(51) Int Cl.: H05F 3/02 ( ) F16K 1/22 ( )

Transcription

1 (19) (11) EP B1 (12) EUROPEAN PATENT SPECIFICATION (4) Date of publication and mention of the grant of the patent: Bulletin 08/07 (21) Application number: (22) Date of filing: (1) Int Cl.: H0F 3/02 (06.01) F16K 1/22 (06.01) (86) International application number: PCT/US04/ (87) International publication number: WO 0/ ( Gazette 0/01) (4) ELECTRICAL GROUNDING ASSEMBLY FOR CONTROL VALVE ELEKTRISCHE ERDUNGSBAUGRUPPE FÜR EIN STEUERVENTIL ENSEMBLE DE MISE ELECTRIQUE A LA TERRE POUR SOUPAPE DE COMMANDE (84) Designated Contracting States: DE FI FR GB () Priority: US (43) Date of publication of application: Bulletin 06/12 (73) Proprietor: FISHER CONTROLS INTERNATIONAL LLC St. Louis, MO (US) (72) Inventors: MERRILL, Peter, K. Greenland, NH 038 (US) ANDERSON, Joel, R. Berwick, ME (US) (74) Representative: Bohnenberger, Johannes et al Meissner, Bolte & Partner Postfach München (DE) (6) References cited: FR-A GB-A GB-A US-A US-A EP B1 Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). Printed by Jouve, 7001 PARIS (FR)

2 1 EP B1 2 Description TECHNICAL FIELD [0001] The electrical grounding assembly described herein makes known a device to substantially eliminate the electric potential difference between components within a control valve. More specifically, an electrical grounding assembly is disclosed having an arrangement that significantly reduces installation expense and substantially decreases maintenance intervals by creating a shared electrical connection between electrically isolated control valve components within the control valve. BACKGROUND [0002] Control valves are commonly used to control fluid flow through a pipe. As known to those skilled in the art, a control valve regulates the rate of fluid flow as an actuator changes the position of a moveable operator or valve trim within the control valve. Certain process fluids may be very corrosive to the control valve. To counteract the effects of the corrosive process fluid, control valve manufacturers may select special materials that are generally impervious to the corrosive effects of the process fluid. For example, nickel alloy UNS N276 is known to have superior corrosion resistance to a wide range of corrosive agents. Using special corrosion resistant alloys, particularly in valve bodies, can be cost prohibitive for less expensive valves like butterfly-style control valves. Valve manufacturers generally address this cost issue by supplying the valve body with a corrosion resistant, non-conductive liner. [0003] The advantage of a lined valve is that the valve body is not wetted by the process fluid and therefore can be made from less expensive materials when used in corrosive applications. Valve body liners are typically made from elastomers such as ethylene propyl terpolymer (EPDM). These elastomers are typically non-conductive and have dielectric properties. As known to those skilled in the art, the dielectric material substantially insulates the valve trim from the valve body effectively creating a capacitor that may store an electrostatic charge. Additionally, numerous control valve applications do not use packing materials, seals, and/or guide bushings that have conductive properties. Therefore, if the valve trim is not positively grounded to the valve body with a shared electrical connection, fluid flow through the valve body and across the valve trim may create an electrostatic charge transfer that can accumulate similar to a capacitor accumulating an electrostatic charge. The accumulating charge can establish a potential difference of several thousand volts between the valve body and valve trim. As is known, when the accumulated charge exceeds the breakdown voltage of the dielectric or insulator, an arc may result. Also, if a momentary discharge path is created between the valve body and the valve trim, for example a wrench being used during routine maintenance, an are could be struck. As a result, numerous industry standards and governmental regulations require that equipment used in an explosive atmosphere shall be designed to operate safely in that atmosphere. The equipment, including mechanical devices such as valves, must be free of sources that may lead to ignition of the surrounding atmosphere. [0004] Typical solutions include the use of external grounding straps between valve components and conductive packing. Due to cost, however, these solutions are not applicable to all control valve designs. External straps can also be severed during operation subsequently creating an ignition source at the control valve. Lastly, known to those skilled in the art, the external surfaces of valve bodies and actuators are typically painted with a powder-coated paint that provides an extremely durable, scratch resistant coating that also functions as an insulator. Therefore, conventional assemblies require manual removal of the paint from conductive surfaces to provide a shared electrical connection between the valve components. In a manufacturing operation, these manual operations are time consuming and expensive. [000] Further information pertaining to the prior art can be found in US patent 4,66,482 that discloses a top entry trunnion ball valve having a valve body forming seat recesses with seat members movable disposed therein and urged towards sealing engagement with a spherical valve member by spring members and by differential pressure induced force. The valve mechanism is provided with a static electricity grounding spring that is received about a spring retainer pin. The grounding spring and retainer pin are received within an appropriate grounding spring receptacle formed in the lower trunnion member of the ball. SUMMARY [0006] Accordingly, it is the object of the electric grounding assembly to substantially eliminate the electric potential between control valve components used in potentially explosive atmospheres. More specifically, the present electrical grounding assembly places an elastic grounding connector in an outboard bearing hole of a control valve creating a shared electrical connection between the valve trim and the valve body. [0007] The present invention provides a control valve in accordance with independent claim 1 as well as a method to substantially reduce the electric potential across a control valve assembly in accordance with independent claim. Preferred embodiments of the invention are reflected in the dependent claims. [0008] In accordance with one aspect of the present electrical grounding assembly, an electrically conductive, deformable ball is located in a bore within the valve body. The deformable ball is made from stranded metal wire. Upon assembly, the valve trim compresses the deformable ball making contact with the valve trim and valve body thereby creating a shared electrical connection be- 2

