Metal diaphragm-type valve

Abstract: A metal diaphragm type valve includes a valve seat holder (5) supported from a rotatable valve stem, a metal diaphragm (7) and a deflection limiter (6). The valve seat holder has a shaft (5a) extending upwardly through central openings in the diaphragm and the deflection limiter. A diaphragm support step (5c) having an annular flat surface joining an arcuate shoulder is provided around the shaft of the valve seat holder and the inner peripheral edge of the diaphragm rests on the flat surface. The deflection limiter has a flat bottom surface facing the top surface of the diaphragm and an arcuate surface extends radially outwardly from the flat bottom surface. The deflection limiter, diaphragm and valve seat holder are welded together by a weld extending through the flat bottom portion of the deflection limiter and the inner peripheral edge of the diaphragm to the flat surface on the seat holder, the weld forming an air-tight seal between the valve chamber and the passage for the shaft. The radial dimensions of the flat surfaces are different so that bending stresses occur in different regions of the diaphragm depending on whether the valve is opened or closed.

Description: This invention relates to a metal diaphragm type valve suitable for use in a fluid conveying line of, for example, a semiconductor manufacturing plant. More particularly, the invention relates to a seal structure providing a seal between the inner peripheral edge of the metal diaphragm and a seat holder extending through the diaphragm so as to result in a minimum space in which a fluid may be trapped, and distribution of bending stresses in different regions of the diaphragm depending on whether the valve is opened or closed. In the manufacture of semiconductors it is frequently necessary to supply precise volumes of different fluids, say gases, to a treatment chamber, the fluids being conveyed to the treatment chamber in sequence through a fluid feed line controlled by a diaphragm valve. Typically, a first fluid is applied to the treatment chamber through the feed line after which a purge fluid is applied to the feed line to purge any traces of the first fluid. After purging, the second fluid is then applied to the chamber through the feed line. During the purging operation it is desirable to remove as much as possible of the first fluid in the feed line and valve so that the first fluid will not contaminate the second fluid. To accomplish this, the valve interior should have no gaps, crevices or 'dead air spaces' within the chamber where fluid may be caught or trapped so that it is not purged from the valve during the purging operation. As the degree of integration of semiconductors increases, there is a corresponding demand for increased fluid purity and only a very slight amount of fluid trapped in a crevice has a serious effect on the quality of the semiconductor product, and increases the frequency of defective pieces. In metal diaphragm valves, a crevice which traps fluid and prevents complete purging is frequently found where the metal diaphragm is mounted on a seat holder which extends through the diaphragm. Figs. 6 and 7 illustrate a metal diaphragm valve with a diaphragm seal structure as disclosed in EP-A-0708286. This valve includes a valve body 100, a valve chamber 100a, a valve seat 100b, fluid passages 100c, a bonnet 50, a valve seat 160, a bushing 51, a ball 52, a stem 53 and bonnet insert 54. In this arrangement a shaft 91a of a seat holder 91 is inserted through a mounting hole 93a of a diaphragm 93 and a center opening in a weld metal member 90. The inner peripheral edge of the diaphragm 93 is disposed between an annular flat portion 90a formed on the lower surface of the weld metal member 90 and an annular flat portion 91b formed on the upper surface of the seat holder 91. The end portion of the inner peripheral edge of the diaphragm and the portions of the member 90 and the seat holder abutting the end portions of the inner peripheral edge of the diaphragm 93 are welded together at a weld zone W around the entire circumference of the inner peripheral edge of the diaphragm thereby integrally affixing the diaphragm, the seat holder and the weld metal member. In the valve shown in Figs. 6 and 7, bending stress is prevented from being applied to the weld zone W during operation of the diaphragm 93 because movement of the inner peripheral edge of the diaphragm immediately outward of the weld is limited or prevented by abutment of the diaphragm against the flat portion 90a of the lower surface of the weld metal member 90 and the flat portion 91b of the upper surface of the seat holder 91. This arrangement is designed to prevent the fluid being controlled from being caught in the gap between the inner peripheral edge of the diaphragm and the upper surface of the