Valve seat structure of fluid control valve

In a valve seat structure of a fluid control valve comprising a valve element, a body formed with an inlet port and an outlet port, and a valve seat member provided in the body, the fluid control valve being configured to bring the valve element into or out of contact with the valve seat member to control the flow of a fluid, the valve seat member is formed in a ring shape and includes a valve seat portion with which the valve element will come into our out of contact. Assuming that a thickness of the valve seat portion in a radial direction of the valve seat member is a first thickness t1 (0<t1), a second thickness t2 corresponding to a height of the valve seat member in a direction along an axis of the fluid control valve is determined in a range of 0.5 t1≦t2≦1.5 t1.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2010-238305 filed on Oct. 25, 2010, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a valve seat structure of a fluid control valve for controlling the flow of a fluid and more particularly to a valve seat structure of a diaphragm valve for controlling the flow of a fluid such as high-temperature gas (hot gas) in for example a semiconductor manufacturing device and others by bringing a diaphragm valve element into or out of contact with a valve seat.

BACKGROUND ART

In a semiconductor manufacturing process, a liquid crystal panel manufacturing process, and others, when a hot gas, such as H2gas and Ar gas, heated to about 200° C. is to be supplied to a semiconductor manufacturing device and others or shut off, a metal diaphragm valve as disclosed for example in Patent Documents 1 and 2 is used as a fluid control valve for controlling the flow of the hot gas.

FIGS. 6 and 7are views to explain a metal diaphragm valve of Patent Document 1. Patent Document 1 discloses, as shown inFIGS. 6 and 7, a metal diaphragm valve201including a metal diaphragm260made with a Vickers hardness of 500 Hv or more by an age-hardening heat treatment. The diaphragm260is configured to contact with or separate from a valve seat250when pressured or released by a valve rod230. In this metal diaphragm valve201, when the pressure of the valve rod230is released, the metal diaphragm260elastically returns to its original shape.

In Patent Document 1, the metal diaphragm260is hardened to a Vickers hardness of 500 Hv or more. Accordingly, even in an environment that the metal diaphragm valve201is heated to a high temperature, it is possible to prevent a decrease in reactive force from the valve seat250to the diaphragm260at the time of valve closing and thermal expansion of the diaphragm260during valve opening. Even though Patent Document 1 does not disclose any shapes, any materials, any structures, etc. of the valve seat250, it discloses that the diaphragm260made with hardness can keep a gap α between the diaphragm260and the valve seat250constant during control of the flow of hot gas.

FIGS. 8 and 9are views to explain a metal diaphragm valve of Patent Document 2. Patent Document 2 shows a metal diaphragm valve301including a circular metal diaphragm360configured to contact with or separate from a valve seat350when the diaphragm360is pressed by or released from a stem366through a diaphragm holding member365as shown inFIGS. 8 and 9. The metal diaphragm360is a metal thin sheet made of stainless thin sheets and cobalt alloy thin sheets in a lamination configuration and formed into a reversed dish-like shape having a central portion protruding upward. The valve seat350is made of synthetic resin such as PFA and fixed in a valve attachment groove of a body340by crimping or caulking.

Patent Document 2 discloses, as shown inFIG. 9, that a gap ΔS between the diaphragm holding member365and the valve seat350is set to a height corresponding to about 55% to 70% of a maximum protruding height Δh of the central portion of the metal diaphragm360from the valve seat350. Thus, the Cv value of the metal diaphragm valve301can be 0.55 to 0.8.

Although no related art is cited here, there is also a metal diaphragm valve in which a ring-shaped valve seat member made of synthetic resin such as PFA is fixed in a valve attachment groove of a body by crimping or caulking in a similar manner to Patent Document 2.FIG. 10shows the shape of this valve seat member and is an enlarged view corresponding to a part A inFIG. 1mentioned later.

In this metal diaphragm valve, as shown inFIG. 10, assuming that the thickness of a valve seat portion151, which a valve element will contact with and separate from, in a radial direction CR of a valve seat member150is a first thickness t1, the valve seat member150has a second thickness t2in its height direction AX larger about 2.7 times the first thickness t1. In this metal diaphragm valve, when a valve closed state is established, the valve element (not shown) deeply presses against the valve seat member150and reliably comes into close contact with the valve seat member150. Thus, a sealing performance between the valve element and the valve seat member150can be enhanced.

RELATED ART DOCUMENTS

Patent Documents

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

However, the conventional metal diaphragm valves have the following disadvantages. A metal diaphragm valve is arranged to control the flow of a fluid such as hot gas by bringing a valve element into or out of contact with a valve seat. In a valve closed state, the valve element presses against and hence closely contacts with the valve seat to shut off the flow of the fluid. In a valve open state, a flow rate of a fluid flowing in a valve chamber is determined by a stroke (a separation distance) between the valve element and the valve seat when the valve element comes out of contact with the valve seat.

When the valve element contacts with the valve seat for valve closing, the valve seat receives a pressing force from the valve element and a portion of the valve seat that is in contact with the valve element is greatly depressed or compressed. In contrast, when the valve opens from this state, a reactive force caused by the pressing force of the valve element acts on the valve seat and accordingly the depressed portion of the valve seat will attempt to return to a shape before depression (a previous shape).

