ISOLATING APPARATUS FOR A PRESSURE SENSOR FLANGE

Abstract: Pressure fitting (16) for incorporation into a pressure sensor assembly (10) for conveying fluid under pressure through a flange (12) which is coupled to the pressure sensing interface (14) of a pressure sensing module (11). The fluid under pressure enters a fluid chamber (20) where it acts on the pressure sensing interface (14), which in turn affects a sensing element or elements within the pressure sensor module (11). The fitting (16) provides a passageway for conveying the fluid and has end face portions (21) that, in combination with the pressure sensor interface (14), define the fluid chamber (20). The fitting (16) is disposed between the fluid and the flange (12) to substantially isolate the flange (12) from the fluid. The fitting (16) is constructed of material that is substantially chemically non-interactive with the fluid.

Description: ISOLATING APPARATUS FOR A PRESSURE SENSOR FLANGE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to pressure sensor flanges that comprise elements of a pressure sensor assembly, and in par¬ ticular to a fitting for use in conjunction with a flange that is capable of substantially isolating the flange from a fluid, the pressure of which is to be sensed by the pressure sensor assembly. 2. Prior Art In the prior art, flanges have been used to convey fluid under pressure to a pressure sensor module. Conventional flanges are formed from ferrous metal, typically stainless steel, with passageways to convey fluid from impulse piping to the sensor module. This has caused problems in applications of the pressure sensor assembly with corrosive fluids that react with such flanges. In applications with corrosive fluids, solutions in the prior art have been to form the ' entire flange of a material that is substantially chemically noninteractive with the fluid. For low fluid pressure and temperature applications, the entire flange has been formed from a substantially noninteractive plastic. When the fluid has a chlorine content, plastics such as that which is sold under the trademark Kynar and " tetrafluoroethylene (sold under the trademark Teflon) have been found to be suitable. This solution is expensive and has limited practical application due to fluid pressure and temperature limitations. In applications in which the fluid is at high pressure or elevated temperature or combinations thereof, the entire flange has been formed from an exotic metal. For applications with chlorine containing fluids, exotic metals found to be suitable include tantalum, titanium, the alloy sold under the trademark Monel, and the alloy sold under the trademark Hastelloy. This solution has broader pressure and temperature application than use of the plastics but is also more expensive. OMPI SUMMΛRY OF THE INVENTION The present invention relates to a fitting or con¬ nector for use in cooperation with the flanges of a pressure sensor assembly to convey fluid under pressure from a source through a passageway in the fitting to a fluid chamber within the pressure sensor assembly. The fluid chamber is formed in part by the fitting and in part by the pressure sensor interface of the pressure sensor module. The pressure sensor interface is connected to the pressure sensing elements within the pressure sensor module so that pressure applied at the pressure sensor interface is sensed at the pressure sensing elements. By provid the passageway for effecting conveyance of the fluid through the flange and by also forming part of the fluid chamber, the fittin substantially isolates the flange from the fluid. In a preferre embodiment the fitting is constructed of materials that are sub¬ stantially chemically noninteractive with or substantially inert respect to the fluid, typically either an exotic metal or a plast Where the application requires the use of exotic meta use of only a fitting made of su h metal avoids the expense of machining the entire flange of the exotic metals. The flange ma be constructed of stainless steel or other ferrous metal in the conventional manner. In the case of constructing the fitting of plastic, an added benefit is realized in that the standard flang supports the fitting to increase the ability of the plastic fitt to withstand fluid temperature and pressure combinations consid¬ erably above those that can be withstood when the entire flange constructed of plastic. This permits using the low cost plastic in many applications that presently mandate use of an exotic met flange. The fitting is particularly suited for use in that portion of the process industry that uses chlorine or derivative thereof in the process fluid. Each of the aforementioned materi that have been found to be suitable for use with such chlorines is suitable for use in construction of the fitting. " BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a side view of a typical pressure sensor assembly showing a pressure sensor module and connected flanges with a fragmentary section view of the sensor module, impulse piping, and one flange having the fitting made according to the present invention installed; Figure 2 is an enlarged sectional side view of the fitting in combination with the flange, a portion of the pressure sensor module and the pressure sensor interface; Figure 3 is a sectional view taken along line 3--3 in Figure 4, showing an embodiment of the fitting having a plurality of slender passageways to minimize the impact of momentary fluid overpressures; and Figure 4 is an end view of the fitting shown in Figure 3 showing the face portion of the fitting. DESCRIPTION OF THE PREFERRED EMBODIMENTS In Figure 1, a pressure sensor assembly is illustrated generally at 10 and includes pressure sensOr module 11 with flanges 12 secured to both sides of pressure sensor module 11 by bolts 15 such that each flange 12 faces a pressure sensor interface 14 (shown as an isolation diaphragm) formed in the side of pressure sensor module 11. Pressure sensor interface- 14 is connected to pressure sensor element or elements such as a diaphragm as shown within pressure sensor module 11 in a manner such that fluid pressure acting on pressure sensor interface 14 is transmitted to the pressure sensor elements. It is understood that only one such flange is necessary to sense pressure, but that two or more such flanges and sensor modules may be used as desired. In one embodiment, pressure sensor assembly 10 is made according to U.S. Patent 3,618,390, which is incorporated herein by reference, and corresponds to the differential pressure transducer assembly unit therein. Pressure sensor module 11 and flanges 12 of the instant invention correspond with center housing section 15 and end caps 14 and 16 of Patent 