Check valve and check valve arrangement for vacuum systems

Abstract

The check valve for a vacuum system comprises a baffle extending across a flow path of the vacuum system and a valve member. The baffle has an opening, the periphery of which comprises a valve seat. The valve member has a curved sealing surface configured to mate with the valve seat. The valve member and opening are configured to be displaceable so that the valve member obscures the opening and seals with the valve seat in a closed position to prevent fluid flow from the outlet end to the inlet end, and moves away from the valve seat in use to allow fluid flow from the inlet end to the outlet end in an open position, and at least a portion of the surface of the baffle surrounding the opening slopes inwardly toward the inlet end of the check valve so that the opening is smaller at the inlet end than at the outlet end.

Description

[Technical field]

[0001] The field of the invention relates to check valves for use in vacuum systems. This application claims priority to UK Application No. 2012603.3, filed on August 13, 2020, the entire disclosure of which is incorporated herein by reference. [Background technology]

[0002] Check valves are used in vacuum systems to allow fluid to be pumped in one direction and prevent fluid from returning from an area of ​​high pressure to an area of ​​vacuum. They are used, for example, as internal pressure relief valves such as blow-off valves, exhaust check valves in dry pumps, and check valves in abatement systems. Pressure differences within vacuum systems can be large and an effective seal is required.

[0003] In applications with harsh thermal and chemical conditions, such as semiconductor applications, the process chambers may contain strong acid / alkali gases along with solid and condensable by-products. The use of check valves containing elastomers, a material commonly used to seal such valves, becomes increasingly limited by the higher operating temperature requirements of the pump or pipes, especially in corrosive environments. Summary of the Invention [Problem to be solved by the invention]

[0004] It would be desirable to provide an improved check valve that is resistant to corrosive and high temperature process gases and provides an effective seal. [Means for solving the problem]

[0005] In one aspect, a check valve for a vacuum system is provided comprising: a baffle extending across a flow path of the vacuum system, the baffle including an aperture, an outer periphery of the aperture including a valve seat; a valve member including a curved sealing surface configured to mate with the valve seat, the valve member and aperture being configured to be displaceable in use such that in a closed position the valve member obscures the aperture and seals with the valve seat to prevent fluid flow from the outlet end to the inlet end, and in use to move away from the valve seat to allow fluid flow from the inlet end to the outlet end in an open position, wherein at least a portion of a surface of the baffle surrounding the aperture slopes inwardly towards the inlet end of the check valve such that the aperture is smaller at the inlet end than at the outlet end; and diametrically opposed portions of the sloped surface of the aperture subtend an angle between 30° and 70°.

[0006] It has been found that a beveled surface around the opening of the check valve can provide an effective seal with the curved surface of the valve member, and in particular angles between 30° and 55°, and in some embodiments between 30° and 45°, have been found to tightly and robustly receive the valve member and provide an effective seal, while in other embodiments angles between 45° and 55°, and in some cases between 45° and 100°, have been found to be effective.

[0007] The inventors of the present invention have recognized that in cases where compressible elastomer-type materials are not available for sealing, it is particularly important that the sealing surfaces are in good contact in order for the seal to be effective. Furthermore, if the valve is constantly displaced, its direction can change slightly with each displacement, and as a result, it is advantageous if the available sealing surface is not limited to a specific direction. A valve with a curved surface and an inclined valve seat provides an effective sealing surface and can effectively seal the valve member in different directions. In this connection, it would seem advantageous for the valve seat to have a curved cross-section corresponding to the curved cross-section of the valve member, but in order to facilitate manufacture and limit the effect of deformations on the sealing properties, an inclined, preferably conical, valve seat has been found to be effective.

[0008] The angle of inclination and the relative size of the opening and the valve member are selected so that the inclination of the surface of the valve seat is tangential to the curved surface of the valve member at the desired mating position. In this regard, if the valve seat and the valve member are selected to have the same diameter, the valve member will mate with the seat at a position close to the widest part of the valve member where the inclination of the valve member surface is steeper, in which case the appropriate angle is the smaller angle. Having a valve member diameter similar to the valve seat but slightly larger allows for a wider diameter seat and improves conductance. However, it has been found that in vacuum systems, a smaller angle results in a narrower opening at the initial displacement of the valve member, which opens gradually due to the steepness of the valve seat. This gradual opening reduces any tendency of the ball to move in and out of the valve seat by accommodating changes in the back pressure of the system, providing a gradual pressure change and reducing the initial leak rate of gas from the check valve. This can improve the performance of the vacuum system and reduce wear on the valve compared to vacuum systems with check valves having wider angled seats.