In the case where the fluid is a hot gas exemplified above and the flow of this hot gas is to be controlled by the metal diaphragm valve, the valve element, the valve seat, and others in the valve chamber of the metal diaphragm valve are exposed to high temperatures. In this case, the hot gas is allowed to continuously flow from an inlet port to an outlet port through the valve chamber for a long period after valve opening from a valve closed state. Further, the valve seat attempts to gradually return to the shape before depression. The temperature of the valve chamber at that time rises above the temperature in the valve closed state where no hot gas flows. As the temperature rises, the valve seat will thermally expand.

In the metal diaphragm valve, while the fluid is flowing after valve opening, the valve seat undergoes deformation with time by a deformation amount corresponding to the sum of a return amount toward the valve element due to the reactive force and the thermally expansion amount toward the valve element due to the temperature rise in the valve chamber. Accordingly, a real stroke (separation distance) between the valve seat and the valve element varies.

Specifically, just after valve opening, the valve seat remains depressed and also cold because hot gas does not flow in the valve yet. Thus, the upper surface of the valve seat is further away from the valve element than in before depression. Thus, the stroke between the valve seat and the valve element is larger than in before depression. On the other hand, as the time advances by a predetermined time from valve opening, the valve seat returns toward a previous state before depression and also expands because the valve chamber is increased in temperature up to the temperature of flowing hot gas. Thus, the upper surface of the valve seat comes closer to the valve element than in the depressed state and therefore the stroke between the valve seat and the valve element decreases.

Consequently, the stroke between the valve seat and the valve element is different between just after valve opening and after a predetermined time elapsed from valve opening. While hot gas is flowing in the valve chamber during valve opening, the flow rate (a Cv value) of hot gas varies between just after valve opening and after a lapse of a predetermined time from valve opening.

In Patent Document 1, there is no disclosure about the material, the structure, and others of the valve seat250which will be deformed greatly by opening/closing of the metal diaphragm260. However, if the valve seat250is made of metal, the valve seat250will be hardly deformed when the metal diaphragm260contacts with the valve seat250for valve closing.

However, for valve closing, the metal diaphragm260and the valve seat250, both of which are made of metal, contact with each other, thereby likely damaging the valve seat250. When the number of contact times of the valve seat250with the metal diaphragm260reaches about 50,000, the sealing performance begins to decrease, resulting in a defect in durability of the valve seat250.

On the other hand, even if the valve seat250is made of resin capable of providing higher durability than the metal valve seat, no special design is applied to the shape of such valve seat250that is likely to be deformed greatly by opening/closing of the metal diaphragm260under a high temperature.

In Patent Document 2, the gap ΔS between the diaphragm holding member365and the valve seat350is set to a height corresponding to about 55% to 70% of the maximum protruding height Δh of the central portion of the metal diaphragm360relative to the valve seat350, so that the Cv value falls within a range of 0.55 to 0.8.

In Patent Document 2, however, even though the valve seat350is made of synthetic resin, such as PFA, tending to soften earlier than metal, no special design is applied to the shape of such valve seat350that is likely to be deformed greatly by opening/closing of the metal diaphragm360.

In Patent Documents 1 and 2, when hot gas is allowed to flow from the inlet port to the outlet port through the valve chamber for a long period after the valve is opened from the valve closed state, the valve seat250(350) undergoes large deformation with time after valve opening by an amount corresponding to the sum of the return amount toward the metal diaphragm260(360) due to the reactive force and the thermal expansion amount toward the diaphragm260(360) due to the temperature rise in the valve chamber. As a result, the real stroke between the valve seat250(350) and the metal diaphragm260(360) changes. Thus, a difference in the stroke becomes larger with time after valve opening.

As above, when a difference in the stroke between the valve seat250(350) and the metal diaphragm260(360) occurs after valve opening, the flow rate of a fluid flowing during valve opening varies. This results in a problem that a decrease in Cv value after valve opening could not be restrained within 0.2, which is recently demanded as the flow-rate control accuracy of the valve in the manufacturing industry of precision components such as semiconductors.

Further, in the conventional metal diaphragm in which the second thickness t2is set to be as large as about 2.7 times the first thickness t1, the sealing performance between the valve element and the valve seat member150is higher than that of the metal valve seat. However, as in Patent Documents 1 and 2, when the valve is placed in the open state, the flow rate of a fluid allowed to flow varies and the fluid could not flow at an stable flow amount.

The present invention has been made to solve the above problems and has a purpose to provide a valve seat structure of a fluid control valve capable of ensuring sealing performance with respect to a valve element and reducing variations in flow rate while a fluid to be controlled continues to flow.

Means of Solving the Problems

To achieve the above purpose, one aspect of the invention provides a valve seat structure of a fluid control valve comprising a valve element, a body formed with an inlet port and an outlet port, and a valve seat member provided in the body, the fluid control valve being configured to bring the valve element into or out of contact with the valve seat member to control the flow of a fluid, wherein the valve seat member is formed in a ring shape and includes a valve seat portion with which the valve element will come into or out of contact, and assuming that a thickness of the valve seat portion in a radial direction of the valve seat member is a first thickness t1(0<t1), a second thickness t2corresponding to a height of the valve seat member in a direction along an axis of the fluid control valve is determined in a range of 0.5 t1≦t2≦1.5 t1.