seat holder. Furthermore, since the inner peripheral edge of the diaphragm 93, weld metal member 90 and seat holder 91 are affixed and integrated by welding, the sealing performance is extremely high. Also, since the inner peripheral edge of the diaphragm is confined between the flat portion 90a of the weld metal 90 and the flat portion 91b of the seat holder 91, if the screw of the shaft 91a is loosened so that the seat holder 91 slightly moves up or down, a large bending stress is not directly applied to the weld zone W of the diaphragm. In the valve shown in Figs. 6 and 7, when the diaphragm 93 moves up or down, the bending stress in the diaphragm is concentrated in the region or outermost position 94 corresponding to the outward radial extent of the flat bottom surface 90a of the weld metal member 90 and the outward radial extent of the flat upper surface 91b of the seat holder 91. The flat surfaces support diaphragm 93 radially inwardly of position 94 but the diaphragm is free to bend outwardly of this position. As a result, when the diaphragm 93 is operated repeatedly, the part of the diaphragm in the vicinity of the position 94 suffers metal fatigue and cracks earlier than other parts of the diaphragm and it is hard to extend the life of the diaphragm. In the valve shown in Figs. 6 and 7, the spacing between the lower surface of the diaphragm 93 and the planar upper surface 91b of the seat holder 91 is extremely small, so any fluid accumulation in the gap G between these surfaces is minute. However, repeated vertical motion of the diaphragm during normal usage causes the thickness of the diaphragm to gradually decrease, and the volume of the gap G increases. This permits a greater volume of fluid to enter the small gap and the fluid replacement performance of the valve is lowered. It should be noted that since the length dimension ℓ (Fig.8) of the upper flat surface portion 91b of the seat shoulder 91 is selected to be relatively large, a relatively large mass of fluid may enter the gap G and lowering of the fluid replacement performance is a more serious problem. The valve illustrated in Figs. 6 and 7 has a further disadvantage in that it requires a large number of parts such as ball 52, bushing 51, bonnet insert 54 and weld metal member 90. Assembly of these parts is complicated and difficult, and it requires much time and labor to complete its assembly. DE-C-3928678 also discloses a diaphragm valve of the type comprising a metallic diaphragm which is clamped at an outer peripheral edge between a valve body and a bonnet, and mounted on a reciprocable shaft between a diaphragm support and a deflection limiter. The diaphragm support and deflection limiter are formed with opposing flat annular portions for contacting and supporting said diaphragm therebetween, and said diaphragm, diaphragm support and deflection limiter are joined together by a unitary weld about an inner peripheral edge of said diaphragm. An object of the present invention is to provide a metal diaphragm type valve having none of the disadvantages of the prior art described above yet requiring fewer parts, less assembly time and being less expensive to manufacture. Another object of the invention is to provide a metal diaphragm type valve having a seal structure which results in longer diaphragm life. A further object of the invention is to provide a metal diaphragm type valve exhibiting excellent replacement or cleaning performance as compared to the prior art. According to one aspect of the invention therefore, there is provided a metal diaphragm-type valve comprising: a valve body having a fluid inlet passage, a fluid outlet passage, a valve chamber and a valve seat; a stem movably disposed in said valve body; a seat holder having a support shaft, said seat holder being coupled to said stem and comprising a diaphragm support step having a first surface comprising a flat, annular, inner surface portion and an arcuate, outer, shoulder portion formed continuously with the flat, annular, inner surface portion; a deflection limiter having a dish-shape, comprising a thin, annular, inner peripheral portion and a second surface, comprising a flat, annular, inner surface portion and a curved, outer surface portion formed continuously with the flat, annular, inner surface portion, which deflection limiter is penetrated by the support shaft with said second surface opposing the first surface of said support step; and a metal diaphragm disposed within the valve chamber for airtight sealing between the stem and the valve body, said diaphragm being formed with a central mounting hole and having an inner peripheral portion around said mounting hole, the diaphragm being penetrated by the support shaft through said mounting hole and being interposed said first and second opposing surfaces, said inner peripheral portion contacting