WO1983000070A1

WO1983000070A1 - Fluid flow control device

Info

Publication number: WO1983000070A1
Application number: PCT/US1982/000806
Authority: WO
Inventors: Inc. Baxter Travenol Laboratories; Clinton V. Kopp; James Hitchcock; Martin Miller
Original assignee: Baxter Travenol Lab
Priority date: 1981-06-25
Filing date: 1982-06-11
Publication date: 1983-01-06
Also published as: IT8222054A0; IT1151807B; ZA821190B; AR228501A1; ES513483A0; EP0082872A4; EP0082872A1; US4431019A; BR8207766A; CA1173711A; DK95183A; DK95183D0; ES8400031A1; JPS58501012A

Abstract

Fluid flow control devices, and, more particularly, to fluid flow control devices which serve to control fluid pressure. A principal problem with these devices is that they tend to include many moving parts, which create relatively inefficient and expensive manufacturing techniques. As a solution to this problem the present invention includes a minimum of moving parts, which lends itself to relatively efficient and inexpensive manufacturing techniques. Also, this invention includes redundancy in its design to assure consistent and uninterrupted operation. The invention is further designed to provide a fluid flow control device which is suitable for metering the flow of human blood or other parenteral solution and which can constitute an essentially disposable unit. A fluid flow control device (10) comprises first (12), second (14) and third (16) fluid conduits. The first (12) and second (14) fluid conduits are adapted to communicate with separate sources of pressurized fluid (P1), (P2). The third conduit (16) includes an inlet portion (18) in direct flow communication with the first conduit (12) and an outlet portion (20) communicating with the atmosphere. A flexible wall (22) forms an interface between portions of the second (14) and third (16) conduits. In response to fluid pressure fluctuations in the second (14) conduit, the flexible wall (22) simultaneously meters the flow communication through both the inlet (18) and outlet (2) portions of the third (16) conduit. The fluid pressure in the first (12) conduit is thereby elevated until substantial equilibrum with the fluid pressure in the second (14) conduit occurs.

Description

FLUID FLOW CONTROL DEVICE

FIELD OF THE INVENTION

This invention generally relates to fluid flow control devices, and, more particularly, to fluid flow control devices which serve to control fluid pressures.

DESCRIPTION OF THE PRIOR ART

Attention is directed to the following United States Patents which concern various fluid pressure regulating and flow control devices:

Small 1,524,217 January 27, 1925 Boyn on 2,296,833 February 18, 1947 Deck 2,416,161 February 18, 1947 Shabaker 2,850,038 September 2, 1958 einecke et al 2,857,803 October 28, 1958 Pinter et al 2,943,643 July 5, 1960 Boger 3,319,926 May 16, 1967

Brychta et al 3,465,752 September 9, 1969 Ploss 3,693,611 September 26, 1972

Cowan 3,779,267 December 18, 1973

Cibulka 3,853,147 December 10, 1974

Au 4,178,938 December 18, 1979

Stegeman 4,142,523 March 6, 1979

Garrett et al 4,181,245 January 1, 1980

Attention is also directed to two pending U.S. Patent Applications entitled "MEMBRANE PLASMA- PHERESIS APPARATUS AND METHOD" (Clint Kopp and James Hitchcock) and "FLUID FLOW CONTROL DEVICE"

(Clint Kopp and James Hitchcock) , both of which share the same filing date as this application and which are assigned to the assignee of this invention.

One of the principal objects of this invention is to provide a fluid flow control device which is adapted for use in any system in which the control of fluid pressure is desirable, which operates with a minimum of moving parts, and which lends itself to relatively efficient and inexpensive manufacturing technigues.

Another principal object of this invention is to provide a fluid flow control device which includes redundancy in its design to assure consistent and uninterrupted operation.

