BELLOWS VALVE

Abstract: An inverted bellows valve has a two-piece stem (44) interconnecting the valve and actuator for reciprocating axial movement of the stem tip (48). Tapered surfaces (224,230) are advantageously utilized between co-operating elements for self-centering the valve assembly. An annular gland (126) disposed along the exterior of the valve stem (44) has concentric innter and outer O-rings (132,134) which permit the stem to float and compensate for misalignment. A closing ring (30) closing the open end (26) of the valve chamber forms a step seal (34, 36, 37) with the open end (26).

Description: This invention pertains to valves and more particularly to valves of the type commonly referred to as bellows valves. The invention is particularly applicable to an inverted bellows valve and will be described with particular reference thereto. However, it will be appreciated that the invention has broader applications and is adaptable to use in other environments and applications. Increased use of bellows valves has been fostered by the need to seal the valve interior from the external environment as may, for example, be encountered in special handling of corrosive type fluids. The term 'inverted bellows' refers to the fact that the bellows is sealed relative to the stem or stem tip such that the system fluid acts externally on the bellows, rather than internally. It has been found that the bellows in such valves can withstand greater external forces than internal forces, thus permitting use of inverted type bellows valves at higher system pressures. Many of the prior art devices have maximum pressure ratings of approximately 600 psi (41 bar), and the valve described in US-A-4,201,366 has a pressure rating of 1000 psi (67.7 bar) maximum. Reliable shutoff operation under any condition of pressure or vacuum within its rating is also an important requirement along with decreased distortion of the bellows as it is cycled under pressure. Increased standards required for industrial utilization have not heretofore been met by the known prior art devices. It has, therefore, been desirable to improve on the basic design whereby the valve structure would be capable of withstanding higher pressure applications without loss of quality in the valving assembly. An object of the invention is to provide a new and improved inverted bellow-type valve capable of higher pressure ratings. US-A-4201366 discloses a bellows valve comprising valve body having inlet and outlet passages, a valve chamber in fluid communication with one of said passages, and a valve seat disposed between the valve chamber and the other of said passages; a closing ring closing an open end of the valve chamber; a valve stem having a stem tip at one end thereof for selective sealing engagement with said valve seat for controlling fluid flow between said inlet and outlet passages; actuating means for effecting selective opening and closing movements of the valve stem; and a bellows surrounding a portion of said stem and sealingly secured at the opposite ends thereof respectively to said closing ring and to said valve stem for isolating said stem from fluid passing through said valve chamber, whereby the fluid exerts an external compressive force on said bellows. In US-A-4201366, the closing ring comprises an adapter nut and a flat seal ring is captured between a shoulder in the valve body and a shoulder on the adapter nut. Thread misalignment between the adapter nut and the valve body can lead to a faulty seal. GB-A- 2125581 discloses a similar bellows valve but the closing ring closes a bore in a guide port which axially guides a supporting member for the valve closure member. A bellows valve, according to the invention, is characterised in that the closing ring forms a step seal with the open end of the valve chamber, is annularly shaped for receiving said valve stem, includes an elongated bushing in surrounding relation to said stem to effect centering and guiding of the stem, and has a tapered surface for centering said ring and bellows relative to said open end of the valve chamber. Use of the step seal ensures adequate sealing of the fluid within the valve chamber. A bonnet preferably co-operates with a retaining nut to forcibly bring the bonnet and closing ring into close engagement with the valve body at the open end of the valve chamber. The tapered surface provided on the closing ring assures a precise fit between the ring and valve body and assists in axially aligning the valve stem. The stem may comprise first and second screw-threadedly interconnected coaxial portions. Such a threaded connection provides positive stem return as well as facilitating removal of the bellows subassembly in one piece for ease of maintenance and replacement. Conveniently, a fluid pressure actuator urges the stem either axially inwardly or axially outwardly against the force of opposing spring biasing means. In a normally-closed embodiment, the biasing force is advantageously provided by a pair of concentric, inner and outer helical springs which co-operate with a wobble collar. The wobble collar abuts the valve stem and has a tapered inner surface to compensate for any uneven spring force which may arise In accordance with one embodiment of the invention, the actuator housing includes a closure member screw-threadedly engaged therewith. The closure member has an opening adapted to receive the valve stem in conjunction with the bonnet. A close fitting tolerance between the closure member and the actuator housing maintains axial alignment of the actuator with respect to the remainder of the valve assembly. One advantage of the present invention is the provision of a new inverted bellows valve useable at higher system pressures. Another advantage of the invention resides in a structural arrangement which assures axial alignment