DOME-SHAPED PRESSURE VESSEL AND METHOD FOR OPTIMIZING SAME

Abstract: A dome-shaped pressure vessel (36), contained in a pumping segment (10) for incorporation into a fluid delivery system, with an optimal shape for interfacing with a pressure sensing element (200), and which is capable of uniformly distributing pressure across its interfacing structure (130) and being optimally pre-loaded against the pressure sensing element. The pumping segment (10) includes a lateral restraint (150) to inhibit rupture of the unloaded pressure vessel (36) when experiencing high internal pressures.

Description: DOME-SHAPED PRESSURE VESSEL AND METHOD FOR OPTIMIZING SAME BACKGROUND OF THE INVENTION This invention relates generally to fluid delivery systems and, more particularly, to an interface for pressure transfer to a pressure sensor. In many fluid delivery systems, it is desirable to monitor the pressure in tubing functioning to deliver a fluid to a subject. Fluid line pressure may be monitored for a number of reasons. In various medical and industrial applications, it may be important to deliver precise amounts of fluid at predetermined rates. In such cases, fluid line pressure may be monitored to assure that the precise volumes of fluids are delivered at the appropriate rates. Likewise, it may be important to the consistency of a process that fluid be delivered at a specific pressure. Similarly, it may be important to maintain the pressure within a specific range for safety reasons. Where a specific fluid line pressure is expected but the actual pressure varies from the expected value, an occlusion or other problem may be present in the line. By monitoring fluid line pressure and observing unexpected pressure variances, the operator can take the necessary steps to remove the occlusion or remedy the other problem or problems present in the fluid line. Traditional fluid delivery systems take pressure measurements directly from conventional cylindrical tubing used to conduct the parenteral fluid to the patient. Because of the manufacturing variances in making such tubing and the possibility of deformation of the tubing over use resulting in a change in its shape, there is generally a less than optimal interface between fluid line pressure and the sensing element. A poor interface can result in reduced accuracy of the pressure readings. Additionally, the positioning of the pressure sensor in the infusion pump during manufacture can vary due to standard manufacturing procedures and tolerances. This variance in sensor position in the instrument can also contribute to reduced accuracy because the tubing may not be optimally positioned in relation to the sensor when in use. It would be desirable to provide a system w compensates for such manufacturing tolerances to achieve an optimum interface A further consideration is the uniformity in interface characteristics across sensor when the conduit is installed. Specifically, in traditional fluid deli systems, the shape of the pressure transferring element often produces a non-unif stress distribution across itself upon coupling with a pressure sensor, thereby redu the accuracy of the pressure information transferred. Moreover, such traditional systems often lack a pre-load feature where conduit is loaded against the pressure sensor with sufficient force so that the range of possible negative pressures that may be experienced in the conduit ca sensed. Such a pre-load can apply increased stress on the pressure transfer element and may reduce the uniformity of stress across the element. Optimizing interface for such pre-load conditions is also desirable. Another system used for transferring pressure to a sensor is a diaphr contained on a rigid component that is incorporated into conventional tub Pressure levels in an infusion conduit can reach relatively high levels and diaphragm must be formed so that such pressures do not cause it to rupture. W placed in contact with a pressure sensor, the sensor provides support for diaphragm thus decreasing the chances of rupturing. However, cases may o where the diaphragm is in the unloaded or "free" state in which it is not in con with the sensor. The diaphragm is subject to increased risk of rupture w subjected to large internal pressures. Increasing the thickness or stiffness of the diaphragm may reduce possibility of rupture in the free configuration but may also reduce its sensitivit internal pressures, thus decreasing the accuracy of pressure readings. It would desirable to increase the resistance of a diaphragm to rupture while not lowerin interface characteristics with the sensor so that accurate pressure readings may taken. Accordingly, there remains a need for a segment, to be used in a fluid deliv system that has a pressure transferring element with a shape optimized for unifor distributing pressure created stress across its face, an optimal interface with a sensing element, and an optimal pre-load displacement upon coupling with a sensing element. There also is a need for a pressure transferring element that is capable of receiving the relatively high internal pressures without rupture or bulge while at the same time, able to transfer internal pressures to the sensor accurately. The present invention fulfills those needs. SUMMARY OF THE INVENTION Briefly, and in general terms, the invention provides a new and improved pressure transferring element for a fluid pumping segment for fluid flow that cooperates with a fluid delivery system. The segment has a dome-shaped pressure vessel contoured to optimize the interface with a sensing element, that uniformly distributes pressure across its interfacing structure, that facilitates an optimal pre-load displacement upon coupling with a sensing element, that allows negative internal pressure to be sensed with the dome-shaped pressure vessel/sensor interface to remain intact, and that isolates the center region of the dome from the effects of variations in pre-load displacement caused by manufacturing deviations.. In a fluid pumping segment having an elastomeric membrane, a pressure vessel is formed having a hollow crown portion and a membrane peripheral portion extending away from a bottom of the crown. A top of the crown includes an outer rim region defined by the top of a cylindrical sidewall and a flexible central dome that closes the top end of the sidewall. The outer rim serves as an stiff isolation ring to prevent external factors from influencing center dome region stresses. The membrane peripheral region functions as a flat washer spring providing restraint stiffness and allowing the central dome region to be flattened and the outer rim to be properly pre-loaded against a sensing element. A lateral restraint is included to constrain the vessel in the lateral direction. In one aspect, the lateral restraint is formed in a stationary structure that retains the membrane peripheral portion. In another aspect, the lateral restraint is disposed around the cylindrical sidewall of the dome. The present invention also includes a method for optimizing the conto the top region of the dome so that it uniformly distributes stress across its face, a method to optimize the pre-load displacement of the pressure vessel so that a pr interface exists for all expected internal fluid pressure conditions including neg pressure. Briefly, the method for optimization of the top contour involves deri an initial top contour and applying uniform stresses to the rim and center d region respectively. When the initial center dome region contour is substant flattened in response to the applied uniform stresses, the initial contour is dee optimized because, when applied to and substantially flattened against a pres sensor, it functions to present the sensor with uniform stresses and, therefore, a accurate transfer of fluid pressure information. In another aspect, this con resulting in uniform stresses provides increased immunity against positioning er of either the sensor or the vessel in relation to each other resulting f manufacturing deviations. Even if positioned outside the design position, accu pressure information can still be communicated between the two because of uniformity of stresses provided by the center dome region contour. Regarding the method of optimizing pre-load displacement, it gener involves selecting an initial pre-load displacement of the rim and center dome reg under zero internal pressure conditions. The stresses existing in the rim and ce dome regions are then determined for this initial pre-load displacement. Next expression is developed which represents the relationship between the stresses in rim and center dome regions for all internal pressures and the stresses in the rim center dome regions for the initial pre-load displacement. Finally, the stresses in rim and center dome regions are checked for sufficiency for the worst case inte pressure levels including negative pressures and if deemed sufficient, the initial load displacement of the rim and center dome regions is deemed optimal. These and other features and advantages of the invention will become appa from the following more detailed description taken in conjunction with accompanying drawings of illustrative