Yet another principal object of this invention is to provide a fluid flow control device which is suitable for metering the flow of human blood or other parenteral solutions and which can constitute an essentially disposable unit. SUMMARY OF THE INVENTION

To achieve these and other objects, the invention provides a fluid flow control device comprising first, second, and third conduit means. The first and second conduit means are each adapted to communicate with a separate source of pressurized fluid and serve to conduct pressurized fluid from the associated source. The third conduit means conducts pressurized fluid from the first conduit means and includes an inlet portion, which conducts pressurized fluid from the first conduit means into the third conduit means, and an outlet portion, which conducts pressurized fluid out of the third conduit means. The third conduit means further includes generally flexible wall means which forms an interface with a portion of the second conduit means. The flexible wall means is operative in ^response to fluid pressures in the second conduit means for metering the conduction of pressurized fluid through both the inlet and outlet portions of the third conduit means. The metering action of the flexible wall means adjusts the fluid pressure in the first conduit means, until it achieves substantial equilibrium with the fluid pressure then existent in the second conduit means. Furthermore, should the flexible wall means fail to properly meter the conduction through one of the inlet and outlet portions, the ongoing, simultaneously metering of the other inlet and outlet portion assures a steady, uninterrupted operation.

OMPI n one embodiment, the fluid flow control device includes means for defining more than a single path for the fluid traversing the third conduit means to follow. Thus, should one flow path become blocked or obstructed, there is another flow path to assure uninterrupted fluid conduction.

In one embodiment, the device takes the form of a compact housing which lends itself to the efficient manufacture from plastic materials suited for contact with parenteral fluids and the like.

Other features and advantages of the invention will be pointed out in, or will be apparent from, the specification and claims, as will obvious modifications of the embodiments shown in the drawings,

DESCRIPTION OF THE DRAWINGS

Fig. 1 is an exploded perspective view of a fluid control device which embodies various of the features of the invention;

Fig. 2 is an assembled section view of the fluid flow control device taken generally along line 2-2 in Fig. 1;

Fig. 3 is a top view of the device generally taken along line 3-3 in Fig. 2;

Fig. 4 is an enlarged section view of the interior portion of the device; and

Fig. 5 is a diagrammatic view of the fluid flow control device shown in Figs. 1 through 4 used in association with a membrane plasmapheresis apparatus

OMPI __ Before explaining the embodiments of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description and as illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A fluid flow control device 10 is shown in Figs. 1 and 2. The device 10 includes first, second, and third conduit means, respectively, 12, 14, and 16. The first and second conduit means 12 and 14 are each adapted to communicate with a separate source of pressurized fluid (generally designated PI and P2 in Fig. 1) , and each serves to conduct pressurized fluid from the associated source.

The third conduit means 16 serves to conduct pressurized fluid from the first conduit means 12 and, for this purpose, includes an inlet portion 18, which is in direct flow communication with the first conduit means 12, as well as an outlet portion 20, which is spaced from the inlet portion 18 and is in flow communication with the atmosphere.

OMPI The third conduit means 16 also includes flexible wall means 22 which forms an interface with a portion of the second conduit means 14 (see Fig. 2) . The flexible wall means 22 is operative, in response to fluid pressures in the second conduit means 14, to simultaneously meter the conduction of pressurized fluid through both the inlet and outlet portions 18 and 20 of the third conduit means 16. Substantial equilibrium between the fluid pressures in the first and second conduit means 12 and 14 is thereby established and maintained by the device 10.

The device 10 as heretofore described may be variously constructed, depending upon the particular operative objectives a'nd environment in which use is contemplated. In the illustrated embodiment (as best seen in Figs. 1 and 2), the device 10 includes a compact housing 24 in* which an open interior area 26 is defined. The flexible wall means 22 extends transversely across this interior area 26 and thereby compartmentalizes the area 26 into two chambers 28 and 30. One of the chambers, which will hereafter be referred to as the first chamber 28, forms a portion of the heretofore described third conduit means 16. The other chamber, which will hereafter be referred to as the second chamber 30, forms a portion of the heretofore described second conduit means 14.

The housing 24 itself may be variously con¬ structed. However, in the illustrated embodiment (and see, in particular, Fig. 1) , the housing 24 includes first and second generally circular housing portions, which are designated 24a and 24b, between which the flexible wall means 22 is sandwiched. The first chamber 28 is formed within the housing portion 24a, and the second chamber 30 is formed within the housing portion 24b.

