Patent Publication Number: US-6341757-B1

Title: Flow regulator

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of provisional application No. 60/150,538 filed Aug. 25, 1999 and of application Ser. No. 09/319,456 filed as a U.S. national phase of international patent application No. PCT/US97/21617 which was filed Nov. 25, 1997 as a continuation-in-part of application Ser. No. 08/759,438 filed Dec. 5, 1996, now U.S. Pat. No. 5,718,409. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a flow regulator. More particularly, this invention relates to a flow regulator of the type which compresses a tube to vary a flow rate of a fluid passing through the tube. Even more particularly, this invention relates to a flow regulator of the roller type. The invention is useful in medical applications, to control the flow rate of intravenous fluids, parenteral fluids, blood, plasma, etc. 
     BACKGROUND OF THE INVENTION 
     Intravenous tubes have been widely used for supplying nutrients and medication to patients. Most existing manually adjustable clamps for regulating the flow rate through an intravenous tube have a high degree of inaccuracy, particularly after the clamped tubing has been in use for a period of time in excess of one hour. In addition, existing manually actuated clamps cannot be used where the fluid being delivered through the tubing is viscous, for example, blood. If a substantial degree of accuracy in flow rate maintenance is required, it has been necessary to utilize an expensive pump system. Even pumps systems are limited in their accuracy. 
     A particularly common kind of flow regulator in medical applications is the so-called Adelberg clamp which uses the combination of an inclined plane or V-grooved surface and a roller that is moved along the inclined plane or grooved surface to variably compress the tube to allow more or less liquid to flow through the tube. Although widely used, the Adelberg clamp is less than ideally accurate and reliable, so as to require continual monitoring and adjustment to maintain a desired flow rate. The position of the roller is easily shifted in the V-grooved and ramped versions since the clamp design has not taken into consideration the direct effect of stress and strain as a critical contributing factor in maintaining an accurate and consistent flow rate through the roller clamp. 
     OBJECTS OF THE INVENTION 
     An object of the present invention is to provide an improved manually adjustable flow regulator of the above-described roller type. 
     Another object of the present invention is to provide a manually adjustable flow regulator which has enhanced accuracy and reliability. 
     An additional object of the present invention is to provide such a flow regulator which is inexpensive and easy to manufacture. 
     A further object of the present invention is to provide a manually adjustable flow regulator which is utilizable where a medical fluid is to be delivered through a flexible tube. 
     These and other objects of the present invention will be apparent from the descriptions and illustrations herein. It is believed that each of the above-described objects is achievable in one or more embodiments of the invention described herein. 
     BRIEF DESCRIPTION 
     A flow regulator comprises, in accordance with the present invention, a pair of side walls extending generally parallel to one another, a bottom wall connecting the side walls to one another and defining an elongate channel for receiving a compressible tube, a roller rotatably and shiftably mounted to the side walls for rolling along the tube in the channel and compressing the tube against the bottom wall. The bottom wall is provided with a formation which varies from a first end of the channel towards an opposite, second end thereof, whereby a compressive force applied to the tube via the roller is different at different longitudinal positions of the roller along the channel. A reinforcement bracket is disposed about the side walls at one end of the channel. The bracket is in contact with outer surfaces of the parallel side walls only in regions of the side walls spaced from the bottom wall. In a different embodiment, the bracket is replaced with a bridge of relatively flexible construction spanning the two side walls, disposed at the flow regulator shut off end. Advantageously, the side walls and a bottom wall, including all parts of the clamp with the exclusion of the bracket or bridge, are made from a material more rigid than the material from which the bracket or bridge is made. 
     As suggested above, prior V-grooved or ramped roller clamps suffer from setpoint drift attributable to shifting of the roller position. The prior clamp structures are not believed to have taken into adequate consideration the direct effect of stress or strain as a critical contributing factor in degrading an accurate flow rate performance of the roller clamp. The relationship of a stiffness of the bridge to the flow regulator chamber or channel walls, as well as the contributory factor of differences in intrinsic elasticity of the materials used for component manufacture are critical in maintenance of accurate device performance. The present invention describes an effective method of taking cognizance of stress and strain in the device, and controlling these factors for optimum performance. 
     U.S. Pat. No. 5,718,409 to the same inventor implicitly dealt with stress and strain in a roller clamp by introducing a reinforcing bracket to an existing design. In further tests of similar devices it has become evident that modifying the flexibility or stiffness relationships between the chamber walls and the bridge or bracket component further improved the accuracy and consistency of the device, by limiting the flexing of the side walls and simultaneously reducing a strain state of the bridge or bracket. 