3 3 EP B1 4 tween the valve trim and the valve body. BRIEF DESCRIPTION OF THE DRAWINGS [0009] The features of this present electrical grounding assembly are set forth with particularity in the appended claims. The present electrical grounding assembly may be best understood by reference to the following description taken in conjunction with the accompanying drawings in which like reference numerals identify like elements in the several figures and in which: FIGURE 1 is a cross-sectioned side view of an elastomer lined butterfly-style control valve with a deformable stranded metal ball providing a shared electrical connector within the control valve. FIGURE 2 is a partial cross-section side view of an elastomer lined butterfly-style control valve using a conical spring in combination with the stranded metal ball to create a shared electrical connection within the control valve. FIGURE 3 is a partial cross-section side view of an elastomer lined butterfly-style control valve using a single conical spring to create a shared electrical connection within the control valve. This embodiment does not form part of the invention as claimed. DETAILED DESCRIPTION [00] To fully appreciate the advantages of the present electrical grounding assembly, its functions and features are described in connection with a butterfly-style control valve. However, one skilled-in the art would appreciate the present electrical grounding assembly could be used in other types of valves. [0011] Referring now to Figure 1. a cross-sectioned side view of an elastomer lined butterfly-style control valve is depicted with a deformable stranded metal ball providing a shared electrical connection within the control valve. The butterfly-style control valve is comprised of a valve body 12 and the valve trim 1. The valve trim 1 is typically defined as the internal components of the control valve that regulate the flow of the process fluid.-in the present embodiment, the valve trim 1 is comprised of a valve shaft 18 and a control disk or vane, both being fabricated from non-corrosive stainless steel such as UNS S The control disk is attached to the valve shaft 18 with two taper pins 22a and 22b pressed into alignment holes (not shown) in both the valve shaft 18 and the control disk. The process fluid is contained within the valve body 12 by non-conductive valve packing 2 and non-conductive o-ring seals 26a and 26b. A non-conductive guide bushing on the inboard side of the valve body 12 and an outboard-bearing hole 32 align the valve trim 1 within the valve body 12. An actuator (not shown) is fastened to the inboard side of the valve body 12 with actuator bolts (not shown) completing the attachment through the actuator mounting holes 38a and 38b. The actuator directly couples to inboard end 19 of the valve shaft 18 and rotates the valve trim 1 about a longitudinal axis 0 defined by the valve shaft 18. The exterior of the actuator and the valve body 12 are typically painted with a non-conductive powdercoated paint process that insulates the actuator from both the valve body 12 and the valve trim 1. [0012] A non-conductive elastomer liner 42 concomitantly creates a soft annular seating surface 27 for the control disk to engage during operation and forms a barrier between the valve body 12 and the process fluid. Subsequently, the barrier provided by the elastomer liner 42 electrically isolates the valve trim 1 from the valve body 12. As known to those skilled in the art, the dielectric properties of the elastomer liner 42 effectively establish a capacitor between the valve body 12 and the valve trim 1 that can store an electrostatic charge. The accumulation of the charge may create a safety hazard by presenting an ignition source when used in a potentially explosive environment. Therefore, the charge must be prevented from accumulating by creating an electrical ground around the capacitor established by the elastomer liner 42. [0013] As shown in Figure 1, the preferred electrical grounding assembly is comprised of a conductive, stranded metal ball 4 formed to fill the outboard-bearing hole 32 of the valve body 12. The stranded metal ball 4 is fashioned from substantially random windings of stranded metal similar to conventional steel wool. In the preferred embodiment, the stranded metal ball 4 is preferably made from a corrosion resistant metal such as stainless steel S31600, but other corrosion resistant, conductive materials can be used. During assembly of the control valve, the valve shaft 18 is placed through the non-conductive guide bushing and the valve packing 2. The stranded metal ball 4 is placed within the outboard bearing hole 32 prior to final installation of the valve shaft 18. Upon final installation, the valve shaft 18 is loaded into the outboard-bearing hole 32 consequently compressing the stranded metal ball 4. Due to the resiliency of stranded metal, the stranded metal ball 4 inherently forms an elastic region within the stranded metal ball that maintains contact between the conductive surface of the stranded metal ball, the bare metallic walls of the outboard-bearing hole 32 in the valve body 12, and the valve trim 1 through the valve shaft 18 during operation of the control valve. This shared electrical connection grounds the electrostatic charge accumulation by eliminating the electrical isolation between the valve trim 1 and the valve body 12. [0014] Unlike conventional external grounding straps that provide a single connection point, the numerous strands of metal within the stranded metal ball 4 maintain a plurality of electrical contact points between the outboard bearing hole 32 and the valve trim 1, thereby providing an improved shared electrical connection. Additionally, by maintaining an internal shared electrical connection within the control valve, the potential for 3