As can best be seen in Fig. 2, the first chamber 28 is peripherally bounded on one side by the flexible wall means 22 and on another side by an interior wall or surface 32 of the housing portion 24a. The interior wall 32 directly faces the flexible wall means 22. Furthermore, the first chamber 28 includes laterally spaced ends 34 and 36, and the inlet and outlet portions 18 and 20 of the third conduit means 16 include, respectively, an inlet opening 38 formed in the interior wall 32 in the chamber end 34 and a corresponding outlet opening 40 formed in the interior wall 32 in the other chamber end 36.

In*this arrangement (see Figs. 1 and 2), the first conduit means 12 takes the form of a first, generally rigid member 42 which extends outwardly from the housing portion 24a. The member 42 includes a bore 43 which constitutes a fluid passage leading to the inlet opening 38 of the first chamber 28.

The outlet portion 20 of the third conduit means 16 similarly includes a second generally rigid member 44 which extends outwardly from the same housing portion 24a. The member 44 also includes a bore 45 which constitutes a fluid passage leading from the outlet opening 40 of the first chamber 28.

In the illustrated construction, the inlet and outlet openings 38 and 40 are generally diametrically spaced across from each other in the first chamber 28

OMPI (see Figs. 1 and 3) , and the first and second members 42 and 44 are correspondingly spaced on the exterior of housing portion 24a.

Similarly, the second conduit means 14 includes laterally spaced third and fourth generally rigid members, respectively 46 and 48, which extend outwardly from the other housing portion 24b. The members 46 and 48 each include a bore, respectively 47 and 49, which constitute inlet and outlet fluid passages leading into and out of the second chamber 30.

Each of the outwardly extending rigid members 42, 44, 46 and 48 are suited to accommodate lengths of flexible tubing 52 (shown in phantom lines in Fig. 2) , which serve ,to conduct pressurized fluids to and from the device 10. As shown in Figs. 1 and 2, the members 42, 44, 46, and 48 are preferably tapered at their outer end portions to facilitate their attachment to the flexible tubing 52.

As best seen in Figs. 1, 2 and 4, the inlet and outlet openings 38 and 40 of the first chamber 28 are each circumferentially enclosed by an upstanding annular member 54 which extends axially of the respective openings 38 and 40 outwardly from the interior wall 32 and into the first chamber 28. Each member 54 terminates in a generally planar surface 56 (as best seen in Fig. 4) which extends in a close, normally non-contiguous relationship with the flexible wall means 22 when there are no fluids being conducted through the first and second chambers 28 and 30. While the members 54 associated with the openings 38 and 40 can each constitute a separate annular structure, in the generally circular configur¬ ation of the housing 24 in the illustrated embodiment, the members 54 are part of a continuous upstanding circular ridge 58 formed within the first chamber 28 (see Figs. 1 and 3) .

Second and third members 60 and 62 are diametrically spaced, respectively, inwardly and outwardly of each ofthe first mentioned annular members 54 (see Figs. 2 and 4). Like the annular members 54, the second and third members 60 and 62 each terminates in a generally planar surface 50 which faces the flexible wall means 22 in the same close, normally non-contiguous relationship as the members 5 ; this is, the distance between the surfaces 50 and the flexible wall means 22 is generally the same as the comparable distance between the surfaces 56 and the flexible wall means 22.

The members 60 and 62 serve as points of support for the flexible wall means 22 radially in¬ wardly and outwardly of the planar surfaces 56 and assure that the wall means 22 is maintained in a generally planar configuration with respect to the surfaces 56, notwithstanding movement, or flexing, of the flexible wall means 22 toward the interior surface 32. This enhances the overall metering effect of the flexible wall means 22.

The members 60 and 62 can constitute various shapes to serve this support junction. However, corresponding to the "single-ridge" construction of

iREA OMPI the members 54 of the illustrated embodiment, (i.e., the single ridge 581, the second and third shoulders 60 and 62 are each a part of corresponding second and third upstanding circular ridge 61 and 63, which ridges 61 and 63 are respectively positioned concentrically inwardly and outwardly of the first mentioned ridge 58.