Effects of the Invention

According to the above aspect, the following effects can be provided. In a semiconductor manufacturing process, for instance, when the flow of hot gas, such as H2gas and Ar gas, heated to about 200° C. is to be controlled by the fluid control valve including the aforementioned valve seat structure, if the hot gas continues to flow from an inlet port to an outlet port through a valve chamber for a long period after a valve opening operation from a valve closed state, a difference in a stroke (a separation distance) between the valve seat member and the valve element between just after valve opening and after a lapse of a predetermined time from valve opening can be made smaller. This can reduce variations in flow rate of a fluid (e.g., hot gas) flowing in the valve chamber of the fluid control valve.

Accordingly, it is possible to restrain the decrease in Cv value after valve opening to 0.2 or less which is recently demanded as the flow-rate control accuracy of the valve in the manufacturing industry of precision components such as semiconductors. This can reduce variations in flow rate of the fluid flowing while the valve is in an open state. In contrast, when the valve is placed in a closed state, the valve element firmly presses against the valve seat member and comes into close contact with the valve seat member, thereby ensuring high sealing performance. The flow of a fluid such as hot gas can be shut off without leakage toward the outlet port.

In the aforementioned valve seat structure of a fluid control valve, specifically, the valve seat member is formed in the ring shape and includes the valve seat portion with which the valve element comes into or out of contact. Assuming that the thickness of the valve seat portion in the radial direction of the valve seat member is the first thickness t1(0<t1), a second thickness t2of the valve seat member, i.e., the height in a valve seat height direction along an axis direction of the fluid control valve is determined in a range of 0.5 t1≦t2≦1.5 t1.

In the valve seat structure of the conventional metal diaphragm in which the second thickness is set to about 2.7 times the first thickness, when the pressing force of the valve element acts on the valve seat portion of the valve seat member, a depression amount of the valve seat portion is for example 0.5 mm. In contrast, in the valve seat structure of a fluid control valve according to the aforementioned aspect of the invention, even by the same level of pressing force, a depression amount is reduced to for example as small as 0.25 mm, half the conventional depression amount. The return amount of the valve seat member toward the valve element due to the reactive force after valve opening is also reduced to about half, as with the depression amount.

As exemplified, when the hot gas continues to flow from the inlet port to the outlet port through the valve chamber for a long period after valve opening from a valve closed state, the temperature of the valve chamber increases more than that in the valve closed state where no hot gas flows in the valve. Thus, the valve seat member (the valve seat portion) tends to thermally expand. Even in comparison between the valve seat structure of the fluid control valve in the aforementioned aspect of the invention in which the second thickness is 1.5 times or less the first thickness and the valve seat structure of the conventional metal diaphragm valve in which the second thickness is about 2.7 times the first thickness, the thermal expansion amount of the valve seat member of the valve seat structure of the fluid control valve in the aforementioned aspect is smaller than that of the valve seat structure of the conventional metal diaphragm valve by the second thickness being smaller than the valve seat height of the valve seat member.

In the valve seat structure of the fluid control valve in the aforementioned aspect of the invention, accordingly, the deformation amount of the valve seat member corresponding to the sum of the return amount due to the reactive force and the thermal expansion amount associated with the temperature rise in the valve chamber after valve opening can be made smaller than that in the valve seat structure of the conventional metal diaphragm valve.

When the flow of hot gas (fluid) is to be controlled by the above fluid control valve, the real stroke between the valve seat member and the valve element while the hot gas continues to flow from the inlet port to the outlet port through the valve chamber for a long period after the valve opening operation from the valve closed state has little stroke difference between just after valve opening and after a lapse of a predetermined time from valve opening.

As a result, while hot gas continues to flow in the valve chamber during valve opening, it is possible to reduce variations in flow rate of hot gas. In the conventional structure, the Cv value after valve opening is decreased by as much as 0.4. In contrast, in the valve seat structure of the fluid control valve in the aforementioned aspect of the invention, a decrease in Cv value after value opening can be restrained within 0.2 which is recently demanded in the manufacturing industry of precision components such as semiconductors.

Here, the Cv value will be explained below. The Cv value is the dimensionless number defined as a number representing that, in a valve open state where a valve element of a fluid control valve is opened at a predetermined degree, “the flow rate of fresh water, at 60° F. (about 15.5° C.), that will flow through the valve while keeping a differential pressure (a pressure drop) of 1 psi (6.895 kPa) between an inlet port side and an outlet port side, in terms of US gal/min (1 USgal=3.785 L) (gpm)”.

The Cv value is determined by actual measurement using a known measuring device such as a fluid flow meter and a fluid pressure meter. The Cv value is assumed to be 1 when the valve opening degree of the valve element is full and the fresh water at about 15.5° C. flows with a differential pressure of 6.895 kPa and a flow rate of 3.785 L. The Cv value is calculated by the following expression:
Cv=Q·(G/ΔP)^(½)
where Q (gpm) is a flow rate of a fluid, G is a specific gravity, ΔP (psi) is a differential pressure of a fluid.

