BACKGROUND OF THE INVENTION
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1. Field of the Invention
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The present invention relates to an evacuation apparatus for evacuating a tank, a chamber, and the like; wherein a mechanical booster pump for vacuums is provided at an up-stream side of an exterior side vacuum pump.
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2. Description of the Related Art
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In order to evacuate a tank, a chamber and the like, with a rapid pumping speed, a mechanical booster pump for vacuums is conventionally utilized by being placed at an up-stream side (a vacuum side) of an exterior side vacuum pump (a back pump) with a lower pumping speed. As for the mechanical booster pump, Roots type vacuum pumps are applied in general. And Roots type vacuum pumps perform compression/discharge works by rotating pairs of Roots type vanes.
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In case of a Roots type vacuum pump 020 as shown in FIG. 4, while a pair of axes of Roots type rotors rotate each other to reverse directions, suction and discharge of gas are performed by changing a volume of a closed space. However, the ultimate pressure to be attained (the pressure to be lowered) is not advantageous one because of the small compression ratio due to Roots type rotors.
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As a vacuum pump of large compression ratio, a claw type vacuum pump 026 (FIG. 5), which has a claw (like a nail of raptorial birds) shaped rotor 024, has been known. However, the claw type vacuum pump 026 is apt to suffer from power loss (increased power consumption) and/or heat loss (increased heat generation), since the claw type vacuum pump 026 has a large interior discharge resistance for the diameter of a discharge opening 028 for discharging compressed gas being small. Further, the exterior side vacuum pump (the back pump) installed at the down-stream side can not be fully utilized due to the large discharge resistance, there arises a problem that an improved discharge speed by placing a booster pump is difficult to be obtained.
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On the other hand, for instance, in Japanese granted utility model publication No. JP7-19554 (hereafter referred to as reference 1) is disclosed an evacuation apparatus, wherein a booster pump like a mechanical booster pump is provided at the up-stream side of a vacuum pump, and wherein gas discharge is performed by the two stage vacuum pumps in series.
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In the technology of the patent reference 1, as quoted in FIG. 6, a preliminary discharge line (passage) A and a main discharge line B start from the inside of a chamber and are connected to each other. On the preliminary discharge line A, a stop valve 03 a and a butterfly valve 04 are provided in series. And the preliminary discharge line A is connected to a preliminary pump 01. On the main discharge line B, stop valves 03 b 1, 03 b 2 and a discharge pump 02 are provided. According to the embodiment, a main discharge (evacuating) is performed through the preliminary pump 01 and the discharge pump 02; wherein the stop valve 03 a and the butterfly valve 04, on the preliminary discharge line A, are closed; and the stop valves 03 b 1, 03 b 2 and the discharge pump 02, on the main discharge line B, are opened.
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As an example of vacuum pumps installed in two stages, is known an embodiment as described in FIG. 7; wherein a booster pump 012 is connected to an intermediate stage of a dry Roots pump 010 of a multi-stage type or the last stage 011 of the Roots pump 10 so that the reduction of power consumption is aimed at (Patent reference 2; JP: 2003-155988, A).
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However, according to the technology of the reference 1, since only the preliminary pump 01 discharges gas at the time of the preliminary discharge, an improved pumping speed cannot be expected. Further, although both of the preliminary pump 01 and the discharge pump 02 discharge gas in two stages at the time of the main discharge, there arises a problem that, depending on a characteristic of the discharge pump 02, the improvement of the ultimate pressure is difficult because of the low compression ratio and/or a problem that the improvement of the pumping speed is difficult even when the compression ratio is high and the ultimate pressure is improved.
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In addition, the booster pump 012 in the patent reference 2 aims at the reduction of power consumption necessary for driving the dry vacuum pump 010. Improving an ultimate pressure as well as securing the pumping speed is not mentioned in the patent reference 2.
SUMMARY OF THE INVENTION
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In view of the above-stated background, a subject of the present invention is to realize an evacuation apparatus for evacuating a tank, a chamber, and the like; wherein a mechanical booster pump for vacuums is provided at an up-stream side of an exterior side vacuum pump so as to improve an ultimate pressure of the exterior side vacuum pump as well as to secure a pumping speed by utilizing the performance of the exterior side vacuum pump.