embodiments. BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a perspective view of the preferred embodiment of the present invention, illustrating an upper side of an engineered pumping segment; FIG. 2 is an exploded view of the engineered pumping segment of FIG. 1 showing the base, the membrane, the cover, and the slider from the lower side view perspective; FIG. 3 is a partially assembled view of the engineered pumping segment shown in FIG. 1 showing the lower side and showing the slider distal to the segment; FIG. 4 is an exploded view of the engineered pumping segment of FIG. 1 from the upper side view perspective and without the slider; FIG. 5 is an enlarged cross-sectional view taken along lines 5-5 of FIG. 1; FIG. 6 is an enlarged fragmentary view of the fluid regulation portion of the base of the exploded engineered pumping segment shown in FIG. 2; FIG. 7 is an enlarged fragmentary cross-sectional view of the flow regulation area of the segment showing the slider with ball in a proximal position; FIG. 8 is a side elevational view of the engineered pumping segment of FIG. 1, shown in partial cross-section; FIG. 9 is an enlarged fragmentary view of the cross-sectional view of FIG. 7; FIG. 10 is a partial cross-sectional view of the air ejection portion of the pumping segment; FIG. 11 is a top view of the air ejection apparatus of FIG. 10; FIG. 12 is a perspective view of the engineered pumping segment of FIG. 1, shown being placed into an infusion system; FIG. 13 is an enlarged fragmentary view of FIG. 12, showing the engineered pumping segment and the corresponding portion of the infusion system; FIG. 14 is an enlarged cross-sectional view taken along line 14-14 of FIG. 1; FIG. 15 is the cross-sectional view of FIG. 14, showing the engineered pumping segment coupled to a pressure sensor; FIG. 16 is schematic cross-sectional representation of the pressure ve portion of the engineered pumping segment of FIGS. 14 and 15, showing press applied thereto; and FIG. 17 is a side view of a pumping mechanism peristaltic finger usable the membrane and groove shown in FIG. 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As is shown in the drawings, which are provided for purposes of illustrat and not by way of limitation, the invention is embodied in an engineered pump segment that, in a single device, facilitates effective and accurate pumping of fluid a pumping system, regulates fluid flow, and provides an effective interface for sens fluid pressure. Referring now to the drawings, and more particularly to FIG. 1, ther shown an engineered pumping segment 10. Generally, the engineered pump segment 10 is a device that is to be releasably mounted to a pumping system (sho in FIG. 10) which functions to control the transfer of fluid from a reservoir t delivery site. The pumping system delivers fluid from the reservoir to a proximal 15 of the pumping segment 10 by way of conventional tubing. The fluid pa through the pumping segment 10 and exits a distal end 17 of the pumping segm 10. Attached to the distal end 17 is additional conventional tubing of the pump system that transports the fluid away from the pumping segment 10 and towards delivery site. The engineered pumping segment 10 includes three basic components. A best seen in FIG. 5, which is a cross-sectional view, the preferred embodiment of engineered pumping segment 10 includes an elastomeric membrane 12 that sandwiched between a base 14 and a cover 16. When assembled, the cover 1 either level with or below the height of the base 14. As shown in FIG. 5, the co is level with the base flange. Generally, the path that fluid takes through pumping segment 10 is defined by the membrane 12 and the base 14. The cover generally functions to sealingly retain the membrane 14 against the base 14 as as against itself. The configurations of the membrane 12, base 14 and cover 16 will be described in detail below. The pumping segment 10 performs three different functions. Near the proximal end 15 of the engineered pumping segment 10, there is structure functioning to regulate flow rates through the pumping segment 10. In an intermediate section 13 of the pumping segment 10, there is structure adapted to cooperate with the pumping system to peristaltically pump fluids through the pumping segment 10. Near its distal end 17, the pumping segment 10 has structure adapted to cooperate with the pumping system to sense the pressure of fluid passing through the pumping segment 10. Fluid flow regulation is generally accomplished in the pumping segment 10 through the cooperation of the use of a slider 18. The configuration of the slider 18 will be described in detail below. Near the proximal end 15 of the pumping segment 10, the cover 16 provides access to the elastomeric membrane 12. By way of the access provided by the cover 16, the slider 18 functions to depress the membrane 12 against the fluid flow path, whereby the cross-sectional area through which fluid may flow is altered. As the slider 18 travels along the base 14 it depresses the membrane 12 sealingly against the base 14 thus occluding flow except in the variable cross- section groove 60. By altering the fluid flow path and by doing so to varying degrees, the slider 18 regulates the flow of fluid through the pumping segment 10. Turning now to the peristaltic pumping of fluids through the pumping segment 10, peristaltic pumping is facilitated primarily through the cooperation of the membrane 12 and base 14 of the pumping segment 10. At the intermediate section 13 of the pumping segment 10, the cover 16 provides further access to the membrane 12, through which a peristaltic pumping mechanism (not shown) of the pumping system operates. Generally, the peristaltic pumping mechanism operates to sequentially alternatively depress adjacent portions of the membrane 12 against the fluid flow path against the groove in the base 14 to thereby advance fluid through the pumping segment 10. Pressure sensing of fluids flowing through the pumping segment 10 facilitated primarily through the cooperation of the membrane 12 and cover 16 of pumping segment 10. Near the distal end 17 of the pumping segment 10, the co 16 again provides access to the membrane 12. In this area, the membrane 1 formed into a generally hollow and flexible closed cylinder having a crown, part which includes a dome-shaped section. For convenience in description, the vessel is referred to as a dome-shaped pressure vessel 36. The vessel acts as a press diaphragm for transferring pressure information regarding the fluid flowing thro the pumping segment 10. Now that the basic functions and components of the engineered pump segment 10 have been identified, a more detailed description of the structure of pumping segment 10 will follow. The overall configuration of the pumping segm 10 is first described followed by basic descriptions of the overall configurations of components of the pumping segment 10. Thereafter, the details of the compone and their functions are individually addressed as well as their cooperation w associated structure of the pumping system to which the pumping segment 10 releasably mounted. In the preferred embodiment, as shown in FIG. 1, the engineered pump segment 10 is elongate in shape with longitudinal and lateral axes 111, 113. length of the elongate pumping segment 10 is greater than both its width and height and the width of the pumping segment 10 is greater than its height. The overall length of the pumping segment 10 shown was selected accordance with anthropometric studies to be approximately equal to the average (fifty percentile) adult female hand width so that the segment 10 can pressed with some fingers to the palm and the thumb can manipulate the slider Thus, one-handed operation of the pumping segment 10 is greatly facilitated. The overall outer configuration of the pumping segment 10, when viewed that its entire width can be seen, generally approximates an elongated oval with o of its ends being truncated. The proximal end 15 of the pumping segment includes the truncated portion of the elongated oval and the distal end 17 includes the rounded end of the elongated oval. Extending from the proximal end 15 and parallel to the longitudinal axis 111 of the elongate pumping segment 10 is a cylindrical tubing fitting 44 that is adapted to attach to conventional tubing of the pumping system and that defines an entrance for the passage of fluid into the pumping segment 10. Similarly, extending from the distal end 17 and parallel to the longitudinal axis 111 of the pumping segment 10 is another cylindrical tubing fitting 45 that also is adapted to attach to conventional tubing of a pumping system and that defines an exit port for fluid passing through the pumping segment 10. The overall configurations of the base 14, cover 16, membrane 12 and slider 18 are described next. Referring now to FIG. 2, which is an exploded view of the pumping segment 10, the base 14 generally defines the overall truncated oval-shaped configuration of the pumping segment 10 as described above and includes the cylindrical tubing fittings 44, 45. The base 14 is formed of a bottom portion 17 and a sidewall 19 which extends substantially around a perimeter 63 of the bottom portion 17. The sidewall 19 and bottom portion 17 define an interior region 42 of the base 14. A groove 21 formed in the bottom portion 17 of the base 14 and parallel to the longitudinal axis 111 of the pumping segment 10 defines a lower portion of a channel 22 (see FIG. 5) for fluid flow. As will be addressed in more detail later, the channel 22 communicates with the tubing fittings 44, 45. Referring now to FIG. 4, which is an upside down exploded view of the pumping segment 10 without the slider 18, the overall configuration of the cover 16 is described. The cover 16 has a generally matching (relative to the base 14) truncated oval-shaped configuration, with a generally planar top portion 47 and a sidewall 49 extending therefrom in a substantially perpendicular manner substantially around a perimeter 65 thereof to define an interior region 52 within the cover 16. At a proximal end 50 of the cover 16, rather than following the truncated oval-shaped perimeter 65 of the cover 16, the sidewall 49 forms a semi-circular shape that mimics a semi-circular shape of the sidewall 49 extending from a distal end 51 of the cover 16. As such, the sidewall 49 has an elongate oval-shaped configuration that is truncated. The overall configuration of the cover 16 is slightly smaller than that of base 14 and is adapted so that the perimeter 65 and sidewall 49 of the cover 16 sn fit within the sidewall 19 of the base 14 when the cover 16 is placed within the 14 with the interior region 52 of the cover 16 facing the interior region 42 of the 14. Further, the sidewall 49 of the cover 16 is adapted to fit around a perimete of the membrane 12. The overall configuration of the membrane 12 is depicted in FIG. 2. perimeter 28 of the membrane 12 has a generally elongated and oval-shaped ove configuration that is adapted to sealingly seat within the interior region 42 of the 14 and the interior region 52 of the cover. The oval-shaped membrane 12 incl a proximal rounded terminal end 24, a distal rounded terminal end 25 and a cen planar region 23. A concavity 33 is included adjacent the proximal end 24. In embodiment shown, it is oval in overall shape and the membrane is thinner, altho the underside of the membrane remains planar. The ball 20 of the slider, as discu below in detail, fits into the concavity 33 at the full flow position. The redu amount of membrane material at this position reduces the chances of the depressing the membrane into the groove and then reducing the amount of fl The other details of its configuration, including those relative to the hollow flexible dome-shaped pressure vessel 36, will be described in more detail below. As can be noted, the membrane is flexible and a change in head height cause it to move away from or closer to the conduit 22 which results in a chang the fill volume of the conduit. The distance across the membrane, width and de of the groove were seleαed so that only a four percent change of the fill volum the pumping segment would occur if the fluid reservoir were moved to result i pressure change of 30 inches of water. In one embodiment, this resulted in a cha of 2.4μl. Also, in the preferred embodiment, the engineered pumping segment includes the slider 18. The slider 18 is adapted to fit around and travel alon portion of the pumping segment 10 near its proximal end 15. The motion of the slider 18 along the pumping segment 10 is parallel to the longitudinal axis 111. As shown in FIG. 2, the overall configuration of an embodiment of the slider 18 generally approximates a hollow rectangular sleeve, and since it fits around the pumping segment 10, the slider 18 also has a width that is greater than its height. Further, the length of the slider 18 is less than its width and is similar in magnitude to its height. The slider 18 is adapted to receive a ball 20. Additional details of the individual components of the pumping segment 10 will now be discussed. The membrane 12 may be produced by liquid injection molding or by other methods and may comprise an elastomeric material, such as silicone GE 6030 made by; General Electric, having sufficient strength and resiliency so that it may repeatedly perform desired functions efficiently and with accuracy over a relatively long period of time. Referring to FIG. 2, the upper surface 26 of the membrane 12 is best seen. The upper surface 26 includes a central planar region 23. Extending the entire perimeter 28 of the upper surface 26 and projecting from the central planar region 23 of the membrane 12, is an upper sidewall 29. The upper sidewall 29 is configured so that it forms a first sealing relationship with the cover 16. Located near the distal terminal end 25 of the membrane 12 and projecting from its central planar region 23, is the flexible dome-shaped pressure vessel 36 which functions as the pressure diaphragm. The dome-shaped pressure vessel 36 has a cylindrical sidewall 126 and extends a predetermined distance from the upper surface 26 of the membrane 12 so as to create an interface that may be preloaded against and in direct contact with a pressure sensor (shown in FIG. 12 and discussed further below). Referring now to FIG. 4, a lower surface 27 of the membrane 12 is shown. The lower surface 27 also includes a central planar region 23. Extending the entire perimeter 28 of the membrane 12 and projecting from the central planar region 23 of the lower surface 27 is a lower sidewall 30. The lower sidewall 30 is configured so that it forms a second sealing relationship with the base 14. Formed at the terminal ends 24, 25 of the membrane 12 and in the lower sidewall 30 are semi- circular archways 32 which engage associated structure of the base 14 defining entrance and exit to the channel 22 for fluid flow. The lower surface 27 of membrane 12 also includes a cavity 37 that forms the underside of the hollow flexible dome-shaped vessel 36. Turning again to FIG. 2, additional details of the base 14 are described. interior 42 of the base 14 includes structure that is configured to receive and m with the sidewall 49 of the cover 16 and the lower sidewall 30 of the membrane Accordingly, formed in the interior 42 of the base 14 is an oval membrane recess adapted to receive and seal with the oval lower sidewall 30 of the membrane Further, an oval cover recess 48 adapted to receive the oval sidewall 49 of the co 16 is formed in the interior 42 of the base 14. The membrane and cover recesses 48, therefore, form concentric oval-like troughs in the base 14, with the membr recess 46 residing inwardly of the cover recess 48. Formed near each end 40, 41 of the base 14 and in either end of the oval co recess 48, are elongate rounded projections 31 lying in parallel with a longitudi axis 115 of the base 14. The rounded projections 31 each have an internal bore (only the bore in the proximal rounded projection 31 can be seen in the drawin and each are in fluid communication with an associated tubing fitting 44, 45 thereby provide inlets and outlets to the interior 42 of the base 14. Further, near distal end 41 of the base 14 and in the groove 21, the interior 42 of the base 14 formed therein an upwardly extending protrusion which acts as a bubble ejector The outlet fitting 45 has a length selected to result in less curvature of attached fluid line near the pumping segment 10. As shown in FIG. 12, the pump segment 10 is being installed in a pump 300. The outlet fitting 45 has a flexible fl line tubing 334 that is directed towards an air-in-line sensor system 336 and is me to be captured by the air-in-line system as it rotates into position. Because the out fitting 45 is relatively rigid, the fluid tubing 334 does not begin any curl it acquire from packaging until some point downstream from its point of connecti with the outlet fitting 45. The length of the outlet fitting is selected to move t curl point as far downstream as possible so that the tubing is less likely to curl severely before the air-in-line sensor. Referring to FIGS. 2 and 6, near a proximal end 40 of the base 14, the groove 21 has an elevated section that operates as a fluid control region 59. Formed in the fluid control region 59 and extending parallel to a longitudinal axis 115 of the base 14 is another groove 60 having a variable depth and/or width (variable cross-section size) and a cross-sectional area ranging from zero 310 to some desired depth 312 suitable for allowing a maximum desired flow rate. The base 14 also includes a flange 62 extending substantially perpendicularly from the top of the sidewall 19 of the base 14 and away from the interior 42 of the base 14. The flange 62 is formed about the distal end 41 and on either side of the midsection of the base 14 and terminates at parallel longitudinal locations on either side of the base 14 distal to the longitudinal position of the fluid control region 59. Further, rectangular notches 63 are cut into the flange 62 at parallel longitudinal locations along the base 14 near the distal end 41 of the base 14. As shown in FIG. 4, formed on an exterior 117 of the base 14 are two click stops 80, which are two upwardly extending low profile projections. The click stops are spaced laterally apart at the same longitudinal position along the base 14 and are located near where the flange 62 terminates. Corresponding click stop upwardly extending projections 314 are also located on the slider (FIG. 2). The interaαion of these click stops 80 and 314 provides an affirmative sensory indication to an operator of the slider 18 attaining a predetermined position, in this case, the flow stop position. An audible sound is also generated. Continuing to refer to FIG. 4, the details of the cover 16 are next described. The cover 16 is elongate and has proximal and distal terminal ends 50,51 and a generally concave interior 52 and a generally convex exterior 53. Formed in the sidewall 49 at each terminal end 50,51 of the cover 16 are cover recesses 54 which approximate semi-circles and which are adapted to receive the elongate rounded projections 31 of the base 14. Within the interior 52 of the cover 16 is an oval- shaped membrane indentation 55 configured to receive and mate with the genera oval shaped upper sidewall 29 of the membrane 12. In the preferred embodiment, the cover 16 also has apertures which, when pumping segment 10 is in its assembled form, provide access to various portions the membrane 12. A circular aperture 56 is formed near the distal terminal end and substantially in the center of the width of the cover 16. Surrounding aperture 56 is a projection 152 that assists in centering the membrane during assem of the pumping segment 10. The projeαion 152 proceeds completely around aperture 56 and interaαs with the pressure vessel 36 portion of the membrane center it in the aperture 56 during assembly of the segment 10. Without projeαion, the vessel may tend to move longitudinally during manufacture and located off center when assembled. Formed in an intermediate portion of the cover and also substantially cente in its width, is an elongate intermediate aperture 57. Finally, an elongate fl control aperture 58 is centered in the cover 16 near the proximal terminal end 50 the cover 16. Referring now to FIG. 2, a channel 338 is formed between the pumpi section 340 of the base and the pressure vessel 36 section. This channel 338 dimensions selected to lessen the transmission of pumping noise from the pumpi section 340 to the pressure sensing section 36. In the embodiment shown, the len of the channel 338 was selected to be three times its width. It was found that th dimensions decreased the amount of pumping noise reaching a sensor coupled to pressure vessel 36. The base and cover were, in one embodiment, made from polymer acry such as acrylic cyro XT250 from Cyro Industries, 100 Valley Road, Mt. Arlingt NJ. Next, in referring to FIG. 2, additional details of the slider 18 are describ As mentioned above, in the preferred embodiment, the slider 18 is adapted to rece a ball 20. In one embodiment, the ball was formed of stainless steel and the sli was formed of acetal polymer such as BASF W2320 from BASF, 100 Cherry Road, Parsippany, NJ. The slider 18 is a generally hollow structure having a generally reαangular cross-section and a sufficient length to facilitate manipulation by hand. The slider 18 has a first long side 68 and a second long side 69 and a pair of short sides 61 completing the generally reαangular cross-seαional shape. The exterior of the slider is smooth without sharp edges so that it is less likely to catch on anything in its environment of use (such as operator clothing) and be moved inadvertently. Formed in substantially the center of the first long side 68 is a groove 74. The configuration of the groove 74 resembles a palm view of a right hand without fingers, but including a thumb pointing towards one of the short sides 61 and including a portion of what may be described as a wrist extending therefrom. Formed substantially in the center of the first long side 68 and within the groove 74, is a socket 71 which is adapted to receive and retain the ball 20. The diameter of the socket 71 is less than the diameter of the ball 20; hence, once the ball has been pressed through the socket 71, the socket retains the ball between it and the membrane. Further, formed into the short sides 61 of the slider 18 and extending the length of the slider 18 and substantially perpendicularly therefrom, are rounded low- profile projections or ears 82. As best seen in FIG. 3, the center portion of the second long side 69 includes a ramped projection 79 extending therefrom at an angle to the length of the slider 18. The ramped projeαion 79 has a concave shape well suited for receiving an operator's thumb. Formed in the concave-shaped ramped projeαion 79 are a plurality of parallel ridges 72 extending laterally across the ramped projeαion 79, which funαion to aid the operator in gripping the slider 18. As seen in FIGS. 1, 2, 3, 7, and 13, the slider includes a strain relief notch 316 that tends to inhibit the socket 71 and slider 18 from breaking during assembly of the ball 20 through the socket. In a further feature shown in FIG. 7, the socket 71 includes a counter-bore 318 at its upper surface. This counter-bore facilitates assembly of the ball through the socket in that the ball must pass through less material now to reach its ultimate destination. The remaining slider material between the ball and the counter-bore is sufficient to withstand the pressures that ma experienced during operation Now that the details of the individual components of the pumping seg 10 have been described, their interaαion and assembly will be addressed. Refer to FIG. 2, to assemble the pumping segment 10, the membrane 12 is placed wi the base 14 with the flexible dome-shaped pressure vessel 36 pointing away from interior 42 of the base 14 and overlaying the bubble ejector 64 of the base 14. N the cover 16 is placed within the base 14 so that the circular aperture 56 of the c 16 fits around the dome-shaped pressure vessel and so that the interior 52 of the c 16 faces the interior 42 of the base 14. As mentioned above, the projection 152 as in centering the membrane in the cover. Further, as may be appreciated from FIG. 3, once the membrane 1 sandwiched between the base 14 and cover 16, the slider 18 may be placed about base 14 and cover 16. The slider 18 is oriented so that its second long sid overlays the exterior 117 of the base 14 and so that the most elevated portion of ramped projeαion 79 is positioned closest to the proximal end 40 of the pum segment 10. Finally, to complete the assembly of the pumping segment 10, the 20 is pressed through the counter-bore 318 and the socket 71 to now be held in p between the socket 71 and the membrane. Because the ball is now between the sl and the membrane, it retains the slider on the assembled base when the slide moved towards the proximal end of the segment 10 because the ball will encou the end wall 81 of the cover and be prevented from moving further. As shown in FIG. 5, in the preferred embodiment, the membrane 12 and 14 form a sealed channel 22 for fluid flow. As stated above, the base 14 includ groove 21 extending longitudinally along and substantially the length of the base When the pumping segment 10 is assembled, the membrane 12 is placed between base 14 and cover 16 with its upper and lower sidewalls 29, 30 sealingly seated wit the membrane recess 46 of the base 14 and the membrane indentation 55 of the c 16 respeαively, and with its lower surface 27 overlaying the groove 21. When pumping segment 10 is so assembled, space for fluid flow exists between the lo surface 27 of the membrane 12 and the groove 21 of the base 14 in the form a sealed channel 22. (It is to be noted that all further references to the structure of the pumping segment 10 and the components thereof, will be of an assembled pumping segment 10.) That channel is sealed by means of the configuration of the membrane edge and shapes of the base and cover that receive that membrane edge. Because of that configuration, a self-energizing seal is formed. Referring now to FIGS. 5, 14 and 15, the edge 28 of the membrane 12 is shown. In FIGS. 14 and 15, that edge in its relaxed configuration can be seen. In FIG. 5, the edge is compressed into its operational shape between the base 14 and cover 16. Although FIGS. 14 and 15 show the membrane assembled with the cover and base, the edge 28 is the membrane is not shown compressed for clarity of illustration only. The base 14 includes a raised seal member 320 having a slanted surface 322 for engaging the edge 28 of the membrane 12. The point of the seal member 320 interacting with the membrane provides a first seal to fluid in the groove 22. Should fluid pressure overcome the first seal, it would attempt to migrate between the slanted surface 322 and the membrane edge 28. However, the slanted surface 322 receives the force of the compressed edge 28 against it and operates as an O-ring seal prohibiting further leakage. For this reason, the seal is commonly referred to as a self-energizing seal. The path for fluid flow through the assembled pumping segment 10 will be described next. Referring to FIG. 8, the tubing fitting 44 formed at the proximal end 40 of the pumping segment 10 defines the entrance to the pumping segment 10. Fluid entering the tubing fitting 44 first encounters the portion of the channel 22 defined by the fluid control region 59 formed in the groove 21 and the portion of the membrane 12 overlaying the control region 59. From there, fluid advances through the intermediate section 13 of the pumping segment 10. Next, the interaαion of the slider 18 with the other components of the pumping segment will be described. As previously stated, the slider 18 is adapted to longitudinally travel along the pumping segment 10 near its proximal end 40. Referring now also to FIG. 9, the longitudinal motion of the slider 18 toward the distal end 41 of the pumping segment 10 is limited by terminating ends 119 o flange 62 of the base 14. Also, the slider 18 causes the click stops 80 and 314 (F 2 and 4) to engage as the slider 18 approaches the terminating ends 119 of the fl 62, causing an audible "clicking" and an identifiable feel, which indicate that slider has been moved to the middle of the pumping segment 10 or to its most d position, i.e., toward the distal end 41 of the pumping segment 10. As is shown in FIGS. 7 and 9, the ball 20 of the slider 18 is adapted to tr within the fluid regulation aperture 58 of the cover 16 and functions to depress membrane 12 sealingly against the control region 59 of the base 14, thus preven flow except through the variable cross-seαion groove 60 (see FIG. 6). Because regulation seαion 59 has the approximate shape of the ball 20 and memb compressed by the ball, fluid will not flow through the seαion except through variable cross-seαion groove 60. Thus, moving the ball along the regulation se 59 will expose more or less area of the groove thereby controlling the flow. S movement funαions to control the rate of fluid flow through the pumping seg 10. When the slider 18 is placed in its most distal position, the ball 20 depresses membrane 12 against the portion of the regulation seαion 324 that has no gr thus completely stopping flow through the pumping segment 10. It is also t noted that, in addition to the ends 119 of the flange 62 limiting the travel of slider 18 in the distal direαion, as the slider 18 is moved within the fluid regula aperture 58, the longitudinal motion of the slider 18 along the pumping segmen in the proximal direction is also limited by the engagement of the ball 20 longitudinally spaced apart end walls 81 and 83 of the fluid regulation aperture In another embodiment (not shown), the slider 18 has structure w substitutes for the ball 20 and funαions to depress the membrane 12 against the 14. For example, it is contemplated that the slider 18 may embody a proje having a predetermined width and extending a predetermined distance from underside of the first side of the slider 18 so that a sufficient portion of membrane 12 interacts with the control region 59 of the base to thereby control flow. As shown in FIGS. 8, 10 and 11, fluid encounters a runnel 120 which is that portion of the channel 22 formed by the bubble ejeαor 64 projeαing from the base 14 and the dome-shaped pressure vessel 36 formed in the membrane 12. The dome- shaped pressure vessel 36 is mounted so that it receives the fluid of the conduit but is not in the direα flow path of that fluid. Therefore, air bubbles in the conduit may colleα in the pressure vessel due to the lack of flow to wash them out. The air bubble ejeαion system redirects the flow of the fluid through the conduit so that it proceeds through the vessel 36 to wash out any air bubbles that may enter the vessel. Generally speaking, the bubble ejeαor 64 cooperates with the interior 37 of the pressure vessel 36 to eliminate dead space and to inhibit the produαion of bubbles in fluid that is caused to flow through the runnel 120. Thus, the accumulation of compressible air bubbles in the pressure sensing vessel is inhibited and accuracy is improved. Because air is compressible, the accuracy of a pressure reading taken from the vessel having air bubbles within it may be compromised. The fluid passes through the runnel 120 and then exits the pumping segment 10 through the tubing fitting 45 formed at the distal end 41 of the base 14. The vane 64 is positioned in the conduit under the vessel 36 to guide the flow of the fluid from the conduit into the vessel so that the vessel now lies directly in the flow path of fluid through the conduit. The redireαed fluid washes the vessel 36 of any air bubbles that may have accumulated there. The vane is shaped so that the redirected fluid from the conduit reaches all parts of the vessel to remove any bubbles. In the embodiments shown, the vane 64 has the appearance of an hour glass with the edges rounded. It has been found that this shape causes fluid flowing at the vane 64 to be direαed upward into the interior 37 of the vessel where it reaches all parts of the vessel before flowing down the distal side of the vane and out the exit fitting 45. In the embodiment shown, the vane is disposed at a right angle to the conduit 22 and has a size that varies according to its height so that the flow path across the vane and through the interior 37 of the vessel 36 has an approximately constant cross- seαional area. The height is seleαed to result in the approximately constant cross seαion flow area through the runnel 120 when the dome 36 is deformed inwa during standard preload installation in a pressure sensor. Such deformation is sh in FIG. 15 and is described in detail below. As best observed to FIG. 10, the vane 64 of the bubble ejeαor is aligned the central axis of the vessel 36. Furthermore, the vane 64 is shaped to provide gradual and non-abrupt fluid flow transitions while still maintaining a uniform passage area 120. The flow area transitions are defined by substantially smo curved surfaces extending over approximately ninety degrees across the direαio fluid flow. Fillets have been added in order to smooth out the angle of curvature to provide for the gradual and non-abrupt transitions. Gradual transitions provided to result in more controlled fluid flow and to reduce the amoun turbulence generated. Referring particularly to FIG. 11, the vane 64 does not completely span width of the conduit 22 and some flow will occur around the vane. Howeve sufficient amount of flow is direαed upward into the interior 37 of the vessel to out bubbles. In a preferred embodiment, the bubble ejeαor 64 is formed of the s material and as an integral part of the engineered pumping segment base However, it will be appreciated by those skilled in the art that other materials methods of manufacture may be used. Referring now to FIG. 14, attention is direαed toward the cooperation of dome-shaped pressure vessel 36 of the membrane 12 and the cover 16. In preferred embodiment of the pumping segment 10, the cover 16 includes struct functioning as a lateral restraint 150. The lateral restraint 150 surrounds and supp the dome-shaped pressure vessel 36 when there are internal pressures existing in pressure vessel 36 and the pressure vessel 36 is not coupled to a sensor. When coupled to the pressure sensor, the sensor provides substantial struct support to the pressure dome giving it the capability to withstand very high inte fluid pressures. However, when the pumping segment is uncoupled from the pu the pressure dome does not have the structural support of the sensor. The dom this "free" state must carry the entire dome internal pressure loading. The dome must maintain structural integrity and not bulge or rupture under these conditions. It has been found that by only limiiting the lateral displacement of the dome side wall region, a significant gain in resistance of the entire dome region to bulge and rupture under high pressure can be achieved. By providing a limited clearance between the dome side wall and the lateral restraint feature in the cover, the lateral defleαion of the dome side wall region is not inhibited from responding to normal fluid pressures but is prevented from rupturing when experiencing high fluid pressures. Thus, the linearity performance of pressure sensing will not be impaαed with fluid pressures in the normal operating range. Essentially, the lateral restraint 150 includes that portion of the cover 16 that forms the circular aperture 56 surrounding the dome-shaped pressure vessel 36 that can also be observed in FIG. 2. A lateral clearance 151, for example 12 mils, exists between the cylindrical sidewall 126 (shown in cross-seαion in FIG. 11) of the dome- shaped vessel 36 and the lateral restraint 150. Also, the lateral restraint 150 includes a projection 152 extending from the lateral restraint 150 and direαed towards the interior 42 of the base 14. The lateral restraint projeαion 152 also surrounds the pressure vessel 36. The projection 152 includes a 45° chamfer formed on the end thereof which extends away from and which aids in supporting the dome-shaped pressure vessel 36. The chamfer avoids interference with the normal operation of the pressure vessel by the lateral restraint 150 yet continues to provide a sufficient amount of material for use as the lateral restraint. In use, as shown in FIG. 12, the pumping segment 10 is placed within an elongate receiving cavity 199 of a peristaltic pumping system 300 that operates to peristaltically pump fluids through the pumping segment 10 as well as control fluid flow and measure fluid line pressure. The varied outer shape of the segment 10 assists in proper loading of the segment. Because it is rounded at one end and flat at the other, it can be installed in only one orientation. Additionally, as better seen in FIG. 13, the reαangular notches 63 in the flange 62 of the pumping segment 10 cooperate with lateral tabs 263 in the receiving cavity 199. The lateral tabs 263 have a configuration that is adapted to mate with the reαangular notches 63 and assure the pumping segment 10 is properly placed in the receiving cavity 199. The pumping segment 10 also includes flats for assistance in proper moun in the receiving cavity 199. A proximal flat 326 meets with a shoulder 328 in cavity to aid in alignment. A distal flat 330 also meets a distal shoulder 332 in cavity 199. These flats/shoulder combinations control the distance that the pum segment can be inserted into the cavity 199. Further, rounded cut-outs 282 similarly cooperate and mate with the ear extending from the slider 18 of the pumping segment 10 to assure that the pum segment 10 is placed in the pumping system 300 with its slider 18 in the flow s position although in FIG. 13 the slider 18 is shown in its full flow position. T the slider 18 must be moved to its most distal or its fluid stop position before pumping segment 10 can be placed in the receiving cavity 199 because it is onl this position that the ears 82 are received within the rounded cut-outs 282. With slider 18 in its flow stop position, one or more pump/slider projections 220 exten perpendicularly from a rotatable circular plate 274 included in the elongate recei cavity 199 of the peristaltic pumping system 300 are positioned within the groov formed in the slider 18. A latch arm 259 of the peristaltic pumping system which is mechanically connected to the rotatable circular plate 274, is closed to re the pumping segment 10 in the pumping system 300. As the latch arm 259 is clo the rotatable circular plate 274 turns and motion is translated from the rotat circular plate 274 to the groove 74 to cause the slider 18 to move to its most proxi position along the engineered pumping segment 10. At this position, the maxi contemplated flow is permitted except where the pumping segment is installed i pump, in which case, one or more peristaltic fingers will occlude the flow p downstream. When the slider is moved in the proximal direαion, the ears 82 m under ridges 334 located on either side of the cavity 199. The ridges 334 retain slider 18 and so the pumping segment in the cavity 199 so that it cannot be remo unless the slider is moved to its flow stop position. Once the engineered pumping segment 10 is positioned within the peristaltic pumping system 300, peristaltic pumping fingers 230 projeαing substantially perpendicularly from the elongate receiving cavity 199 may work within the intermediate aperture 57 formed in the cover 16 and upon the central planar region 23 of the membrane 12 overlaying the groove 21. The peristaltic pumping fingers 230 systematically rise and f ll in a perpendicular motion relative to the membrane 12 and depress adjacent portions of the membrane 12 against the groove 21, to thereby force fluid through the engineered pumping segment 10. Pressure sensing is also accomplished when the engineered pumping segment 10 has been placed in the peristaltic pumping system 300. In order to accomplish pressure sensing, the dome-shaped pressure vessel 36 is brought into continuous and direct contaα with a pressure sensitive region of a sensor 200 mounted within the elongate receiving cavity 199 to form an effeαive interface for sensing pressures created by fluid flowing through the engineered pumping segment 10. As shown in FIG. 15, in the preferred embodiment, the pressure vessel 36 is coupled to an essentially planar sensor 200 so that fluid pressure readings may be taken of fluid flowing through an interior 37 of the vessel 36. The structural configuration of the pressure vessel 36 is seleαed to ensure optimum interfacing with the sensor 200, as will be described in detail below. In general, an optimum initial top contour of the pressure vessel 36 is achieved by employing a novel method. Additionally, another novel method is used to optimize sensor/dome preload displacement. By preloading an optimally shaped pressure vessel 36 against the pressure sensitive region of a sensor with optimal preload displacement, proper interface contaα stress with the sensor 200 is assured, thereby ensuring pressure communication from the vessel 36 to the sensor even in situations where there is negative pressure existing in the pumping segment 10. Referring again to FIG. 14, the detailed configuration of the dome-shaped pressure vessel 36 is described. In the preferred embodiment, the dome-shaped pressure vessel 36 has a crown 122 and a membrane peripheral region 124 which connects the crown 122 to the perimeter 28 and planar portion of the membrane 12. The crown 122 has cylindrical sidewalls 126 which extend substantially perpendic from the planar portions of the membrane and which define an outer rim region The outer rim region 128 is defined by the top of the cylindrical sidewalls 126 is itself circular in shape. Completing the crown 122 is a center dome region The center dome region 130 is the cap of the vessel 36 or that portion of the v that closes one end of the cylindrical sidewalls 126. From its conneαion to sidewalls 126, the center dome region 130 has an arcuate surface contour gradually extends further away from the planar portions of the membrane 12 forms a dome-like shape. The membrane peripheral region 124 is a curved portion of the membran extending away from the sidewalls 126 to provide a transition to the upper and lo sidewalls 29, 30 formed at the distal terminal end 25 of the membrane as well transition to the central planar region 23 (not shown in FIG. 14) extending to the proximal terminal end 26 of the membrane. The membrane peripheral re 124 funαions as a flat washer spring. As will be developed, the membrane periph region 124 provides resilient stiffness while allowing the central dome region 13 be flattened and the rim region 128 to be preloaded against the sensor 200. It is also contemplated that the crown height, thickness and modulu elasticity will be selected to provide acceptable pressure transferring characterist Likewise, the sidewall 126 thickness and modulus of elasticity as well as that of membrane peripheral region 124 will be seleαed with such charaαeristics in m In particular, the physical charaαeristics of the membrane peripheral region 124 be chosen to prevent dome/sensor lift-off under conditions of negative IV pressure. Additionally, the diameter of the central dome region 130 is contempl to be more than twice that of the largest dimension of the sensing portion 231 of pressure sensor 200, thereby minimizing the effeα of lateral position errors on se accuracy. In the preferred embodiment, the wall thickness of the crown 122 and ce dome region 130 range from 0.033-0.035 inches. The radius of the crown port from the outside of the sidewalls 126 to a longitudinal axis running through crown is 0.107-0.109 inches. The height of the cylindrical sidewalls 126 from a point near where the membrane peripheral region 124 meets the upper sidewall 29 is 0.105- 0.107 inches. The curvature of the upper side 26 of the membrane peripheral region 124 where it meets the cylindrical sidewalls 126 has a radius of approximately 0.032 inches, whereas the curvature of the lower side 27 has a radius of approximately 0.072 inches. Accordingly, the wall thickness of the membrane peripheral region 124 increases from 0.038-0.040 inches to approximately 0.065 inches. The center dome region 130 gradually inclines to a height of 0.011-0.013 inches above the outer rim region 128. A description of a preferred center dome region 130 contour in terms of radial position and height above the outer rim region 128 is summarized below. RADIUS HEIGHT (inch) (inch) 0.0000 0.01200 0.0024 0.011979 0.0048 0.011952 0.0072 0.011883 0.0096 0.011801 0.0120 0.011683 0.0144 0.01155 0.0168 0.011376 0.0192 0.011175 0.0216 0.010961 0.0240 0.010715 0.0264 0.010448 0.0288 0.010151 0.0312 0.009835 0.0336 0.009487 0.0360 0.009133 0.0384 0.008761 RADIUS HEIGHT (inch) (inch) 0.0408 0.008351 0.0432 0.007919 0.0456 0.007483 0.0480 0.007028 0.0504 0.006543 0.0528 0.006053 0.0552 0.005556 0.0576 0.005078 0.0600 0.004606 10 0.0624 0.004188 0.0648 0.003769 0.0672 0.003489 0.0696 0.003274 0.0720 0.0003076 15 0.0744 0.002875 0.0768 0.002631 0.0792 0.002363 0.0816 0.002103 0.0840 0.001882 20 0.0864 0.001697 0.0888 0.001419 0.0912 0.001293 0.0936 0.001125 0.0960 0.000952 25 0.0984 0.000789 0.1008 0.000613 0.1032 0.000352 0.1056 0.000133 RADIUS HEIGHT (inch) (inch) 0.1080 0.0 The dome-shaped pressure vessel 36 has an uncoupled initial top surface contour such that, upon coupling to a sensor face, relatively uniform central dome region contaα stress distribution will result at the interface between the sensor 200 and the dome 130 for any given internal fluid pressure. By approximating a uniform contaα stress distribution, a more accurate transfer of fluid pressure information from the dome 130 to the sensor 200 is achieved since the entire dome portion 130 is presenting the sensor 200 with the same information. This feature compensates for various manufacturing tolerances. For example, if the pressure sensor were to be mounted in a position displaced from its design position during manufacture of a pump, the chances of the pressure sensing system functioning accurately are increased due to the uniform contact stress distribution provided by the vessel. Likewise, the pressure vessel may be mounted to the pressure sensor in a displaced position from the design position and still function accurately because of the uniform contact stress distribution provided by the dome-shaped contour of the vessel. In order to determine a proper initial contour, a preferred embodiment of which is provided in the table above, a novel method for providing the dome-shaped pressure vessel 36 with an optimal top contour is employed. The following is a description of this method. To determine an optimal top contour (see FIG. 16), it will be appreciated that a first uniform contaα stress P r 134 (represented by arrows) and a second uniform contaα stress P c 136 (represented by arrows) are applied to the rim region 128 and the center dome region 130 respectively. Uniform contaα stresses P r 134 and P c 136 simulate the forces applied to the dome-shaped pressure vessel 36 upon coupling with a sensor 200. Stresses P r 134 and P c 136 are necessarily different due to differences in the stiffness or rigidity of the rim 128 and center dome 130 regions and, P r 134 is substantially greater because of the greater rigidity of the rim 128. Further, it is -28- important that the stresses be uniform, especially for the central dome stress P c because it is desired to contaα the sensor 200 with a uniform stress distribut Upon the application of sufficient stresses or upon coupling to the sensor 200, top portion of the dome-shaped pressure vessel 36 is to be substantially flatt against the sensor face. It is to be understood that merely coupling a deform irregular shaped surface against a flat sensor surface so as to flatten the irregul shaped surface, does not necessarily result in a uniform stress distribution across deformable irregular shaped surface. Such a shaped surface likely has areas of va stress distribution across its flattened surface since it would likely require var stresses to flatten different areas of the surface. Additionally, coupling a flat sur supported by sidewalls projecting perpendicularly therefrom, against a flat se surface will likely result in the seαions of the flat surface near the sidewalls ha a different distribution stress than that of the center portion of the flat sur Accordingly, the method of optimizing the initial top surface contour of the do shaped pressure vessel 36 results in providing the engineered pumping segmen with superior means to transfer pressure information to a sensor. To establish the optimum top. contour, an initial contour h(d c , d r ) (represented by the conneαed points in FIG. 16) is selected, where d c 142 and d. (both depiαed as arrows in FIG. 16) represent the defleαion coordinates of the d center 130 and dome rim 128 respeαively. In this method, γ(d c ,ά I ) 141 represents absolute displacement response of h(d c ,d r ) 140 to the application of uniform stre P r 134 and P c 136. To understand the relationship between y(d c ,d r ) 141 and h(d 140, one must conceptually replot h(d c ,d r ) 140 as a straight line 143, where bot 142 and d r 141 equal zero, and visualize displacement response y(d-,d-) 141 as expression of the changes in defleαion coordinates d c 142 and d. 144 to app stresses. It is desired that, in response to applied stresses, the initial contour h(d 140 equal the relative displacement response y(d c ,d r ) 652 so that the center d region 130 is substantially flattened. After observing a relative response y(d-,d-) (represented by arrows in FIG. 16) of the top portion to uniform stresses P r 134 P c 136, it may be required to determine a revised contour h(d c ,d-)\ That is, rev initial contour h(d-.,d r )' may be necessary where y(d c ,d r ) 141 is not the desired relative response of the top portion of the pressure vessel to applied uniform stresses P r 134 and P c 136. Once h(d c ,d r ) 140, or more precisely some revised estimation h(d c ,d r )' of h(d c ,d r ) 140, equals y(d c ,d r ) 652, the optimal contour of the top portion of the vessel 36 has been achieved. Upon coupling to sensor 200 or through the application of uniform contaα stresses P r 134 and P c 136, the optimally shaped top portion will defleα sufficiently to flatten the central dome region 130 (see FIG. 15). Further, the membrane peripheral region 124, in performing as a flat washer spring, deforms an amount corresponding to the deflection of the rim region 128, thereby absorbing the forces applied to the rim region 128 and enabling the sidewalls 126 to remain substantially straight. Generally speaking, in an optimally shaped dome-shaped pressure vessel 36, where the central dome region 130 is sufficiently flattened in response to uniform stresses, relatively uniform stress distribution exists across the center dome region 130. Therefore, upon coupling, the dome 130 transfers a uniform and accurate pressure to the sensing portion 131 of the sensor 200. To increase accuracy, it is desirable to provide a pressure vessel that interfaces with a pressure sensor such that the contaα stresses between the vessel and sensor are linear across the entire design range of internal pressures of the vessel. The present invention also includes a method to optimize the preload displacement of the dome- shaped pressure vessel 36 so that, when coupled to the sensor 200 (see FIGS. 15 and 16), the rim region 128 isolates the central dome region 130 from external conditions and so that a proper interface exists for all expeαed mechanical tolerance deviations and for worst case negative pressure conditions, i.e., - 4 psi. To arrive at an optimum preload displacement, an initial nominal preload displacement under conditions of zero internal pressure is assumed and the resulting stresses between the rim and central dome regions 128, 130 and the sensor 200 are determined for the worst case negative pressure conditions expeαed. If sufficiently positive compressive resulting stresses are computed, then the assumed nominal preload displacement is deemed optimized. On the other hand, if the resulting stresses are not sufficiently positive, a new assumption for the initial nominal displacement is made and the result stresses are again monitored for sufficiency. In order to obtain other assumptions initial nominal displacement, it may be necessary to modify the membrane stiffn by adding material or by changing its composition. To accomplish optimal preload displacement for all expeαed internal fl pressures, an initial preload displacement is seleαed for the rim region 130 and cen dome region 128 under zero internal pressure conditions. The stresses existing in rim and center dome regions are then determined for this initial preload displaceme Next, an expression is developed which represents the relationship between result contaα stresses P c 134 and P r 136 for all expeαed internal pressures and, contact str values for zero internal pressure P co and P ro and pressure transfer coefficients C c C r . Finally, the resulting stresses are evaluated for sufficiency. Stress values P c0 and P ro are initially approximated from the followi equations which represent linear estimations of central dome 130 and rim region stresses under conditions of zero internal pressure for small displacement deviati d c , d,., from nominal. Pco - Pco, nθ m + (dPco/ddc) x (d c - d c>no J Pro - Pro, n om + (& ) X (d r - d.^ In the above two equations, the assumed initial nominal preload deflections, d c nom a d r ?nom , under zero internal pressure conditions, are known. They are determined knowing the optimal initial top surface contour, as arrived at using the meth described above, and by observing the change in the optimal initial top surf contour upon coupling to the sensor 200 to the assumed degree. For such assu initial nominal preload defleαion, there are known associated nominal central do and rim stresses P^ om and P ro>nom . Due to mechanical tolerance deviations, howev the actual contact stresses between the dome-shaped pressure vessel 36 and the sen 200, P ∞ and P ro , will not equal the nominal values. The above equations are utiliz to take into account small displacement deviations from nominal that are likely occur in the contaα stresses of the rim region P ro and central dome region P co un zero internal pressure conditions. This is accomplished by adding to the nomi contaα stress values the effeα small deviations in displacement from nominal have on the contaα stress values. The actual central dome region and rim region contaα stresses, P.,. and P ro , are then calculated for some displacement deviations, d c and d,, from nominal which are representative of expeαed deviations and for some associated known change in actual central dome and rim contaα stresses with respeα to the expeαed deviations in central dome and rim displacements, dP^/dd. and dP ro /dd.. It is to be noted that dP ∞ /dd c and dP ^ /άά. are known by observing the change in central dome and rim region contaα stress under zero internal conditions for various displacements of the central dome and rim regions 130, 128. Therefore, what is arrived at is a more realistic and better approximation of the actual contaα stresses under zero internal pressure conditions. Once P co and P ro are estimated, they are utilized to calculate resulting contaα stresses P r 134 and P c 136 for each expeαed internal vessel pressure P int from following relationships. * ■ r ™ ■* ro "*" * ■ - ■ ,. χ l int In order to make such a calculation, pressure transfer coefficients C c and C r are estimated, based upon the response of the vessel 36 to the application of stresses P r 34 and P c 36, using a finite element stress analysis, for example the finite element stress analysis program from MARC Analysis Research Corporation, Palo Alto, California, for a given preload displacement. For any internal pressure P j ,,,, therefore, P c 136 and P r 134 may be determined. Where sufficiently positive compressive contaα stresses P c 136 and P r 134 are computed, that is, through the application of the contaα stresses the central dome region 130 is sufficiently isolated by the rim region 128 under expeαed worst case negative pressure conditions, then the assumed displacement of the pressure vessel 36 utilized in the analysis is optimal. Otherwise, the dome adjacent region membrane may be increased in thickness (or stiffened) and a larger preload displacement value utilized. In such a case, the complete optimization analysis described would then be again performed using the new assumptions with the stresses P c and P r , again be monitored for adequacy. It must be noted that the previously described optimal contour and opti preload displacement methods are dependent upon the specific application physical charaαeristics of the subjeα pressure transferring element. Altho different applications will have varying results, the method outlined will prov means for optimizing the performance of a pressure transferring element. Our attention is now turned to another basic funαion of the pump segment 10, namely fluid flow regulation. Briefly, referring to FIG. 13, to regul flow rates through the pumping segment 10, the pumping segment 10 must removed from the pumping system 300 and the slider 18 must be manipulated hand. As may be recalled, when the latch arm 259 is closed to retain the pump segment 10 within the pumping system 300, the slider 18 is moved to its m proximal position where fluid flow through the pumping segment 10 is its maxim Further, it may be recalled that to place the slider 18 within the pumping system 3 the slider 18 must be in its most distal or its flow stop position, only later to moved to its maximum flow position when the latch arm 259 is closed. Theref since the position of the slider 18 is constrained to be in its maximum flow positi when it is retained against the pumping system 300, the slider 18 must be remo from the pumping system 300 and manipulated by hand should flow regulation desired. Under such conditions, gravity causes the fluid coming from the reserv (not shown) to pass through the pumping segment 10, the rate of fluid flow thro which is determined by the slider 18. Referring now to FIG. 17, the shape of a peristaltic finger 342 is shown t is usable with the pumping segment 10 presented. As shown, the finger 342 ha complex curve at its distal end for compressing the membrane 12. While the comprises a convex curve, the parts of the finger tip between the center and the ed 344 comprise concave curves. It was found that this shape of the finger 342 res in less wear on the membrane during the pumping action. From the foregoing, it will be appreciated that the present invention provides an engineered pumping segment 10 having a simple design and that in a single device facilitates efficient and accurate peristaltic pumping of fluid over long periods of time, that provides an effeαive interface for sensing fluid pressure under all conditions of line pressure, and that provides regulation of fluid flow while minimizing system inaccuracies. While several particular forms of the invention have been illustrated and described, it will be apparent that various modifications can be made without departing from the spirit and scope of the invention. Accordingly, it is not intended that the invention be limited, except as by the appended claims.

Claims: WHAT IS CLAIMED IS: 1. In a segment for fluid flow, a pressure vessel for interfacing with a se and for transferring fluid pressure of the segment to the sensor, the pressure v comprising: a hollow crown portion for engaging the sensor, having a cylindrical side a closed upper end and an open lower end formed of a flexible material, wi which the fluid pressure is received; and a membrane peripheral portion conneαed to and extending away from open lower end of said hollow crown portion. 2. The segment of claim 1, wherein said membrane peripheral porti adapted to be retained by stationary structure, thereby allowing said memb peripheral portion to perform as a flat washer spring for said crown portion o pressure vessel. 3. The segment of claim 2 wherein: said stationary structure comprises a lateral restraint configured to limit lateral movement of the side wall in response to fluid pressure. 4. The segment of claim 3 wherein the lateral restrain is disposed compl around the cylindrical side wall of the hollow crown portion and is configure limit the amount of lateral movement of the side wall in response to internal pressure. 5. The segment of claim 1, wherein said closed upper end includes: a rim region defined by the top of said cylindrical sidewall, said rim re being substantially perpendicular to said sidewall; and a center dome region conneαed to said rim region, said rim region and center dome region defining a top of said crown portion. 6. The segment of claim 5, wherein said top of said center dome region has a pre-determined contour adapted to uniformly distribute stresses across its face when applied to the pressure sensor. 7. The segment of claim 1 further comprising: a lateral restraint configured to limit the lateral movement of the side wall in response to fluid pressure. 8. The segment of claim 7 wherein the lateral restrain is disposed completely around the cylindrical side wall of the hollow crown portion and is configured to limit the amount of lateral movement of the side wall in response to internal fluid pressure. 9. In a segment for fluid flow, a method for optimizing a top surface contour of a pressure vessel, comprising: selecting an initial top surface contour; applying a rim uniform contaα stress to a rim region of said pressure vessel; applying a central uniform contaα stress to a central dome region of said pressure vessel; observing a response of said top surface contour to the application of said rim contaα stress and said central contact stress; comparing said response of said top surface contour with said initial top surface contour; and modifying said initial top surface contour so that upon application of said rim uniform contaα stress and said central uniform contaα stress said response of said top surface contour approximates said initial top surface contour. 10. A method for determining an optimal pre-load displacement of a pressure vessel, comprising: calculating a rim uniform contaα stress and a central uniform contaα st each existing in the pressure vessel when applying the pressure vessel to a senso an initial degree; and determining sufficiency of said rim uniform contaα stress and said cen uniform contact stress. 11. The method of claim 10, wherein said calculating a rim uniform con stress and a central uniform contaα stress includes: determining a zero internal pressure rim contact stress and a zero inte pressure central contact stress of the pressure vessel applied to the sensor un conditions of zero internal pressure; determining a central pressure transfer coefficient of said central dome reg and a rim pressure transfer coefficient of said rim region; applying an internal pressure to the pressure vessel; measuring said internal pressure of the pressure vessel; combining said zero internal pressure rim contact stress with a product of s rim pressure transfer coefficient and said measured internal pressure, ther calculating said rim uniform contaα stress; and combining said zero internal pressure central contaα stress with a produc said central pressure transfer coefficient and said measured internal pressure, ther calculating said central uniform contaα stress. 12. The method of claim 11 wherein said determining sufficiency s includes: observing whether said rim region maintains a sufficient pre-load compress to isolate said central dome region from external influences.

Inventors: BUTTERFIELD ROBERT D, CLEMENS CHARLES E, MARTIN STEPHEN A, BUTTERFIELD, ROBERT, D., CLEMENS, CHARLES, E., MARTIN, STEPHEN, A.
Applicants: IVAC CORP, IVAC CORPORATION
Application year: 1995
Main classification: G01L7
IPC codes: G01L7, G01L19