the flat, annular, inner surface portion of said support step and the flat, annular, inner surface portion of the deflection limiter; the inner peripheral portion of the diaphragm and the respective flat, annular, inner surface portions of the support step and deflection limiter being welded together by a circumferential weld, such that said diaphragm, seat holder and deflection limiter are integrally affixed to form an airtight seal; characterised in that the outer radii of the flat, annular, inner surface portions of the support step and deflection limiter are different from one another. The deflection limiter diaphragm and seat holder may be welded together by a circumferential weld which provides an air-tight seal between the diaphragm and the annular flat surface portion of the seat holder, the weld extending to the outer circumference of the annular flat surface portion of the seat holder so that no crevice exists between the diaphragm and annular flat surface in which fluid may be trapped. Following is a description by way of example only, with reference to the accompanying drawings of embodiments of the present invention. Fig. 1 is a longitudinal sectional view showing an example of a metal diaphragm type valve according to the invention; Fig. 2 is a longitudinal sectional view showing an example of a deflection limiter used in the invention; Fig. 3 is a magnified partial longitudinal sectional view of an inner peripheral edge of the metal diaphragm shown in Fig. 1; Fig. 4 is a magnified partial longitudinal sectional view of an inner peripheral edge of a metal diaphragm of a valve according to a second embodiment of the invention; Fig. 5 is a magnified partial longitudinal sectional view of an inner peripheral edge of a metal diaphragm of a valve according to a third embodiment of the invention; Fig. 6 is a longitudinal sectional view of a prior art valve as disclosed in EP-A-0708286 and, Fig. 7 is a magnified partial longitudinal sectional view of an inner peripheral edge of the metal diaphragm shown in Fig. 6. Fig. 1 is a longitudinal sectional view of a metal diaphragm type valve employing a seal structure according to a first embodiment of the invention wherein the inner peripheral edge of a metal diaphragm 7, the inner peripheral edge of a deflection limiter 6, and a seat holder 5 are integrally affixed by welding. The weld eliminates the requirement of any mechanism for clamping (gripping) of the inner peripheral edge of the diaphragm, as used in the prior art. The metal diaphragm valve comprises a body 1 having a fluid inlet passage 1a, a fluid outlet passage 1b, a valve chamber 1c, and a valve seat 1d. A bonnet nut 2 is screwed into the body 1 and a stem 3 is screwed into and supported for vertical movement, by the bonnet nut. A handle 4 is attached to the upper end of the stem 3 and a seat holder 5 is attached to the lower end of the stem so as to move vertically therewith. A deflection limiter 6 has a central opening and the upwardly projecting support shaft 5a of a seat holder 5 extends through the opening. The deflection limiter 6 rests on the diaphragm which in turn rests on a shoulder or support step 5c provided on the lower portion of the shaft 5a. The metal diaphragm 7 has an outer peripheral edge gripped and supported between the body 1 and the bonnet nut 2 as the bonnet nut is screwed into the body. The inner peripheral edge of the diaphragm is welded to the seat holder 5 and deflection limiter 6. The stem 3 is made of stainless steel (SS316) in a nearly columnar form, and an engaging recess 10, having an expanded middle portion 10a, is formed in the lower part of the stem. Screw threads 3a are formed on the outer circumference of the stem 3, and engage screw threads 2a formed on the interior of bonnet nut 2 so that the stem 3 is supported elevatably in the bonnet nut. The stem 3 may be raised or lowered by rotating the stem relative to the bonnet nut. The handle 4 is attached to the stem by a screw 14 so that rotation of the handle raises or lowers the stem relative to the bonnet nut. An O-ring 9 is provided to prevent contaminants from entering the valve between the bonnet nut 2 and the stem 3. The seat holder 5 is made of metal such as stainless steel (SS316L) and has, in addition to the upwardly projecting cylindrical support shaft 5a, an expanded lower part 5b. The support step 5c for supporting the diaphragm is formed at the boundary of the columnar support shaft 5a and the lower part 5b. The diaphragm support step comprises a flat annular surface portion 5d and a smooth arcuate shoulder 5e formed continuously therewith, as shown in Fig. 3. A seat insert (seat) 8, made of a polymer or synthetic resin or metal, is provided at the lower end of the lower part 5b. The upper part of the support shaft 5a is inserted into engaging recess 10 of the stem 