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  Evacuation apparatusUSPTO Application #: 20080080984Title: Evacuation apparatus Abstract: The present invention discloses an evacuation apparatus for evacuating a tank, a chamber, and the like; wherein a mechanical vacuum booster pump is provided at an up-stream side of an exterior side vacuum pump; wherein the mechanical booster pump has a discharge openings for low compression 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 all of the discharge openings for low compression and the discharge opening for discharging a high compression gas and, in case when the discharged gas pressure reaches afterward an ultimate pressure (a medium vacuum) 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. (end of abstract)
Agent: Rossi, Kimms & Mcdowell LLP. - Ashburn, VA, US Inventors: Shiro TANIGAWA, Takamitsu NAKAYAMA, Ryusuke MUTO, Minako TODA USPTO Applicaton #: 20080080984 - Class: 417205 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20080080984. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001]1. Field of the Invention [0002]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. [0003]2. Description of the Related Art [0004]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. [0005]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. [0006]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. [0007]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. [0008]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 03a 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 03b1, 03b2 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 03a and the butterfly valve 04, on the preliminary discharge line A, are closed; and the stop valves 03b1, 03b2 and the discharge pump 02, on the main discharge line B, are opened. [0009]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). [0010]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. [0011]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 [0012]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. [0013]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. [0014]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. [0015]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. [0016]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. [0017]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. [0018]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. [0019]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. [0020]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. [0021]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. [0022]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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