JP2009002230A - Vacuum pump - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve emissions performance in a high-pressure region substantially equal to an atmospheric pressure. <P>SOLUTION: A pump chamber 3 of at least first stage from upstream end side of a vacuum pump is designed to have a capacity greater than those of pump chambers 4, 5, 6, 7 at a downstream side. Further, the pump chamber 3 includes a bypass valve mechanism 8 provided to communicate from a flow path of an exhaust port side of the pump chamber at the downstream end side in the pump stage with larger capacity to a flow path of the exhaust port side of a pump chamber at the downstream side bypassing at least one or more stages out of a plurality of pump stages of pump chambers. Then, the bypass valve mechanism 8 has a valve 8a that is opened at a high-pressure region where the pressure of a pump intake port 1 of the pump chamber 3 located at the first stage is substantially equal to atmospheric pressure, and configured to exhaust gas to a flow path at the exhaust port side of a pump chamber located at the downstream side from the pump chamber at downstream end side in a pump stage with larger capacity. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention is a mechanical pump that pumps gas from an intake port to an exhaust port by rotationally driving a rotor disposed in a pump chamber, and is a multistage vacuum pump in which a plurality of pump chambers are connected in series About.

  A mechanical pump that pumps gas from an intake port to an exhaust port by rotationally driving a rotor disposed in a pump container, and a plurality of pump chambers arranged coaxially and partitioned are connected in series. A multistage dry vacuum pump is known (see Patent Document 1). As this type of dry vacuum pump, a configuration of a plurality of pump stages of about 4 to 6 stages using a roots type rotor or the like has been put into practical use.

  FIG. 11 shows a configuration example of a conventional multi-stage dry vacuum pump, and FIG. 12 shows a schematic diagram of exhaust speed characteristics of the multi-stage dry vacuum pump. FIG. 11A to FIG. 11D show a configuration example of a typical five-stage pump chamber. Each of these configuration examples shows a configuration example in which the volume of the pump chamber is changed according to the exhaust capacity of the target vacuum pump. A general method for achieving a large pump capacity vacuum pump in this multistage dry vacuum pump is to increase the volume of the first or second pump chamber from the pump inlet 51 side of the dry vacuum pump. It is. Basically, it is advantageous in terms of exhaust performance to make the volume of the pump chamber located on the downstream side as large as possible. However, considering the size of the vacuum pump, the required power of the motor, the length of the rotary shaft that supports the rotor, etc., the volume of the downstream pump chamber is optimized to the minimum necessary size. .

  In FIG. 11, FIG. 11 (A) is a configuration example in which the volumes of the pump chambers from the first stage to the fifth stage are configured to be equal and the exhaust capacity is adopted for a relatively small pump chamber. FIGS. 11B, 11C, and 11D show the first stage arranged on the pump intake port 51 side in order to ensure a relatively high exhaust speed and configure a pump corresponding to a large exhaust capacity. In addition, a configuration example in a case where the volume of the second-stage pump chamber is relatively large is shown. Here, for easy understanding of the description to be described later, the volumes of the pump chambers of the first stage in FIG. 11B and the first and second stages in FIG. It is shown to be about twice as large as the volume of the pump chamber shown in (A). Further, it is assumed that the volume of the first-stage pump chamber in FIG. 11D is approximately three times the volume of the pump chamber in FIG.

FIG. 12 is a diagram schematically showing the exhaust speed characteristics in the multistage dry vacuum pump shown in FIG. Curves A, B, C, and D in FIG. 12 indicate exhaust speed characteristics corresponding to the configuration examples shown in FIGS. 11A, 11B, 11C, and 11D, respectively. Strictly speaking, the exhaust speed characteristics vary depending on the volume of each pump chamber, the volume ratio, the compression performance, the timing of mutual rotation, and the like. Is shown. Also, in FIG. 12, for comparison purposes, the exhaust speed characteristics (S1) obtained with the basic configuration shown in FIG. 11 (A) are each doubled (2 × S1) and tripled. The curve (3 × S1) is shown with a broken line. This exhaust speed characteristic corresponds to the exhaust speed characteristic obtained in total when two and three pumps having the basic configuration shown in FIG. 11A are used in parallel. As in the results shown in FIG. 12, in a reduced pressure region that is generally used in a vacuum apparatus, the volume of the first-stage pump chamber is doubled or tripled so that a pump with a relatively small volume can be obtained. Exhaust speed characteristics substantially equivalent to the case where two or three multistage dry vacuum pumps configured in a chamber are used in parallel can be easily realized. Such a vacuum pump has an effective configuration corresponding to a large exhaust capacity.
Japanese Unexamined Patent Publication No. 7-305589