As the Cv value is larger, the fluid control valve has a wider flow channel through which a fluid passes. The valve seat structure of the fluid control valve in the aforementioned aspect is directed for example to a fluid control valve configured such that, when the fluid to be controlled is mainly gas and the valve element is placed in a full open state, a full stroke (a maximum separation distance) between a valve seat member and a valve element is about 1 mm.

Specifically, the valve seat structure of the fluid control valve in the aforementioned aspect is directed for example to a fluid control valve configured such that the stroke between the valve seat member and the valve element is 0.9 mm and the Cv value is 0.7 in a valve full open state just after valve opening. In the manufacturing industry of precision components such as semiconductors, fluid control valves like the aforementioned one are often used. Accordingly, a demand to restrain a decrease (a difference) in Cv value after valve opening to 0.2 or less arose from the manufacturing industry of precision components in order to meet the marketing needs for high precision and high quality of products. For this demand, which is assumed as an indication or target to ensure the quality of precision components (products), the valve seat structure of the aforementioned aspect of the invention is configured to prevent the Cv value from decreasing, after a predetermined time elapsed from valve opening, to less than 0.5 corresponding to a 30% reduction of 0.7 which is a Cv value just after valve opening.

On the other hand, the valve seat member is formed with the second thickness larger by 0.5 times or more than the first thickness. Thus, the valve seat member can have sufficient deformation allowance allowing the valve element to press against the valve seat member more deeply when the valve is placed in a closed state. Accordingly, the valve seat member can come into close contact with the valve element to ensure high sealing performance. This can shut off the flow of a fluid such as hot gas without leakage toward the outlet port.

Consequently, the valve seat structure of the fluid control valve in the aforementioned aspect of the invention can provide the effects that sealing performance with respect to the valve element can be ensured and variations in flow rate of a fluid to be controlled can be reduced while the fluid is flowing.

MODE FOR CARRYING OUT THE INVENTION

A detailed description of a preferred embodiment of the present invention will now be given referring to the accompanying drawings.

A fluid control valve in this embodiment is for example a gas control valve1for controlling the flow of hot gas (fluid), such as H2 gas and Ar gas, heated to about 200° C. to supply or shut off the gas with respect to a semiconductor manufacturing device and others in a semiconductor manufacturing process, a liquid crystal panel manufacturing process, and other processes. In this embodiment, a valve seat structure of such a gas control valve1is explained.

FIG. 1is an explanatory view showing a gas control valve in Example 1 of the present embodiment, showing a valve closed state.FIG. 2is an enlarged view of a part A inFIG. 1to explain the valve seat structure of the gas control valve in Example 1.

The gas control valve1(the fluid control valve) includes a diaphragm valve element60(a valve element), a body40formed with an inlet port41and an outlet port42, and a valve seat member50provided in the body40. The gas control valve1is configured to bring the valve element60into or out of contact with the valve seat member50to control the flow of hot gas.

The gas control valve1roughly consists of an air control section2and a valve control section3as shown inFIG. 1.

The air control section2will be first explained. This air control section2in the present embodiment includes two cylinders, i.e., a first cylinder10and a second cylinder15, two pistons, i.e., a first piston21and a second piston22, a partition member23, and others. All of these components are made of metal such as stainless steel. The first cylinder10is formed with a first breathing hole12and a second breathing hole13. The first cylinder10and the second cylinder15are joined by screw connection into one piece. The partition member23is held between the first cylinder10and the second cylinder15to divide the internal space of those first and second cylinders10and15into a first pressure chamber25and a second pressure chamber26. The first cylinder10is formed with the first breathing hole12for the first piston21and the second breathing hole13for the second piston22.

The first piston21is placed between the first cylinder10and the partition member23. The second piston21is placed between the second cylinder15and the partition member23. In the internal space of the first and second cylinders10and15, an upper portion of a piston rod30extending in a direction of the axis AX (an “axis direction AX”) is disposed. This upper portion of the piston rod30is formed with a pilot hole30H extending in the axis direction AX. Two through holes, i.e., a first through hole31H and a second through hole32H are formed to extend in a radial direction CR perpendicular to the pilot hole31H and in communication with the pilot hole31H. A lower portion of the piston rod30is disposed in the valve control section3mentioned below.

The valve control section3includes the body40, the valve seat member50, the diaphragm valve element60, a valve element holding member65, a stem66, a spring67, a guide member71, a spring support member72, a connecting member73, a fixing member74, and others. All of these components are made of metal such as stainless steel.

The body40has the inlet port41and the outlet port42as shown inFIGS. 1 and 2. Between these inlet port41and outlet port42, the valve seat member50which is a separate part from the body40is provided. Further, the body40is formed with a pair of annular grasping portions43defining a groove therebetween in which the valve seat member50is fitted. The grasping portions43extend circumferentially about the axis AX and are arranged inside and outside in the radial direction CR.

The valve seat member50is formed in a ring shape and includes a valve seat portion51with which the diaphragm valve element60will come into and out of contact, and a fixed portion52located under the valve seat portion51. The valve seat member50is made of fluorocarbon resin, which is, in the present embodiment, PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer).

