Abstract:
A novel double block and double bleed stream switching system includes a common stream path for a multitude of fluid streams from, for example, a process pipeline. The common stream path includes a blocking port and a bleed port, and connects to at least one sample shut off. Preferably, the common stream path and sample shut off are shallow channels machined in a multi-layered block, with integrated pistons and ports controlling the flow from each stream and through the stream switching system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to provisional application 60/141,357 filed Jun. 28, 1999. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     It is often very important to know what fluids are flowing through a conduit such as a pipeline. For example, a buyer and seller of gas may agree upon a price for the fluid flowing through a process pipeline based upon the content of the fluid stream. Thus, the fluid content must be measured. Where multiple pipelines are positioned near one another, it may be economical to use a single meter or measurement device to monitor all of the fluid flows. The device used to extract and deliver the fluid to the measurement device is traditionally referred to as a sampling system. 
     FIG. 1 includes a stream sampling system (“sampling system”)  100 . Although only a single pipeline is shown, it is to be understood that multiple pipelines may be present. Sampling system  100  includes a sample point attached to pipeline  110 , an analyzer  130 , and tubing  120  from the sample point to the analyzer  130 . Analyzer  130  may include a stream switching system  140  and gas chromatograph  150 . In operation, fluid flow through a process pipeline  110 . The sample point (preferably a probe) obtains a sample of fluid and delivers it to analyzer  130  via tubing  120 . Analyzer  130  measures the content of the fluid sample and either returns the sample to the pipeline or vents the sample to the ambient environment. 
     One problem with such a layout is the large distance from the analyzer  130  to the pipeline  110 , which creates a large “dead volume” of fluid. Increased dead volume results in undue mixing of consecutive fluid samples. This mixing of fluid samples results in “carry over” between samples for gas chromatograph analysis. Carry over is undesirable because accurate analysis requires that the analysis is representative of the fluid in the process pipeline. Since the volume of transport tubing and stream sampling components must be flushed a minimum of ten times to ensure a representative sample, the “dead volume” results in significant lag time between sample analysis. Therefore, upon a sampling of fluid from the pipeline  110 , the “dead volume” of fluid must be vented or otherwise disposed of before the new sample can be measured at the analyzer  130 . Further, although the magnitude of the “dead volume” could be reduced by placing the analyzer  130  closer to the sample point  110 , regulations and safety concerns mandate a minimum 50 feet distance between them. If placed closer than 50 feet from the pipeline  110 , the analyzer  130  must be contained in an expensive explosion-proof housing. 
     FIG. 2 includes a stream switching system  140  attached to an analyzer oven  250  that is part of gas chromatograph  150 . Three pipes or tubes  210 ,  220 ,  230  attach to switching system  140 , and correspond to first, second and third flow paths. The first pipe or tube  210  connects to a first sample point  212  and carries a first sample of unknown composition from, for example, a process pipeline. Included along “stream  1 ” are pressure regulator  214  and pressure gage  215 , shut-off valve  216 , particulate filter  217 , and a first stream switching valve  218 . Second pipe or tube  220  connects to a second sample point  222  and carries second gas stream of unknown composition. Included along “stream 2” are pressure regulator  224  and pressure gage  225 , shut-off valve  226 , particulate filter  227 , and a second stream switching valve  228 . The third pipe or tube  230  connects to a third sample point  232  and a calibration sample of known composition. Included along the third path are pressure regulator  234  and pressure gage  235 , shut-off valve  236 , particulate filter  237 , and a third switching valve  238 . Third switching valve  238  connects not only to filter  237 , through one port, but also to first and second switching valves  218 ,  228  through another. Yet another port of third switching valve  238  attaches to regulator  240  and flow meter  245 . Flow meter  245  attaches through a relatively long tube to sample shut-off valve  255  housed in analyzer oven  250 . Shut off valve  255  connects to a sample valve in the oven, and then connects to the vent  260 . As can be appreciated, although only two streams of unknown fluids are shown, additional streams could be added by the use of a greater number of flow paths. 
     During operation, a gas chromatograph housed in analyzer oven  250  is calibrated using the calibration sample from sample point  232 . The pressure and flow rate of this stream are maintained by pressure regulator  234 , regulator  240  and flow meter  245 . Because the composition of the calibration sample is known, it may be used to calibrate the gas chromatograph. The calibration sample flows through third switching valve  238 , through the gas chromatograph  150  and out sample vent  260 . If a measurement of the fluid at sample point  222  is desired, the gas along the second pipe is allowed to flow by actuation of second stream switching valve  228 , through first stream switching valve  218 , and through third stream switching valve  238 . The third switching valve  238  is the only valve in the stream switching system that on its own can prevent or block the flow of fluid from all the sample points. Thus, this configuration is referred to as a “single block” stream switching system. One drawback of this design is that the fluid from sample point  222  flows through all of the first, second, and third switching valves prior to arrival at the gas chromatograph, and malfunction of only a single one of these switching valves prevents the measurement of a sample of fluid from stream  2 . 