[0009] In some embodiments, the valve member is made of metal, and in other embodiments, is made of ceramic.

[0010] In some embodiments, the valve member is made from stainless steel, and in some embodiments, the valve seat is made from stainless steel.

[0011] Stainless steel seals are robust, hard, resistant to high temperatures and provide an effective sealing surface.

[0012] In some embodiments, the valve member is made of a different metal than the valve seat, and in some embodiments, the valve member is made of a nickel-chromium-molybdenum alloy, possibly Hastelloy C276® (57% nickel, 15-17% molybdenum, 14.5-16.5% chromium, 4-7% iron).

[0013] By forming the valve seat and the valve member from different metals, it is possible to prevent them from bonding at high temperatures. In particular, nickel-chromium-molybdenum alloys such as Hastelloy C276 (registered trademark) are an ideal material for the valve body because they can withstand harsh environments and high temperatures.

[0014] This check valve configuration allows for an effective seal without the use of compressible elastomeric materials that can degrade at high temperatures and in corrosive environments, allowing the use of materials such as metals that are robust and resistant to many harsh environments.

[0015] In some embodiments, the sloped portion of the surface surrounding the opening extends from the outlet-facing surface of the check valve towards the inlet-facing surface and becomes steeper where it extends to the inlet-facing surface, and the valve seat is at or near the change in the slope angle.

[0016] In some embodiments, the angle of the slope is steeper towards the inlet end, which allows the seat to be located closer to the steepened area and away from the edge of the inlet opening, creating a more robust seat where the portion of the seat supporting the valve member is not close to the edge of the opening.

[0017] In some embodiments, the material forming the valve seat has a roughness between 0.1 and 1.0 Ra, preferably between 0.3 and 0.5 Ra.

[0018] In some embodiments, the material forming the valve member has a roughness between 0.01 and 0.5 Ra.

[0019] The roughness of the valve member and the valve seat affects the quality of the seal, and this effect can be particularly important if the valve member and the valve seat are made of metal rather than a more resilient material. It has been found that a roughness between 0.1 and 1.0 Ra, preferably between 0.3 and 0.5 Ra, provides an effective surface for the valve seat and an effective seal. Moreover, such a surface can be manufactured in a cost-effective manner. It may be advantageous for the valve member to be formed to be smoother than the valve seat.

[0020] In another embodiment, the angled surface of the opening comprises a recess which provides an area of ​​no contact with the curved surface of the valve member such that the valve member contacts the valve seat at two points on either side of the recess, which can be effective for sealing, essentially providing two sealing positions.

[0021] In some embodiments, the valve member is solid, while in other embodiments, the valve member is hollow. The valve member can be formed from many materials, can be hollow or solid, and is generally configured to have a mass that is selected to provide adequate protection against backflow of gas, but not so large that it creates significant backpressure in the vacuum system.

[0022] In some embodiments, the check valve comprises a protrusion extending from the curved surface of the valve member, the protrusion extending through the opening and comprising a retention portion extending outwardly from the protrusion and configured to limit movement of the valve member toward the outlet end when the check valve is in the open position.

[0023] The valve member must be retained within the check valve, which may be accomplished with a cage-type mechanism to restrict movement of the valve member toward the outlet, or alternatively, with a protrusion extending through the opening and a retaining portion extending from the protrusion that is wider than the opening.

[0024] In some embodiments, the baffles can extend across the pipe, and if a cage-type mechanism is used, it can also extend across the pipe and in some embodiments can be held within the pipe with an interference fit.

[0025] In a further aspect, there is provided a check valve device for a vacuum system comprising check valves for the vacuum system according to one aspect arranged in series with respect to each other such that fluid from an inlet end of the check valve device flows through a first of the check valves and then through a second of the check valves.