  However, as is apparent from the results shown in FIG. 12, in the high pressure region almost equal to the atmospheric pressure, the multi-stage dry vacuum pump with the pump chamber volume on the pump inlet side having a large capacity can sufficiently improve the exhaust speed. It has not been made. In other words, if the volume of the first-stage pump chamber is set to a large value, for example, twice or three times to ensure a large exhaust capacity, there is almost no compression effect due to pressure in a high pressure region almost equal to atmospheric pressure. The volume of the exhausted gas is mainly determined by the volume of the pump chamber. For this reason, the gas exhausted in the first and second (upstream) pump chambers at twice and three times the volume is exhausted in the pump chamber having a relatively small volume connected to the subsequent (downstream) pump chamber. I can't do it. That is, since the volume of the pump chamber connected to the subsequent stage of the pump chamber having a relatively large volume is small, the gas becomes excessive at the intake port of the subsequent pump chamber, resulting in an increase in pressure. And about the gas exceeding the compression rate which can be maintained in the pump chamber of the front | former stage, it will result in flowing back to the pump inlet side of the upstream end side of a vacuum pump, and gas will not be exhausted effectively. In addition, the compression performance itself of the pump chamber generally used in multistage dry vacuum pumps may decrease in a region where the operating pressure is high, which will cause a significant decrease in the exhaust performance of the vacuum pump as a whole. It is.

  In short, even if an attempt is made to achieve a large exhaust capacity by ensuring a large pump stage volume close to the pump inlet and increasing the exhaust performance by two or three times, the volume located at the rear stage of this pump stage is relatively small. The amount of gas that can be exhausted in the pump chamber becomes the rate-limiting factor. As a result, the exhaust gas cannot be sufficiently transferred to the pump exhaust port on the downstream end side of the vacuum pump.

  This problem is particularly noticeable when the volume of the exhausted container connected to the vacuum pump and exhausted by the vacuum pump is very large. Although not shown in the figure, when a very large volume of a container to be exhausted is evacuated to an ultimate pressure that is lower than the ultimate pressure of a multistage vacuum pump that can be evacuated from atmospheric pressure, A vacuum pump of the type will be used together. For example, generally known large roots blower pumps or molecular pumps are used as main pumps, but these vacuum pumps cannot operate the pumps directly from atmospheric pressure.

  For this reason, it is necessary to pre-evacuate to a certain vacuum pressure state with a vacuum pump that can be evacuated from atmospheric pressure, such as a multistage dry vacuum pump shown in FIG. At this time, from the viewpoint of practical use, as the exhaust time required to reach a desired pressure, usually, most of the time is spent for preliminary exhaust from atmospheric pressure. Considering the takt time of the entire system, when shortening the exhaust time required to achieve the desired pressure, it is a major issue to shorten the preliminary exhaust time by increasing the exhaust speed of the vacuum pump used in the preliminary exhaust. It is.

  The substantial gas exhaust flow rate in vacuum is represented by “volume × pressure”. Therefore, when the vacuum exhaust proceeds and the pressure at the pump inlet becomes sufficiently low, even if the volume of the first-stage pump chamber close to the pump inlet is doubled or tripled, The pressure in the pump chamber following the latter stage is easily compressed twice or three times by the compression performance. For this reason, it does not become excessive as the amount of gas to be exhausted substantially, and as the exhaust characteristics shown in FIG. 12, it is substantially twice the exhaust speed of the multi-stage dry vacuum pump as the basic configuration, Three times the exhaust speed can be obtained.

  Therefore, the present invention is to solve the above-described problems, and an object of the present invention is to provide a vacuum pump that can improve the exhaust performance in a high pressure region substantially equal to the atmospheric pressure.