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In order to solve the above-mentioned problem, the present invention proposes an evacuation apparatus for evacuating a tank, a chamber and the like; wherein a mechanical booster pump is provided at the up-stream side of an exterior side vacuum pump; wherein the mechanical booster pump comprises a discharge opening for discharging a low compression gas and a discharge opening for discharging a high compression gas; wherein, in case when the exterior side vacuum pump starts discharging a gas, the gas is sent to the exterior side vacuum pump through both the discharge opening for discharging a low compression gas and the discharge opening for discharging a high compression gas and, in case when the discharged gas pressure reaches afterward an ultimate pressure attainable by the exterior side vacuum pump, the gas is sent to the exterior side vacuum pump only through the discharge opening for discharging a high compression gas.
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The above embodiment of the present invention, for evacuating a tank, a chamber and the like, realizes a medium vacuum (an ultimate pressure) of the exterior side vacuum pump without deteriorating a pumping speed in a manner comprising the steps of: (i) discharging a gas into the exterior side vacuum pump through both the discharge opening for discharging a low compression gas and the discharge opening for discharging a high compression gas of the mechanical booster pump in case when the vacuum is within a range from the pressure of the discharge commencement till the attainable pressure of the exterior side vacuum pump, (ii) restraining the discharging resistance of the mechanical booster pump by means of securing a large cross sectional area of the discharge opening of the mechanical booster pump, and (iii) obtaining an increased pumping speed and utilizing the performance intrinsic to the exterior side vacuum pump. Furthermore, this invention usefully contributes to the reduction of heat loss and power loss of the mechanical booster pump because of the low compression ratio of the gas emitted through the discharge opening for discharging a low compression gas and the discharge opening for discharging a high compression gas.
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After the ultimate pressure attainable by the exterior side vacuum pump is reached, gas is sent to the exterior side vacuum pump only through the discharge opening for discharging a high compression gas. Therefore, the compression ratio of the mechanical booster pump is utilized so that a differential pressure is generated, lowering the ultimate pressure further as a result. Thus, a high vacuum inside a tank, a chamber and the like is realized.
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As described above, the invention makes it possible to lower the ultimate pressure in view of the whole equipment while the pumping speed is secured.
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Another preferable embodiment of the invention further includes: (i) a pressure sensor for detecting the pressure in a tank, a chamber and the like, and (ii) a controller for opening/closing, by a signal from the pressure sensor, an open/close valve which is placed between the discharge opening for discharging a low compression gas and the exterior side vacuum pump; wherein the controller closes the open/close valve when the controller recognizes the ultimate pressure by the signal mentioned above.
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In the above embodiment of the invention, after the pressure sensor detects the gas pressure in the tank, the chamber and the like, the controller automatically closes, based on a signal from the sensor, the open/close valve between the discharge opening for discharging a low compression gas and the exterior side vacuum pump, when the ultimate pressure is reached. Therefore, the embodiment makes it possible that the gas is sent to the exterior side vacuum pump through both the discharge opening for discharging a low compression gas and the discharge opening for discharging a high compression gas before the ultimate pressure is reached and the gas is sent to the exterior side vacuum pump only through the discharge opening for discharging a high compression gas after the ultimate pressure is reached.
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Another preferable embodiment of the invention, includes (i) a controller for opening/closing an open/close valve which is placed between the discharge opening for discharging a low compression gas and the exterior side vacuum pump; wherein the controller closes the open/close valve in case when a predetermined time passes after the exterior side vacuum pump starts discharging a gas till the ultimate pressure is attained.
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In the above embodiment of the invention, the controller automatically closes the open/close valve between the discharge opening for discharging a low compression gas and the exterior side vacuum pump, in case when a predetermined time passes after the exterior side vacuum pump starts discharging a gas till the ultimate pressure is attained. Therefore, the embodiment makes it possible that the gas is sent to the exterior side vacuum pump through both the discharge opening for discharging a low compression gas and the discharge opening for discharging a high compression gas before the ultimate pressure is reached and the gas is sent to the exterior side vacuum pump only through the discharge opening for discharging a high compression gas after the ultimate pressure is reached.
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Another preferable embodiment of the invention comprises: a vacuum pump of a claw type as the mechanical booster pump; wherein the discharge opening for discharging a high compression gas is located at the wall of the pump casing, the wall being in a plane vertical to the axes of the pump rotors, while the discharge opening for discharging a high compression gas faces the compression space; wherein the discharge opening for discharging a low compression gas is located in a plane parallel to the plane containing both rotation axes of the pump rotors as well as the discharge openings for low compression located on a side-wall-surface of the pump casing; and further wherein the cross-sectional area of the discharge opening for discharging a low compression gas is formed more greatly than the cross-sectional area of the discharge opening for discharging a high compression gas.