3,618,390, respective- ly. The pressure sensor element of the instant figures, corresponds to interior sensing cell assembly 26 of Patent No. 3,618,390 and pressure sensor interface 14 disclosed herein corresponds to iso¬ lation diaphragm 44 or 45 in Patent No. 3,618,390. Leads 18 in the present invention are connected to suitable readout circuitry and to the interior sensing cell assembly as shown in Patent No. 5,618,390. It is understood that fitting 16 shown in section in the left side of pressure sensor assembly 10 in Figure 1 preferably is duplicated on the right side for differential pressure appli- cations of pressure sensor assembly 10. The fitting 16 also may be used with other pressure sensor assemblies, having various types of prcssui'e sensor elements. As used herein, the longitudinal dimen¬ sion of fitting 16 is that dimension that is axial to passageway 17 in fitting 16.and perpendicular to end face portion 21. Opening 15 in flange 12 couples interface 14 to the ex¬ terior of pressure sensor assembly 10 when flange 12 is mated to pressure sensor module 11. Opening IS is suitably formed to re- • ceive fitting 16 therein. Impulse piping 19 is connected at one end to a .passageway 17 which extends longitudinally through fitting 16, and at the other end to fluid vessel 28. In differential pressure applications of pressure sensor assembly 10, fluid vessel 2S is typically a pipe as illustrated in Figure 1.. Λ means for creating a differential pressure, typically an or ice plate is mounted in fluid vessel 2S between the points of connection of impulse piping 19. Fluid pressure from fluid vessel 28 acts through impulse piping 19 and passageway 17 to fluid chamber 20. Fluid chamber 20 is formed by two cooperative parts, the first part being interface 14 and the second part being the end face portion 21 of fitting 16. Within pressure sensor assembly 10, the fluid being sensed is confined within a volume defined by passage way 17 and fluid chamber 20, thereby substantially isolating flange 12 from the fluid. In order to effect fluid tightness, fluid chamber 20 is sealed adjacent to the juncture of the end face portion 21 of fitting 16 and interface 14. In a preferred embodiment shown in Figure 2, an 0 ring 22 is compressed between tapered" surface 23 of fitting 16 and a shoulder surface 32 in pressure sensor module 11. Tapered face 23 and shoulder 32 are in alignment when flange 12 with fitting 16 inserted therein is mated-to pressure sensor module 11. 0 ring 22 is compressed as flange 12 is securely fastened to pressure sensor module 11, thereby effecting the fluid tight seal. To insure both adequate sealing and formation of fluid chamber 20, fitting 16 must be suitably positioned longitudinally with respect o both flange 12 and pressure sensor module 11. In the preferred embodiment shown in Figure 2, groove 29, the side and base of which form an L shape, is formed in flange 12, effectively expanding the diameter of opening 15 where opening 15 intersects inner surface 33 of flange 12. Fitting 16 is constructed. ith an annular shoulder 24 formed to be closely received by groove 29. Shoulder 24 butts against the base of groove 29 when fitting 16 is inserted into opening 15. Fitting 16 is compressibly. held in contact with both flange 12, through the contact at the base of groove 29, and 0 ring 22, through the contact with tapered surface 23, when flange 12 is securely mated to pressure sensor 5 module 11, thereby correctly positioning fitting- 16 for effective. sealing of the fluid. The longitudinal position of fitting 16 also determines the volume of fluid chamber 20 by determining the distance between end face portion 21 of fitting 16 and interface 14. This distance is a function of the longitudinal dimensions of both groove 29 and shoulder 24. For applications in which fitting 16 is cylindrical in shape and is therefore free to rotate within opening 15, Figure 2 shows a set screw arrangement for preventing such rotation. Preferably, a threaded bore 27 is machined in flange 12 so that the axis of threaded bore 27 intersects the longitudinal axis of fitting 16 at a desired angle. Threaded bore 27 extends from opening 15 to the exterior of the flange. Set screw 30 is threaded into threaded bore 27 and tightened down against fitting 16 or a key way formed in fitting 16 at the point of contact. The set screw holds fitting 16 from rotation, while impulse piping 19 is being threaded into passageway 17. Additionally, set screw 30 prevents rotation of fitting 16 caused by fluid pressure fluctua- t ions. Such rotation may cause undesirable working of impulse piping 19 and disruption of the 0 ring seal for fluid chamber 20. For applications in which fitting 16 is formed without shoulder 24, set screw 30 additionally is used to fix the longi- tudinal positioning of fitting 16 in order to effect the seal and establish the volume of fluid chamber 20. Figures 3 and 4 illustrate an embodiment of apparatus 16 for use with impulse piping 19 as shown in Figure . 1 in which.,the firs portion of passageway 17 is formed and threaded as shown in Figure 1. Here, liowever, passageway 17 is not extended through the full longi¬ tudinal dimension of apparatus 16, but terminates in a plurality of slender passageways 35, which extend through fitting 16 from the 'termination of passageway 17 to end face portion 21. The material through which slender passageways 17 are bored is preferably the same as the fitting. The path of fluid flow from impulse piping 19 is first to passageway 17 and then through the slender passageway 35 to fluid chamber 20. Passageways 35 admit sufficient fluid to fluid chamber 20 (shown in Figures 1 and 2) to permit sensing of the fluid pressure. In the event of a momentary overpressure which would other- wise tend to rapidly deflect the sensing diaphragm and interface 14, passageways 35 act as a buffer by responding relatively slowly to the overpressure, thereby protecting interface 14 from damage. Preferably, fitting 16 is substantially chemically non¬ interactive with the fluid or substantially inert with respect to the fluid. The end face portion forms one portion of the chamber which receives the fluid to be sensed and the 0 ring seal closes off any contact of the corrosive fluid being sensed with the flange. Interface 14 is a flexible isolation diaphragm and generally is corrugated for permitting movement when the center sensing diaphragm deflects. The fluid movement in passageway 17 occurs only during deflection of the sensing diaphragm. The fitting preferably is made of a plastic such as tetrafluorocthylene, a plastic sold under the trademark Kynar, titanium, tantalum, or metal alloys sold under the trademarks Monel or Hastclloy, or other suitable material.

Claims: WHAT IS CLAIMED IS: 1. In a pressure sensor assembly having a flange affixed to a pressure sensor module wherein a fluid under pres¬ sure is conveyed from a source through an opening in the flange to a fluid chamber formed in part by a pressure sensor interface of the pressure sensor module to impinge upon the pressure sensor interface in order to affect a pressure sensing element coupled to the pressure sensor interface and located within the pressure sensor module, the combination with the flange of a fitting having passageway means therethrough coupling the fluid source to the fluid chamber, said fitting having a face portion forming a second part of the fluid chamber in combination with the pressure sensor interface, the fitting being so disposed in the opening in the flange to substantially isolate the flange from the fluid. 2. An apparatus as claimed in Claim 1 wherein the apparatus is constructed of a material substantially inert with respect to the fluid. 3. An apparatus as claimed in Claim 1 wherein the apparatus is constructed of a material substantially inert with chlorine in all its forms. 4. In a pressure sensor assembly having a flange affixed to a pressure sensor module wherein a fluid under pressure is transmitted from a source through an opening in the flange to a fluid chamber formed in part by a pressure sensor interface of the pressure sensor module to act upon the pressure sensor - interface, the combination with the flange of a fitting having passageway means therethrough fluidly coupling the fluid source to the fluid chamber and having an end face portion partially enclosing , the fluid chamber means, seal means surrounding the face portion and effecting a substantially fluid tight seal between the fitting and the pressure sensor interface to prevent fluid in the fluid chamber from- contacting the flange, and means for retaining the fitting in position in the opening and in engagement with the seal means. 5. An apparatus as claimed in Claim 4 where the apparatus is constructed of a material that is substantially inert in the presence of the fluid being sensed. 6. An apparatus as claimed in " Claim 4 in which the sea means between the fitting and the pressure sensor interface is sub¬ stantially inert in the presence of the fluid being sensed. 7. An apparatus as claimed in Claim 4 in which the mea for retaining the fitting comprises a shoulder on the fitting annul to the face portion of the fitting, and an annular groove in the fl surrounding the opening for receiving the shoulder, the longitudinal dimensions of the groove being located to longitudinally position t fitting to insure formation of the fluid chamber in combination with the seal means when the flange is mated with the pressure sensor module. 8. An apparatus as claimed in Claim 4 in which the mean of retaining the fitting within the opening in the flange is a set screw turned into a threaded bore through the flange radial to the fitting to butt against the fitting. 9. An apparatus as claimed in Claim 4 in which the seal means between the fitting and the pressure sensor interface comprise an 0 ring held- under compression between the fitting and the pressur sensor interface. 10. An apparatus as claimed in Claim 4 in which the fitting has a tapered annular surface at the end face portion, and t pressure sensor module has surfaces defining a groove therein sur¬ rounding the pressure sensor interface and in which the seal means comprises an 0 ring positioned between the tapered surface and the surfaces defining the groove. 11. An apparatus as claimed in Claim 4 in which the pressure sensor interface comprises a deflectable diaphragm, and the passageway means consists of a first part suitable for connection to the 'fluid source, and a second part connecting the first part to the fluid chamber and comprising a plurality of slender passageways of size selected to permit movement of fluid to the fluid chamber yet restricted enough to protect the pressure sensor interface from damage as it deflects due to a momentary fluid overpressure. -BURE OMPI 12. An apparatus as claimed in Claim 4 wherein the fitting is constructed of a material selected from the group com¬ prising tetrafluoroethylcnc, a plastic sold under the trademark Kynar, titanium, tantalum and the separate alloys sold under the trademarks Monel and Hastelloy.

Inventors: GUETSCHOW R
Applicants: ROSEMOUNT INC
Application year: 1981
Main classification: F01B19
IPC codes: G01L19