     U.S. Pat. No. 5,718,409, the disclosure of which is incorporated herein, shows a bracket contacting the outer surface of the sidewalls of the roller clamp body at a shut-off or maximally restricted flow end of the device. In the prior art, the roller tended to roll towards the shut off end during operation of the clamp. The movement is presumed to have arisen as an effect of operating stresses in the interrelated parts of the roller clamp assembly. As the roller pinches the tube, pressure is generated on the plastic walls of the device. This pressure causes an end of the clamp to flair open to various degrees, depending on a position of the roller. In order to control the effect of stress on the device, structure defining the roller clamp chamber requires a more rigid material construction. The elastic relationship of the roller clamp chamber structure—comprising parallel side walls and bottom wall—to the bracket or bridge structure is an important design parameter, as the two parts structure interact to accommodate the varying stresses resulting from different roller setting in the operating device. 
     The bracket previously described in U.S. Pat. No. 5,718,409 serves to maintain flow constancy by controlling a change in a gap distance between the parallel side walls of the roller clamp, engaging the walls predominantly at the shut off end. Simultaneously, the bracket provides the side walls with a controlled springy effect which means that, as the roller starts to roll towards the shut off end, the controlled springy flexibility of the walls will respond to the roller&#39;s tendency to roll down; at times when the amount of fluids delivered lessen, it would cause a decrease in the degree of stress and strain between the bracket and the chamber, and the pressure between the roller and the tube where the roller might otherwise change its position, with bracket feature on the clamp the roller will be held constant by the springy effect of the parallel side walls. After this discovery was initially made by the inventor by numerous in-house tests and several official laboratory tests, improvements were made in the design which make this device easier and less expensive to manufacture, while maintaining the original objectives of maintaining superior and constant flow regulating. These improvements result in a device having a predetermined and controlled elastic performance relationship during stress effects which involve the entire assembly. 
     The bracket or bridge is preferably disposed at the end of the flow regulator where the tube is subjected to the greatest compressive forces and the controlled flow rate is the lowest. The bracket prevents an undue flexing of the side walls away from each other under forces exerted by the roller and the compressed tube. In one version or embodiment of the present invention, the bracket mounts around the parallel side walls and the bottom wall connecting the parallel sides. In another version, the bracket fits over the parallel side walls only, at the shut off end of the clamp. In yet another version, the bracket is mounted in such a manner that it interfaces with the bottom wall and the side walls and the bracket clips over the top edge of the side walls, leaving a section of a gap between the parallel side walls open. The thickness of the bracket ends is sufficient to stop the roller from accidentally rolling past the end of the channel housing. 
     In accordance with a feature of the present invention, it is contemplated that the side walls at the bracketed end of the channel are connected to one another only by the bottom wall at one side and the bracket at an opposite side. Thus, a web or strut which extends between the side walls at the low-flow-rate end of a conventional regulator is omitted. 
     The bracket is made of a less rigid material, or exhibits less stiffness or resistance to bending, than the walls of the flow regulator chamber or channel. In another version or embodiment of the present invention, the bridge, also made of a less rigid material than the bottom wall and sides walls of the roller clamp, is disposed between the side walls at the shut off end of the flow regulator. This bridge has a curved formation of a bow like structure. This convex formation of the bridge points away from the shut off end and in opposite direction from the open end of the flow regulator. 
     Pursuant to another feature of the invention, the bracket includes portions spaced from the side walls in a region about the bottom wall. 
     In a specific embodiment of the present invention, the bracket is substantially U-shaped, with legs having free ends provided with fingers contacting the bottom wall. The fingers are substantially collinear and oriented towards one another. 
     In accordance with a further feature of the present invention, the side walls are provided along inwardly facing surfaces with respective grooves, the roller having a pair of shaft elements extending laterally in opposing directions along an axis of the roller, each of the shaft elements being provided at a free end with a friction enhancing formation. The friction enhancing formation may take the form of knurling, a layer of high friction material, embedded grit particles, or a series of axially extending ridges and interleaved longitudinal grooves. 
     In accordance with a yet another feature of the present invention, the flow regulator further comprises a pointer member coupled with the roller to move therewith as the roller negotiates the channel. A series of marks are disposed along the outer surface of one of the side walls for cooperating with the pointer to provide an indication of flow rate. 