of the various valve and valve actuator components. The invention will be described further, by way of example with reference to the accompanying drawing, which is a sectional elevation of an inverted bellows valve constructed in accordance with a preferred embodiment of the present invention. Referring now to the drawing wherein the showing is for purposes of illustrating a preferred embodiment of the invention only, and not for purposes of limiting same, a valve A has a valve actuator B disposed in operative relation thereto. Valve A has a valve body 10 which includes an inlet passageway 12 and an outlet passageway 14. Suitable end fittings 12a, 14a are provided on the valve body in surrounding relation to the outer ends of the passageways for connection with an external fluid system as is known. The outlet passageway 14 communicates with a valve chamber 16 and an annular valve seat 18 is arranged between the inlet passageway 12 and the valve chamber. The identification of passageways 12 and 14 as inlet and outlet respectively, is for illustrative purposes only, and the designations may be reversed, or several inlet and outlet passages may be used. The valve chamber 16 has a closed end 24, in fluid communication with the valve seat and the outlet passage, and an open end 26. An annular closing ring 30 has a through passage 32 adapted to receive the valve stem 44 as will be explained further hereinbelow. A stepped surface 34 along the outer periphery of the closing ring 30 is designed for mating engagement with a stepped surface 36 on the valve body 10 at the open outer end 26 of valve chamber 16 with a gasket 37 disposed therebetween. The stepped surfaces and gasket form what is commonly referred to as a step seal due to the mating surfaces 34, 36. The closing ring 30 has an annular chamfered surface 38 disposed radially inward from the stepped surface 34. This chamfered or tapered surface ensures self centering of the ring 30 with respect to the valve body 10 during assembly. The valve stem 44 has a first or lower portion 46 received in the valve chamber 16. One end of the first portion 46 receives a stem tip 48 which is constructed from KEL-F or any other suitable material to suit a particular valve application. Such other materials may advantageously be employed without in any way departing from the overall scope of the invention. The stem tip 48 is illustrated as having a tapered surface 50, although a ball tip or other configuration may be employed satisfactorily. When in the closed position, the stem tip 48 engages the valve seat 18 as shown to prevent fluid flow between inlet and outlet passageways 12, 14. At an open position of the valve, the stem tip 48 is spaced a predetermined distance from the valve seat 18, whereby fluid communication occurs between the passageways 12, 14. As illustrated, there is a wide radial clearance 52 between the stem tip 48 and the outlet passage 14. This clearance facilitates cleaning and prevents entrapment of process fluids as has been encountered in prior art valves. The valve may be easily purged and cleaned due to the presence of clearance 52. A bellows 60 is constructed of stainless steel in the preferred embodiment and is pleated, or folded, as generally shown at 62 to accommodate axial movement of the stem. The bellows 60 is welded or otherwise sealingly secured by convenient means to the first stem portion 46 at a peripheral area 64 located adjacent to the stem tip 48. The other end of the bellows is welded or otherwise secured to the closing ring 30 at an area 66. In this manner, the pressure of system fluid entering valve chamber 16 is sealingly isolated from the valve stem 44 by bellows 60. In this valve construction, it is important to maintain axial alignment of the bellows during stem movement since distortion of the bellows from an axial path will result in undue stresses, wearing, and premature failure of the bellows seal. Provisions for maintaining the necessary degree of axial alignment will be described hereinbelow in detail. The mean diameter D₁ of the bellows 60 is substantially equal to the diameter D₂ of the stem tip 48. Due to the equal diameters of the bellows and the stem tip, the valve is bidirectional. Bidirectional refers to the fact that either of passages 12, 14 may serve as the fluid pressure inlet of the valve. Preferably, passage 12 is the inlet so that, if a bellows failure occurs, the valve may be closed and system fluid cannot enter the valve chamber 16. Therefore, since the valve can be pressurized from either passage, and function in an identical manner, it is considered bidirectional. External screw threads 68 on valve body 10 engage internal threads 70 of a bonnet retaining nut 72. The retaining nut 72 has exterior polygonal surfaces 80 which define wrench flats for tightening the nut with respect to the valve body. A radially inwardly extending shoulder 82 on the nut co-operates with a radially outwardly extending flange 88 on a bonnet 90. A first end 92 of the bonnet abuts a radial face 94 of the closing ring 30 so that the stepped surfaces 34, 36 of the closing ring gasket and the valve body are tightly sealed with respect to one another by the gasket 37 when nut 72 is tightened. The closing ring 30 also accommodates an elongated annular bushing 100 disposed in the through passage 32. Preferably, the bushing 100 is constructed from bronze or some other suitable material. A first or lower end 102 of the bushing 100 abuts against a washer 104, while an intermediate, notched area 106 engages a retaining lip 108 of the closing ring 30. The bushing 100 has a cylindrical inner surface 110 which closely centres and guides the first portion 46 of the valve stem 44. The washer 104 is constructed of stainless steel and functions as a stop surface which co-operates with a shoulder 114 formed on the