     If after the above-described measurement of stream  2 , it is desired to measure the fluid from stream  1 , the system must be purged of the previous fluid sample. Purging of the old fluid stream from the system prevents contamination between the streams. Thus, the stream switching system of FIG. 2 would switch from stream  2  to stream  1 . At that time, adequate accuracy by the gas chromatograph has likely been assured if all the other necessary criteria have been met. Many refer to a configuration having a single sample vent as a “single bleed” stream switching system. 
     Thus, a “dead volume” of fluid in a stream switching system is a significant problem. Another problem encountered in a stream switching system is the reliability and maintenance of the system. Because an operator may visit a particular stream switching system only infrequently, the system should be accurate, reliable, as immune to breakdown as possible, and simple to repair when problems do occur. This highly sought after combination of features is not available with current stream switching systems. It would also be desirable to have a multi-use gas sampling system that can be rapidly reconfigured in the field, at a sampling site, or in a manufacturing facility for semi-custom application. 
     Another drawback in many prior systems is their difficulty in analyzing a complex fluids because of limitations in the associated gas chromatographs. It would be desirable if a stream switching system could be developed that could quickly transfer fluid sample to the analyzer. This drawback also reduces the usefulness of a stream sampling system. 
     A stream sampling system is needed that is faster, more reliable, more flexible, and more accurate than previous stream sampling systems. Ideally, such a stream sampling system could reduce the adverse effects of “dead volume.” This ideal stream sampling system would also be less prone to breakdown than previous models, while providing much faster and more accurate measurements. 
     SUMMARY OF THE INVENTION 
     The invention features a stream switching system including a housing forming at least one common stream path. The common stream path of this housing includes an actuatable input port corresponding to a first fluid sample, an actuatable input port corresponding to a second fluid sample, and a first actuatable output port to direct the first and second fluid samples away from the common stream path portion. Each of these actuatable input and output ports is actuatable between an open and a closed position. The stream switching system may also include a first sample shut off portion in communication with the common stream path portion, the first sample shut off portion having a third input port and a second output port. At least one of these ports in the first sample shut off is actuatable. The common stream path may include another output, this being a bleed path. The housing may include one or more pistons, the first actuatable input allowing a flow of the first fluid sample through the first fluid sample input when the first piston is in a first position and not allowing a flow of the first fluid sample through the first fluid sample input when the first piston is in a second position. Associated solenoids may be attached to the housing. Preferably, the housing is made up of a plurality of layers, with each layer separated from an adjacent layer by one or more gas impermeable diaphragms. One or more layers may be easily reconfigured to modify operability. The common stream path portion may be a cavity formed between a pair of these layers. 
     Thus, the present invention comprises a combination of features and advantages which enable it to overcome various problems of prior devices. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention, and by referring to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more detailed description of the preferred embodiment of the present invention, reference will now be made to the accompanying drawings, wherein: 
     FIG. 1 is a prior art sample handling system. 
     FIG. 2 is a prior art stream switching system. 
     FIG. 3 is a schematic of a stream switching system according to an embodiment of the present invention. 
     FIG. 4 is an exploded side view of the embodiment of FIG.  3 . 
     FIG. 5 is a magnified view of FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 3 shows a “double block and double bleed” of one preferred embodiment of a stream switching system according to the invention. The stream switching system  300  includes four streams upstream of a stream handling portion  391 . Four streams include a calibration sample  301 , stream  1   302  corresponding to a first fluid sample, stream  2   303  corresponding to a second fluid sample, and stream  3   304  corresponding to a third fluid sample. It is to be understood that more or fewer ports can be included and that one or more separate stream switch systems could be included. 
     Streams  301 - 304  supply various fluid samples to the sample wetted portion, and connect respectively to actuatable calibration port  311  and actuatable stream ports  312 - 314 . Actuatable ports  315 - 316  and  332 - 333 , as well as ports  331  and  334 , are also part of the sample wetted portion  391 . Each actuatable port may be actuated into either an open or closed state as controlled by eight connected solenoids  350 - 357  (also labeled SV 1 -SV 8 ) which correspond respectively to ports  311 - 316 ,  332 - 333 . When a port is in an open state, fluid may pass freely through the port. When a port is in a closed state, fluid is prevented from flowing through that port. Also shown in FIG. 3 are solenoid pressure line  358  and solenoid vent line  359 , as well as gas path  342  extending from port  315  to ports  333  and  332 . 
