VALVE FOR PREVENTING REVERSE-FLOW

Technical field The present invention relates to a valve for preventing a reverse flow, and more particularly, to a reverse-flow preventing valve positioned between a vacuum chamber and a vacuum pump to prevent a reverse flow of air, wherein the reverse-flow preventing valve comprises a cylindrical valve body; first and second connection portions protruding from both ends of the valve body and connected to exhaust pipes extending from the vacuum chamber and the vacuum pump, respectively; a cutoff plate that is positioned within the valve body, has a diameter larger than an inner diameter of the first connection portion and smaller than an inner diameter of the valve body, and can move along a cutoff plate guide in an upward and downward direction toward the first connection portion in response to pressure difference so as to cut off a flow of a fluid; a cutoff ring moving toward the first connection portion to support the cutoff plate when a vacuum line is in an abnormal state; and a pneumatic cylinder for moving the cutoff ring in the upward and downward direction.

Background Art

Upon manufacturing semiconductors, plasma display panels (PDP) or the like, an etching process, a deposition process, an exhaust process and the like are performed.

When these processes are performed, an apparatus such as a vacuum chamber is generally used and a vacuum pump for generating a vacuum state is also used. However, if the operation of the vacuum pump is stopped due to a breakdown thereof, an electricity failure,

or the like, water vapor or other contaminants in the atmosphere may flow backward into such a vacuum chamber, resulting in contamination of products that are being subjected to the manufacturing processes.

Therefore, there has been proposed a method or apparatus for protecting products in a vacuum chamber by preventing a reverse flow of external air upon accidental stoppage of a vacuum pump and blocking the interior of the chamber from the external air. Korean Patent Laid-Open Publication No. 2004-0085926 discloses a semiconductor fabricating apparatus in which an exhaust unit having a switching valve sets up the environment of a processing chamber, a cleaning unit cleans out contaminants discharged by the exhaust unit, and a reverse- flow preventing unit is placed between the exhaust unit and the cleaning unit to prevent a reverse flow of the contaminants. At this time, the reverse-flow preventing unit has reverse flow preventing piping that comprises a first protrusion member protruding inwardly from one side in the section of the piping and a second protrusion member protruding inwardly from the other side and is formed within piping for introducing contaminants discharged from the exhaust unit into the cleaning unit, thereby obstructing the flow of the contaminants such as water flowing backward from the cleaning unit to the exhaust unit. Further, Korean Utility Model Laid-Open Publication No. 1993-016166 discloses a reverse flow preventing valve in which a slider is coupled around a discharge port formed on a vacuum line so that it can be slid along an axis, wings are formed on an outer periphery of the slider such that the slider can greatly affected by air pressure, bearings for smooth operation are inserted on an inner surface of the slider, and an O-ring for maintaining hermetic sealing is fixedly inserted at a connection interface between the discharge port and the slider. Furthermore, Korean Patent Laid-Open

Publication No. 2000-0007260 discloses a reverse flow preventing valve that comprises a support shaft fixed to cross an inner passage of a discharge pipe; a left pivot wing of which one side is hingedly connected to the left of the support shaft and the other side is pivotally rotated by air pressure when external air flows backward, thereby closing a portion of the internal passage positioned to the left of the support shaft; a right pivot wing of which one side is hingedly connected to the right of the support shaft and the other side is pivotally rotated to close a portion of the internal passage positioned to the right of the support shaft; and stoppers for fixing the left and right pivot wings at respective positions where the wings close the internal passage when the external air flows backward. However, since the reverse flow preventing methods or apparatuses disclosed in the above references have structures that cannot meet bidirectional blocking, they have a disadvantage in that it is difficult to prevent damage due to accidental stoppage of an operation of a vacuum pump. In order to solve such a problem, the present inventor filed a Korean patent application for a cutoff valve, before the filing of the present application. The cutoff valve of the prior patent application comprises a first cylindrical body that is

sealed by a first cover having an inlet connected to a pipe on the side of a vacuum chamber and a second cover having an inlet connected to a pipe on the side of a vacuum pump and has an inner space; a second cylindrical body which is in the form of a cylindrical disk having a donut shape with a central hollow of a predetermined radius, is inserted into and assembled to the empty space of the first cylindrical body, has a protrusion structure on an outer surface of the second cylindrical body to form a vertical channel defined by a gap between both peripheral surfaces of the first and second cylindrical bodies when the second cylindrical body is inserted into the first cylindrical body, and has channel

formation guides formed on upper and lower surfaces of the cylindrical disk with the donut shape to form a horizontal channel; a third cylindrical body which is inserted into and assembled to the central hollow of the second cylindrical body, has a protrusion structure on a peripheral surface thereof to form a vertical channel defined by a gap between both peripheral surfaces of the second and third cylindrical bodies, and has a central empty space to form a channel to the inlet of the second cover; and a cutoff plate which is mounted between the third cylindrical body and the first cover to open and close the channel while moving in vertically upward and downward directions depending on pressure difference between the vacuum chamber side and the vacuum pump side {see Korean Patent Application No. 2004-0104557).