  In order to achieve the above-described object, a vacuum pump according to the present invention has a pump container provided with an intake port and an exhaust port, and a rotor disposed in the pump container. A plurality of pump chambers for pumping gas from the intake port to the exhaust port are provided, and the pump chambers are connected in series by a plurality of pump stages. Further, at least the first pump chamber from the upstream end side of the vacuum pump has a larger volume than the downstream pump chamber. In addition, the vacuum pump bypasses at least one or more of the plurality of pump stages in the pump chamber from a flow path on the exhaust port side of the pump chamber on the downstream end side in the pump stage having a large volume. A bypass valve mechanism provided in communication with the flow path on the exhaust port side of the chamber; The bypass valve mechanism has a valve that is opened in a high pressure region in which the pressure in the suction port of the pump chamber located in the first stage is almost equal to the atmospheric pressure, and the pump on the downstream end side in the pump stage having a large volume The gas is exhausted to the flow path on the exhaust port side of the pump chamber located downstream of the chamber.

  According to the present invention, it is possible to improve a decrease in exhaust speed in a high pressure region substantially equal to the atmospheric pressure, and a vacuum pump suitable for a large capacity exhaust system can be realized at a relatively low additional cost.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, each structure and exhaust speed characteristic show the typical embodiment roughly to such an extent that this invention can be understood. Therefore, the present invention is not limited to the following embodiments, and can be changed into various forms based on the description of the scope of claims.

  FIG. 1 is a schematic diagram showing a multistage dry vacuum pump according to the first embodiment. In the dry vacuum pump according to the first embodiment, the flow path on the exhaust port side of the pump chamber disposed on the upstream end side and having a relatively large volume is disposed on the exhaust port side of the pump chamber disposed on the downstream end side. Is connected to the flow path via a bypass valve mechanism.

  As a first embodiment, FIG. 1A shows a configuration example in which the first stage is composed of a pump chamber having a relatively large volume. In addition, as the first embodiment, FIG. 1B shows a configuration example in which the first stage and the second stage are each configured by a pump chamber having a relatively large volume.

  As shown in FIGS. 1A and 1B, the dry vacuum pump of the embodiment includes a first-stage pump chamber 3 to a fifth-stage pump chamber 7. Although not shown, each pump chamber 3, 4, 5, 6, and 7 has a pump container provided with an intake port and an exhaust port, and a rotor disposed in the pump container, and the rotor is driven to rotate. By doing so, gas is pumped from the intake port to the exhaust port. The rotors of the pump chambers 3, 4, 5, 6, 7 are rotationally driven by a drive motor 9.

  The pump chambers 3, 4, 5, 6, and 7 are arranged in series on the same axis, and are connected in series via pipes that connect the pump chambers 3, 4, 5, 6, and 7, respectively. Connected and configured. Further, this dry vacuum pump has a flow path on the exhaust port side of the first-stage pump chamber 3 or the second-stage pump chamber 4 and an exhaust port side of the pump chamber 7 located on the downstream end side of the dry vacuum pump. A bypass valve mechanism 8 is provided in communication with the flow path.

  In the configuration example of the embodiment shown in FIG. 1A, the volume of the first-stage pump chamber 3 located on the upstream end side of the dry vacuum pump (hereinafter also referred to as the pump intake port 1 side of the dry vacuum pump) is as follows. The volume of the pump chambers 4, 5, 6, 7 on the downstream side of the first-stage pump chamber 3 is about twice as large. The bypass valve mechanism 8 of this configuration example includes a flow path on the exhaust port side of the first-stage pump chamber 3 positioned on the pump intake port 1 side, and an exhaust port of the pump chamber 7 positioned on the downstream end side of the dry vacuum pump. Two channels (hereinafter also referred to as the pump exhaust port 2 side of the dry vacuum pump) are provided in communication with each other.