4 EP B1 6 catastrophic failure of the connection due to -physical separation is substantially eliminated. The preferred electrical grounding assembly also reduces assembly time and saves manufacturing costs by eliminating the need to manually remove paint to expose conductive surfaces and eliminates the drilling and tapping of bolt holes to attach an external grounding strap. [001] Turning now to Figure 2, an elastic grounding connector according to another embodiment of the present electrical grounding assembly is depicted. For a butterfly-style control valve 1 with a deep outboard bearing hole 132, as depicted, the stranded metal ball 14 can be biased to wards the outboard end 12 of the valve shaft 118 with a helical bias spring 148. The helical bias spring 148 compensates for variations in depth of the outboard-bearing hole 132 and will assure that the stranded metal ball 14 stays in contact with the valve shaft 118 in applications where the valve shaft 118 can oscillate along its longitudinal axis. [0016] In Figure 3, another embodiment, which does not form part of the invention as claimed, of the elastic grounding connector of the present electrical grounding assembly is illustrated. A single conical spring 248 is placed in the outboard-bearing hole 232. The spring 248 makes contact between the outboard end 22 of the valve shaft 218 and the valve body of 212 through the bare metallic surface of the outboard-bearing hole 232. As known to those skilled in the art, the conical winding of the spring 248 is formed such that the outboard end 2 of the spring 248 is slightly larger than the diameter of the outboard-bearing hole 232 to retain the spring 248 in the outboard-bearing hole 232 during assembly. [0017] The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modifications will be obvious to those skilled in the art. For example, it can be appreciated by those skilled in the art that the present electrical grounding assembly is not limited to spherical or ball shaped geometry, but may assume any shape to fill the outboard-bearing hole to create a shared electrical connection. Furthermore, one skilled in the art can further appreciate the elastic connector could be permanently attached to the outboard end of the valve shaft with a screw or rivet to ensure constant contact between the valve trim and the valve body a valve body (12); a valve trim (1) electrically isolated from the valve body; and an elastic grounding connector (4; 14, 148) having in combination an elastic region and an electrically conductive surface compressed between the valve body and the valve trim to form and maintain an internal electrical contact between the valve body and valve trim, characterized in that the elastic grounding connector comprises deformable stranded metal (4; 14). 2. The control valve of claim 1, wherein the valve body has a bore (32) adjacent to the valve trim for receiving the elastic grounding connector. 3. The control valve of claim 1, wherein the deformable stranded metal is generally formed as a ball. 4. The control valve of claim 3, wherein the elastic grounding connector includes a bias spring (148) such that the bias spring places the deformable stranded metal ball in continuous contact with the valve trim and the valve body.. A method to substantially reduce the electric potential across a control valve () assembly wherein the control valve assembly comprises at least a valve body (12) and a valve trim (1), the valve trim being electrically isolated from the valve body, the method comprising: providing an elastic conductive grounding connector (4; 14, 148) comprising a deformable stranded metal (4; 14); forming the valve trim from at least a valve shaft (18) and a control element (), the valve shaft having an outboard end (12; 22); forming the valve body with a bore (32) sized to receive the elastic conductive grounding connector and the outboard end of valve shaft; filling the bore with the elastic grounding connector; and placing the valve trim within the valve body with the outboard end of the valve shaft in the valve body bore so that the outboard end of the valve shaft compresses the elastic conductive grounding connector thereby forming a shared electrical connection between the valve body and the valve trim. Claims 1. A control valve () comprising: 0 6. The method of claim, wherein the deformable stranded metal is generally formed as a ball. 7. The method of claim 6, wherein the elastic grounding connector includes a bias spring (148) such that the bias spring places the deformable stranded metal ball in continuous contact with the valve trim and the valve body. 4

