Abstract:
An assembly for measuring differential pressures includes a manifold valve and pressure transducer assembly including two pressure transducers. The manifold valve includes two pressure inlet ports and two pressure outlet ports that communicate through the manifold&#39;s isolation valves. An equalization valve connects the two pressure lines. Mating flanges on the manifold valve and pressure transducer assembly are bolted together to form a pressure tight seal between the manifold valve outlet ports and the pressure transducer assembly inlet ports. The pressure transducer assembly also includes a mounting plate for supporting the pressure transducers. The transducers generate an electrical signal corresponding to inlet pressure. Signals from pressure transducers and an optional thermistor for each are wired to an electrical connector mounted on the side of the assembly. The signals are electronically compared with an external signal processing circuit that outputs a representative signal of the differential pressure.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to manifold valves and pressure transducers in fluid communication with main fluid pressure lines, and more particularly to assemblies of manifold valves and pressure transducers for outputting signals representing pressures in two pressurized fluid lines. 
     Manifold valves are known in the art. Manifold valves typically are mounted between the main fluid pressure lines and the pressure transducers. Manifold valves permit isolating the pressure lines from the pressure transducers in order to facilitate their removal or replacement and are required for calibration purposes. The manifold valve of the present invention includes a first inlet port and a second inlet port with internal passageways that run past isolation valves to a first outlet port and second outlet port that are connected to corresponding inlet ports on the pressure transducers. 
     Differential pressure transmitters are known in the art. Manifold valves are used in conjunction with differential pressure transmitters. The manifold valve in the present invention has an integral flange that mates with differential pressure transmitters as in U.S. Pat. No. 6,279,401 B1, incorporated herein by reference in its entirety. The flange connection is standard in the industry and is used to directly mount a manifold valve to a differential pressure transmitter without the use of piping components. Differential pressure transmitters of this type include pressure-sensing components, which include pressure transducers, with signal processing circuits and are typically manufactured as a complete unit. The signal processing circuit of the differential pressure transmitters combines the low-pressure and high-pressure output signals of the pressure sensors into a single output signal that is indicative of the pressure difference. The costs of these types of transmitters typically are higher than the cost of the manifold valve. 
     Fully integrated manifold valves and differential pressure transmitters also are known in the art. They typically combine a manifold valve and differential pressure transmitter into a single manufactured unit. U.S. Pat. No. 4,865,360, incorporated herein by reference in its entirety, relates to this type of fully integrated assembly. The time required to assemble these units into fluid pipelines is significantly lower than assembling separate manifold and pressure transducers, but the costs of these units also are higher. 
     Pressure transducers, manifold valves and signal processing circuits can be purchased on a stand-alone basis and assembled using standard piping components. The costs of the individual components are relatively low, but the costs associated with assembling them into fluid pipelines are significantly higher than integrated units. An optimal manifold valve and differential pressure transmitter assembly would use low cost standard components that can be assembled rapidly using a minimal amount of piping components. Known manifold valve and differential pressure transmitter assemblies have attempted to accomplish this. U.S. Pat. No. 6,349,735 B2, incorporated herein by reference in its entirety, relates to an example of this type of assembly. This assembly, however, still makes use of piping components, and although the manifold valve is modular, the pressure transducers are not. 
     Further, U.S. Pat. No. 4,466,290, incorporated herein by reference in its entirety, relates to a differential pressure transmitter attached to a three valve manifold employing a standard mounting flange used in the industry and incorporated between a three valve manifold and a single transmitter. 
     Further improvements are needed that make use of standard low cost, interchangeable components that can be quickly assembled with the same functionality as their more expensive counterparts. 
     SUMMARY OF INVENTION 
     The present invention provides a novel means for monitoring the pressure in a fluid pipeline. The pressure indicating assembly uses a manifold valve assembly and a pressure transducer assembly comprising two pressure transducers. These components are attached in a unique way so as to allow accessibility and interchangeability with commercially available transducers and manifold valve assemblies. The invention improves on known assembly and mounting means between the pressure transducers and the manifold valve. 