     In accordance with an additional feature of the present invention, at least one of the sidewalls is provided with a seat receiving the bracket. The seat may be defined by a recess in the side wall or a shoulder on the side wall. The seat assists in retaining the bracket on the regulator. 
     The bracket may be bonded to one or both of the side walls, for example, by ultrasonic welding. 
     In a specific embodiment of the invention, the reinforcement bracket includes a first U-shaped portion spanning the channel on a side thereof opposite the bottom wall of the flow regulator and disposed in contact with outer surfaces of the side walls only in regions of the side walls spaced from the bottom wall. In this embodiment, the reinforcement bracket further includes a second U-shaped portion partially surrounding the first U-shaped portion, the second U-shaped portion having legs extending generally parallel to and spaced from the side walls of the flow regulator, the legs having free ends provided with fingers disposed in contact with the first U-shaped portion. 
     A manually adjustable flow regulator in accordance with the present invention provides substantially enhanced accuracy and reliability. The improved performance results from the addition of a single part to existing roller-type clamps. Accordingly, the flow regulator of the present invention is inexpensive and easy to manufacture. A manually adjustable flow regulator in accordance with present invention is utilizable where a medical fluid, for example, a parenteral solution, saline, plasma or blood, is to be delivered through a flexible tube. 
     In another feature of the present invention, it has been determined by experimentation that an unexpected benefit is accrued in terms of flow stability if the pair of side walls and bottom wall defining the elongate channel are manufactured utilizing material and dimensions creating a relatively stiff profile, while the bracket is manufactured using material and dimensions resulting in a relatively flexible reinforcing bracket or clip anchoring the side walls. Since one of ordinary skill in the art would likely have thought it desirable to make all components as stiff as possible to limit shifting of the roller, the relative advantage of a less stiff bridge or bracket part is an unexpected result. 
     An improvement made here over U.S. Pat. No. 5,718,409 accordingly originates in an observation that the rigidity or flexibility relationship between the chamber walls and the bracket (or bridge) is a significant feature in controlling performance of the flow clamp device. In specific embodiments of the present invention, the bridge or bracket is more flexible in its structure than the roller clamp chamber housing. 
     In accordance with a further feature of the present invention, the side walls and the bottom walls are made of a substantially less flexible material than the bracket or convex bridge are made of. 
     A manually adjustable flow regulator in accordance with the present invention provides an enhanced accuracy and reliability. The improved performance results from a substantially rigid chamber housing and a less rigid bracket or bridge assembly in a roller-type clamp. By incorporating these improvements a flow clamp device will prove easier and less expensive to manufacture, while yet advantageously maintaining desirable critical features of the device previously disclosed in the referenced patent, the matter of which is incorporated herein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a side elevational view, on an enlarged scale, of an intravenous flow regulator in accordance with the present invention. 
     FIG. 2 is a transverse cross-sectional view, on a larger scale, taken along line II—II in FIG.  1 . 
     FIG. 3 is a transverse cross-sectional view, on a similarly large scale, taken along line III—III in FIG.  1 . 
     FIG. 4 is a top plan view of a roller member and a slidable frame entrained thereto, both shown in FIG.  1 . 
     FIG. 5 is a front view of the roller of FIG. 1 and a pair of axle members, showing the axle members projecting into tracks or grooves in side walls of the flow regulator. 
     FIG. 6 is a transverse cross-sectional view, similar to FIG. 2, showing an alternative construction for the invention. 
     FIG. 7 is a transverse cross-sectional view, similar to FIGS. 2 and 6, showing another alternative construction for the invention. 
     FIG. 8 is a transverse cross-sectional view, similar to FIGS. 2,  6  and  7 , showing yet another alternative construction for the invention. 
     FIG. 9 is a schematic perspective view of alternative embodiment of the present invention, showing a mounting of an end cap or clip. 
     FIG. 10 is a cross-sectional view including a clip similar to the clip of FIG.  9 . 
     FIG. 11 shows an alternative embodiment of the clip of FIG.  10 . 
     FIG. 12 shows yet an alternative embodiment of the clip of FIG.  10 . 
     FIG. 13 is a schematic perspective view of yet a further embodiment of the present invention, employing a bow or bridge. 