5 7 EP B1 8 Patentansprüche 1. Steuerventil (), das Folgendes aufweist: einen Ventilkörper (12); eine Ventilgarnitur (1), die gegenüber dem Ventilkörper elektrisch isoliert ist; und einen elastischen Schutzverbinder (4; 14, 148), der in Kombination einen elastischen Bereich und eine elektrisch leitfähige Oberfläche hat, die zwischen dem Ventilkörper und der Ventilgarnitur zusammengedrückt ist, um einen inneren elektrischen Kontakt zwischen dem Ventilkörper und der Ventilgarnitur zu bilden und aufrechtzuerhalten, 1 Vorsehen eines elastischen leitfähigen Schutzverbinders (4; 14, 148), der ein verformbares verseiltes Metall (4; 14) aufweist; Bilden der Ventilgarnitur aus mindestens einer Ventilstange (18) und einem Steuerelement (), wobei die Ventilstange ein außenseitiges Ende (12; 22) hat; Ausbilden des Ventilkörpers mit einer Bohrung (32), die so bemessen ist, dass sie den elastischen leitfähigen Schutzverbinder und das außenseitige Ende der Ventilstange aufnimmt; Ausfüllen der Bohrung mit dem elastischen Schutzverbinder; und Anordnen der Ventilgarnitur in dem Ventilkörper mit dem außenseitigen Ende der Ventilstange in der Ventilkörperbohrung, so dass das außenseitige Ende der Ventilstange den elastischen leitfähigen Schutzverbinder zusammendrückt, wodurch eine gemeinsame elektrische Verbindung zwischen dem Ventilkörper und der Ventilgarnitur gebildet wird. 6. Verfahren nach Anspruch, wobei das verformbare verseilte Metall allgemein als eine Kugel ausgebildet ist. 7. Verfahren nach Anspruch 6, wobei der elastische Schutzverbinder eine Vorspannfeder (148) aufweist derart, dass die Vorspannfeder die verformbare verseilte Metallkugel in kontinuierlichen Kontakt mit der Ventilgarnitur und dem Ventilkörper bringt. dadurch gekennzeichnet, dass der elastische Schutzverbinder ein verformbares verseiltes Metall (4; 14) aufweist. 2. Steuerventil nach Anspruch 1, wobei der Ventilkörper eine Bohrung (32) nahe der Ventilgarnitur hat, um den elastischen Schutzverbinder aufzunehmen. 3. Steuerventil nach Anspruch 1, wobei das verformbare verseilte Metall allgemein als eine Kugel ausgebildet ist. 4. Steuerventil nach Anspruch 3, wobei der elastische Schutzverbinder eine Vorspannfeder (148) aufweist derart, dass die Vorspannfeder die verformbare verseilte Metallkugel in kontinuierlichen Kontakt mit der Ventilgarnitur und dem Ventilkörper bringt.. Verfahren, um das elektrische Potential über eine Steuerventilanordnung () erheblich zu reduzieren, wobei die Steuerventilanordnung mindestens einen Ventilkörper (12) und eine Ventilgarnitur (1) aufweist, wobei die Ventilgarnitur gegenüber dem Ventilkörper elektrisch isoliert ist, wobei das Verfahren die folgenden Schritte aufweist: Revendications 1. Soupape de commande () comprenant : un corps de soupape (12) ; un mécanisme de soupape (1) isolé électriquement du corps de la soupape ; et un connecteur de mise à la terre élastique (4, 14, 148) comprenant en combinaison une région élastique et une surface électriquement conductrice comprimée entre le corps de soupape et le mécanisme de soupape pour former et maintenir un contact électrique intérieur entre le corps de soupape et le mécanisme de soupape ; caractérisée en ce que : le connecteur de mise à la terre élastique comprend un métal toronné déformable (4, 14). 2. Soupape de commande selon la revendication 1, dans laquelle le corps de soupape comprend un alésage (32) adjacent au mécanisme de soupape pour recevoir le connecteur de mise à la terre élastique. 3. Soupape de commande selon la revendication 1, dans laquelle le métal toronné déformable a globalement la forme d une bille. 4. Soupape de commande selon la revendication 3, dans laquelle le connecteur de mise à la terre élastique comprend un ressort de poussée (148) de telle sorte que le ressort de poussée place la bille de métal toronné déformable en contact continu avec le mécanisme de soupape et le corps de soupape.. Procédé destiné à réduire sensiblement le potentiel électrique dans un ensemble de soupape de commande (), dans lequel l ensemble de soupape de commande comprend au moins un corps de soupa-