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Since the above embodiment of the invention is characterized in that the discharge opening for discharging a high compression gas is located at the wall of the pump casing, the wall being in a plane vertical to the axes of the pump rotors, while the discharge opening for discharging a high compression gas faces the compression space; wherein the discharge opening for discharging a low compression gas is located in a plane parallel to the plane containing both rotation axes of the pump rotors as well as the discharge openings for low compression located on a side-wall-surface of the pump casing; and further wherein the cross-sectional area of the discharge opening for discharging a low compression gas is formed more greatly than the cross-sectional area of the discharge opening for discharging a high compression gas, the invention realizes a booster pump provided with the discharge opening for discharging a high compression gas and the discharge opening for discharging a low compression gas.
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The present invention can realize an evacuation apparatus for evacuating a tank, a chamber and the like, comprising a mechanical booster pump at the up-stream side of an exterior side vacuum pump, wherein the mechanical booster pump utilizes the performance of the exterior side vacuum pump and improves an ultimate pressure of the exterior side vacuum pump without deterioration of pumping speed.
BRIEF DESCRIPTION OF THE DRAWINGS
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The present invention will now be described in greater detail with reference to the preferred embodiments of the invention and the accompanying drawings, wherein:
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FIG. 1 shows a whole embodiment of a first embodiment of the present invention;
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FIG. 2 shows a view of the A-A cross-section in FIG. 1;
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FIG. 3 illustrates a characteristic of an evacuating process for a vacuum;
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FIG. 4 shows an explanation of a Roots-type vacuum pump;
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FIG. 5 shows an explanation of a claw-type vacuum pump;
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FIG. 6 illustrates a conventional technology; and
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FIG. 7 illustrates a conventional technology.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
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Hereafter, the present invention will be described in detail with reference to the embodiments shown in the figures. However, the dimensions, materials, shape, the relative placement and so on of a component described in these embodiments shall be only for explanation and shall not be construed as limiting the scope of the invention thereto, unless any specific mention is placed.
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FIG. 1 shows a whole embodiment of the embodiment of the present invention and FIG. 2 shows a view of the A-A cross-section in FIG. 1.
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As shown in FIG. 1, an evacuation apparatus 1 is equipped with an exterior side vacuum pump (a vacuum pump) 3 and a mechanical booster pump (a mechanical booster pump for a vacuum) 5 which is provided at the up-stream side of the vacuum pump 3 so that a vacuum in a vacuum tank 7 is obtained by running the both pumps 3 and 5.
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The mechanical booster pump 5 is of a claw type vacuum pump 9, comprising a pair of pump rotors 11 a and 11 b, a gas suction port 13, and a gas discharge port 15. The mechanical booster pump 5 further comprise a pump casing (a housing) 17; wherein the pair of pump rotors 11 a and 11 b are built-in, and a rotating mechanism; wherein shafts 19 rotates the pump rotors 11 a and 11 b by transferring powers from a motor (not shown) as a power source to the rotors. In addition, the type of the exterior side vacuum pump 3 is not limited to a Roots-type and can be any other type of vacuum pumps such as a claw type, a screw type, a gear type and so on.
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While the above-mentioned rotating mechanism makes the pump rotors 11 a and 11 b rotate in a reverse direction each other (as shown with the arrows S in FIG. 1), gas suction and gas discharge are carried out by means of volumetric changes of the sealed spaces environed with the pump casing 17 and the pump rotors 11 a and 11 b.
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The pump rotors 11 a and 11 b have protrusive parts 21 a and 21 b like a claw (a nail of raptorial birds) respectively. And the protrusive parts 21 a and 21 b fit into counter-depressed parts 23 b and 23 a respectively. Thus, the fitting space forms a compression space 25.
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The gas discharge port 15 has two openings, namely, a discharge opening for discharging a low compression gas (a DOLC) 27 and a discharge opening for discharging a high compression gas (a DOHC) 29. The DOLC 27 discharges the gas compressed within the mechanical booster pump at a stage of a lower compression ratio, while the DOHC 29 discharges the gas when a stage of a higher compression ratio is realized. In addition, the DOLC 27 is placed so that the gas inhaled through the gas suction port 13 is discharged before the gas is compressed into a compression space 25 formed by the pump rotors 11 a and 11 b. Further, the DOLC 27 is comprised of a first discharge opening for discharging a low compression gas 27 a corresponding to the pump rotor 11 a and a second discharge opening for discharging a low compression gas 27 b corresponding to the pump rotor 11 b.