Together, the ridges 58, 61 and 63 provide points of support along the entire span of the flexible wall means 22. The ridges 58, 61, and 63 thus prevent the flexible wall means 22 from assuming an outwardly bowed or convex configuration in the first chamber 28, particularly in the interval between the inlet and outlet openings 38 and 40. This promotes a smooth and even metering of the fluid flow into and out of the first chamber 28.

The* third conduit means 16 further includes means defining more than one fluid path or channel for conducting fluid through the first chamber 28. The particular number and configuration of the flow paths utilized can vary according to the specific interior configuration of the first chamber 28. In the generally circular configuration of the illustrated embodiment (as best seen in Fig. 3), a first, or inner, fluid flow path 66 is formed between the adjacent concentric ridges 58 and 61, and second, or outer, fluid flow path 68 or channel is formed between the adjacent concentric ridges 58 and 63.

Referring now principally to Fig. 4, when a condition exists in which the fluid pressure in the second chamber 30 exceeds the fluid pressure in the first conduit means 12 (and, hence, in the first chamber 28 as well) , the flexible wall means 22 will be displaced by the pressure differential away from the second chamber 30 and, thus, toward the surfaces 56 which circumferentially enclose the inlet and outlet openings 38 and 40 of the first chamber 28. This movement is generally shown by arrows in Fig. 4.

Because of the close proximity of the flexible wall means 22 to the planar surfaces 56, the flow of pressurized fluid through both the inlet and outlet openings 38 and 40 will be metered, or restricted, simultaneously, though independently, and by generally the same amount. This restriction generates resistance, or back pressure, to the flow of pressurized fluid in the first conduit means 12. This back pressure, in turn, causes the fluid pressure in the first conduit means 12 to rise. The elevation in fluid pressure in the first conduit means 12 will continue until a "steady state" condition is achieved in which the pressure in the first conduit means 12 equals the pressure in the second conduit means 14.

It should be appreciated that the particular position of the flexible wall means 22 relative to each of the surfaces 56 necessary to bring about this state of pressure equalization will depend upon the particular magnitudes of the then prevailing pressures in the first and second chambers 28 and 30, as well as the then prevailing fluid flow rates through the first and second chambers 28 and 30.

Should the fluid pressure in the second chamber

30 subsequently increase or decrease, the flexible wall means 22 will correspondingly change its position relative to ea.ch of the surfaces 56 by jnoying toward a new position, respectively, closer to or farther away from the surfaces 56. This automatically changes the previously imposed restriction to the fluid flow through each of the openings 38 and 40 in lieu of a new restriction. The conduction of fluid into and out of the first chamber 28 will thus be metered at a new rate until a new state of equilibrium at the higher or lower fluid pressure level occurs.

The flexible wall means 22 is thus movable through a range of positions which are progressively spaced closer to or farther away from the surfaces 56. The particular position assumed by the flexible wall means within this range will depend upon the particular fluid pressures and flow rates then prevailing.

It^should be appreciated that the movement of the flexible wall means 22 as just described occurs virtually instantaneously with pressure fluctuations occurring within the second chamber 30. Thus, the device 12 is operative to continuously and automatically maintain pressure equilibrium between the first and second conduit means 12 and 14.

In the illustrated and preferred embodiment, the planar surfaces 56 facing the flexible wall means 22 include a grooved or roughened outer configuration 69. This roughened configuration 69 serves to break any surface tension that might develop between the planar surfaces 56 and the closely adjacent flexible wall means 22. The configuration 69 thus prevents the flexible wall means 22 from completely seating against the planar surfaces 56 to completely block fluid flow through the associated opening 38 and 40. A continuous conduction of pressurized fluid into and through the first chamber 28 is thus maintained by the device 10, notwithstanding the continuous and automatic metering of the flexible wall means 22 and its continuously close proximity to the surfaces 56. Furthermore, periodic spikes of pressure in the first conduit means 12, occassioned by intermittent closure of either the inlet or outlet openings 38 and 40, are virtually eliminated.