6 9 EP B1 pe (12) et un mécanisme de soupape (1), ledit mécanisme de soupape étant isolé électriquement du corps de soupape, ledit procédé comprenant : la fourniture d un connecteur de mise à la terre conducteur élastique (4, 14, 148) comprenant un métal toronné déformable (4, 14) ; la formation du mécanisme de soupape à partir d au moins un axe de soupape (18) et un élément de commande (), ledit axe de soupape comprenant une extrémité extérieure (12, 22) ; la formation du corps de soupape avec un alésage (32) dimensionné pour recevoir le connecteur de mise à la terre conducteur élastique et l extrémité extérieure de l axe de soupape ; le remplissage de l alésage avec le connecteur de mise à la terre élastique ; et le positionnement du mécanisme de soupape à l intérieur du corps de soupape, avec l extrémité extérieure de l axe de soupape dans l alésage du corps de soupape de telle sorte que l extrémité extérieure de l axe de soupape comprime le connecteur de mise à la terre conducteur élastique, formant ainsi une connexion électrique partagée entre le corps de soupape et le mécanisme de soupape Procédé selon la revendication, dans lequel le métal toronné déformable a globalement la forme d une bille. 7. Procédé selon la revendication 6, dans lequel le connecteur de mise à la terre conducteur élastique comprend un ressort de poussée (148) de telle sorte que le ressort de poussée positionne la bille de métal toronné déformable en contact continu avec le mécanisme de soupape et le corps de soupape

7 EP B1 7

8 EP B1 REFERENCES CITED IN THE DESCRIPTION This list of references cited by the applicant is for the reader s convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard. Patent documents cited in the description US A [000] 8