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In addition, while the cross-sectional area of the first discharge opening for discharging a low compression gas 27 a is the same as that of the second discharge opening for discharging a low compression gas 27 b, the cross sectional area of the openings 27 a and 27 b is formed more greatly than the cross-sectional area of the DOHC 29.
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As shown in FIG. 2, the DOHC 29 is located at the wall of the pump casing 17, the wall being in a plane vertical to the axes of the pump rotors 11 a and 11 b, while the DOHC 29 faces the compression space 25 so as to discharge highly compressed gas.
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Moreover, as shown in FIG. 2, the gas suction port 13 is located in a plane parallel to the plane containing both the rotation axes of the pump rotors 11 a and 11 b as well as the gas suction port 13 is located on one side-wall-surface of the pump casing 17, while the first and second discharge openings for low compression 27 a and 27 b are located in a plane parallel to the plane containing both the rotation axes of the pump rotors 11 a and 11 b as well as the first and second discharge openings for low compression 27 a and 27 b are located on another side-wall-surface of the pump casing 17.
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Thus, by forming a discharge port on a casing-wall-surface vertical to the axes of the pump rotors 11 a and 11 b and on a casing-wall-surface parallel to the plane containing both axes of the pump rotors 11 a and 11 b, a mechanical booster pump 5 provided with a DOHC 29 and a DOLC 27 can be composed.
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On a first low compression discharge passage 30 which communicatively connects the first discharge opening for discharging a low compression gas 27 a and the exterior side vacuum pump 3, is provided an open/close valve 34, the opening/closing of which is controlled by the a controller 32. On the other hand, a second low compression discharge passage 36, which feeds the gas through the second discharge opening for discharging a low compression gas 27 b, flows into the first low compression discharge passage 30 at the up-stream side of the valve 34. Moreover, a high compression discharge passage 38, which feeds the gas through the discharge opening for discharging a high compression gas 29, flows into a passage 30 at the down-stream side of the valve 34. Thus, the passages 30, 36 and 38 meet together and feed the gas toward the exterior side vacuum pump 3.
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Here, an explanation as to the controller 32 will be given.
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Pressure signals from the vacuum tank 7 or inlet pressure signals from the mechanical booster pump 5 are inputted into a controller 32 via a pressure sensor 40, and elapsed-time signals are inputted into the controller 32 from a timer 42.
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At the beginning of gas discharging, the open/close valve 34 is opened, the exterior side vacuum pump 3 is started, and the mechanical booster pump 5 is consecutively started. In this way, the discharged gas from the first discharge opening for discharging a low compression gas 27 a, the second discharge opening for discharging a low compression gas 27 b, and/or the DOHC 29 is sent to the exterior side vacuum pump 3 through the first low compression discharge passage 30, the second low compression discharge passage 36, and/or the high compression discharge passage 38 respectively.
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At a stage of operation wherein all the passages mentioned above are communicatively opened, a large amount of gas is discharged from the mechanical booster pump 5. The reason is that, at the stage mentioned above, the value of compression ratio is kept lower, and the discharging capability of the exterior side vacuum pump 3 is not deteriorated. Namely, the discharging resistance of the mechanical booster pump is restrained, and an increased pumping speed (discharging speed) is attained. And the exterior side vacuum pump 3 realizes a possible ultimate pressure (of medium vacuum) based on the capability of the exterior side vacuum pump 3 itself regarding compression action.
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Thus, while the medium vacuum is realized without a deteriorated pumping speed, in a pressure range to the ultimate pressure of the exterior side vacuum pump 3, the power loss as well as the heat loss in the mechanical booster pump 5 can be reduced because of the lower compression ratio.
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In a second stage, the controller 32 closes the open/close valve 34 by an input signal from the pressure sensor 40, when a predetermined ultimate pressure based on the capacity of the exterior side vacuum pump 3 is reached. Thus, a discharge from the first discharge opening for discharging a low compression gas 27 a as well as from the second discharge opening for discharging a low compression gas 27 b is intercepted, and the discharge only from the DOHC 29 remains. As a result, a differential pressure by the compression action of the compression space 25 in the mechanical booster pump 5 can be generated, and the mentioned differential pressure is added to the medium vacuum generated based on the capability of the exterior side vacuum pump 3. Consequently, a high vacuum, thereof pressure is lower than a pressure of the medium vacuum, can be attained.