In the illustrated embodiment, the entire extent of the ridge 58 facing the flexible wall means 22 is roughened to any break surface with the wall means 22 along this area.

The provision of two independent flow paths 66 and 68 within the first chamber 28 and the simul¬ taneous, th<?ugh independent, metering of each of the inlet and outlet openings 38 and 40 by the flexible wall means 22, provide redundancy in the design of the device 10. Thus, for whatever reason, should the flexible first wall means 22 fail to properly meter the conduction of fluid flow through either one of the openings 38 or 40, the ongoing independent metering of the other opening 38 or 40 will continue to maintain and establish the condition of substantial equilibrium desired. Furthermore, for whatever reason, should one of the flow paths 66 or 68 in the first chamber 28 become blocked or obstructed, the other open flow path 66 or 68 will continue to conduct the fluid through the first chamber 28. While the device 12 may be variously manu¬ factured, in the illustrated embodiment, the first and - second housing portions 24a and 24b constitute separately molded plastic pieces, such as from an injection molded, polyvinyl chloride plastic or plexiglass material. The three ridges 58, 61, and 63 and the fluid flow paths 66 and 68 positioned therebetween form integrally molded portions of the housing portions 24a, as are the outwardly extending members 42 and 44. The same is true for the second chamber 30 and members 46 and 48 associated with the housing portion 24b.

In this construction, the flexible first wall means 22 takes the form of a generally circular- diaphragm made of silicon rubber or the like. The diaphragm 22 includes an annular ring 70, and the housing portion 24a includes a corresponding annular groove 72 in which the ring 70 is seated when the housing portions 24a and 24b are properly assembled together, such as by heat or solvent bonding, or by encapsulation. This assembly assures that the flexible diaphragm 22 remains generally uniformly planar within the housing 24 and does not become wrinkled, warped or otherwise incorrectly positioned during the manufacturing or use. This assembly also serves to seal the first and second chambers 28 and 30 from each other to prevent the intermixing of fluids between the first and second conduit means 12 and 14.

This compact structural arrangement also lends itself to construction utilizing a relatively few pre-formed pieces and a minimum of moving parts. The device 10 can thus be manufactured in an efficient and economical manner and constitute an essentially disposable unit. It also lends itself well to construc¬ tion utilizing only plastic materials and the like which have been approved for contact with human blood or other parenteral fluids.

The device 10 as heretofore described is applicable for use in numerous diverse environments. As is shown in Fig. 5, the device 10 is particularly well suited for use to stabilize the transmembrane pressure of a membrane plasmapheresis apparatus 74.

In this environment, the apparatus 74 includes a module 76 or cell defining a housing in which two sheets 78 of a microporous membrane having a pore size of about 0.1 micron to 2 microns are positioned in a facing, spaced-apart relationship. A fluid path 80 is thus formed between the interior surfaces of the membranes. Open volumes 82 are also formed between the outer surfaces of the membranes and the interior surfaces of the housing. Alternately, a module (not shown) in which a cluster of hollow fiber membranes is supported can be utilized in lieu of the sheet membranes shown in Fig. 5.

In normal operation, whole blood, typically from a patient-donor, is pumped under a predetermined pressure through the fluid path 80 between the sheet membranes 78. The whole blood experiences a determinable pressure drop as it proceeds across the length of the module 76. This causes the red cells, leukocytes, and platelets (known collectively as plasma-poor blood) to proceed in a laminar path across the inner surfaces of the membranes 78, typically for return to the donor via a transfusion set 84. A transmembrane pressure is also generated which, when within a desirable range of between 50 mmHg and 100 mmHg, acts as a driving force to cause the plasma to pass through the pores of the membranes 78 into the volumes 82. A collection conduit 86 communicates with the volumes 82 for transmitting the plasma filtrate to an external container or bag 88. However, should the transmembrane pressure exceed a critical level (approximately 120 πεsHg) , red cells can themselves be driven into the pores of the membranes 78 and be damaged or destroyed, causing hemolysis.