  Further, in the configuration of the embodiment shown in FIG. 1B, the volume of the first and second pump chambers 3 and 4 located on the pump intake port 1 side is larger than that of the second pump chamber 4. It is formed about twice as large as the volume of the downstream pump chambers 5, 6, 7. The bypass valve mechanism 8 of this configuration example is provided by connecting a flow path on the exhaust port side of the second-stage pump chamber 3 located on the pump intake port 1 side and a flow path on the pump exhaust port 2 side. .

  FIG. 2 shows evacuation speed characteristics in the dry vacuum pump of each configuration example shown in FIGS. 1 (A) and 1 (B). The exhaust velocity characteristics corresponding to the respective configuration examples shown in FIGS. 1A and 1B are shown by a curve A and a curve B in FIG. For comparison, FIG. 2 shows a pumping speed characteristic (S1) obtained by the basic configuration of the conventional multistage dry vacuum pump shown in FIG. 11A and a curve obtained by doubling this characteristic. (2 × S1) is also indicated by a broken line. Further, FIG. 2 shows the exhaust speed characteristics in the configuration examples shown in FIGS. 1 (A) and 1 (B) without the above-described bypass valve mechanism 8 as curves A and B, respectively. These are also shown by broken lines.

  According to the present embodiment, it is possible to improve the exhaust speed in a high pressure region that is substantially equal to atmospheric pressure (close to atmospheric pressure) as shown by curve A and curve B, respectively. When the configuration example shown in FIG. 1A is compared with the configuration example shown in FIG. 1B, the performance of the configuration shown in FIG. The degree to which it is done is large. However, in the configuration shown in FIG. 1A, the volume of the second-stage pump chamber 4 is smaller than that in the configuration example shown in FIG. It is advantageous.

  In the present embodiment, a bypass valve mechanism 8 is provided that connects the flow path side of the exhaust port of the pump chamber having a relatively large volume to the flow path on the pump exhaust port 2 side, and the pressure of the pump intake port 2 is high. In the region, the valve 8a is opened and the gas is exhausted through the bypass valve mechanism 8. With this configuration, the gas exhausted in a relatively large amount at a time in a pump stage having a relatively large volume is controlled by a pump stage having a relatively small volume connected to the subsequent stage of the pump stage and is pressurized. Therefore, the gas can be exhausted outside the dry vacuum pump.

  Connecting the flow path on the exhaust port side of the pump chamber located on the pump intake port side of the vacuum pump to the flow path on the pump exhaust port side of the vacuum pump that is basically at atmospheric pressure This is not possible when the ultimate pressure is reached in the operating state. However, in the high pressure region where the pressure at the pump intake port is almost equal to the atmospheric pressure, the flow path on the exhaust port side of the pump stage formed with a relatively large volume corresponds to at least the compression performance of the pump chamber in the atmospheric pressure region. Because of the above factors, a pressure state higher than atmospheric pressure is generated, so that gas can be exhausted to the outside of the vacuum pump according to the pressure difference from atmospheric pressure. By closing the valve before the pressure on the upstream side of the bypass valve mechanism becomes smaller than the pressure on the downstream side of the flow path of the bypass valve mechanism, there is no problem as a vacuum pump and it is connected to the vacuum pump. It does not adversely affect the vacuum container side of the exhausted system. The pressure on the downstream side of the flow path of the bypass valve mechanism is almost atmospheric pressure when the exhaust port of the pump chamber located on the downstream side is a pump exhaust port, and bypasses to the intake port side of the subsequent pump stage. If they are connected, the pressure at the inlet of the pump stage is obtained.

  FIG. 3 shows still another configuration example of the first embodiment. In the dry vacuum pump of this configuration example, the first-stage pump chamber 3 located on the pump inlet 1 side is the first stage in the basic configuration of the conventional multi-stage dry vacuum pump shown in FIG. The volume of the eye pump chamber is approximately three times the volume. FIG. 4 shows the exhaust speed characteristics of the dry vacuum pump of this configuration example. In FIG. 4, as in FIG. 2, the pumping speed characteristic (S1) obtained with the basic configuration of the conventional dry vacuum pump shown in FIG. The curved line (3 × S1) is shown with a broken line. Further, in FIG. 4, the exhaust velocity characteristic in the configuration example shown in FIG. 3 that does not include the above-described bypass valve mechanism 8 is indicated by a broken line in accordance with the curve A. Also in this configuration example, it is possible to improve the exhaust speed in the high pressure region substantially equal to the atmospheric pressure as indicated by the curve A.

  FIG. 5 shows a multistage dry vacuum pump according to the second embodiment. In the dry vacuum pump of this embodiment, the volume of the first-stage pump chamber 3 located on the pump inlet 1 side is larger than the volumes of the pump chambers 4, 5, 6, and 7 on the downstream side of the first stage. Is formed. This dry vacuum pump has at least one stage of a flow path on the exhaust port side of a first-stage pump chamber having a relatively large volume and a pump chamber having a small volume continuously connected downstream from the first stage. A bypass valve mechanism 8 is provided that bypasses the above and communicates with the flow path on the exhaust port side of the downstream pump chamber.

  In the configuration example shown in FIGS. 5A and 5B, the first-stage pump chamber on the side of the pump inlet 1 is provided with the basic structure of the conventional multistage dry vacuum pump shown in FIG. Each of the first-stage pump chambers is configured to have a volume that is approximately three times the volume of the first-stage pump chamber.

  In the configuration example shown in FIG. 5A, the downstream side of the flow path of the bypass valve mechanism 8 is connected between the fourth-stage pump chamber 6 and the fifth-stage pump chamber 7. In the configuration example shown in FIG. 5B, the downstream side of the flow path of the bypass valve mechanism 8 is connected between the third-stage pump chamber 5 and the fourth-stage pump chamber 6.

  FIG. 6 shows evacuation speed characteristics in the dry vacuum pump corresponding to the respective structural examples shown in FIGS. 5 (A) and 5 (B). 6, as in FIGS. 2 and 4, for comparison and reference, an exhaust speed characteristic (S1) obtained by the basic configuration of the conventional multistage dry vacuum pump shown in FIG. A curve (3 × S1) obtained by multiplying this characteristic by 3 is shown with a broken line. Further, in order to show the difference in the effect of each configuration example, the volume of the first-stage pump chamber is the same as the configuration example shown in FIG. 5, and the conventional multistage dry vacuum pump shown in FIG. The first configuration shown in FIG. 3 is configured to be approximately three times the volume of the first-stage pump chamber, which is the basic configuration of FIG. 3, and the bypass valve mechanism 8 is connected to the pump exhaust port 2 of the dry vacuum pump. The exhaust velocity characteristics (the exhaust characteristics are illustrated in FIG. 4) of the configuration example of the embodiment are indicated by broken lines. The improvement characteristics of the obtained pump characteristics differ depending on the position of connecting the flow path on the downstream side of the flow path of the bypass valve mechanism 8 (the side closer to the pump exhaust port 2). Therefore, it is possible to select a configuration more suitable for the required exhaust performance. In addition, when it is allowed to increase the physical space and the manufacturing cost, it is possible to obtain a maximum exhaust characteristic by providing a plurality of bypass valve mechanisms and optimally interlocking the plurality of bypass valve mechanisms. Is possible.

  FIG. 7 shows a multistage dry vacuum pump according to a third embodiment. As shown in FIG. 7, the dry vacuum pump of the present embodiment includes a pressure measuring device 10 as pressure measuring means. In the present embodiment, the valve 8a of the bypass valve mechanism 8 is controlled to open and close based on the measurement result by the pressure measuring instrument 10, so that the valve 8a is in a high pressure region where the pressure of the pump inlet 1 is substantially equal to the atmospheric pressure. It is configured to automatically open and close.

  When the pressure measuring device 10 is built in the dry vacuum pump, as shown in FIG. 7B, pressure is applied to the exhaust port side of the first-stage pump chamber having a relatively large volume, that is, the upstream side of the bypass valve mechanism 8. The configuration in which the measuring device 10 is arranged is the simplest in controlling the bypass valve mechanism 8. Basically, it may be controlled so that the valve 8a of the bypass valve mechanism 8 is opened in a condition range in which the pressure measured by the pressure measuring instrument 10 is higher than the pressure at the pump exhaust port 2.