[0026] The check valve of the embodiment can be used as a double check valve to provide additional protection against backflow. The check valve provides a possible leakage path for gas from a higher pressure outside the vacuum system into the vacuum system. This can be particularly problematic in valves where traditional elastomeric sealing means are not used due to the harsh conditions experienced. The leakage rate depends on the pressure difference across the check valve. A double check valve has an intermediate volume between the two check valves, which is at an intermediate pressure when the valves are closed, and the pressure loss across each check valve is less than the pressure loss across a single check valve. As a result, the leakage rate of each check valve, and therefore the combined check valve, is less than when using a single check valve.

[0027] In some embodiments, the system further comprises an intermediate volume providing a flow path between two valve seats, the length of the flow path being between 1.5 and 10 times, preferably between 1.5 and 6 times, the diameter of said valve seats.

[0028] For a double check valve to be particularly effective, there needs to be a volume between the two check valves so that the pressure difference between the vacuum system and the outside is divided across the two check valves. The smaller the intermediate volume, the more quickly the pressure in the intermediate volume will reach an equilibrium steady-state value when the check valves close. However, this volume needs to be sufficient to allow each check valve to be opened and closed without physically affecting the other check valve.

[0029] In some embodiments, the intermediate volume is in a pipe connecting the intermediate first and second check valves.

[0030] In some embodiments, the two check valves can be independent units and can be connected by a connecting pipe. The length of the connecting pipe is selected to provide a suitable intermediate volume. In some embodiments, the diameter of the valve seat is between 1.5 and 10 times the length of the pipe between the two valve seats of the two check valves.

[0031] In other embodiments, the device includes a combined outer housing for housing both the first and second check valves.

[0032] Advantageously, the double check valve can be mounted on the device and formed from a single housing, thereby reducing the number of sealing means required, which is advantageous since, as mentioned above, sealing means deteriorate in corrosive and high temperature environments.

[0033] In some embodiments, the coupled outer housing is configured such that the flow path between the check valves includes a portion that extends in an opposite direction to the inlet and outlet flow paths of the check valve device.

[0034] The coupled housing can be configured such that the two check valves are positioned substantially side-by-side such that the flow path between them redirects out of the first check valve and back towards the second check valve. The inflow and outflow direction of the gas can be unidirectional with a simple change in flow direction when passing between each check valve.

[0035] Further particular and preferred aspects are set out in the dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate and in combinations other than those explicitly set out in the claims.

[0036] Embodiments of the invention are further described below with reference to the accompanying drawings. [Brief description of the drawings]

[0037] [Figure 1] 1 illustrates a schematic diagram of a non-return check valve according to a first embodiment; [Diagram 2] 13A-B are schematic diagrams of a non-return check valve having a wider angle slope; [Diagram 3] 13 illustrates diagrammatically a non-return check valve according to a further embodiment; [Figure 4] 1 illustrates a double check valve according to one embodiment. [Diagram 5] 1 illustrates another embodiment of a double check valve. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] Before describing the embodiments in more detail, an overview will first be provided.

[0039] In applications with severe thermal and chemical challenges (e.g., semiconductor applications), a high temperature pump combined with a check valve capable of operating at high temperatures with good corrosion resistance is desired. The embodiments provide a check valve that can be made entirely of metal that exhibits good sealing performance. In some embodiments, stainless steel is used, and the stainless steel of the valve seat is machined to have a surface roughness between 0.1 and 1 Ra, preferably between 0.3 and 0.5 Ra. In some embodiments, the valve member is machined to have a surface roughness between 0.01 and 0.5 Ra. In some embodiments, the valve member is made of a different metal than the valve seat, and in some embodiments, is made of a nickel-chromium-molybdenum alloy. In some embodiments, the use of a double check valve further improves sealing.

[0040] Embodiments provide a check valve with a valve member having a curved surface that abuts an inclined seat. The angle of inclination of the seat is selected in conjunction with the size of the valve member and the opening to provide an effective seal. In some embodiments, the valve member is comprised of a ball having a diameter of 30 mm. The inside diameter of the seat is 26 mm. The contact between the ball and the seat is a single line contact. In some embodiments, the valve is a metal valve, while in other embodiments, the valve body and seat can be formed of ceramic. Metals and ceramics are suitable for high temperature and corrosive environments.

[0041] In some embodiments, the valve member and the valve seat are formed of the same material, while in other embodiments they are formed of different materials.

[0042] In some embodiments, check valves are installed in the pipes of the system, while in other embodiments, pipe connectors are used.