The valve seat member50is fixed to the body40as shown inFIG. 2in such a way that the fixed portion52is placed between the grasping portions43and one of the grasping portion43located inside in the radial direction CR and the other grasping portion43located outside in the radial direction CR are deformed or crimped toward each other, thereby holding or pinching the valve seat member50in the radial direction CR.

To be concrete, the fixed portion52is designed to be wider than a first thickness t1of the valve seat member50(the valve seat portion51) and is fixedly pinched in the radial direction CR of the valve seat member50by the grasping portions43which are a part of the body40.

The valve seat member50is designed so that, assuming that the thickness of the valve seat portion51in the radial direction CR is the first thickness t1(0<t1), the second thickness t2corresponding to the height of the valve seat member50in the axis direction AX of the gas control valve1is determined in a range of 0.5 t1≦t2≦1.5 t1. The relationship between the first thickness t1and the second thickness t2will be described in detail later.

The diaphragm valve element60is, for example, a metal diaphragm valve element made of metal, such as Ni alloy and Co alloy, subjected to a treatment for preventing heat distortion and others in a hot gas atmosphere at about 200° C. This valve element60is formed in a reversed dish-like shape protruding upward and capable of returning upward in the axis direction AX to its original shape by its own elastic force (elasticity). The valve element60is placed integral with the valve element holding member65held by the guide member71in such a way that a central portion of the valve element60in the radial direction CR contacts with a curved lower surface of the valve element holding member65.

Further, a peripheral edge portion of this diaphragm valve element60in the radial direction CR is sandwiched and fixed between the body40and the guide member71. The guide member71is fixed to the body40by screw connection between the body40and the connecting member73. Screw connection between the connecting member73and the fixing member74makes the spring support member72integral with the connecting member73.

A stem66is connected to a lower end portion of the piston rod30. The stem66will come into contact with an upper surface of the valve element holding member65. The metal spring67is placed between the stem66and the spring support member72to urge the stem66downward.

Herein, the concept of the Cv value is explained. The Cv value is the dimensionless number defined as a number expressing that, in a valve open state where a valve element of a fluid control valve is opened at a predetermined degree, “the flow rate of fresh water, at 60° F. (about 15.5° C.), that will flow through the valve while keeping a differential pressure (a pressure drop) of 1 psi (6.895 kPa) between an inlet port side and an outlet port side, in terms of US gal/min (1 USgal=3.785 L) (gpm)”.

This Cv value is determined by actual measurement using a known measuring device such as a fluid flow meter and a fluid pressure meter. The Cv value is assumed to be 1 when the valve opening degree of the valve element is full and the fresh water at about 15.5° C. flows with a differential pressure of 6.895 kPa and a flow rate of 3.785 L. The Cv value is calculated by the following expression:
Cv=Q·(G/ΔP)^(½)
where Q (gpm) is a flow rate of a fluid, G is a specific gravity, ΔP(psi) is a differential pressure of a fluid.

As the Cv value is larger, the fluid control valve has a wider flow channel through which a fluid passes. The valve seat structure of the gas control valve1in the present embodiment is directed for example to a fluid control valve configured such that, when the fluid to be controlled is mainly gas (e.g., H2gas or Ar gas) and the diaphragm valve element60is placed in a full open state, a full stroke (a maximum separation distance) between the valve seat member50and the valve element60is about 1 mm.

Specifically, in the gas control valve1in the present embodiment, the stroke (the separation distance) St between the diaphragm valve element60in the full open state and the valve seat portion51of the valve seat member50is set to 0.9 mm in an atmosphere of 200° C. and just after valve opening. The Cv value at that time is 0.7.

Operations of the gas control valve1will be explained below. While no pilot air is supplied to the operation port11, the stem66is urged to contact with the valve element holding member65by the spring67, thereby pressing the central portion of the valve element60in the radial direction CR through the holding member65. Accordingly, as shown inFIG. 1, the valve element60is placed in contact with the valve seat portion51of the valve seat member50, thus shutting off the flow of hot gas from the inlet port41to the outlet port42.

While the gas control valve1is in a closed state, the first through hole31H communicates with the first pressure chamber25and the second through hole32H communicates with the second pressure chamber26.

On the other hand, when pilot air is supplied to the operation port11, the pilot air flows in the first through hole31H and the second through hole32H via the pilot hole30H to pressurize the first pressure chamber25and the second pressure chamber26at the same time. Accordingly, the first piston21and the second piston22are moved upward by the pressurized pilot air against the urging force of the spring67. At that time, the air present on the upper side of the first piston21and on the upper side of the second piston22in the first and second cylinders10and15are respectively discharged through the first breathing hole12and the second breathing hole13. As the first and second pistons21and22are moved upward, the stem66separates together the piston rod30from the valve element holding member65. The central portion of the valve element60in the radial direction CR then returns upward by its own elastic force. Accordingly, the valve element60comes out of contact with the valve seat portion51of the valve seat member50for valve opening, thereby allowing hot gas to flow from the inlet port41to the outlet port42.

When the diaphragm valve element60is to be closed from the open state, the pressurized pilot air is discharged from the first pressure chamber25and the second pressure chamber26through the operation port11.

Concrete shapes of the valve seat member50will be described below in Examples 1 and 2 by showing the relationship between the first thickness t1and the second thickness t2with reference toFIGS. 2 and 3.FIG. 3is an enlarged view corresponding to a part A inFIG. 1to explain a valve seat structure of a gas control valve in Example 2.