     As explained further below, each actuatable stream port  312 - 314 , as well as actuatable calibration port  311 , is positioned in an area  320  that creates a common sample path. Also positioned in the common sample path  320  are an actuatable “blocking” port  315  and an actuatable “bleed” port  316 . In addition, area  321  creates a first sample shut off that contains two “blocking” ports  332  and port  331 . Area  322  creates a second sample shut off that contains two “blocking” ports  333  and port  334 . As shown, ports  332  and  333  are actuatable, while ports  331  and  334  are not. It is to be understood, however, that all of these ports could be actuatable, or that ports  332  and  333  could be actuatable while ports  331  and  334  are not. 
     Two channels, channel  1   340  and channel  2   345 , are output tubing that direct fluid sample away from the stream switching system. As used with reference to the invention, the term tubing is used in a general manner and includes other fluid transportation mediums such as piping. The channels connect to, for example, downstream gas chromatographs including valve, heating, and measurement devices. Each channel thus may be separately analyzed by a gas chromatograph. Each channel can also be used as a flow path to “bleed” the system when switching from sample point to sample point. 
     As can also be appreciated, first and second sample shut offs correspond to first and second channels  340 ,  345 . Consequently each channel is associated with two solenoids  350  and  357 , either one of which can be actuated to prevent the flow of any fluid through the channel. It can be appreciated that the use of a solenoid to prevent the flow of fluid is not absolutely necessary, and any suitable mechanical or electrical gas flow actuation switch may be used. In the illustrated embodiment, the flow of fluid through channel  1  may be prevented by closing either actuatable blocking port  315  or actuatable port  332  in the first sample shut off. Similarly, the flow of fluid through channel  2  may be prevented by closing either actuatable blocking port  315  or the actuatable port  333  in the second sample shut off. Thus, because the flow of fluid may be prevented through a channel at either of two locations, this is a “double block” design. In addition, the system may be bled through sample bleed port  316 . Thus, because the system may be bled either through a channel or through the sample bleed port  316  the embodiment is a “double bleed” design. 
     Referring now to FIG. 4, a side exploded view of the stream switching portion  391  is shown. In this embodiment, the stream switching portion constitutes upper, middle, and lower plates aligned and connected together by dowel pins  470  and torque screws  471 - 475 . The lower plate, referred to as a manifold plate  410 , includes eight actuation ports  411 - 418  connected by tubing to solenoids  350 - 357  (not explicitly shown in FIG.  4 ). The middle plate, also called a piston plate  420 , includes eight locations  421 - 428  designed to receive respective pistons  450 - 457 . Middle plate  420  also includes shallow channels, chambers, or grooves that form areas  320 - 322 , as described with reference to FIG.  3 . The upper plate, referred to as the primary plate  430 , includes screw holes corresponding to the torque screws, as well as three exemplary fluid ports  316 ,  332 , and  331 . Eight pistons  450 - 457  (corresponding to ports  311 - 316 ,  332 - 333 ) as well as a pair of actuating diaphragms  440  lie between manifold plate  410  and middle plate  420 . Sealing diaphragm  465  and cushion diaphragm  460  lie between the primary plate  430  and middle plate  420 . These diaphragms ensure a leak-free fit between each pair of plates and between a piston and its corresponding port. The actuating diaphragms may be made from Kapton of about 3 mm thickness. Similarly, the sealing diaphragms may be made from Teflon coated Kapton. However, as would be appreciated by those of ordinary skill, the invention is not limited solely to these sealing diaphragms. 
     FIG. 5 includes a close-up view of piston  454 , manifold plate  410  with attached solenoid or other appropriate fluid flow activation switch, middle plate  420 , primary plate  430  including passage  530  (corresponding to one of the ports illustrated in FIGS.  3  and  4 ), and diaphragms  440 ,  460 , and  465 . The left portion of FIG. 5 includes a fluid stream  510  such as a calibration gas or fluid sample. The right portion of FIG. 5 includes actuation gas  520 . When a port is open (as shown on the left side of FIG.  5 ), a fluid stream  510  between primary plate  430  and diaphragm  465  exits through passage  530 . Conversely, when a port is closed (as shown on the right), there is no flow of a fluid stream  510 . Instead, an actuation gas  520  is applied by the solenoid  525  against the piston head of piston  454 . The piston  454  is forced upward, with its narrow end abutting the lower end of passage  530  formed in primary plate  430 . Because the relatively large surface area of its head is presented to the actuating fluid  520 , the piston  454  inherently multiplies the force available such that a gas tight seal is formed against the passage  530 . As can be appreciated, a piston is not the only possible actuation member, with suitable devices including solenoids, flapper valves, direct diaphragm valves, and others. 