3, and a washer 11 and a retaining ring 12 secure the support shaft 5a within the expanded portion 10a of the recess while permitting relative rotation between the shaft and the stem. A bearing 13 may be provided between the upper surface of support shaft 5a and the upper end surface of recess 10 to reduce friction between the stem 3 and the support shaft. This bearing may be omitted in some cases. The deflection limiter 6 (Fig. 2) is made of metal such as stainless steel (SS304L) in a circular dish form. An insertion hole 6a is provided in the center of the deflection limiter and the support shaft 5a (Fig. 1) of the seat holder 5 extends through the insertion hole. The inner peripheral edge 6b of the deflection limiter 6 is formed with a thickness t of about 2mm. The length ℓ of the peripheral edge 6b having the thickness t defines a weld zone W (Fig. 3) where the deflection limiter is welded to the upper surface of the metal diaphragm. The lower side of the deflection limiter (left side as viewed in Fig. 2) has a flat annular surface portion 6c of length ℓ 0 larger than or nearly as large as, the length ℓ. A moderate curvature 6d extends upwardly and continuously from the outer end P of the flat portion 6c to the outer periphery of the deflection limiter. The metal diaphragm 7 is formed by overlaying a plurality of (two or three) ultrathin metal plates (thickness: about 0.1 to 0.2mm) in a dish form. The plates may be made of stainless steel (SS316L), a Co-Ni alloy steel such as Elgiloy™, or the like. Elgiloy™ contains C = 0.15, Mn = 1.5 to 2.5, Ni = 14 to 16, Cr = 19 to 21, Mo = 6 to 8, Be = 0.1 or less, Co = 39-41, and Fe = remainder (all contents by wt.%). A mounting hole 7a is provided at the center of the diaphragm for receiving the shaft 5a of the seat holder 5. In this embodiment, the outer diameter of the diaphragm 7 is selected to be about 38mm. The inner peripheral edge of the metal diaphragm 7 is, as shown in Fig. 3, positioned between the flat annular surface portion 6c of the deflection limiter 6, and the flat annular surface portion 5d of the diaphragm support step 5c on the seat holder 5, and is welded to both the limiter and the support step. As shown in Fig. 3, the inner peripheral edge of the diaphragm 7, the flat portion 6c of the deflection limiter 6 abutting against the inner peripheral edge of the diaphragm 7, and the flat portion 5d of the seat holder abutting the inner peripheral edge of the diaphragm 7 are welded together by a weld W. The weld is in ring form, extending around the whole circumference of the deflection limiter 6 in the portion of length Q. This integrally affixes, in an airtight manner, the inner peripheral edge of the diaphragm 7, the inner peripheral edge of the deflection limiter 6, and the flat portion 5d of the seat holder 5. Referring to Figs. 1 and 3, the valve operates in the following manner. When the stem 3 is moved up or down by rotating the handle 4, the seat holder 5 ascends or descends, and the seat 8 contacts the valve seat 1d or departs from the valve seat and the fluid passage 1a is opened or closed so that fluid may flow between passages 1a and 1b. When the fluid passage 1a of the valve is open, the metal diaphragm 7 returns to an initial state of upward curvature as shown in Fig. 1, and almost no bending stress is applied to the inner peripheral edge of the diaphragm. If, however, the diaphragm 7 is pulled up at a time the valve is opened, a downward bending stress is applied to the inner peripheral edge of the diaphragm so that the diaphragm tends to bend downwardly radially outwardly of the support step 5c. The resulting curved portion of the diaphragm is supported by the arcuate shoulder 5e on the seat holder 5. That is, the lower surface of the diaphragm in the region A (Fig. 3) contacts and is supported by the shoulder 5e. On the other hand, when the valve is operated to close the fluid passage 1a, an upward bending stress is applied to the inner peripheral edge of the diaphragm. In this case, the upper surface of the diaphragm in the region B contacts and is supported by the curvature 6d of the deflection limiter 6. Thus, in the diaphragm valve of the invention, unlike the conventional metal diaphragm type valve, the inner peripheral edge of the diaphragm 7 is not clamped. Instead, the inner peripheral edge of the diaphragm is supported by the curvature 6d of the deflection limiter 6 or the arcuate curvature 5e of the seat holder 5 when the diaphragm is bent. Accordingly, bending stress is not directly applied to the weld zone W. As a result, cracks and the like are not formed in the weld zone. It should be noted that upon upward bending of the diaphragm the bending begins at a point P where the flat surface 6c of the deflection limiter joins the curved surface 6d, but upon downward bending the diaphragm bends about point