Example 1 shows a configuration that the second thickness t2is 1.25 t1as with the shape of the valve seat member50shown inFIG. 2. Concretely, in this configuration, for example, the thickness of the valve seat portion51(the first thickness) is t1=1.2 mm and the height of the valve seat member50(the second thickness) is t2=1.5 mm.

In Example 1, the gas control valve1is opened from a valve closed state. Hot gas is continuously supplied to flow from the inlet port41to the outlet port42through the valve chamber for a long period. After a lapse of a predetermined time from a valve opening time, the stroke St between the valve element60in a full open state and the valve seat portion51of the valve seat member50and the Cv value at that time are measured.

FIG. 5is a table showing a relationship between the time elapsed from valve opening and the flow rate of flowing hot gas by comparing the valve seat structure of the gas control valve in Example 1 and a valve seat structure of a conventional gas control valve as Comparative example.

In Example 1, the stroke St just after valve opening in an atmosphere of 200° C. is 0.9 mm and the stroke St after a predetermined time elapsed from the valve opening time is 0.7 mm as shown inFIG. 5. When the Stroke St just after valve opening is 0.9 mm, the Cv value is 0.7. When the stroke after the predetermined time elapsed from the valve opening is 0.7 mm, the Cv value is 0.5. Specifically, between just after valve opening and after a predetermined time elapsed from valve opening, a stroke difference ΔSt is 0.2 mm. The Cv value is decreased by a difference of up to 0.2.

On the other hand, in Comparative example, the stroke St just after valve opening is 0.9 mm, whereas the stroke St after a predetermined time elapsed from valve opening is 0.5 mm. The Cv value for the stroke St just after valve opening being 0.9 mm is 0.7, whereas the Cv value for the stroke St after a predetermined time elapsed from valve opening being 0.5 mm decreases down to 0.3. In other words, between the time just after valve opening and the time after a predetermined time elapsed from valve opening, a stroke difference ΔSt is 0.4 mm. The Cv value is decreased by a difference of as much as 0.4.

Results of Example 1 and Comparative example are studied below.

The gas control valve1is a valve for controlling the flow of a fluid such as hot gas by bringing the diaphragm valve element60into or out of contact with the valve seat member50. In the valve closed state, the valve element60presses against the valve seat portion51of the valve seat member50and hence closely contacts with the valve seat portion51, thereby shutting off the flow of hot gas or the like. In the valve open state, the flow rate of hot gas or the like flowing in the valve chamber is determined by the stroke St between the valve seat member50and the valve element60separated from the valve seat member50.

When the valve element60contacts with the valve seat portion51of the valve seat member50for valve closing, the valve seat portion51receives the pressing force from the valve element60and thus a portion of the valve seat portion51contacting with the valve element60is greatly depressed or sinks. When the valve is opened from this state, on the other hand, the reactive force resulting from the pressing force of the valve element60acts on the valve seat member50. The depressed portion of the valve seat member50then attempts to return to its previous shape, i.e., a shape before depression.

In the case where the fluid is the hot gas exemplified above and the flow of this hot gas is to be controlled by the gas control valve1, the valve element60and the valve seat member50located in the valve chamber of the gas control valve1are exposed to a temperature of about 200° C. In this case, when the hot gas is allowed to continuously flow from the inlet port41to the outlet port42through the valve chamber for a long period after the valve is opened from the closed state, the depressed valve seat portion51of the valve seat member50attempts to gradually return to its shape before depression after valve opening. Furthermore, since the temperature of the valve chamber at that time rises above the temperature in the valve closed state where no hot gas flows, the valve seat member50also will thermally expand due to the temperature rise.

In the gas control valve1, while hot gas is flowing after valve opening, the valve seat portion51(the valve seat member50) is deformed with time after valve opening by an amount corresponding to the sum of the return amount of the valve seat portion51toward the valve element60by the reactive force and the thermal expansion amount of the valve seat portion51toward the valve element60due to the temperature rise in the valve chamber. This changes the real stroke St between the valve seat portion51of the valve seat member50and the valve element60.

Specifically, the valve seat portion51remains depressed at the instant following the valve opening and also the valve seat portion51remains cold at a temperature before hot gas flows. Accordingly, the upper surface of the valve seat portion51is in a position further away from the valve element60than in the shape before depression. Thus, the stroke St between the valve seat portion51and the valve element60is larger than in the shape before depression.

After the predetermined time elapsed from valve opening, on the other hand, the valve seat portion51elastically returns toward its previous shape and also expands because the valve chamber increases in temperature up to the temperature of the flowing hot gas. Thus, the upper surface of the valve seat portion51is in a position closer to the valve element60than in the depressed shape and the stroke St between the valve seat portion51and the valve element60is smaller than in the depressed shape. Consequently, between just after valve opening and after a predetermined time elapsed from valve opening, the stroke St between the valve seat portion51and the valve element60changes. While hot gas is flowing through the valve chamber during valve opening, therefore, the flow rate (the Cv value) of hot gas varies between just after valve opening and after a predetermined time elapsed from valve opening.

In the present embodiment, as described above, the valve seat member50is formed in a ring shape and includes the valve seat portion51which will come into or out of contact with the diaphragm valve element60. Assuming that the thickness of the valve seat portion51in the radial direction CR of the valve seat member50is the first thickness t1(0<t1), the second thickness t2which is the thickness of the valve seat member50in the valve seat height direction along the axis direction AX of the gas control valve1is set to 1.25 times the first thickness t1, i.e., t2=1.25 t1falling within a range of 0.5 t1≦t2≦1.5 t1.

In the valve seat structure of the conventional metal diaphragm valve (Comparative example) formed with the second thickness about 2.7 times larger than the first thickness, when the pressing force of the diaphragm valve element60acts on the valve seat portion51of the valve seat member50, for example, the depression amount of the valve seat portion is 0.5 mm and the return amount of the valve seat portion is 0.3 mm.

In contrast, in the valve seat structure of the gas control valve1of the present embodiment, the depression amount of the valve seat portion51is about 0.25 mm, which is smaller by about half the conventional depression amount even through the pressing force is the same magnitude as in the conventional valve seat structure. Further, as well as the depression amount, the return amount of the valve seat portion51of the valve seat member50toward the diaphragm valve element60by the reactive force after valve opening is 0.15 mm which is smaller by about half the conventional return amount.

When hot gas continues to flow from the inlet port41to the outlet port42through the valve chamber for a long period after the valve is opened from the valve closed state, the temperature of the valve chamber increases above the temperature in the valve closed state where no hot gas flows, thereby causing thermal expansion of the valve seat member50(the valve seat portion51). In comparison between the valve seat structure of the gas control valve1of the present embodiment in which the second thickness t2is set to be 1.5 times or less the first thickness t1and the valve seat structure of the conventional metal diaphragm valve in which the second thickness t2is set to be about 2.7 times the first thickness t1, the valve seat structure of the gas control valve1of the present embodiment can achieve a smaller thermal expansion amount (e.g., 0.05 mm) of the valve seat member50(the valve seat portion51) because of the second thickness t2smaller than the valve seat height of the valve seat member50as compared with the thermal expansion amount (e.g., 0.1 mm) in the valve seat structure of the conventional metal diaphragm valve.

In the valve seat structure of the gas control valve1of the present embodiment, accordingly, the deformation amount of the valve seat member50after valve opening corresponding to the sum of the return amount due to the reactive force and the thermal expansion amount due to the temperature rise in the valve chamber can be restrained to be smaller than in the valve seat structure of the conventional metal diaphragm valve.

Specifically, when the flow of the exemplified hot gas (fluid) is to be controlled by the gas control valve1, the real stroke St between the valve seat member50and the valve element60while the hot gas continues to flow from the inlet port41to the outlet port42through the valve chamber for a long period after the valve opening operation from the valve closed state provides a smaller stroke difference between just after valve opening and after the predetermined time elapsed from valve opening than in the conventional valve seat structure. As a result, while the hot gas is continuously flowing through the valve chamber during valve opening, it is possible to reduce variations in the flow rate of hot gas. Although the Cv value after valve opening in the conventional configuration is decreased by as much as 0.4, the valve seat structure of the gas control valve1in the present embodiment can restrain a decrease (difference) in Cv value to 0.2 or less which is recently demanded in the manufacturing industry of precision components such as semiconductors.

In the manufacturing industry of precision components such as semiconductors, fluid control valves like the gas control valve1are often used. A demand to restrain a decrease (difference) in Cv value after valve opening to 0.2 or less arose from the manufacturing industry of precision components in order to meet the marketing needs for high precision and high quality of products. This demand is assumed as an indication or target to ensure the quality of precision components (products) after a predetermined time elapsed from valve opening by preventing the Cv value from decreasing to less than 0.5 corresponding to a 30% reduction of 0.7 which is a Cv value just after valve opening.

On the other hand, the valve seat member50in the valve seat structure of the gas control valve1of the present embodiment is formed with the second thickness 0.5 times or more larger than the first thickness. Thus, the valve seat member50can have sufficient deformation allowance allowing the valve element60to press against the valve seat member50more deeply when the valve is placed in a closed state. It is therefore possible to make the valve seat member50come into close contact with the valve element60to ensure high sealing performance. This can shut off the flow of a fluid such as hot gas without leakage toward the outlet port42.

A valve seat member50A in Example 2 is configured as shown inFIG. 3, as with Example 1, such that a fixed portion52A is placed between the grasping portions43. One grasping portion43located inside in the radial direction CR and the other grasping portion43located outside in the radial direction CR are deformed or crimped toward each other, thereby pinching the valve seat member50A in the radial direction CR to fix the valve seat member50A in the body40.

In Example 2, the valve seat member50A inFIG. 3is designed to have a second thickness t2=0.63 t1. To be concrete, for example, a thickness t1of a valve seat portion51A is 2.2 mm and the height (the second thickness) t2of the valve seat member50A is 1.5 mm. In this case, the depression amount of the valve seat portion51A is 0.13 mm and the return amount of the valve seat portion51A is 0.10 mm.

A modified example of Example 2 is shown inFIG. 4which is an explanatory view of a valve seat structure of a gas control valve in the modified example of Example 2. In this example, as shown inFIG. 4, a valve seat member50B is fixed to the body40in such a way that fixed portions52Bi and52Bo are placed between the grasping portions43and one grasping portion43located inside in the radial direction CR and the other grasping portion43located outside in the radial direction CR are deformed or crimped toward each other, thereby pinching the valve seat member50B in the radial direction CR.

To be concrete, the body40is provided with an intermediate protrusion44between the grasping portions43in the radial direction CR to extend circumferentially and protrude upward inFIG. 4. On both sides of the intermediate protrusion44, the fixed portion52Bi is located inside in the radial direction CR and the fixed portion52Bo is located outside in the radial direction CR. The valve seat member50B is positioned in place by the fixed portions52Bi and52Bo and the intermediate protrusion44and thus can be fixed by being firmly pressed by the grasping portions43and the intermediate protrusion44.

Example 2 and the modified example are brought under the same review as Example 1 mentioned above. The details thereof are not repeated here.

Operations and effects of the valve seat structure of the gas control valve1in the present embodiment configured as above will be explained.

In the present embodiment, the valve seat structure of the gas control valve1includes the diaphragm valve element60, the body40formed with the inlet port41and the outlet port42, and the valve seat member50provided in the body40and is configured to bring the valve element60into or out of contact with the valve seat member50to control the flow of hot gas. The valve seat member50is formed in a ring shape and includes the valve seat portion51with which the valve element60will come into or out of contact. Assuming that the thickness of the valve seat portion51in the radial direction CR of the valve seat member50is the first thickness t1(0<t1), the second thickness t2defined as the height of the valve seat member50in the direction of the axis AX of the gas control valve1is determined in a range of 0.5 t1≦t2≦1.5 t1. Accordingly, in a semiconductor manufacturing process, for example, when the flow of hot gas, such as H2gas and Ar gas, heated to about 200° C. is to be controlled by the gas control valve1provided with the valve seat structure in the present embodiment, while the hot gas continues to flow from the inlet port41to the outlet port42through the valve chamber for a long period after valve opening from the valve closed state, the stroke St between the valve seat portion51of the valve seat member50and the valve element60can be achieved with a reduced stroke difference between just after valve opening and after the predetermined time elapsed from the valve opening time. Accordingly, it is possible to reduce variations in flow rate of hot gas (fluid) flowing through the valve chamber of the gas control valve1.

Consequently, the decrease (difference) in Cv value after valve opening can be restrained to 0.2 or less which is recently demanded as the flow rate control accuracy of the valve in the manufacturing industry of precision components such as semiconductors. This can reduce variations in flow rate of the fluid flowing in the valve in an open state. When the valve is closed, on the other hand, the diaphragm valve element60firmly presses against the valve seat portion51of the valve seat member50and thus closely contacts with the valve seat portion51of the valve seat member50, ensuring high sealing performance. It is therefore possible to shut off the flow of a fluid such as hot gas without leakage toward the outlet port42.

The gas control valve1in the present embodiment can consequently ensure the sealing performance with the diaphragm valve element60and reduce variations in the flow rate while hot gas to be controlled continues to flow.

In the gas control valve1in the present embodiment, the valve seat member50is made of fluorocarbon resin such as PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer). Accordingly, for example, the diaphragm valve element60made of metal or the like can have appropriate hardness to moderately press against the valve seat portion51of the valve seat member50. Thus, the valve element60is able to easily come into close contact with the valve seat portion51. Even when a corrosive fluid is to be controlled, the valve seat member50will not corrode by this fluid.

In the gas control valve1in the present embodiment, furthermore, the valve seat member50is a separate part from the body40and fixed to the body40with the grasping portions43by deforming or crimping. Thus, the valve seat member50can be attached to the body40by a simple work.

In the gas control valve1in the present embodiment, the valve seat member50includes the fixed portion52under the valve seat portion51. The fixed portion52is designed with a thickness wider than the first thickness t1. The fixed portion52of the valve seat member50is pinched and fixed in the radial direction CR of the valve seat member50by the grasping portions43which are a part of the body40. The valve seat member50is thus fixed in a stable state. While the valve is closed, even if the diaphragm valve element60does not vertically contact with the valve seat portion51of the valve seat member50along the axis direction AX of the gas control valve1due to abnormal operations of the valve element60and the valve element60contacts with the valve seat portion51at a slant with respect to the axis AX, the valve seat member50is less likely to become displaced in the radial direction CR.

The above embodiment is a mere example and does not give any limitations to the present invention. The present invention may be embodied in other specific forms without departing from the essential characteristics thereof.

(1) For instance, in the above embodiment, the air control section2is provided with two cylinders, i.e., the first cylinder10and the second cylinder15, and two pistons, i.e., the first piston21and the second piston22, to generate a pressure against the urging force of the spring67. However, the number of cylinders and the number of pistons installed in the air control section2may be changed appropriately.

(2) In the above embodiment, the gas control valve1is a normal close type which is opened when supplied with pilot air through the operation port11. Alternatively, the invention may be applied to a fluid control valve of a normal open type which is closed when supplied with pilot air through the operation port.

DESCRIPTION OF THE REFERENCE SIGNS