) applies. Ideally, p_12(k) and p_12(i) are the same, i.e. their values preferably deviate from each other by a maximum of 25%, particularly preferably by a maximum of 15%, most preferably by a maximum of 10%, most preferably by a maximum of 5%. The vacuum chamber j/20′ is not connected to any of the pump inlets and is brought to the initial pressure p_02(j) in parallel.

The valve position is then changed from valve position 42 to valve position 43. During the change, none of the vacuum chambers i/20, j/20′ and k/20″ is connected to an inlet of the pump.

In the third valve position 43, the vacuum chamber j/20′ is connected to the fore-vacuum inlet 2 and the vacuum chamber k/20″ is connected to the high vacuum inlet 1. The vacuum chamber k/20″ is evacuated from the initial pressure p_01(k) to the final pressure p_11(k) in an evacuation time t_p1(k), while, preferably simultaneously (t_p2(j)=t_p1(k)), the vacuum chamber j/20′ is evacuated from an initial pressure p_02(j) to the final pressure p_12(j) in an evacuation time t_p2(j). In this case, p_02(j)>p_12(j)≥p_01(k)>p_11(k) applies. Ideally, p_01(k) and p_12(j) are the same, i.e. their values preferably deviate from each other by a maximum of 25%, particularly preferably by a maximum of 15%, most preferably by a maximum of 10%, most preferably by a maximum of 5%. The vacuum chamber i/20 is not connected to any of the inlets of the pump and is brought to an initial pressure p_02(i) in parallel.

The valve position is then changed from valve position 43 to valve position 41 and the cycle starts again from the beginning.

FIG. 4 shows a cross section of an embodiment of the rotary vane vacuum pump 10 according to the invention with six vanes 7, 7′, 7″ etc. in the corresponding slots 8, 8′, 8″ etc., with the arrow at the top indicating inlet 1, the arrow at the bottom right indicating inlet 2 and the arrow at the bottom left indicating outlet 3

FIG. 5 also shows a cross section of an embodiment of the rotary vane vacuum pump 10 according to the invention with six vanes 7, 7′, 7″ etc. in the corresponding slots 8, 8′, 8″ etc., with the arrow at the top indicating inlet 1, the arrow at the bottom right indicating inlet 2 and the arrow at the bottom left indicating outlet 3. The rotary vane vacuum pump according to FIG. 5 differs from that according to FIG. 4 in the position of the first inlet 1.

In the embodiment according to FIG. 4 the two inlets 1 and 2 are separated by at least one vane. In the rotor position shown, the two inlets 1 and 2 are separated by exactly one vane 7. The conveying chambers 9 und 9′ are connected to the inlet 1, while the conveying chamber 9″ is connected to the inlet 2. In the state shown in FIG. 5, the conveying chamber 9 separates inlet 1 (connected to conveying chamber 9′) from inlet 2 (connected to conveying chamber 9″). This leads to increased internal tightness, since two vanes and thereby a complete conveying chamber 9 between the two inlets 1 and 2 serves as buffer between them. The return flow losses are thereby less, which leads to a better end pressure and suction capability. This means that the pump-down times are shorter than they would be without this buffer.

LIST OF REFERENCE NUMERALS

• • 10 vacuum pump, in particular rotary vane vacuum pump
  • 1 first inlet/high-vacuum inlet
  • 2 second inlet/fore-vacuum inlet
  • 3 outlet
  • 11 connection for the first inlet
  • 12 connection for the second inlet
  • 4 cylinder
  • 5 rotor
  • 6 conveying chamber
  • 7, 7′, 7″ etc. vane
  • 8, 8′, 8″ etc. slot(s)
  • 9, 9′, 9″ etc. conveying chamber(s)
  • 14 inner wall of the cylinder
  • 17, 17′, 17″ etc. sealing point(s)
  • 20, 20′, 20″ etc. vacuum chamber(s)
  • 21 high-vacuum pump
  • 22 fore-pump
  • 31 high-vacuum stage
  • 32 fore-vacuum stage
  • 41, 42, 43 valve position