     Where structures in FIGS. 6,  7  and  8  are identical to structures in FIG. 2, the same reference designations are used. Where structures of FIG. 7 are repeated in FIG. 8, reference designations are also repeated. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The drawings illustrate a flow regulator  10  intended for use with a compressible medical feed tube  12 . The tube can deliver saline, blood, plasma, total parenteral fluids and other liquids to a patient, for example, to a blood vessel of the patient. Regulator  10  has a pair of side walls  14  and  16  which extend generally parallel to one another. A bottom wall  18  extends substantially the length of side walls  14  and  16  and connects the side walls to one another to define an elongate channel  20  for receiving tube  12 . Channel  20  is generally open towards one side, as indicated at  21  in FIG.  3 . 
     A roller  22  is rotatably and shiftably mounted to side walls  14  and  16 . Roller  22  is partially disposed in channel  22  and partially extends through opening  21  for enabling the manual application of a torque to roller  22 . Roller  22  is in frictional engagement with tube  12  for rolling along the tube in channel  20 , under the manual application of torque, and compressing tube  12  against bottom wall  18 . Bottom wall  18  is provided with a conventional formation such as a ramp (not shown) and/or a tapered V-shaped groove (not shown) which has a shape varying from a first end  24  of regulator  10  (and channel  20 ) towards an opposite, second end  26  thereof. Thus, compressive force applied to tube  12  via roller  22  is different at different longitudinal positions of roller  22  along channel  20 . 
     A bracket assembly  28  is disposed about side walls  14  and  16  at the one end  26  of channel  20 . End  26  is that terminal portion of flow regulator  10  where tube  12  is subjected to the greatest compressive forces and the controlled flow rate is the lowest. Bracket assembly  28  serves to prevent an undue flexing of side walls  14  and  16  away from one another under the forces exerted by roller  22  and compressed tube  12 . This bracing action of bracket assembly  28  limits side wall flexing at virtually all longitudinal positions of roller  22  along channel  20 . 
     Bracket assembly  28  is in contact with outwardly facing surfaces (not labeled) of side walls  14  and  16  only in regions thereof spaced from bottom wall  18 . More particularly, bracket assembly  28  includes an inner U-shaped bracket element  30  and an outer U-shaped bracket element  32 . Bracket elements  30  and  32  may be a unitary injected molded polymeric piece or two separate polymeric pieces joined by ultrasonic or heat welding before or after assembly to side walls  14  and  16 . Inner bracket element  30  engages side walls  14  and  16  only along free edges and outer surfaces thereof spaced from bottom wall  18 . Outer bracket member  32  surrounds inner bracket element  30 , as well as side walls  14  and  16  and bottom wall  18 . Outer bracket element  32  is spaced from side walls  14  and  16  by virtue of inner bracket element  20 . In particular, there are gaps  34  and  36  between outer bracket element  32  and side walls  14  and  16  in region about bottom wall  18 . 
     As shown in FIG. 3, side walls  14  and  16  at the bracketed end  26  of regulator  10  and channel  20  are connected to one another only by bottom wall  18  at one side and bracket assembly  28  at an opposite side. There is no web or strut extending between side walls  14  and  16  at the low-flow-rate end  26  as there is in conventional flow regulators. 
     Outer bracket element  32  has legs  38  and  40  having free ends provided with fingers  42  and  44  which are in contact with bottom wall  18 . Fingers  42  and  44  are substantially collinear and oriented towards one another. 
     Side walls  14  and  16  are provided along inwardly facing surfaces (not labeled) with respective grooves  46  and  48  (FIG. 5) as in conventional intravenous flow regulators. Roller  22  has a pair of axle or shaft elements  50  and  52  extending laterally in opposing directions along an axis  53  of roller  22 . Each shaft element  50  and  52  is provided at a free end with friction enhancing longitudinal ridges  54  defined by interleaved longitudinal grooves (not separately labeled). The friction enhancing function of ridges  54  may be performed by other formations such as knurling, a layer of high friction material, or embedded grit particles. 
     As illustrated in FIGS. 1,  3  and  4 , flow regulator  10  is provided with a rectangular frame  56  traversed by roller  22 . Frame  56  is entrained to roller  22  to travel therewith along channel  20 . Frame  56  has one or two arms  58  and  60  which extend generally in parallel along respective side walls  14  and  16  and which are provided at free ends with inwardly turned hooks  62  and  64 . Hooks  62  and  64  engage respective longitudinally extending shoulders  66  and  68  on side walls  14  and  16  to thereby anchor frame  56  to the side walls of the flow regulator. A pointer member  70  projecting from one arm  58  is coupled via frame  56  to roller  22  to move therewith as the roller negotiates channel  20 . A series of marks  72  are disposed along the outer surface of side wall  14  for cooperating with pointer  70  to provide an indication of flow rate. 
     As shown in FIG. 2, side walls  14  and  16  are formed with respective recesses  74  and  76  which define seats receiving inner bracket element  30 . Recesses or seats  74  and  76  assist in retaining the bracket assembly  28  on regulator side walls  14  and  16 . More specifically, side walls  14  and  16  have stops or lips  78  (see FIG. 1) at regulator end  26  for preventing the bracket assembly  28  from sliding off the flow regulator. This feature is particularly useful where bracket assembly  28  is retrofitted to a pre-existing flow regulator. In addition, bracket assembly  28  may be bonded to one or both side walls  14  and  16 , for example, by ultrasonic welding. 
     A flow regulator as described herein has been tested using a McGaw 1000 cc D5W plastic IV solution bag, a standard McGaw 87 inch microdrip (60 gtts) IV tubing, and a 19 gauge 1½ inch metal needle. The test was conducted at a temperature of 75° F., a drip chamber height of 36 inches above an infusion site, and a flow regulator height of 5 inches below the bottom of the drip chamber. During a test period of four hours, a count of 30 drops was made every thirty minutes with an extra count at ten minutes after the initial count. The time in seconds for counting thirty drops was recorded at each count. The difference in seconds from the initial count and the percent change were calculated and recorded. The average change in the 30 drop time over the four hour period was 0.81 seconds and the average percent changes was 0.31%. 
     As illustrated in FIG. 6, an alternative construction for the roller clamp assembly particularly at the one end  26  (FIG. 1) of channel  20 , includes a bracket assembly  128  disposed about side walls  14  and  16 . Bracket assembly  128  is designed to decrease, reduce or eliminate undue flexing of side walls  14  and  16  away from one another under the forces exerted by roller  22  and compressed tube  12 . This bracing action of bracket assembly  128  limits side wall flexing at virtually all longitudinal positions of roller  22  along channel  20 . 
     Bracket assembly  128  is in contact with outwardly facing surfaces (not labeled) of side walls  14  and  16  only in regions thereof spaced from bottom wall  18 . More particularly, bracket assembly  128  includes an inner U-shaped bracket element  130  and an outer U-shaped bracket element  132 . Bracket elements  130  and  132  may be a unitary injected molded polymeric piece or two separate polymeric pieces joined by ultrasonic or heat welding before or after assembly to side walls  14  and  16 . Inner bracket element  130  engages side walls  14  and  16  only along free edges and outer surfaces thereof spaced from bottom wall  18 . Outer bracket member  132  surrounds inner bracket element  130 , as well as side walls  14  and  16  and bottom wall  18 . Outer bracket element  132  is spaced from side walls  14  and  16  by virtue of inner bracket element  130 . In particular, there are gaps  134  and  136  between outer bracket element  132  and side walls  14  and  16  in region about bottom wall  18 . 
     In the embodiment of FIG. 6, as in the embodiment of FIG. 2, side walls  14  and  16  at the bracketed end  26  of regulator  10  and channel  20  are connected to one another only by bottom wall  18  at one side and bracket assembly  128  at an opposite side. There is no web or strut extending between side walls  14  and  16  at the low-flow-rate end  26  as there is in conventional flow regulators. 
     Outer bracket element  132  has legs  138  and  140  having free ends provided with fingers  139  and  141  which are in contact with inner bracket element  130 . Fingers  139  and  141  are substantially collinear and oriented towards one another. At ends opposite fingers  139  and  141 , legs  138  and  140  are connected to one another by a bight member  142  which is in contact with bottom wall  18 . 
     In contrast to bracket  28 , bracket  128  extends 360° about channel  20 . 
     As depicted in FIG. 7, another alternative construction for the roller clamp assembly includes a substantially U-shaped bracket  228  disposed about side walls  14  and  16 . As in other constructions of the roller clamp assembly discussed herein, bracket  228  is designed to decrease, reduce or eliminate undue flexing of side walls  14  and  16  away from one another under the forces exerted by roller  22  and compressed tube  12 . This bracing action of bracket  228  limits side wall flexing at virtually all longitudinal positions of roller  22  along channel  20 . 
     Bracket  228  is in contact with outwardly facing surfaces (not labeled) of side walls  14  and  16  only in regions thereof spaced from bottom wall  18 . Bracket  228  substantially surrounds side walls  14  and  16  and bottom wall  18 . Bracket  228  includes a pair of legs  238  and  240  spaced along their lower portions (not separately designated) from side walls  14  and  16  by gaps  234  and  236 . 
     In the embodiment of FIG. 7, side walls  14  and  16  at the bracketed end  26  of regulator  10  and channel  20  are connected to one another only by bottom wall  18 , as reinforced by bracket  228 . As in other embodiments of a roller-type flow regulator described herein, there is no web or strut extending between side walls  14  and  16  at the low-flow-rate end  26 . 
     Legs  238  and  240  have thickened free ends  230  and  232  which contact outer surfaces of side walls  14  and  16  at ends thereof spaced from bottom wall  18 . Fingers  239  and  241  at the tips of legs  238  and  240  extend over the free ends of side walls  14  and  16  and cooperate therewith to attach bracket  228  to regulator  10  in a snap-lock fit. Fingers  239  and  241  are substantially collinear and oriented towards one another. At ends opposite fingers  239  and  241 , legs  238  and  240  are connected to one another by a bight member  242  which is in contact with bottom wall  18 . 
     As depicted in FIG. 8, a modified alternative construction for the roller clamp assembly includes a substantially U-shaped bracket  328  disposed about side walls  14  and  16 . Bracket  328  is substantially identical to bracket  228  except that bracket  328  includes flanges  344  and  346  connected to ends of fingers  239  and  241 . Flanges  344  and  346 , together with thickened ends  230  and  232 , define slots  348  and  350  which receive free ends or edges of side walls  12  and  14 . Thus, bracket  328  is more firmly locked to flow regulator  10 . 
     To comprehend a feature of roller clamp embodiments described below with reference to FIGS. 9 through 13, a concept of bending modulus will be introduced. For the purposes of this disclosure, a bending modulus is defined as a force divided by an angular deviation of a structure. In particular, the bending modulus of a portion of a roller clamp comprising side walls and a bottom wall will be taken as a force exerted on a defined location on the side walls tending to separate those sidewalls divided by a resulting angular deviation from parallelism of inside surfaces of the sidewalls, assumed not to deviate significantly from parallel in an unstressed rest configuration. The modulus is assumed to be measured at small displacements, within a realm of linear elasticity of all components subject to flexure. In this case the modulus may be assumed to be additive, that is, equal to a sum of forces on various components which would be exerted separately, acting at the same location to achieve an identical displacement in the individual components (carried if necessary by fictitious components in an event that a point of application resides in a particular component). To emphasize that a bending modulus in a second component may be measured additively with that of a first component, with an assumption of linearity, that is, that the modulus so measured is identical to that which would be measured by replacing the first component by a “phantom” or stress-free intermediate, the modulus of the second component may be referred to as an “effective bending modulus”. An “effective bending modulus” when used in this application shall be construed to be synonymous with a “bending modulus”. When it is desired to emphasize a location and plane of operation of the bending modulus, the bending modulus previously defined may also be described as about the longitudinal axis of the channel, in a body formed by the side walls and bottom walls. Since only one bending modulus is considered in connection with this disclosure, any of the above given descriptions of bending moduli shall be deemed synonomous. A motivation of this description in characterizing a feature of the present invention will become more readily understood hereinbelow. 
     The bending modulus may be measured in any consistent system of units, since a feature of the invention will be characterized by an inequality, and not by an absolute value of the modulus. In particular, a further feature of invention will be characterized by a value of the bending modulus measured at the sidewalls adjacent to top surfaces thereof, and adjacent to a location of a reinforcing bracket or clip, and further in particular by a relation of the bending modulus measured at this fixed location with no bracket or clip in place, and with a reinforcing bracket or clip in place. The invention is ideally characterized by an increment of the bending modulus with the clip in place which is smaller than the existing bending modulus. A meaning of this requirement may be understood by the additivity of moduli in the realm of small displacements, or linear elasticity, as discussed above. In effect, an increment in bending modulus by addition of a reinforcing clip or bracket is the same as an independent value of a bending modulus of the bracket in a similar configuration, with forces carried by “phantom” parts (since a point of application of the force is not directly on the bracket). In a most simple sense, the bracket or clip is less stiff than a surrounding structure. To reiterate, ideally a reinforcing clip or bracket is less stiff, i.e. more flexible, than a remaining structure of the invention, and this situation is more carefully characterized by a requirement on a measurement of a bending moment, as defined and motivated above. The definition and required inequality may course be taken as a condition of a preferable mode of the present invention without reference to a justification or motivation thereof, which is included as an aid to understanding the invention. 
     The bending moment is taken to be a measure of an angular deviation of inner surfaces of the side walls from parallelism under an action of a force in a defined location. The angular deviation is to be measured in an identical location, or particularly in a transverse or cross-sectional plane at this identical location. 
     Ideally, for reasons of mechanical stability and reproducibility of flow, a deviation of the inner surfaces of the side walls from parallelism will be substantially constant over a length of the flow clamp. In particular, a variation in angular separation of the walls over a longitudinal dimension or length of the clamp will ideally be no more that 10%. Still more ideally, a variation in an angular deviation of the inner surfaces of the sidewalls over a length of the clamp in the present invention will be no greater than 5%. It will be understood that these percentages express ratios of angles, and thus are free of units. 
     A colloquial description of a requirement that an angular deviation of the side walls preferably vary by less than 10% over a length of the invention, and yet more preferably or ideally by less than 5%, is that the walls are longitudinally stiff or rigid. For present purposes, when the walls are said to be “longitudinally stiff”, this shall be construed to represent the specific requirement described in the above given percentages. The given percentage requirements are to apply to a flow control device over a full range of flows or tube compressions. A full range of tube compressions shall mean from an uncompressed state to a complete occlusion. A standard hospital IV drip tube shall be used in establishing this standard. The side walls are designed to be longitudinally stiff under application of forces generated by a compressed tube and a roller by a suitable choice of side wall thickness, and also a bottom wall thickness in relation to sidewall thickness. Given the stiffness requirement, material dimensioning is a straightforward engineering problem for one skilled in the art, or solved empirically by prototyping. 
     A mechanism for an improvement in roller clamp function as result of the requirement of longitudinal stiffness or rigidity, i.e., a mechanism for increasing flow stability in a roller clamp as described herein, is thought to lie in maintaining substantial parallelism of the walls. In particular, it may be understood that as the side walls deviate from parallelism, a compressive force is exerted on spindles or axles attached to a roller trapped therebetween. If the side walls are parallel, this force will tend to increase a frictional force between axles and walls and beneficially trap an axle at a fixed location. However, if the walls are substantially flexible, and deviate from parallel, the compressive force will have a longitudinal component tending to force the axles to move along a length of the side walls. The axles and roller may thereby over time creep from an initially set position, a phenomenon which is likely to be aided by jostling or movement of a flow clamp, or by moisture on an exposed mechanism of a flow clamp, conditions which are not unlikely in a patient care setting. Alternatively, a roller setting may be disturbed by peristaltic action of the flowing fluid in the tube. In this case, a roller will tend to drift in setting towards one end of the device. 
     An alternative mechanism of roller drift in a flow-control roller clamp is that insufficiently rigid wall components may creep plastically, or relax, tending at first to increase drip flow as pressure is relieved on the tube, then decrease flow as the roller drips towards the cut off end under peristaltic action. In practice, it is found that drift effects towards rather than away from the cut-off end typically predominate in the prior art. 
     The aforesaid condition on relative bending moments in turn facilitates a maintenance of parallelism of the inner walls, while allowing a degree of constraint of angular separation of the sidewalls under compressive forces. It may be comprehended that a reversal of relative bending moments; a relatively stiff reinforcing bracket engaging relatively a relatively flexible clamp body, or side walls and bottom wall, would tend to lead to pinching of the body of the clamp, and a deviation from parallelism; the concept of relative stiffness in bending having again been more carefully defined above, an explanation of an efficacy of these conditions in maintain flow accuracy again being by way of an aid to understanding. 
     Advantageous conditions of longitudinal stiffness and relative bending moments may be incorporated into any previously described embodiment of the invention. Those skilled in the art will readily comprehend that stiffness and bending are elastic effects which may be modified by choice of material and by thickness of material. However, a further series of embodiments of reinforcing brackets or clips is represented in FIG. 9 et seq., informed by these specific considerations. 