However, since the reverse-flow preventing valves disclosed in the above references and the prior patent application of the present inventor have structures for

simply obstructing a reverse flow or are operated by using pressure difference between a vacuum chamber and a vacuum pump, they are complicated in their structures and may not be operated if the pressure difference is smaller than an operation threshold or the bearings and the like become stiff, and thus, they cannot prevent contaminants such as air outside the vacuum chamber from flowing backward into the vacuum chamber, resulting in contamination of the interior of the vacuum chamber.

Disclosure of Invention

Technical Problem

Accordingly, an object of the present invention is to provide a reverse-flow preventing valve, which is pneumatically operated to allow the valve to be rapidly opened

and closed and to eliminate a possibility that the valve will not work, thereby improving the reliability of the valve.

Technical Solution To achieve the above object, the present invention provides a reverse-flow preventing valve positioned between a vacuum chamber and a vaαium pump to prevent a reverse flow of air, wherein the reverse-flow preventing valve comprises a cylindrical valve body; first and second connection portions protruding from both ends of the valve body and connected to exhaust pipes extending from the vacuum chamber and the vacuum pump, respectively; a cutoff plate that is positioned within the valve body, has a diameter larger than an inner diameter of the first connection portion and smaller than an inner diameter of the valve body, and can move along a cutoff plate guide in an upward and downward direction toward the first connection portion in response to pressure difference so as to cut off a flow of a fluid; a cutoff ring moving toward the first connection portion to support the cutoff plate when a vacuum line is in an abnormal state; and a pneumatic cylinder for moving the cutoff ring in the upward and downward direction.

The reverse-flow preventing valve of the present invention may further comprise a cylindrical flow obstruction portion protruding from the second connection portion toward the interior of the valve body so that the flow of the fluid in the reverse-flow preventing valve is curved.

In the reverse-flow preventing valve of the present invention, a single pneumatic cylinder may be positioned at the center of the cutoff ring, or a plurality of pneumatic cylinders may be positioned on a circle along a periphery of the cutoff ring.

In the reverse-flow preventing valve of the present invention, if the pneumatic cylinders are positioned on the circle along the periphery of the cutoff ring, the number of pneumatic cylinders may range from 3 to 6.

The reverse- flow preventing valve of the present invention may further comprise an annular elastic member for improving airtightness, which is positioned at a periphery of an opening of the first connection portion inside the valve body with which the cutoff plate is brought into contact.

In the reverse-flow preventing valve of the present invention, the cutoff plate may be in the form of a disk or cone. The reverse-flow preventing valve of the present invention may further comprise a bypass passage running to the valve body from the first connection portion with which the cutoff plate is brought into contact, and a bypass valve capable of controlling the opening or closing of the bypass passage.

Advantageous Effects

As described above, since the reverse-flow preventing valve of the present invention employs the pneumatic cylinder to actuate the cutoff ring, a reverse flow due to accidental stoppage of the vacuum pump can be rapidly and safely cut off, thereby preventing contamination of the vacuum chamber. Furthermore, even when the cutoff plate adapted to be actuated by pressure difference is not operated properly, the cutoff plate can be forcibly moved to close the valve, thereby improving the reliability of the reverse- flow preventing valve.

Brief Description of Drawings

Fig. 1 is a sectional view illustrating a state before a reverse- flow preventing valve according to an embodiment of the present invention is operated.

Fig. 2 is a sectional view illustrating a state after the reverse-flow preventing valve according to the embodiment of the present invention is operated.

Fig. 3 is a partially exploded perspective view of the reverse-flow preventing valve according to the embodiment of the present invention.

Fig. 4 is an enlarged sectional partial view illustrating the structure of a bypass passage and a bypass valve of the reverse-flow preventing valve according to the embodiment of the present invention.