[0043] Figure 1 shows a cross section through a check valve 5 according to one embodiment. The check valve 5 comprises a valve member 18 in the form of a ball with a projection and a retaining member 22 extending therefrom. The retaining member is perforated to allow gas to pass. The valve member 18 extends across the pipe in which the check valve is mounted and fits into a valve seat 22 formed in a baffle 14 with an opening having a first angle and a steeper inclined surface 25. The valve seat 22 is located adjacent to the change in angle of inclination.

[0044] The check valve 5 is mounted via a seal within the pipe, allowing gas to flow from the vacuum system towards the outlet in the direction of arrow 7. When pressure within the vacuum system increases, a force is exerted on the valve member 18, which pushes it away from the valve seat 23 to an open position, allowing gas to flow out the top of the pipe through the opening which is now no longer obscured by the valve member 18. When pressure within the system decreases, the valve member 18 moves back into the opening under its own weight, sealing against the valve seat 23 to prevent gas at higher pressure outside the vacuum system from entering the vacuum system.

[0045] The opening of the baffle 14 has a sloping surface 25 adjacent to the outlet that forms a 60° angle with the diametrically opposite sloping surface of the opening, providing a suitable slope for mating with the curved surface of the ball to provide a good seal. The slope is steeper toward the inlet of the valve, and the location of the valve seat is well defined and not facing one end of the slope, so that the ball can be securely held and the valve seat is not easily damaged.

[0046] However, an angle of 60° has been found to be effective for valve members in which the diameter of the ball is close to the diameter of the valve seat. In some embodiments, a smaller angle between 35° and 40° may be preferred when the diameter of the ball is between 5% and 18% larger than the diameter of the opening, preferably between 5% and 10% larger. This angle provides an initially narrow flow path as the ball moves away from the seat, allowing for more gentle control of pressure changes.

[0047] FIG. 2 shows an alternative, where the angle of the inclined surface 25 is less steep, in this embodiment forming a 90° angle with the opposite inclined surface in the diametric direction of the opening. As in the previous embodiment, the inclination is steeper towards the inlet so that the valve seat is at a defined location on the surface. In this example, the diameter of the valve member and the diameter of the valve seat are more different and the valve member is held in a position not close to the center of the valve member, so the inclination angle of the curve is shallower and matches the inclination of the valve seat. In this embodiment, the diameter of the ball is between 15% and 30% larger than the diameter of the valve seat. In this case, the displacement of the valve member causes a larger initial change in the fluid flow, which may result in poorer performance in pumping the vacuum system compared to a valve seat with a steeper angle.

[0048] Figure 3 shows an alternative embodiment where the surface profile of the opening which forms the valve seat has a depression 27 in it such that two valve seats 22 are formed on either side of the depression. The inlet side of the opening is smaller than the outlet side, providing a good seal as the valve member is retained at both points and an effective seal is provided in two places.

[0049] FIG. 4 shows another embodiment, where two check valves 5a and 5b from the above embodiment are used to provide a double check valve 60. The two check valves form a double check valve, where gas enters at the inlet 32 ​​and contacts the first check valve 5a. When the pressure at the inlet 32 ​​rises above the pressure in the intermediate volume in the pipe 50, the first check valve 5a opens and gas enters the intermediate volume of the pipe 50. When the pressure here rises, the second check valve 5b opens and gas flows out of the system. When the pressure at the inlet falls below the pressure in the intermediate volume 50, the check valve 5a closes. Similarly, when the pressure in the intermediate volume falls below the external pressure, the second check valve 5b closes. In a vacuum system, when the pump starts, the pressure downstream of the check valve 5a rises and the check valve 5a opens. The pressure at the pump inlet falls (vacuum) and the pressure at the pump outlet rises due to compression of the gas. The pressure in intermediate volume 50 will rise, causing check valve 5b to open. As long as the pump is running, there will usually be enough gas flow to maintain the pressure differential and check valves 5a and 5b will remain open.

[0050] When the pump stops, the pressure downstream of check valve 5a drops so that it can no longer support the weight of check valve 5a and check valve 5b closes. Similarly, the pressure in intermediate volume 50 drops and check valve 5b closes.