     A partial flow assembly  360  is shown in FIG. 9, having a body element  362 . The body element is provided with internal tracks  365 ,  367  for engagement of axles  374  of roller  372  (FIG.  10 ). A reinforcing clip or bracket  364  is disposed on an end  366  of body  362 ; it can be seen in this embodiment that a top portion of sidewalls (not separately designated) of body  362  have been cut away or notched in a region to receive clip  364 . It may be perceived that, because of a closed shape of clip  364 , the clip is preferably manufactured of an elastomeric material in order to maintain an effective ratio of bending moduli, as discussed above. Clip  364 , as well as the corresponding clips of FIGS. 10-12, may be advantageously snapped into place subsequent to a setting of roller  372 , in fixing a flow rate. This sequence of operations allows an easy setting of roller position, followed by a mechanical locking step. Alternatively, the clips may be pre-assembled to the clamp body, and the roller positioned by means of a firmer thumb pressure. 
     FIG. 10 shows a modification of the embodiment of FIG. 9, in cross section, with a clip  368  in place on an un-notched clamp body  370 . Clip  368  may be described as being in contact with a full outer circumference of body  370 . Clip  368  and those in FIGS. 9,  11 ,  12  may be held in place by way of detents (not shown) as a means of snapping-into-place. FIG. 10 also shows greater mechanical detail of the flow clamp, showing roller  372  mounted on axle  374 , affixed in tracks  376 ,  378 . The roller is shown partially compressing a drip tube  373 . 
     An alternative style of clip or clip-lock  380  is shown in FIG. 11, being open or generally U-shaped in shape rather than closed, and having flanges  382 ,  384  adapted to slip into an internal channel (not separately designated) of body  370 . Clip  380  may be described as being in contact with a full outer circumference of body  370 , with flanges protruding into a reentrant portion or channel of the body. Because of the open shape, it may be perceived that clip  380  may be manufactured of a relatively stiff material, such as stainless steel. The open shape only requires a given flexibility in bending in order to maintain a design ratio of bending moments, discussed above, as opposed to a deformation in tension required of closed-shape clip  368 . 
     A further open-shape clip  386  is shown in FIG. 12; it may be seen that in contrast to clip  380 , open on a top, clip  386  is open on a bottom portion. Clip  386  may also be manufacture advantageously of spring steel or stainless steel. Of course a greater thickness of plastic may be used to achieve an equivalent ratio of bending moduli. It may also be noted from FIGS. 10 through 12 that a greater thickness of material is shown in sidewalls (not separately designated) than in a bottom wall, or channel containing tube  373 . While partially to accommodate tracks  376 ,  378 , this greater thickness may also be appreciated to contribute to an advantageous longitudinal stiffness to clamp body  370 . 
     As a final embodiment, a clamp body  390  shown in FIG. 13 incorporates a bridge or bow  392  as a reinforcing element in lieu of a bracket or clip. This bridge is similar in construction to struts closing a clamp body near an end of greater flow constriction in the prior art. While such struts were located close to a position of maximum stress, it may be appreciated now how a straight strut would contribute a much higher effect bending moment than the sidewalls, hence fail to meet the bending moment condition, hence tend to overcome longitudinal stiffness of the clamp body. In other words, since the strut could not stretch, the sidewalls of the clamp may be expected inevitably to bend when a roller was pushed into a restricted end of the channel. The bow or bridge shape of  392  will however provide a greater degree of flexibility in angular deviation of the walls as compared to a straight strut. 
     Although the invention has been described in terms of particular embodiments and applications, one of ordinary skill in the art, in light of this teaching, can generate additional embodiments and modifications without departing from the spirit of or exceeding the scope of the claimed invention. For example, frame or carriage  56  may take different forms, the function of pointer  70  may be performed by arm  58 , and recesses or seats  74  and  76  may be replaced by beads or other stop elements on side walls  14  and  16 . 
     Also, it is to be understood that inner bracket  30  may be used alone, without outer bracket  32 , to perform the functions of bracket assembly  28 . In that event, bracket  30  is preferably bonded to flow regulator side walls  14  and  16 , whether by adhesive and/or ultrasonic welding or other technique. Where bracket assembly  28  is retrofitted to a pre-existing flow regulator  10 , outer bracket  32  may be held onto inner bracket by friction, adhesive and/or stop  78 . 
     Accordingly, it is to be understood that the drawings and descriptions herein are proffered by way of example to facilitate comprehension of the invention and should not be construed to limit the scope thereof.