<Explanation of Reference Numerals for Main Portions in Drawings> 10: Valve body 20: First connection portion

30: Second connection portion 40: Cutoff plate

41 : Cutoff plate guide 50 : Cutoff ring 60: Pneumatic cylinder 70: Bypass passage

71 : Bypass valve 80: Flow obstruction portion

90: Elastic member 100: Reverse-flow preventing valve

Best Mode for Carrying Out the Invention Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

Figs. 1 and 2 are sectional views illustrating states before and after a reverse-flow preventing valve according to an embodiment of the present invention is operated,

respectively, and Fig. 3 is a partially exploded perspective view of the reverse-flow preventing valve according to the embodiment of the present invention. As can be seen in Figs. 1, 2 and 3, the reverse-flow preventing valve of this embodiment comprises a cylindrical valve body 10; first and second connection portions 20 and 30 protruding from both ends of the valve body 10 and connected to exhaust pipes extending from a vacuum chamber and a vacuum pump, respectively; a cutoff plate 40 that is positioned within the valve body 10, has a diameter larger than an inner diameter of the first connection portion and smaller than an inner diameter of the valve body, and can move along a cutoff plate guide 41 in an upward and downward direction toward the first connection portion 20 in response to pressure difference so as to cut off a flow of a fluid; a cutoff ring 50 that is moved toward the first connection portion 20 to support the cutoff plate 40 when a vacuum line is in an abnormal state; and a pneumatic cylinder 60 for moving the cutoff ring 50 in the upward and downward direction.

As described above, the reverse- flow preventing valve 100 of the present invention is positioned between the vacuum chamber and the vacuum pump to function to prevent a reverse flow of air. In a conventional reverse-flow preventing valve, the opening or closing of the valve is controlled by pressure difference without using an additional power unit, and thus, there may be a case where the valve may not be operated at desired timing or may be in an inoperative state if bearings of the valve are not smooth, leading to a case where the vacuum chamber cannot be prevented from being contaminated. However, the reverse-flow preventing valve 100 of the present invention is characterized in that an additional power unit, i.e., the pneumatic cylinder 60, is used to move the cutoff ring 50 so that even though the cutoff plate 40 does not move in spite of pressure difference, the

cutoff plate 40 can be forcibly actuated to isolate the vacuum chamber. Such a feature of the present invention can improve the reliability of the reverse-flow preventing valve and enhance airtightness of the vacuum chamber during a cutoff operation of the reverse- flow preventing valve. The reverse-flow preventing valve 100 of the present invention includes the cylindrical valve body, and the first connection portion 20 and the second connection

portion 30 which protrude from both ends of the valve body and are connected to exhaust pipes extending from the vacuum chamber and the vacuum pump, respectively. Since there is only slight difference between the aforementioned structure of the present invention and a corresponding structure of a conventional reverse-flow preventing valve, the aforementioned structure will not be described any more herein.

The reverse-flow preventing valve 100 of the present invention includes the cutoff plate 40, which is positioned within the valve body, has a diameter larger than the inner diameter of the first connection portion 20 and smaller than the inner diameter of the valve body, and can move along the cutoff plate guide 41 in the upward and downward direction toward the first connection portion 20 in response to pressure difference so as to cut off a

flow of a fluid. If there is certain pressure difference between the vacuum chamber and the vacuum pump with the cutoff plate 40 positioned therebetween, i.e., the pressure of the vacuum chamber is lower than the pressure of the vacuum pump due to a breakdown of the vacuum pump, the cutoff plate 40 automatically moves toward the vacuum chamber, i.e., toward the first connection portion 20, thereby functioning to isolate the vacuum chamber. The shape of the cutoff plate 40 is not specifically limited but may be any shape capable of causing the first connection portion 20 and the valve body to be separated from each other.

However, it is preferred that the cutoff plate 40 be in the form of a disk or a cone in consideration of airtightness.

Furthermore, the reverse-flow preventing valve 100 of the present invention includes the cutoff ring 50 that is moved toward the first connection portion 20 to support

the cutoff plate 40 when a vacuum line is in an abnormal state. As described above, the vacuum chamber may be isolated by the presence of the cutoff plate 40, which is actuated due to the pressure difference, in a case where the vacuum line is in an abnormal state. However, if a frictional force existing between the cutoff plate guide 41 and the cutoff plate 40 increases, there may be a case where the cutoff plate 40 does not move. In this case, even though the cutoff plate 40 is actuated and then isolates the vacuum chamber, there may be a risk that airtightness will be deteriorated slightly. Accordingly, as a solution for improving the reliability of the valve by adding a constitutional feature capable of supporting the cutoff plate 40 in addition to the pressure difference, the pneumatic cylinder 60 is used to actuate the cutoff ring 50 in the present invention so that the cutoff ring can support the cutoff plate 40 to improve airtightness. Even though the cutoff plate 40 fails to be actuated, the pneumatic cylinder 60 forcibly pushes upward the cutoff plate 40 to prevent a reverse flow of air.