F where the flat portion 5d of the seat holder joins the arcuate surface 5e. Points P and F are located at different distances (ℓ o and (ℓ 1 ) from the seat support shaft 5a in the radial direction because the diameter of the flat annular surface 6c of the deflection limiter is different from the diameter of the flat annular surface 5d on the seat holder. Thus, the diaphragm 7 bends at two different positions A and B (Fig. 3) as compared to the conventional case where bending occurs at the clamped portion only regardless of the direction in which the diaphragm is flexed. Thus, the life or durability of the diaphragm is improved substantially. Moreover, since the weld zone W covers almost the whole area of the flat portion 5d of the diaphragm support step 5c as shown in Fig. 3, there is a gap G 1 outward of where the weld W joins the diaphragm and the support step 5c and the lower side of the diaphragm 7. This greatly enhances the fluid replacement performance and the purging of waste gases from the valve. In addition, since the inner peripheral edge of the diaphragm 7, the deflection limiter 6, and the seat holder 5 are integrally affixed in an airtight manner, the fluid in the valve chamber 1c will never leak out from the inner peripheral edge portion of the diaphragm and the sealing performance is extremely high. Fig. 4 is a magnified partial view showing a second embodiment of the invention. In this embodiment, the length ℓ 0 of the flat portion 6c at the lower side of the deflection limiter 6 is made shorter than in the case of Fig. 3 so that the bending region A at the lower side of the diaphragm and the bending region B at the upper side of the diaphragm during operation of the diaphragm 7 are closer to each other as compared to the embodiment of Fig. 3. Although this tends to reduce the advantage of distributing stresses in the diaphragm depending on the direction it is flexed, this arrangement tends to make more equal the support provided to the diaphragm by the seat holder and the deflection limiter. Fig. 5 is a partial magnified view showing essential parts of the metal diaphragm type valve according to a third embodiment of the invention. In this embodiment, the length ℓ 0 of the flat portion 6c at the lower side of the deflection limiter 6 is selected longer than in the case of the first embodiment (Fig. 3), and a recess 6e is formed in the flat portion 6c, so that a portion in the region of recess 6e does not contact the diaphragm 7. In the embodiment of Fig. 5, the space between the bending region A at the lower side and the bending region B at the upper side during operation of the diaphragm 7 is wider, so that the life span of the diaphragm is further increased. An opening and closing durability test was conducted on a valve constructed according to the first embodiment described above. The diaphragm comprised two pieces of Elgiloy™ having an outer diameter of 38mm and a thickness of 0.1 to 0.2 mm. The fluid pressure of the fluid being controlled was 375psi. The valve was cycled (opened and closed) at a rate of once/sec and the diaphragm did not crack or fail after 16470 cycles. By contrast, the life of a conventional metal diaphragm type valve is about 3000 cycles. In the metal diaphragm valve of the invention, the bending stress applied to the inner peripheral edge of the diaphragm 7 when the valve is closed is mainly supported at the lower side 6d of the deflection limiter 6, and the bending stress applied to the inner peripheral edge when the valve is opened is mainly supported at the arcuate shoulder 5e of the diaphragm support step 5c. As a result, bending stress is not directly applied to the weld zone W of the inner peripheral edge of the diaphragm, and cracks or the like do not form in the weld zone W. Furthermore, the bending stress receiving regions of the diaphragm 7 (the regions A and B) differ and are spaced from each other in the radial direction so that, depending on whether the valve is opened or closed, the bending stress is dispersed in two regions. Hence, as compared with the conventional case of where the metal diaphragm 7 is clamped from above and below at one position, breakage of the diaphragm is less likely to occur. Moreover, as compared with the conventional case where coupling of the seat holder and shaft is accomplished by a screw mechanism clamping the diaphragm at one position, the number of parts for forming the valve is smaller, and assembly of the valve is much easier. In addition, since the gap G 1 between the lower side of the metal diaphragm 7 and the upper side of the seat holder 5 is not formed by a structure for clamping the diaphragm, the gap is almost nil and very little fluid is caught therein. As a result, the fluid replacement performance and the cleaning/purging performance of the inside of the valve are extremely enhanced.