[0051] The intermediate volume 50 of the pipe is at an intermediate pressure when the two check valves are closed, such that the pressure drop between the inlet 32 ​​and the outside is divided across each of the different check valves, which reduces leakage in the reverse direction. In this connection, since the leakage across each valve depends on the pressure drop across it, reducing the pressure drop by dividing it between the two valves reduces leakage. The intermediate volume must be selected so that the two valves do not physically collide during operation, but preferably not significantly larger than this. A large intermediate volume increases the time to reach the equilibrium intermediate pressure when the double check valves are closed, which would affect the vacuum system to which the check valves are attached.

[0052] 5 shows another embodiment, where multiple check valves 60 are mounted within a single housing 70. The single housing allows the valves to be easier to mount in the system and also reduces the number of seals required to seal the system. As mentioned above, sealing for high temperature corrosive systems can be problematic and reducing the number required can be advantageous.

[0053] This embodiment provides a particularly compact check valve that can fit into tight spaces. Since the two check valves are mounted side-by-side, this requires that the gas flow change direction as it travels through the valve.

[0054] Although the double check valve is shown with a valve member having a protrusion and a retaining member 22, it may also use a curved valve member and some other retaining means such as a grid or cage between the valve member and the outlet.

[0055] Although exemplary embodiments of the invention are disclosed in detail herein with reference to the accompanying drawings, it should be understood that the invention is not limited to the precise embodiments, and that various changes and modifications may be made by those skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents. [Explanation of symbols]

[0056] 5, 5a, 5b Check valve 7 Gas Flow 14 Baffle 18 Valve member 22 Holding part 23 Valve seat 25 Slanted opening surface 50 Mid pipe 52 Seal 60 Multiple check valve 70 Housing

Claims

1. 1. A check valve for a vacuum system, comprising: a baffle extending across a flow path of the vacuum system, the baffle including an opening, the periphery of the opening including a valve seat; a valve member including a curved sealing surface configured to mate with the valve seat, the valve member and the opening being configured such that in a closed position the valve member obscures the opening and seals with the valve seat to prevent fluid flow from the outlet end to the inlet end, and in use is displaceable away from the valve seat to allow fluid flow from the inlet end to the outlet end in an open position; Equipped with at least a portion of a surface of the baffle surrounding the opening is inwardly tapered toward the inlet end of the check valve such that the opening is smaller at the inlet end than at the outlet end; diametrically opposed portions of the aperture's inclined surfaces subtend an angle between 30° and 70°; the angle of the inclined surface and the relative sizes of the opening and the valve member are selected such that the inclined surface is tangential to the curved sealing surface of the valve member at the valve seat; 11. A check valve for a vacuum system, wherein a sloped portion of the surface surrounding the opening extends from a surface facing the outlet end of the check valve toward a surface facing the inlet end and becomes steeper at the portion extending to the surface facing the inlet end, and wherein the valve seat is at or near a change in the angle of slope.

2. 2. The check valve of claim 1, wherein diametrically opposed portions of the inclined surfaces of the opening form an angle between 30[deg.] and 55[deg.].

3. 3. A check valve for a vacuum system according to claim 1 or 2, wherein diametrically opposed portions of the inclined surfaces of the opening form an angle between 30[deg.] and 45[deg.].

4. A check valve for a vacuum system according to any one of claims 1 to 3, wherein the material forming the valve member has a roughness between 0.01 and 0.5 Ra.

5. A check valve for a vacuum system according to any one of the preceding claims, wherein the material forming the valve seat has a roughness between 0.1 and 1.0 Ra, preferably between 0.3 and 0.5 Ra.

6. A check valve for a vacuum system according to any one of claims 1 to 5, wherein the check valve is made entirely of metal.

7. A check valve for a vacuum system according to claim 1 , wherein the valve member and the valve seat are formed from stainless steel.

8. A check valve for a vacuum system according to claim 1 , wherein the valve member and the valve seat are formed from different metals.

9. 9. A check valve for a vacuum system according to claim 1, further comprising a cage-type mechanism for retaining the valve member within the check valve, the cage-type mechanism limiting movement of the valve member towards the outlet end of the check valve.

10. 10. A pipe comprising a check valve of a vacuum system according to claim 9, wherein the baffle and the cage-type mechanism extend across the pipe.

11. The pipe of claim 10 , wherein the cage-type mechanism is retained within the pipe with an interference fit.

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