  Although not shown, desirably, the pump exhaust port 2 is also provided with a similar pressure measuring device 10, and by controlling the differential pressure with the pressure measuring device 10, control can be performed more reliably. FIG. 7A shows the relationship between the pressure inside the dry vacuum pump relative to the pressure at the pump inlet 1, particularly the relationship between the upstream pressure and the downstream pressure with respect to the valve 8 a of the bypass valve mechanism 8. As described above, the pressure measuring device 10 may be disposed in the vicinity of the pump inlet 1. Further, as shown in FIG. 7C, the valve 8a of the bypass valve mechanism 8 is controlled based on the measurement result by the pressure measuring device 10 provided in the exhausted vacuum vessel 11 connected to the dry vacuum pump. Then, it may be configured to open and close.

  FIG. 8 is a schematic diagram showing a bypass valve mechanism 8 used in the multistage dry vacuum pump of the fourth embodiment. As shown in FIG. 8, the bypass valve mechanism 8 in the present embodiment is a valve that automatically opens and closes the valve 8a when the upstream pressure and the downstream pressure with respect to the valve 8a become a predetermined differential pressure. An opening / closing mechanism 8b is provided. The valve opening / closing mechanism 8b is configured to be able to automatically open and close by controlling the valve 8a in a high pressure region where the pressure at the pump inlet 1 is substantially equal to the atmospheric pressure.

  FIG. 8A shows a configuration example of a valve opening / closing mechanism 8b using a ball-shaped valve seal 12 as the valve 8a. As shown in FIG. 8A, the valve opening / closing mechanism 8b includes a valve seal 12 disposed so as to be able to open and close the flow path, and a valve piston 14 that supports the valve seal 12 movably along the flow path. Have. The valve opening / closing mechanism 8 b includes a pair of valve guides 15 and 16 that guide the moving direction of the valve piston 14, a valve spring 13 that urges the valve seal 12 to close the flow path, and the valve seal 12. And a sealing surface portion 17 to be pressed.

  FIG. 8B shows another configuration of the valve opening / closing mechanism 8b using the valve piston 14 provided with an O-ring shaped valve seal 18 as the valve 8a. As shown in FIG. 8B, the valve opening / closing mechanism 8b includes a valve piston 14 having a valve portion 14a arranged to open and close a flow path, a valve seal 18 provided on the valve portion 14a, and the valve seal. 18 has a sealing surface portion 17 to which the pressure contact is made. The valve opening / closing mechanism 8b includes a valve guide 15 that guides the moving direction of the valve piston 14, and a valve spring 13 that urges the valve portion 14a to close the flow path.

  When the pressure on the upstream side of the valve 8a is larger than the pressure on the downstream side of the valve 8a plus the pressure by the urging force of the valve spring 13, the valve opening / closing mechanism 8b of each configuration example described above be opened.

  FIG. 9 shows a bypass valve mechanism 8 used in the dry vacuum pump of the fifth embodiment. As shown in FIG. 9, in the bypass valve mechanism 8 in the present embodiment, a heating mechanism 19 for heating the pipe is provided on the outer periphery of the pipe constituting the flow path in which the valve 8a is arranged. According to the heating mechanism 19, it is possible to prevent the product having condensability from being deposited in the vicinity of the valve 8a. Although not shown, it is desirable that the temperature around the valve 8a be controlled using, for example, a temperature measuring device or the like. The control temperature must be appropriately selected according to the type of reaction product expected to flow from an external device (not shown) using a dry vacuum pump.

FIG. 10 shows a bypass valve mechanism used in the dry vacuum pump of the sixth embodiment. As shown in FIG. 10, the bypass valve mechanism 8 in this embodiment has a purge mechanism 20 as a purge means for diluting and purging a flow path in which the valve 8a is disposed with an inert gas such as N ₂ . . According to the purge mechanism 20, it is possible to prevent the product having condensability from being deposited on the inner wall of the flow path or in the vicinity of the valve 8a. The inert gas is introduced from the introduction port of the purge pipe 21, and the flow rate is appropriately controlled by the flow rate adjusting valves 20 a and 20 b, and is introduced around the valve 8 a of the bypass valve mechanism 8. Note that whether or not the inert gas is allowed to flow in a state where the valve 8a is opened should be appropriately set according to the use of the vacuum pump.