To stabilize the transmembrane pressure within acceptable levels, the fluid control device 10 as illustrated in Figs. 1 through 4 is connected downstream of the module 76 in flow communication with both the transfusion set 84 and the plasma collection conduit 86. More particularly, the first member 42 (i.e., the first conduit means 12 of the device 10) , is attached in flow communication with the plasma filtrate volumes 82 downstream of the module 76, and the second member 44 (i.e., part of the outlet portion 20 of the third conduit means 16) is attached in flow communication with the plasma collection container 88.

As a result of this interconnection, plasma filtrate flows out oϋ the volumes 82, subject to a determinable plasma pressure, through the first conduit means 12, and thence into and through the third conduit means 16 on its route to the plasma collection container 88, subject to metering by the flexible wall r-εans 22.

ζ3RE OMPI The inlet and outlet members 46 and 48 of the second conduit means 14 are connected in-line with the transfusion set 84 downstream of the module 76 and upstream of a bubble trap 90 and any auxiliary equipment 92 (such as a blood warmer) associated with the apparatus 74.

As a result of this in-line connection, the plasma-poor blood exiting the fluid path 80 flows through the second conduit means 14, subject to any back pressure or fluid flow resistance generated by equipment downstream of the module 76. The blood pressure of the patient-donor and any movement of his or her arm during the procedure can also contribute to the back pressure.

At the outset of the plasmapheresis procedure, a pressure differential will virtually always exist between the plasma pressure, which is typically at 0 mmHg, and the backside blood pressure, which typically fluctuates randomly between 20 mmHg and 150 mmHg.

By virtue of the pressure differential between the first chamber 28 (at the plasma pressure) and the second chamber 30 (at the then prevailing backside blood pressure) , the flexible first wall means 22 of the device 10 will be immediately displaced as heretofore described toward the surfaces 56 associated with the inlet and outlet openings 38 and 40. This is generally shown by arrows and phantom lines in Fig. 5. This serves to restrict the flow of plasma filtrate into and through the first chamber 28. The plasma pressure entering the first chamber 28 will thus be elevated, until it

PI reaches a state of substantial equilibrium with the backside blood pressure.

It has been observed that, when this state of equilibrium between the plasma pressure and backside blood pressure exists, the magnitude of the transmembrane pressure is stabilized and not effected by ongoing fluctuations in the backside pressure.

The device 10 will thereafter operate to maintain this equilibrium, notwithstanding subsequent variations in the backside blood pressure. Furthermore, as heretofore described, the device 10 will also operate to maintain a continuous flow of plasma filtrate and plasma-poor blood downstream of the module 76.

The fluid flow control device 10 of the present invention can be of various sizes, according to the operational environment in which it is used. In one embodiment suited for operation under the pressures conditions normally encountered during membrane plasmapheresis operations, the housing 24 is approximately 2.0 inches in overall diameter. The maximum depth of the first chamber 28 is approximately .09 inch, and the corresponding maximum depth of the second chamber is approximately .17 inch. In this embodiment, the height of the ridges 58, 61, and 63 extending within the first chamber 28 is approximately .04 inch, and the width of the circular flow paths 64 and 66 is approximately .15 inch. In this operative environment, the diaphragm (i.e., the flexible wall means 22) has a thickness of about .0015 inch, and the normal interval between the diaphragm 22 and the surfaces 50 and 56, absent fluid flow in the first and second chambers, is approximately .005 inch. Also in this operative embodiment, the roughened configuration 68 of the surfaces 56 constitutes a number 32 EDM finish.

Use of this operative embodiment of the device 10 in association with the apparatus 74 has been observed to stabilize the transmembrane pressure, regardless of the magnitude of the then existent backside pressure, at a magnitude which represents only the flow resistance of the module 76 itself, which is a quantity under direct operator control. In particular, when an inlet blood pressure of between 150 mmHg and 200 mmHg and ^ pressure drop across the module 76 of approximately 100 mmHg are maintained by the operator, the device 10 serves to stabilize the transmembrane pressure within the operationally desirable range of between 50 mmHg and 100 mmHg, even though the backside pressure may at the same time be undergoing random fluctuations of between 20 mmHg and 150 mmHg.

In addition, the device 12 has been observed to continuously maintain an uninterrupted flow of plasma filtrate from the module 76 and through the first and third conduit means 12 and 16 at a rate of between 10 cubic centimeters per minute and 80 cubic centimeters per minute. At the same time, the device 10 has been observed to continuously maintain an uninterrupted flow of plasma-poor blood from the module 76 and through the second conduit means 14 at a rate of between 40 cubic centimeters per minute and 300 cubic centimeters per minute.

Use of the fluid flow control device 10 in association with the apparatus 76 permits the use of operationally desirable components of membrane plasmapheresis, such as a smaller, more comfortable needle, and auxiliary equipment such as the blood warmer, without affecting the stability of the transmembrane pressure and without causing hemolysis.

It should be appreciated that various changes and modifications can be made without departing from the scope of the appended claims.

Claims

1. A fluid flow control device comprising first conduit means adapted for communication with a first source of pressurized fluid for conducting pressurized fluid from the first source. second conduit means adapted for communication with a second source of pressurized fluid for conducting pressurized fluid from the second source, and third conduit means for conducting pressurized fluid from said first conduit means and including an inlet portion in direct flow communication with said first conduit means for conducting pressurized fluid from said first conduit means into said third conduit means and an outlet portion in flow communication with the atmosphere for conducting pressurized fluid from said third conduit means, said third conduit means

4 further including generally flexible wall means forming an interface with a portion of said second conduit means and being operative in response to fluid pressures in said second conduit means for metering the conduction of pressurized fluid through said inlet and outlet portions of said third conduit means, to thereby establish substantial equilibrium between the fluid pressures in said first and second conduit means.

2. A fluid flow control device according to claim 1 wherein said flexible first wall means is operative for metering the conduction of pressurized fluid through said inlet and outlet portions of said third conduit means to maintain substantial equilibrium between the fluid pressures in said first and second conduit means, notwithstanding subsequent fluctuations in the fluid pressures in said second conduit means.

3. A fluid flow control device according to claim 1 or 2 and further including means for maintaining a continuous conduction of pressurized fluid through said inlet and outlet portions of said third conduit means, notwithstanding said metering by said flexible wall means.

4. A fluid flow control device according to claim 1 or 2 wherein said third conduit means includes means for defining more than one fluid flow path between said inlet and outlet portions thereof.

5. A fluid flow control device according to claim 1 or 2 w erein said third conduit means includes means defining a first chamber having oppositely spaced ends with said inlet portion of said third conduit means disposed adjacent to one of said chamber ends and said outlet portion of said third conduit means disposed adjacent to the opposite chamber end, and wherein said second conduit means includes means defining a second chamber separated from said first chamber by said flexible wall means.

6. A fluid flow control device according to claim 5 wherein said third conduit means includes second wall means oppositely spaced from said flexible first wall means and, together with said flexible first wall means, peripherally defining the interior boundaries of said first chamber, wherein said inlet portion of said third conduit means includes an inlet opening formed in said second wall means in flow communication with said first conduit means, and, wherein said flexible first wall means is operative for movement in response to fluctuations in the fluid pressures in said second chamber toward and away from said inlet opening to meter the conduction of pressurized fluid into said first chamber.

7. A fluid flow control device according to claim 6 wherein said outlet portion of said third conduit means includes an outlet opening formed in said second wall means in flow communication with the atmosphere, and wherein said flexible first wall means is operative for movement in response to fluctuations in the fluid pressure in said second chamber in a path toward and away from said outlet opening to meter the conduction of pressurized fluid from said first chamber.

8. A fluid flow control device according to claim 7 wherein said third conduit means includes a member circumferentially surrounding each of said inlet and outlet openings and extending from said second wall means into said first chamber and terminating in a closely spaced position from said flexible wall means.

9. A fluid flow control device according to claim 8 wherein each of said members includes a generally planar surface facing said flexible wall means in a generally parallel relationship thereto.