     One object of this invention is to provide a compact, weather-tight enclosure for the pressure transducers that will mount to a standard manifold flange bolting arrangement and be sized to align the manifold outlet ports with the pressure transducers&#39; inlet ports. 
     A further object of this invention is that the transducer assembly enclosure be a simple two-piece design composed of a housing and a mounting plate that can be completely potted for use in an explosive atmosphere. 
     Other objects of this invention are that the transducer mounting plate locates, seals, and secures the transducers with respect to the outlet port of the manifold valve, and that the transducer mounting plate minimizes the distance between the main fluid pressure line and the transducers. 
     Further objects of this invention are that the mounting plate be sandwiched between the manifold valve flange and the transducer housing and that it is free to align itself parallel with the flange seals upon tightening the bolts into the transducer housing. 
     It is a further object of this invention to provide a single electrical connector secured to the side of the transducer housing in order to attach a cable to a variety of modular signal processing circuits. Signals from thermistors mounted on the transducer mounting plate also are sent through this connector. Space is provided in the transducer housing for adding internal signal processing circuits in order to convert it to a differential pressure transmitter. 
     The present invention&#39;s compact design and novel assembly along with other features and advantages will be apparent from the following drawings and detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top view of the manifold valve and pressure transducer assembly including a schematic of the manifold valve operation. 
         FIG. 2  is a right side view of  FIG. 1  showing the manifold valve and pressure transducer assembly. 
         FIG. 3  is a front perspective view of the manifold with the transducer assembly fully exploded. 
         FIG. 4  is a rear perspective view of the manifold with the transducer assembly fully exploded. 
         FIG. 5  is a front view of the transducer assembly. 
         FIG. 6  is a right side view of  FIG. 5   
         FIG. 7  is a top view of  FIG. 5  of the transducer assembly, partially in cross section. 
         FIG. 8  is a front perspective view of the pressure transducer assembly. 
     
    
    
     DETAILED DESCRIPTION 
     A preferred embodiment is shown in  FIG. 1  of an improved manifold valve and pressure transducer assembly consisting of a manifold assembly  11  detachably mounted with four bolts  18  to a pressure transducer assembly  10 . Two of said bolts  18  are shown in  FIGS. 1 and 2 , and all four bolts  18  are shown in  FIG. 4 . Attached to the manifold valve body  14  are two isolation valves  15  and  16  that are used to open and close two segregated fluid passageways between two inlet ports  21  of  FIG. 3  and two outlet ports  22  of  FIG. 4 . The inlet ports  21  are shown as threaded connections but can be any convenient attachment to a fluid pipeline. When mounted to additional manifold valves, the inlet ports  21  can be a flange type similar to the flange connection on the two outlet ports  22  of the manifold body  14 . The flange connection has been adopted by the Manufacturers Standardization Society of the Valve and Fitting Industry (MSS) SP-99 as a standard and is considered a direct mounting connection. This connection eliminates the need for pipe fittings and is utilized in the present invention. Upstream from and between isolation valves  15  and  16  is a passageway joining the segregated fluid passageways that can be opened or closed with an optional equalizing valve  17 . Also, intersecting the passageway between the isolation valves  15  and  16  and the outlet ports  22  are two plugged and threaded bleed ports  20  for attaching a means for testing or venting each fluid passageway. Each valve  15 ,  16  and  17  has a handle that is attached to a flow isolation member known in the art as a stem. These items are attached to the manifold body  14  with a member known in the art as a bonnet. Within the manifold body  14 , two mounting holes  19  are provided to secure the assembly to a supporting structure. An operational schematic, showing hydraulic symbols known in the art, depicts the function of the manifold valve assembly  11  shown in  FIG. 1 . 
     The manifold valve assembly  11  in the preferred embodiment typically incorporates an extruded stainless steel manifold body  14 . The manifold body  14  in the preferred embodiment is further enhanced by a secondary cold drawn process. Cold drawing the shape produces a dimensionally accurate part with smooth, flat surfaces without the need for extra machining. The flange connection on the manifold body  14  would be a costly feature to produce without the use of an extruded shape. The stainless steel material is selected for its strength and corrosion-resistant properties and is compatible with a wide range of industrial fluids. Alternate materials can be used depending on the types of fluids and operating pressures used, as is well known to those skilled in the art. Such materials can include plated steel, titanium and nickel based alloys. 
     In operation, the manifold valve assembly  11  is used to control the flow of fluid from two pressurized fluid lines into the two pressure transducers  23  as shown in  FIG. 3 . The procedure for placing the assembly shown in  FIG. 1  into service includes closing all valves  15 ,  16  and  17 , attaching fluid pressure lines to inlet ports  21 , and then slowly opening the isolation valves  15  and  16  to the fully opened position. Keeping the equalization valve  17  closed allows either of the two inlet ports  21  of the manifold to be a high- or low-pressure line, and a differential pressure reading can be taken between the two lines. If bleed valves are connected to the two bleed ports  20 , the lines would be bled at this time. Because the distance to the pressure transducer is short, little air is entrapped in the valve, and in most cases no bleeding is required. To remove the transducer assembly  10  from service, the isolation valves  15  and  16  are closed, and the equalizing valve  17  is opened to normalize the pressure between the segregated fluid pressure lines. A single test port  20  is cracked open to bleed the pressure between the isolation valves  15  and  16  and the two pressure transducers  23 , and then the transducer assembly  10  can be unbolted from the manifold assembly  11 . 
     The manifold valve assembly  11  can be supplied without the optional equalization valve  17 . The equalization valve  17  can be provided for the convenience of bleeding and calibrating the assembly. Because the manifold body  14  provides a test port  20  upstream of each isolation valve  15  and  16 , removal of the transducer assembly  10  without an equalization valve  17  would require that both bleed ports  20  be bled instead of one. Both transducers  23  can be calibrated using one of pressure inlet ports  21  in a manifold assembly  11  that has an equalization valve  17 . Closing an isolation valve  15  or  16  on an unused inlet port  21  and opening the equalization valve  17  accomplishes this. Without an equalization valve  17 , both inlet ports  21  would need to be pressurized. 
     It is important that the equalization valve  17  does not leak during in-service operation. If a leak occurs, the true differential pressure that exists between the high- and low-pressure lines would be compromised, and the reading of the differential pressure would be false. Leaks are more likely to occur as the differential pressure increases. Using a manifold assembly  11  with or without an equalization valve  17  would be a choice between adding convenience and removing a potential leak path. Additionally, the manifold valve assembly  11  can be manufactured without bleed ports  20  on pressurized fluid systems that do not require bleeding or have alternate methods of bleeding. Removing the bleed ports  20  would also remove a potential leak path. 
     The exterior components of the pressure transducer assembly  10  consist of a pressure transducer housing  12  and a pressure transducer mounting plate  26  as shown in  FIGS. 3 and 4 . These two components can be customized to fit a variety of pressure transducers  23  and electrical connectors  13  mounted to their surfaces. The interior components as shown in  FIG. 7  consist of two pressure transducers  23  and two thermistors  38  connected by wiring  41  to the electrical connector  13 . The pressure transducer assembly typically is designed to connect to an external signal processing circuit (not shown) that compares the signal from the two pressure transducers  23  and outputs a signal that represents the difference between the two pressure transducers. This is known in the art as a differential pressure transmitter. To convert the pressure transducer assembly into a differential pressure transmitter, the signal processing circuit is incorporated into the interior space  41  and the electrical connector  13  is changed accordingly. 
     The pressure transducer housing  12  typically is a rigid cast stainless steel structure with a minimum wall thickness of ⅛″. On one side of the transducer housing  12 , a  1 / 4 ″ thick section is cast into the housing for machining a threaded port  29  for attachment of an electrical connector  13  as shown in  FIG. 6  and  FIG. 7 . A recess  28  on the exterior of the threaded port  29  provides a smooth flat sealing surface for an o-ring seal as shown in  FIG. 4 . The pressure transducer housing has a fixed bolt hole pattern  34  (for example, 2⅛″×1⅝″) that matches the standard spacing of the flange bolts  18  on the manifold body  14 . Because the bolting pattern is symmetrical about its centerline, the transducer assembly  10  can be installed with the electrical connector  13  protruding from the left or right side of the manifold assembly  11 . In a preferred embodiment, the pressure transducer housing  12  has a bolting face  42  that does not exceed the size of the flange on the manifold body  14 . In a preferred embodiment, the bolting face is 3⅜″ wide×2 7/16 high. In a preferred embodiment, the bolting face  42  extends beyond the ends of the bolts  18  in order to produce blind threaded holes  34 . Thereafter, the transducer housing  12  can be reduced to 3⅜″ wide×1¼″ high, which is the minimum space needed for the pressure transducers  23  and electrical connector  13 . This saves in material use and minimizes the interior space required if the pressure transducer assembly is potted as described hereinafter. Blind threaded holes also protect the bolt  18  threads from corrosion and potential damage that might occur if they were exposed to the environment. 
     The transducer mounting plate  26  has a smooth flat sealing surface  36  that is designed in a preferred embodiment to extend 1/32″ above the bolting face  42  of the pressure transducer housing  12  and is sized to cover the o-ring grooves  39  on the manifold body  14  as shown in  FIGS. 3 ,  4 ,  6  and  8 . The extension of this surface  36  ensures that it is the only surface to contact the manifold body flange  14  during assembly. The mounting plate  26  thickness is also designed to extend beyond the end of the pressure transducer  23  by a few threads as shown in  FIG. 8 . The extra threads can be utilized for inserting a threaded removal tool in case the mounting plate cannot be easily removed from the transducer housing  12 . The mounting plate  26  has a lip  32  running around its perimeter that mates with a recess  33  on the transducer housing  12  as shown in  FIG. 3 . In a preferred embodiment, the standard spacing between the outlet ports  22  of the manifold assembly  11  is 2⅛″, and the transducer mounting plate  26  provides threaded transducer port holes  35  with the same spacing. A preferred pressure transducer mounting plate  26  has SAE J1926 o-ring boss ports  35  that mate with the pressure transducers  23 . Alternatively, the mounting plate  26  can have NPT threads or any threaded port that mates with the pressure transducers. 
     In a preferred embodiment, the sensing technology in the pressure transducers  23  is a thin-film type. The thin-film pressure sensors are selected for their high accuracy, good zero point stability and small temperature errors. The sensor element comprises a cylindrical stainless steel can with a thin end that takes the form of a diaphragm. On the diaphragm is a Wheatstone bridge that is atomically bonded to the stainless diaphragm by methods known to those skilled in the art. This type of sensor is preferred over diffused silicon semiconductors that use a pressure transmitting fluid between the diaphragm and the sensor because complete media separation is achieved without the use of a pressure transmitting fluid. It is also preferred that the thin-film sensor be welded to the transducer pressure port to avoid additional leak paths that may occur with o-rings or adhesive seals. 
     The pressure transducers&#39;  23  compact size is ideal for mounting in the limited space as shown in  FIG. 7 . In a preferred embodiment, the pressure transducer  23  has a 22 mm hex body shape and is 21 mm long excluding the connection length. If longer transducers are used, the transducer housing  12  would be lengthened accordingly. To ease installation, the pressure transducers  23  have a SAE J1926 straight threaded connection  24 . This standard thread has a groove between the threads  24  and the hex body of pressure transducer  23  for installing o-rings  25 . Alternately, if fluid compatibilities, temperatures, or pressures do not allow for o-ring seals, the thread can be a national tapered pipe thread (NPT) which has a metal to metal seal. 