Moreover, the reverse-flow preventing valve 100 of the present invention includes the pneumatic cylinder 60 capable of moving the cutoff ring 50 in the upward and downward direction. The reverse- flow preventing valve 100 of the present invention employs the pneumatic cylinder 60 as a means for actuating the cutoff ring 50. A single pneumatic cylinder 60 may be positioned at the center of the cutoff ring 50, or a plurality of pneumatic cylinders 60 may be positioned on a circle along a periphery of the cutoff

ring 50. The arrangement, size and number of the pneumatic cylinders 60 may be designed at an appropriate level by calculating a required force in consideration of the size, weight and the like of the cutoff ring 50. If the pneumatic cylinders 60 are positioned on a circle along the periphery of the cutoff ring 50, it is preferred that the number of the pneumatic cylinders 60 range from 3 to 6. If less than three pneumatic cylinders 60 are positioned on a circle along the periphery of the cutoff ring 50, airtightness may be deteriorated due to poor balance. On the other hand, if more than six pneumatic cylinders 60 are positioned, the structure is complicated and there is no additional benefit in view of effects of airtightness and the like. The operation of the pneumatic cylinder 60 is controlled by an opening/closing signal from a separate controller (not shown). If the vacuum pump is in an abnormal state, the controller receives an interlock signal and operates the cylinder, so that the cutoff ring 50 can reinforce the airtightness of the cutoff plate 40.

In addition, the reverse-flow preventing valve 100 of the present invention may further include an annular elastic member 90 for improving airtightness, which is positioned at a periphery of an opening of the first connection portion 20 inside the valve body with which the cutoff plate 40 is brought into contact. The annular elastic member 90 is made of a material such as rubber, and is elastically deformed and comes into close contact with the cutoff plate 40 when the cutoff plate 40 is actuated to close the reverse- flow preventing valve 100, thereby functioning to improve the airtightness.

The reverse-flow preventing valve 100 of the present invention may further include the bypass passage 70 which runs to the valve body from the first connection portion 20 with which the cutoff plate 40 is brought into contact; and the bypass valve 71

capable of controlling the opening or closing of the bypass passage 70. If the valve is opened under the cutoff state of the valve in which a position above the valve is maintained at an atmospheric pressure while a position below the valve is maintained in a vacuum state, the pump is subjected to a high load and may be out of order. Therefore, the bypass passage 70 and the bypass valve 71 are to allow a small amount of fluid to flow through a small passage formed in the valve. Fig. 4 is an enlarged sectional partial view illustrating the structure of the bypass passage 70 and the bypass valve 71 of the reverse-flow preventing valve according to the embodiment of the present invention. Since the bypass passage 70 in the present invention causes the first connection portion 20 to communicate with the valve body as can be seen in Fig. 4, a small amount of fluid can flow through the valve body toward the vacuum pump even though the cutoff plate 40 isolates the first connection portion 20 and the valve body from each other. As for the operation of the bypass passage 70 and the bypass valve 71, they are maintained in an opened state for a predetermined period of time set by a timer, and the cutoff plate 40 is moved downward and main pumping is then performed after the predetermined period of time passes.

Furthermore, the reverse-flow preventing valve 100 of the present invention may further include a cylindrical flow obstruction portion 80 protruding from the second connection portion 30 toward the interior of the valve body 10 so that the flow of the fluid in the reverse-flow preventing valve 100 is curved. Due to the presence of the flow obstruction portion 80, the flow of the fluid in the valve body 10 is subjected to obstruction, so that a reverse flow of air can be somewhat delayed when the vacuum pump is stopped.

The aforementioned embodiment of the present invention should not be construed as limiting the technical spirit of the present invention. The scope of the present

invention is defined only by the appended claims. Those skilled in the art can make

various modifications and adaptations within the technical spirit of the present invention. Therefore, so far as such modification and adaptations are apparent to those skilled in the art, they fall within the scope of the present invention.