first stem portion 46. As the valve stem 44 is actuated to an open position, the washer 104 and shoulder 114 abut one another defining the uppermost limit of axial movement of the valve stem. A test port 120 is provided in the bonnet 90 and is adapted to receive a tube connection (not shown). The test port is used to monitor the valve assembly and allow detection of whether any fluid from the valve is bypassing the step seal or bellows seal so that appropriate corrective measures may be taken. A threaded portion 122 of the test port permits threaded engagement of an appropriate tube connection. The bonnet 90 has a radially inwardly extending support flange 124 which supports a means to compensate for misalignment. The misalignment compensating means includes an annular gland 126 having an inner groove 128 and an outer groove 130. These grooves are adapted to receive an inner O-ring 132 and an outer O-ring 134, respectively. The inner O-ring 132 contacts a second or upper stem portion 140. The outer O-ring 134 co-operates with an interior surface 142 of the bonnet. Utilization of the annular gland 126 with the two O-rings in inner and outer grooves 128, 130 compensates for any misalignment of the valve stem since the gland and O-rings permit floating. The gland 126 is designed to receive the second stem portion loosely, the gland, in turn, being received loosely by the bonnet 90. The O-rings 132, 134 deform to stabilize the axial position of the second stem portion 140. A retaining ring 144 maintains the misalignment compensating means axially positioned along the interior surface 142 of the bonnet and support flange 124. The second stem portion 140 includes internal screw threads 146 co-operable with exterior threads 148 at the outermost end of the first stem portion 46. The threaded connection provides positive return of the valve stem 44 during axial movement thereof. The first and second stem portions 46, 140 also have mating close fitting internal and external diameters. These close fitting diameters ensure precise axial alignment of the two stem portions during initial assembly, or at the time of reassembly after maintenance. Use of a threaded connection between the two stem portions facilitates selective removal of the bellows subassembly in one piece without imparting any distortion to the desired axial movement of the bellows. The exterior of the bonnet 90 is provided with a screw-threaded portion 152 which, in turn, engages a screw-threaded area 154 of an opening 156 in an actuator closure member or base 158. The actuator closure member has an outer peripheral surface 160 which includes a screw-threaded region 162 and a groove 164 adapted to receive a seal ring 166. An axial end face 168 of the actuator closure member co-operates with an axial shoulder 170 of the actuator housing 172, defining the innermost insertion of the closure member 158. A groove 174 and associated seal member 176 provide a fluid tight seal between the actuator closure member or base 158 and the exterior of the bonnet 90. An inner shoulder 178 is provided on closure member 158 to receive one end of a spring 180 in one embodiment of the valve. Spring 180 has been shown in phantom since it is only used in an alternative, normally open embodiment of the valve as will be readily understood by those skilled in the art. The alternative, normally open embodiment will be described hereinbelow in greater detail. An actuator 182, specifically shown as a piston, is disposed on the second stem portion 140. Other actuators may be employed with equal success. A nut 184 and washer 186 are provided on the second stem portion 140 for retaining this piston in fixed relation to the stem. Piston 182 sealingly engages the actuator housing 172 by means of an O-ring 192 which is received in an outer peripheral groove 194 in the piston. The inner periphery 196 of the piston is disposed in close-spaced relation to an O-ring 198 received in a peripheral groove 200 in the second stem portion 140. Fluid pressure may be supplied to the interior of the actuator through opening 206 which is illustrated as being in fluid communication with an axial fluid passage 208 provided in the second stem portion 140. Alternatively, the second stem portion may be of a solid configuration with a suitable fluid opening being provided through the actuator housing in a different manner. The fluid passage 208 extends from an outermost end 212 of the stem 44 of a transverse bore 214 located towards the inner end of the second stem portion 140. In this manner, fluid pressure may selectively be directed to an inner face 220 of the piston for axially driving the piston against an opposed, spring biasing force directed against an outer face 222 of the piston. A curvilinear surface 224 on the second stem portion 140 co-operates with a through opening in a wobble collar 226 to compensate for uneven forces exerted by spring biasing means 232, 234. More specifically, the wobble collar 226 has an enlarged through passage 228 which loosely receives the second stem portion 140. A tapered surface 230 engages the curvilinear portion 224 of the second stem portion so that the wobble collar may assume limited angular positions with respect to the stem axis and thereby compensate for uneven forces exerted by springs 232, 234. In the preferred construction, these springs are helical in nature and are concentrically arranged so that one end abuts the wobble collar while the other ends engage annular shoulders 240, 242 in actuator housing 172. A pair of springs is used for the normally closed embodiment since large biasing forces are required for high pressure applications. The alternative, normally-open embodiment has one end of spring 180 abutting the inner shoulder 178 on actuator closure member 158. The other end of the spring 180 abuts the piston actuator 182. The transverse bore 214 is placed at an alternative axial location for applying fluid pressure against the piston outer face 222. This alternative, normally-open embodiment would utilize fluid pressure applied to the piston outer face 222 to overcome the biasing force exerted by spring 180. Only a single spring is required in the alternative embodiment because of the high fluid system pressure in the valve chamber. It will be understood that the springs 180, 232, 234 are not all simultaneously used but, instead, are incorporated selectively in the alternative embodiments. All metal, wetted parts of the inverted bellows valve are preferably constructed of 316 stainless steel, including the bellows itself. The second or upper stem portion 140 may be constructed of hardenable stainless steel while the remaining actuator structure is aluminium. As previously indicated, the stem tip 48 is made of a soft material, such as KEL-F, which seals securely with the valve seat 18. However, the foregoing materials are merely exemplary, and other materials may be suitably employed without in any way departing from the scope of the invention. The subject new development incorporates a tapered, self-centering surface in addition to the wobble collar and misalignment compensating means. The tapered surface assures axial alignment of two major components which, in turn, allow accurate axial movement of the bellows. The wobble collar ensures that uneven forces due to the use of the several concentric springs are not transferred to the valve stem. In like manner, the gland with several concentric O-rings allows the stem to float and thereby compensate for any misalignment. Bushing 100 for centering and guiding of the valve stem is located outside the system fluid, and the threaded interconnections between selected components facilitate ready disassembly and maintenance of the valve. The interaction of these various features provides an inverted bellows valve assembly capable of withstanding pressures reaching 3500 psi (234 bar).

Claims: A bellows valve comprising a valve body (10) having inlet and outlet passages (12,14), a valve chamber (16) in fluid communication with one (14) of said passages, and a valve seat (18) disposed between the valve chamber (16) and the other (12) of said passages; a closing ring (30) closing an open end (26) of the valve chamber (16); a valve stem (44) having a stem tip (48) at one end thereof for selective sealing engagement with said valve seat (18) for controlling fluid flow between said inlet and outlet passages (12,14); actuating means (182) for effecting selective opening and closing movements of the valve stem (44); and a bellows (60) surrounding a portion of said stem (44) and sealingly secured at the opposite ends thereof respectively to said closing ring (30) and to said valve stem (44) for isolating said stem (44) from fluid passing through said valve chamber (16), whereby the fluid exerts an external compressive force on said bellows; characterised in that the closing ring (30) forms a step seal (34, 36, 37) with the open end (26) of the valve chamber, is annularly shaped for receiving said valve stem (44), includes an elongated bushing (100) in surrounding relation to said stem (44) to effect centering and guiding of the stem, and has a tapered surface (38) for centering said ring (30) and bellows (60) relative to said open end (26) of the valve chamber. A bellows valve according to claim 1, wherein said closing ring (30) matingly receives a bonnet (90) on a face (94) remote from said valve chamber (16), a retaining nut (72) co-operating with said bonnet (90) and said valve body (10) for urging said closing ring (36) into a close sealed relationship with said valve body at said open end (26) of the valve chamber. A bellows valve according to claim 2, wherein said bonnet (90) has a port (120) opening to enable monitoring of the sealing integrity of said bellows (60). A bellows valve according to any preceeding claim, wherein the actuating means (182) comprises reciprocating means (180, 182, 232, 234) co-operating with said stem (44) for reciprocating said stem end (48) into and out of sealing relation with said valve seat (18), and is housed within an actuator housing (172) removably connected to said valve body (10), and the stem (44) is in two coaxial portions (46, 140) which are screw-threadedly interconnected, the first stem portion (46) extending into the valve chamber (16) through an open end (26) thereof so that a portion thereof is surrounded by the bellows (60), the reciprocating means (180, 182, 232, 234) co-operating with the second stem portion (140). A bellows valve according to claim 4, wherein said reciprocating means (180, 182, 232, 234) comprises a piston (182) closely received in said actuator housing (172). A bellows valve according to claim 4 or 5, wherein said reciprocating means (180, 182, 232, 234) includes spring biasing means (232, 234 or 180) for effecting shifting said stem in one direction. A bellows valve according to claim 6, wherein said spring biasing means includes a wobble collar (226) and spring means (232, 234) interposed between the actuator housing (172) and said wobble collar (226) with said wobble collar (226) located in abutting relation with said second stem portion (140), said wobble collar (226) having a tapered inner surface (230) compensating for uneven spring force and preventing eccentric loading of said stem (44). A bellows valve according to claim 7, wherein said spring means comprises a pair of concentrically arranged springs (232, 234) interposed between said housing (172) and said wobble collar (226).

Inventors: BORK, CARL RICHARD, DANKO, OLIVER LASZLO, LEVENGOOD, DONALD ALLEN, STEISS, WILLIAM CARL
Applicants: NUPRO COMPANY
Application year: 1986
Main classification: F16K41
IPC codes: F16K41