     Referring to FIGS. 3, a sample from stream  1   302  will be used to illustrate the operation of the device. The pressure in each stream from a pipeline is normally reduced to about 15-25 psi. Consequently, a sample from, for example, a process pipeline travels to channel  320  via port  312  when port  312  is open. Port  312  being open corresponds to piston  454  being in a lower position. As can be understood from FIG.  4  and as is shown in FIG. 5, the piston  454  is forced to this lower position from the fluid pressure applied through stream  1   302  and a lack of actuation pressure applied by solenoid  354 . Gravity may also assist in the piston falling to a lower position. To avoid cross-contamination, when port  312  is open, ports  311 ,  313 , and  314  are, therefore, closed in normal operation. This closure of ports  311 ,  313 , and  314  corresponds to pistons  455 ,  453  and  452  being in an elevated position by activation fluid pressure applied through solenoids  355 ,  353  and  352 . As can consequently be appreciated, the assembly shown in FIG. 4 need not be vertical, but instead can operate from a variety of angles, and the use of terms such as “lower” and “upper” is merely for explanatory purposes. 
     The fluid sample travels through port  312  and along common stream channel  320  to blocking port  315 , which is also open by operation of the associated solenoid. The sample then travels through blocking port  315  and along gas path  342  that includes a “T” at point  343 . This “T” intersection at point  343  splits the sample into two portions. A first portion travels to sample shut off channel  321  via actuatable port  332 . When port  332  is open, the sample travels along the sample shut off channel to port  331 , which then allows this first portion of the sample to flow out channel  1   340  to a first gas chromatograph (not shown). A second portion of the sample travels to sample shut off channel  322  via an open actuatable port  333 . Port  334  allows this second portion of the sample to flow out channel  2   345  to a second gas chromatograph (not shown). As would be appreciated by one of ordinary skill in the art, gas path  342  may be external tubing or may be milled into one or more plates, such as lines permanently drilled into primary plate  430 . 
     The double block and double bleed design of this embodiment has particular advantages. For example, when switching from stream  1  to stream  2 , the system must be bled. First, the sample shut offs are closed to block the flow stream by the closure of sample shut off ports  332  and  333  by actuation of solenoids  350  and  357 . Stream port  312  is also closed to block the flow of pressurized gas from stream  1 . A short time thereafter, sample bleed port  316  in the common stream path is opened while port  315  is still open, allowing the pressurized gas in common stream path  320  to equalize to atmospheric pressure. Simultaneously, inside the associated gas chromatograph  150 , the carrier gas associated with the well-known operation of the chromatographic valve sampling injects an aliquot of sample fluid for analysis by the gas chromatograph. When this occurs, the remaining fluid in the system downstream of the sample shut offs is allowed to equalize to atmospheric pressure. At that time, the sample shut offs can be opened, the sample bleed port  316  closed, and the system purged with the new stream from stream  2 . Because the pressure of the stream switching system has already been lowered to atmospheric pressure, and because stream  2  is under pressure, the sample from stream  2  will quickly flow through the stream switching system. This results in a faster purging with lower volumes of the new sample being necessary. 
     As an additional benefit to this embodiment, the use of two channels allow near-parallel analysis by separate gas chromatographs or detectors within the same gas chromatograph, which can speed the sample analysis of a complex sample having numerous components. For example, an open first sample shut off and closed second sample shut off allows sample to flow through channel  1  for a period of five seconds. An open second sample shut off and closed first shut off could them allow sample to flow through channel  2  for the next five seconds. This results in near-simultaneous analysis by the gas chromatographs or detectors. 
     Moreover, this design is particularly desirable because the advantages recited above are achieved without the expense otherwise necessary (such as for extra valves, etc) to attain a double block and double bleed configuration. Further, the above design can be easily modified for particular situations. For example, additional ports can be freed for use as stream ports if only single blocking or only a single channel is desired. The design can also be modified to be a single bleed design, if desired. The design may also be modified to add or subtract parts as necessary. 
     While preferred embodiments of this invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit or teaching of this invention. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the system and apparatus are possible and are within the scope of the invention. For example, the disclosed stream switching systems may connected to a variety of associated instruments, such as a gas chromatograph, a mass spectrometer, a moisture analyzer, or an infrared analyzer. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims.