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Evacuation apparatusRelated Patent Categories: Pumps, Condition Responsive Control Of Pump Drive Motor, By Controlling Drive Motor Motive FluidEvacuation apparatus description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20080080982, Evacuation apparatus. 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, provided with a mechanical vacuum booster pump and an back pump which is placed at a down-stream side of the mechanical vacuum booster pump in series. [0003] 2. Description of the Related Art [0004] In order to realize a vacuum inside a tank, a chamber and the like, with a rapid pumping speed, a mechanical booster pump for vacuums is conventionally utilized at an up-stream side (a vacuum side) of a vacuum pump (a back pump) with a lower pumping speed. As for the mechanical booster pump, Roots type vacuum pumps 021 are generally applied which perform compression/discharge works by rotating pairs of Roots type vanes 020 as shown in FIG. 5. And it is known that the back pump realizes several times of a maximum pumping speed by the use of the mechanical booster pump. [0005] However, even though the mechanical booster pump feeds a large amount of gas into the back pump provided at the down-stream side, i.e. at the ambient side, an improvement in the pumping speed during an operation in the vicinity around an ambient pressure is not so great, because of the limited pumping speed of the whole apparatus due to the limited discharging-capacity of the back pump. [0006] That is, as the relation between an pumping speed and a pressure in FIG. 3 shows, at the beginning of feeding the gas with the booster pump under an ambient pressure, the pumping speed of the whole apparatus is not improved so effectively with the assistance of the mechanical booster pump because of the limited discharging-capacity intrinsic to the back pump. The improvement effect is obtained as vacuum degree becomes high, but not obtained over a whole pressure range. [0007] On the other hand, for instance, Japanese granted utility model No. JP/7-19554 (hereafter, referred to as reference 1) discloses an application; 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 placed in series. [0008] In the technology of the reference 1, as quoted in FIG. 6, a preliminary discharge line (passage) A and a main discharge line (passage) B start from the inside of a chamber and are connected to each other. The preliminary discharge line A is provided with a stop valve 03a and a butterfly valve 04 in series and connected to a preliminary pump 01. The main discharge line B is provide with stop valves 03b1, 03b2 and a discharge pump 02. According to the constitution, a main discharge (evacuating) is performed through the preliminary pump 01 and the discharge pump 02 by closing the stop valve 03a and the butterfly valve 04 and opening the stop valves 03b1, 03b2 and the discharge pump 02. [0009] In addition, as an example of vacuum pumps installed in two stages, a constitution is disclosed as quoted in FIG. 7 in which a booster pump 012 is connected to an intermediate stage of a dry vacuum pump 10 of a multi-stage type or the last stage of the vacuum pump 10 so that the reduction of power consumption is aimed at (Patent reference 2; JP: 2003-155988,A). [0010] However, according to the patent literature 1, since only the preliminary pump 01 discharges gas when the preliminary discharge is performed, an improved pumping speed cannot be expected. Although the preliminary pump 01 and the discharge pump 02 discharge gas in two stages when the main discharge is operated, the operation control with regard to the discharge pump 02 is not disclosed in the patent literature 1. Therefore, the technology of the reference leaves a problem on how to improve a pumping speed, not only over the pressure range from an ambient pressure to a low vacuum but also over the whole pressure range from a low vacuum to a high vacuum. [0011] In addition, the booster pump 012 in the patent literature 2 aims at the reduction of power consumption necessary for driving the dry vacuum pump 010. Improving the pumping speed is not mentioned in the patent literature 2. SUMMARY OF THE INVENTION [0012] In view of the above-stated background, a purpose of the present invention is to realize an evacuation apparatus for evacuating a tank, a chamber, and the like, which are provided with a mechanical vacuum booster pump and an back pump placed at the down-stream side of the mechanical booster pump in series, so as to increase the pumping speeds over a pressure range from an ambient pressure to a low vacuum, thereby improving the pumping speed over the whole pressure range from an ambient pressure to a high vacuum. [0013] In order to achieve the above-mentioned purpose, the present invention is proposes an evacuation apparatus for evacuating a tank, a chamber and the like, including a mechanical booster pump, an back pump placed at a down-stream side of the mechanical booster pump in series, and