     Two thermistors  38  are installed in holes  37  next to each pressure transducer port  35  on the pressure transducer mounting plate  26 . The holes  37  are sized according to the size of the thermistors  38 . The thermistors  38  are installed to provide feedback of the thermal conditions surrounding the pressure transducers. In a preferred embodiment, the pressure transducers  23  provide integrated temperature compensation within their normal operating temperatures. This compensation insures a linear response to the pressure. To further increase the accuracy of the compensation and to compensate outside the normal operating temperatures, the signals from the thermistors are used in the signal processing circuits. 
     The electrical connector  13  can be any commercially available connector with a threaded panel mounting feature  30  and a seal  31  feature with the desired amount of leads for connection to the internal components. In a preferred embodiment, the electrical connector comprises 8 leads. The electrical connector of that preferred embodiment is available from Turck Inc. of Minneapolis, Minn. under part number “Eurofast FSD 8-0.5”. 
     The pressure transducer assembly  10  can be mated to and held together by the manifold assembly  11  in several steps. The pressure transducers  23  are screwed into the mounting plate  26  until the o-rings  25  are seated in the o-ring ports  35 . The thermistors  38  are inserted into the pressure transducer mounting plate holes  37  and covered with a silicone RTV sealant. The electrical wire leads  40  on the electrical connector  13  are drawn through the threaded hole  29  and connected to the appropriate leads on the pressure transducers  23  and thermistors  38 . The pressure transducer mounting plate  26  is then inserted into the pressure transducer housing  12 , and the electrical connector  13  is screwed into the pressure transducer housing  12 . Two o-ring seals  27  are inserted into the manifold body flange grooves  39 . The assembled transducer is placed onto the manifold body flange  14  and the bolts  18  are tightened in a criss-cross pattern, i.e., by tightening one bolt  18  partially and then another diagonally across from it, and continuing tightening alternatively until tightening is complete. As noted earlier, the pressure transducer mounting plate  26  extends beyond the transducers&#39; housing so a gap ( 1/32″ in a preferred embodiment) exists between the manifold body flange  14  and the pressure transducer housing  12 . While tightening the bolts, the transducer mounting plate  26  is pulled toward the manifold body  14  flange connection by the small contact area between the edge of the transducer housing recess  33  and the lip  32  of the transducer mounting plate  26 . The transducer mounting plate  26  levels itself parallel with the manifold body  14  flange connection due to the small amount of deformation induced on transducer housing recess  33 . This metal-to-metal contact is all that is required to seal the pressure transducer mounting plate  26  to the pressure transducer housing  12 . The contact pressure also maintains a seal between the transducer mounting plate  26  and the flange o-rings  27 . The transducer mounting plate essentially floats or is sandwiched between these two seals. The internal components of the transducer assembly  10  can be easily accessed for repair or exchanged for alternate components by simply removing it from the manifold assembly  11 . 
     The pressure transducer assembly  10  can also be fully potted. Potting is used to permanently seal the internal components from external environments. A preferred embodiment uses a two-component polyurethane potting compound known to those skilled in the art, such as sold under the trade name of APT028/42/1 by GISMA GmbH. Potting can be accomplished by simply unscrewing the electrical connector  13  from the transducer housing  12  while the transducer assembly is secured to the manifold assembly  11 , twisting the electrical wire leads  40  in a counterclockwise direction, filling the internal space with a potting compound, and re-installing the electrical connector  13  before the potting compound cures. This can be useful when the transducer assembly  10  is used in an explosive gas environment. No gas ingress is possible when the potting compound removes the internal atmosphere. Therefore, any shorts that may occur in the electronics cannot ignite a gas. Once the pressure transducer assembly  10  is potted, the transducer mounting plate  26  is permanently bonded to the pressure transducer housing  12  and the manifold valve assembly  11  and bolts  18  are no longer need to secure them together. The potted pressure transducer assembly can then be supplied as a stand-alone modular component as shown in  FIGS. 5–8 . Alternatively, if a stand-alone transducer assembly  10  is desired without potting compound, the transducer mounting plate  26  could be secured to the transducer housing  12  with a sealant such as a silicone RTV applied to the mounting plate lip  32  prior to assembly. 