  Although the dry vacuum pump of each embodiment has been described above, the present invention is not limited to these configurations. For example, in the above-described embodiment, the configuration example in which the volume of the pump chamber of the first stage or the second stage is formed to be relatively larger than the volume of the pump chamber on the downstream side is given, but depending on the specifications of the vacuum pump The first to third pump chambers may be configured as a pump chamber having a large volume. Further, the number of pump chamber stages in the entire vacuum pump is different from that in the above-described embodiment, and the same effect can be obtained even when, for example, the pump chamber is composed of four stages or six stages.

It is a schematic diagram which shows the multistage dry vacuum pump of 1st Embodiment. It is a figure which shows the exhaust speed characteristic in the dry vacuum pump of 1st Embodiment shown in FIG. It is a schematic diagram which shows the other structural example of the dry vacuum pump of 1st Embodiment. It is a figure which shows the exhaust speed characteristic in 1st Embodiment shown in FIG. It is a schematic diagram which shows the dry vacuum pump of 2nd Embodiment. It is a figure which shows the exhaust speed characteristic in the said 2nd Embodiment. It is a schematic diagram which shows the dry vacuum pump of 3rd Embodiment. It is a schematic diagram which shows the structural example of the valve opening / closing mechanism used with the bypass valve mechanism of 4th Embodiment. It is a schematic diagram which shows the heating mechanism used with the bypass valve mechanism of 5th Embodiment. It is a schematic diagram which shows the purge mechanism used with the bypass valve mechanism of 6th Embodiment. It is a schematic diagram which shows the conventional multistage dry vacuum pump. It is a figure which shows the exhaust speed characteristic by the conventional multistage dry vacuum pump shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pump inlet port 2 Pump exhaust port 3 1st stage pump room 4 2nd stage pump room 5 3rd stage pump room 6 4th stage pump room 7 5th stage pump room 8 Bypass valve mechanism 8a Valve 10 Pressure measuring device (pressure measuring means)
11 Vacuum container 19 Heating mechanism (heating means)
20 Purge mechanism (purge means)
20a, 20b Flow control valve 21 Purge piping

Claims (6)

A plurality of pump chambers having a pump container provided with an intake port and an exhaust port, and a rotor disposed in the pump container, and pumping gas from the intake port to the exhaust port by being driven to rotate A vacuum pump in which the pump chamber is connected in series with a plurality of pump stages,
The pump chamber at least at the first stage from the upstream end side of the vacuum pump has a larger volume than the pump chamber on the downstream side,
From the flow path on the exhaust port side of the pump chamber on the downstream end side in the pump stage with the increased volume, bypassing at least one stage of the plurality of pump stages in the pump chamber, A bypass valve mechanism provided in communication with the flow path on the exhaust port side;
The bypass valve mechanism has a valve opened in a high pressure region in which the pressure of the intake port of the pump chamber located in the first stage is substantially equal to atmospheric pressure, and a downstream end in the pump stage having the increased volume A vacuum pump configured to exhaust the gas to a flow path on the exhaust port side of the pump chamber located downstream of the pump chamber on the side.   2. The vacuum pump according to claim 1, wherein the bypass valve mechanism has a downstream end side of a flow path in which the valve is disposed communicated with the exhaust port of the pump chamber located on the downstream end side of the vacuum pump. . Pressure measuring means for measuring the pressure of the gas,
The vacuum pump according to claim 1 or 2, wherein the bypass valve mechanism is configured such that the valve can be automatically opened and closed based on a measurement result by the pressure measuring unit.   3. The vacuum pump according to claim 1, wherein the bypass valve mechanism includes a valve opening / closing mechanism that automatically opens and closes the valve by a differential pressure between an upstream pressure and a downstream pressure with respect to the valve. .   The vacuum pump according to any one of claims 1 to 4, wherein the bypass valve mechanism includes a heating unit that heats a flow path in which the valve is disposed.   The vacuum pump according to any one of claims 1 to 5, wherein the bypass valve mechanism includes a purge unit that dilutes and purges a flow path in which the valve is disposed with an inert gas.

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