a controller for controlling operation of the apparatus; in which the mechanical booster pump has a discharge opening for discharging a low compression gas, through which lowly-compressed gas with low compression ratio on a part way of compression in the booster pump is emitted, and a discharge opening for discharging a high compression gas, through which highly-compressed gas with high compression ratio is emitted; and the controller controls so that, in a stage where gas-discharging is started, the gas is discharged toward the ambient side through the discharge opening for discharging a high compression gas with the operation of the mechanical booster pump and, in a stage where the discharged gas pressure reaches afterward a medium vacuum, the back pump starts operation and the gas is sent to the back pump through the discharge opening for discharging a low compression gas. [0014] According to the above-mentioned embodiment, in the beginning of discharging gas, the gas is discharged toward the ambient side (outside) through the discharge opening for discharging a high compression gas by operating the mechanical booster pump. In this way, the gas of an ambient pressure level in the tank is compressed with a high compression ratio and is discharged directly outside. Since the gas is sent outside without the influence of the back pump, it becomes possible to improve pumping speeds without introducing large back pump of higher discharging capacity so as to secure higher pumping speeds. [0015] Further, since a pumping speed of the booster pump is higher in comparison with that of the back pump, it is possible to discharge gas, maintaining the pumping speed in the beginning when the pressure is an ambient pressure. In the first place, it becomes possible to improve pumping speeds in a range from an ambient pressure to a low vacuum. [0016] When achieving a medium vacuum, which is attainable by means of discharging through the discharge opening for discharging a high compression gas of the mechanical booster pump, then the gas of the medium vacuum is fed from the discharge opening(s) for discharging low compression gas to the back pump, while the back pump is started. Thus, the gas of vacuum state to some extent is fed to the back pump from the discharge opening(s) for discharging a low compression gas. Because of the gas-pressurizing/flow-increasing function of the mechanical booster pump, the pumping speeds of the back pump are enhanced and the enhanced pumping speeds are maintained, thereby a high vacuum is realized. [0017] Therefore, it becomes possible to improve the pumping speeds not only in the range from an ambient pressure to a low vacuum but also over a whole range from an ambient pressure to a high vacuum. [0018] According to another embodiment of the present invention, preferably the controller recognizes the accomplishment of the medium vacuum by means of an elapsed time signal from a timer. [0019] In the above embodiment, the controller automatically controls the operation of the back pump feeds by such construction that the discharged gas is supplied through the discharge opening(s) for discharging a low compression gas to the back pump as well as the back pump is driven. Here, since the control is performed based not on a signal from a pressure sensor but on an elapsed time signal from a timer, risks of malfunction and/or deterioration about pressure sensor are eliminated. Thus, highly reliable control realized. [0020] According a preferable embodiment of the present invention, the mechanical booster pump is a vacuum pump of a claw type, in which the discharge opening for discharging a high compression gas is located at a 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, being located in a plane parallel to the plane containing both rotation axes of the pump rotors. [0021] The above embodiment 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, in which the discharge opening for discharging a high compression gas is located at the wall of the pump casing so as to face the compression space, the wall being in a plane vertical to the axes of the pump rotors, and the discharge opening for discharging a low compression gas is located, on a side-wall-surface of the pump casing, in a plane parallel to the plane containing both rotation axes of the pump rotors. [0022] The present invention realizes an evacuation apparatus for evacuating a tank, a chamber and the like, comprising a mechanical booster pump and a back pump placed at the down-stream side of the mechanical booster pump in series, which can improve the pumping speeds over a whole range from an ambient pressure to a high vacuum by increasing the pumping speed in the range from an ambient pressure to a low vacuum Continue reading about Evacuation apparatus... Full patent description for Evacuation apparatus Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Evacuation apparatus patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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