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When the medium vacuum is attained based on the capability of the exterior side vacuum pump 3, since the vacuum gas is substantially thin, an additional discharge through the compression space 25 in the mechanical booster pump 5 can bring a high vacuum without the difficulties of power loss or heat loss, whereas the difficulties can arise in case when a discharge is performed only through the DOHC 29 from an ambient pressure condition.
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FIG. 3 illustrates a characteristic of an evacuating process for a vacuum. At the operation stage with the open/close valve 34 opened, wherein all the passages 30, 36 and 38 are communicatively opened, the compression action is performed at the exterior side vacuum pump 3. That is, the exterior side vacuum pump 3 performs an evacuating process from an ambient pressure P0 to an ultimate pressure P1. In addition, the starting pressure P0 is lowered to the medium pressure P1.
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Then, the open/close valve 34 is closed, the differential pressure by a compression action of the compression space 25 of a mechanical booster pump 5 is added to the medium vacuum so as to lower a medium vacuum pressure. In this manner, a pressure P2 of a high vacuum condition is realized.
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As described above, according to an embodiment of the present invention, by using a mechanical booster pump 5 provided with a discharge opening for discharging a low compression gas (a DOLC) 27, which discharges a gas of low compression ratio, and a discharge opening for discharging a high compression gas (a DOHC) 29, which discharges a gas of high compression ratio, an ultimate pressure is lowered and a high vacuum can be attained while a pumping speed is secured.
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Next, an explanation on a second embodiment will be given.
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In this second embodiment, an elapsed time signal from a timer 42, instead of a pressure signal from a pressure sensor 40, switches an open/close condition of the open/close valve 34. FIG. 3 describes elapsed time t0, t1, and/or t2 in relation to corresponding vacuum conditions.
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A time t0 is defined as the time of beginning of gas discharging into the exterior side vacuum pump 3; through all the passages of the first low compression discharge passage 30, the second low compression discharge passage 36, and the high compression discharge passage 38 after the open/close valve 34 is opened, the exterior side vacuum pump 3 is driven, and further the mechanical booster pump 5 is driven.
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A time t1 is defined as a time span in which the pressure of gas decreases from an ambient pressure P0 to a pressure P1 (medium vacuum pressure) on the condition that all the passages 30, 36 and 38 are fully communicatively open. Here, the time span (t1 minus t0) is to be predetermined by calculation based on the volume of the vacuum tank 7, the discharging capacity (swept volume) of the exterior side vacuum pump 3, the discharging capacity of the mechanical booster pump 5, driving conditions of each pump, the ambient temperature and so on.
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When the controller recognizes, with a signal from the timer 42, that the time (t1 minus t0) has passed from the time t0, the open/close valve 34 is closed. Then, with the aid of a differential pressure due to the compression action of the compression space 25 of a mechanical booster pump 5, a lower pressure, namely, the high vacuum is realized at the time t2.
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The second embodiment, as well as the first embodiment, makes it possible to improve the ultimate pressure toward a lower pressure, that is, to attain the high vacuum without deteriorating the pumping speed.
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Moreover, in case of the use of the pressure sensor 40, because of dust, refuse particles, or water droplet in the vacuum tank 7 or gas passages, there is a risk of clogging and/or deterioration of the sensor 40, both of which can cause incorrect pressure detection. On the other hand, in case of the use of the timer 42, there is no difficulty of detection failure or deterioration. Therefore, highly reliable control can be performed.
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In addition, in the first and second embodiments described above, it is explained that the controller 32 automatically opens and closes the open/close valve 34. However, as a matter of course, operators can manually open and closes the valve 34, based on their own judgment as to the values detected by the pressure sensor 40.
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As for the mechanical booster pump 5, the explanation was given in consideration that the mechanical booster pump 5 is of a claw type vacuum pump 9. However, it goes without saying that the mechanical booster pump 5 can be of a Roots type pump or of a screw type pump other than of a claw type pump, so long as the mechanical booster pump 5 is provided with the DOLC 27 which discharges the gas of low compression ratio and the DOHC 29 which discharges the gas of high compression ratio.
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Moreover, it should be noted that the explanation was given in consideration that the gas as a medium is any one of general gases including a specific gas such as air.
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The present invention discloses an evacuation apparatus for evacuating a tank, a chamber and the like, wherein a mechanical booster pump is provided at the up-stream side of an exterior side vacuum pump so as to utilize the performance of the exterior side vacuum pump and improve an ultimate pressure of the exterior side vacuum pump without deterioration of pumping speed. And the present invention can be usefully applied to evacuation apparatuses.