Claims: A metal diaphragm-type valve comprising: a valve body (1) having a fluid inlet passage (1a), a fluid outlet passage (1b), a valve chamber and a valve seat (1d); a stem (3) movably disposed in said valve body (1); a seat holder (5) having a support shaft (5a), said seat holder (5) being coupled to said stem (3) and comprising a diaphragm support step (5c) having a first surface comprising a flat, annular, inner surface portion (5d) and an arcuate, outer, shoulder portion (5e) formed continuously with the flat, annular, inner surface portion; a deflection limiter (6) having a dish-shape, comprising a thin, annular, inner peripheral portion (6b) and a second surface, comprising a flat, annular, inner surface portion (6c) and a curved, outer surface portion (6d) formed continuously with the flat, annular, inner surface portion (6c), which deflection limiter is penetrated by the support shaft (5a) with said second surface opposing the first surface of said support step (5c); and a metal diaphragm (7) disposed within the valve chamber for airtight sealing between the stem (3) and the valve body (1), said diaphragm (7) being formed with a central mounting hole (7a) and having an inner peripheral portion around said mounting hole, the diaphragm being penetrated by the support shaft (5a) through said mounting hole (7a) and being interposed said first and second opposing surfaces, said inner peripheral portion contacting the flat, annular, inner surface portion (5d) of said support step (5c) and the flat, annular, inner surface portion (6c) of the deflection limiter (6); the inner peripheral portion of the diaphragm (7) and the respective flat, annular, inner surface portions (5d,6c) of the support step (5a) and deflection limiter (6) being welded together by a circumferential weld, such that said diaphragm (7), seat holder (5) and deflection limiter (6) are integrally affixed to form an airtight seal; characterised in that the outer radii of the flat, annular, inner surface portions (5d,6c) of the support step (5c) and deflection limiter (6) are different from one another. A metal diaphragm-type valve as claimed in claim 1, characterised in that the outer radius of the flat, annular, inner surface portion (6c) of the deflection limiter (6) is greater than the outer radius of the flat, annular, inner surface portion (5d) of the support step (5c). A metal diaphragm type valve as claimed in claim 1 or claim 2, characterised by a recess (6e) formed in the flat annular surface portion (6c) of the deflection limiter. A metal diaphragm-type valve as claimed in any preceding claim, characterised by a bonnet nut (2) that is screwed to said body, and in that said stem (3) and bonnet nut (2) are provided with mutually engaging threads whereby the stem is movable relative to the bonnet. A metal diaphragm type valve as claimed in claim 1, wherein the seat holder (5) has a seat (8) adapted to abut against said valve seat (1d) of said valve chamber (1c). A metal diaphragm type valve as claimed in any preceding claim, characterised in that said metal diaphragm (7) comprises a plurality of thin metal plates. A metal diaphragm type valve as claimed in claim 6, characterised in that the metal diaphragm is formed of three thin plates of Co-Bi alloy steel. A metal diaphragm-type valve as claimed in any preceding claim, characterised in that said stem (3) is formed with an engaging recess (10) having an expanded inner portion (10a), and said support shaft (5a) is rotatably engaged within said recess (10). A metal diaphragm-type valve as claimed in claim 8, characterised by a bearing (13) in the recess between the stem (3) and the support shaft (5a). A metal diaphragm-type valve as claimed in any preceding claim, characterised by means for clamping the diaphragm (7) at an outer circumferential portion thereof. A metal diaphragm-type valve as claimed in any preceding claims characterised in that said weld (w) is an annular weld, securing said diaphragm (7) to said valve seat holder (5) at at least an outer circumferential region of said flat, annular inner surface portion (5d) of said support step (5c).

Inventors: OGAWA SHUHEI, YOSHIKAWA KAZUHIRO, OGAWA, SHUHEI, YOSHIKAWA, KAZUHIRO
Applicants: FUJIKIN KK, FUJIKIN INCORPORATED
Application year: 1998
Main classification: F16K41
IPC codes: F16K7, F16J15, F16K41