10. A fluid flow control device according to claim 9 wherein said third conduit means further includes means adjacent to each of said members for maintaining said flexible wall means in said generally parallel relationship with said planar surface during said movement of said flexible wall means.

11. A fluid flow control device according to claim 9 wherein said planar surface includes means for breaking surface tension between said planar surface and said flexible wall means, whereby a continuous conduction of pressurized fluid is maintained into and through said first chamber.

12. A fluid flow control device according to claim 7 wherein said third conduit means includes means extending into said first chamber for maintaining said flexible wall means in a generally planar position, notwithstanding said movement of said flexible wall means

13. A fluid flow control device according to claim 1 wherein said third conduit means includes means for defining more than one independent fluid flow paths between said inlet and outlet portions thereof.

14. A fluid flow control device according to claim 6 wherein said first and second chambers are generally circular in cross section, wherein said third conduit means includes means within said first chamber for defining independent concentric fluid flow paths between said inlet and outlet portions.

15. A fluid flow control device comprising first conduit means adapted for communication with a first source of pressurized fluid for conducting pressurized fluid from the first source, second conduit means adapted for communication with a second source of pressurized fluid for conducting pressurized fluid from the second source, and a housing having an open interior and including means for c partmentalizing said open interior into a first chamber and a second chamber, said first and second chambers having inlet portions in flow communica- tion, respectively, with said first conduit means and second conduit means and outlet portions communicating with the atmosphere, said means including flexible wall means forming an interface between said first and second chambers and operative for metering the conduction of pressurized fluid through said inlet and outlet portions of said first chamber in response to the fluid pressure in said second chamber to establish substantial equilibrium between the fluid pressures in said first and second conduit means.

16. A fluid flow control device according to claim 15 wherein said flexible wall means is operative for metering the conduction of pressurized fluid through said inlet and outlet portions of said first chamber to maintain substantial equilibrium between the fluid pressure in said first and second conduit means, notwithstanding subsequent fluctuations in the fluid pressures in said second conduit means.

17. A fluid flow control device according to claim 15 or 16 and further including means for maintaining a continuous conduction of pressurized fluid through said first chamber notwithstanding said metering of said flexible wall means.

18 A fluid flow control device according to claim 17 wherein said inlet and outlet portions of said first chamber includes spaced inlet and outlet openings facing said flexible wall means, wherein said flexible wall means is operative for movement in response to fluctuations in the fluid pressures in said second chamber in a path toward and away each of said inlet and outlet openings to meter the conduction of pressurized fluid therethrough.

19. A fluid flow control device according to claim 18 wherein, in response to fluctuations in the fluid pressures in said second chamber, said flexible wall means is movable in said path through a plurality of positions progressively spaced toward and away from said inlet and outlet openings to restrict a conduction of fluid therethrough.

20. A fluid flow control device according to claim 18 wherein said first chamber includes an interior surface oppositely spaced from and facing said flexible wall means, wherein said inlet and outlet openings extend through said interior surface, and further including means extending from said interior surface for preventing movement of said flexible wall means beyond a predetermined point within said first chamber, notwithstanding pressure fluctuations in said second chamber.

4

21. A fluid flow control device according to claim 20 wherein said means extending from said interior surface includes a first member disposed adjacent to said inlet opening, a second member disposed adjacent to said outlet opening, and a third member disposed generally intermediate said inlet and outlet openings.

22. A fluid flow control device according to claim 21 wherein said first and second members circum¬ ferentially surround said respective inlet and outlet openings and each include a generally planar surface facing said flexible wall means.

23. A fluid flow control device according to claim 22 wherein each of said planar surfaces including means for breaking surface tension between said first and second members and said flexible wall means, whereby a continuous conduction of pressurized fluid through said inlet and outlet openings is maintained, notwith¬ standing the proximity of said flexible wall means.

24. A fluid flow control device according to claim 22 wherein said first and second chambers are generally circular in cross section.

25. A fluid flow control device according to claim 24 wh 4erein said third conduit means includes means defining first and second concentric fluid flow paths between said inlet and outlet portions of said first chamber.