     One preferred embodiment of the present invention comprises a method for assembling a pressure monitoring assembly comprising: 
     (A) providing a manifold valve assembly comprising: 
     (1) a rigid manifold body having a first pressure inlet port and a second pressure inlet port, and a first pressure outlet port and a second pressure outlet port, wherein said first pressure inlet port and said first pressure outlet port are in parallel relationship with said second pressure inlet port and said second pressure outlet port, and wherein said outlet ports have a connection to a manifold body flange; 
     (2) a first isolation valve in a fluid passageway between said first pressure inlet port and said first pressure outlet port, wherein said first isolation valve can be adjusted between an open position in which said first pressure inlet port and said first pressure outlet port are in communication through said fluid passageway, and a closed position in which said communication through said fluid passageway is stopped; and 
     (3) a second isolation valve in said fluid passageway between said second pressure inlet port and said second pressure outlet port, wherein said second isolation value can be adjusted between an open position in which said second pressure inlet port and said second pressure outlet port are in communication through said fluid passageway and a closed position in which said communication through said fluid passageway is stopped; 
     (B) providing a pressure transducer assembly comprising: 
     (1) a transducer mounting plate for attaching transducers; 
     (2) a first transducer rigidly secured to a first transducer port in said transducer mounting plate; 
     (3) a second transducer rigidly secured to a second transducer port in said transducer mounting plate in parallel relationship with said first transducer, wherein the spacing between said first transducer and said second transducer equals the outlet port spacing of said rigid manifold valve body; and 
     (4) a pressure transducer housing having sides defining an enclosure which supports said transducer mounting plate and provides threaded holes for attachment to said manifold body flange; 
     (C) inserting said transducer mounting plate into the mating recess of said pressure transducer housing such that said transducer mounting plate extends beyond said pressure transducer housing; and 
     (D) aligning said manifold valve assembly with said pressure transducer assembly such that the bolt holes in the manifold valve body flange align with said threaded holes in said pressure transducer housing; and 
     (E) securing said pressure transducer assembly to said manifold valve assembly in a pressure tight and releasable manner with the use of bolts. 
     Another preferred embodiment of the present invention comprises a pressure monitoring assembly comprising: 
     (A) a manifold valve assembly comprising: 
     (1) a rigid manifold body having a first pressure inlet port and a second pressure inlet port, and a first pressure outlet port and a second pressure outlet port, wherein said first pressure inlet port and said first pressure outlet port are in parallel relationship with said second pressure inlet port and said second pressure outlet port, and wherein said outlet ports have a connection to a manifold body flange; 
     (2) a first isolation valve in a fluid passageway between said first pressure inlet port and said first pressure outlet port, wherein said first isolation valve can be adjusted between an open position in which said first pressure inlet port and said first pressure outlet port are in communication through said fluid passageway, and a closed position in which said communication through said fluid passageway is stopped; and 
     (3) a second isolation valve in said fluid passageway between said second pressure inlet port and said second pressure outlet port, wherein said second isolation valve can be adjusted between an open position in which said second pressure inlet port and said second pressure outlet port are in communication through said fluid passageway and a closed position in which said communication through said fluid passageway is stopped; and 
     (B) a pressure transducer assembly comprising: 
     (1) a pressure transducer mounting plate for attaching transducers; 
     (2) a first pressure transducer rigidly secured to a first transducer port in said pressure transducer mounting plate; 
     (3) a second pressure transducer rigidly secured to a second transducer port in said pressure transducer mounting plate in parallel relationship with said first pressure transducer port, wherein the spacing between said first pressure transducer and said second pressure transducer equals the outlet port spacing of said manifold valve body flange; 
     (4) a pressure transducer housing having sides defining an enclosure which supports said transducer mounting plate and provides threaded holes for attachment to said manifold valve body flange. 
     While specific embodiments are described and shown in the foregoing description and in the accompanying drawings, those skilled in the art will recognize that further modifications made in detail and form are possible without departing from the spirit and scope of the invention.