Flow Control Diverter Valve

Abstract

A valve assembly (10) is disclosed which is configured to maintain a fluid flow therethrough at a constant flow rate. The valve assembly (10) includes a flexible flow control member (50) and an inlet opening (56) leading to an internal fluid chamber (90), the flexible flow control member defining an internal fluid chamber (90) within the flexible flow control member (50). An external fluid chamber (92) is defined between the flexible flow control member (50) and an inner surface (74) of a valve housing (20). The flexible flow control member (50) is configured to bend inwardly and contract the internal fluid chamber (90) in response to a decrease in pressure of the internal fluid chamber (90) relative to the external fluid chamber (92) due to an increase in the inlet flow rate, so as to maintain an outlet flow rate from the valve assembly (10) at a constant flow rate.

Description

Technical Field

[0001] The present disclosure relates to flow regulating valves, such as, for example, flow regulating shunt valves for treating hydrocephalus. Background Art

[0002] This section provides background information related to the present disclosure which is not necessarily prior art.

[0003] The treatment of hydrocephalus is usually achieved by transferring cerebrospinal fluid from the intracranial ventricles to the peritoneal cavity. Fluid flow is controlled by a valve that provides a non-constant flow rate. Although current valves can be used for their intended use, there is still room for improvement. The present disclosure advantageously includes an improved valve that can provide a constant flow rate, as explained in detail herein. Those skilled in the art will appreciate that the present disclosure also provides many additional advantages. Summary of the invention

[0004] This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

[0005] The present disclosure includes a valve assembly configured to control the flow of a fluid therethrough. The valve assembly has a housing, an inlet channel, and an outlet channel, wherein a fluid enters the housing at an inlet flow rate through the inlet channel, and the fluid leaves the housing at an outlet flow rate through the outlet channel. A flexible flow control member is located within the housing. The flexible flow control member defines an internal fluid cavity within the flexible flow control member and an inlet opening leading to the internal fluid cavity. The inlet channel and the outlet channel are in fluid communication with the internal fluid cavity. An external fluid cavity is defined between the flexible flow control member and the inner surface of the housing. The valve assembly is configured such that a fluid flows from the inlet channel into the external fluid cavity, flows from the external fluid cavity into the internal fluid cavity through the inlet opening defined by the flexible flow control member, and flows out of the internal fluid cavity through the outlet channel. The flexible flow control member is configured to bend inwardly and contract the internal fluid cavity in response to a decrease in pressure of the internal fluid cavity relative to the external fluid cavity due to an increase in the inlet flow rate, so as to maintain the outlet flow rate at a constant rate.

[0006] The present disclosure also includes a valve assembly configured to be arranged on a user to provide a constant flow rate of fluid entering or leaving the user through the valve assembly. The valve assembly includes an inlet connector extending from the upstream end of the housing. The inlet connector is configured to be connected to a first conduit that delivers fluid into the housing at an inlet flow rate. The outlet connector extends from the downstream end of the housing and is configured to be connected to a second conduit that delivers fluid out of the housing at an outlet flow rate. A flexible flow control member is located in the housing. The flexible flow control member defines an internal fluid cavity in the flexible flow control member and an inlet opening leading to the internal fluid cavity. A support is located in the housing, and the flexible flow control member is mounted on the support. The support defines an outlet opening leading to an outlet channel. The outlet opening is located in the internal fluid cavity. The external fluid cavity is defined between the flexible flow control member and the inner surface of the housing. The check valve is located at the upstream end of the housing and is configured to allow fluid to flow from the inlet connector into the external fluid cavity and restrict fluid from flowing back to the inlet connector from the external fluid cavity. The valve assembly is configured to allow fluid to flow from the outer fluid cavity into the inner fluid cavity through an inlet opening defined by the flexible flow control member and out of the inner fluid cavity through the outlet opening and the outlet passage. In response to an increase in negative static hydraulic pressure in the outlet passage, the flexible flow control member is configured to bend toward the outlet opening to reduce the flow of fluid through the outlet opening and maintain the outlet flow rate at a constant flow rate.

[0007] The present disclosure also includes a method of using a valve assembly to provide a constant flow rate of a fluid entering or leaving a user through the valve assembly. The method includes the steps of connecting an inlet connector extending from an upstream end of a housing to a first conduit that delivers fluid into the housing at an inlet flow rate; connecting an outlet connector extending from a downstream end of the housing to a second conduit that delivers fluid out of the housing at an outlet flow rate; and arranging the valve assembly relative to the user. The valve assembly is configured such that a fluid that flows into the housing through the inlet connector flows into an outer fluid cavity surrounding a flexible flow control member, flows into an inner fluid cavity defined by the flexible control member through an inlet opening defined by the flexible flow control member, and flows out of the inner fluid cavity through the outlet opening and the outlet connector. In response to a decrease in internal pressure within the inner fluid cavity of the valve assembly relative to the outer fluid cavity due to an increase in the inlet flow rate of the fluid entering the housing, the flexible flow control member is configured to bend inwardly and cause the inner fluid cavity to contract to provide a constant flow rate of the fluid through the valve assembly.

[0008] Further areas of applicability will become apparent from the description provided herein.The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

[0010] Figure 1 An exemplary valve assembly coupled to a subject to regulate fluid flow from the subject is shown in accordance with the present disclosure;

[0011] Figure 2 yes Figure 1 A perspective view of a valve assembly;

[0012] Figure 3 yes Figure 1 An exploded view of the valve assembly;

[0013] Figure 4A It is along Figure 2 a cross-sectional view of the valve assembly taken along line 4A-4A;

[0014] Figure 4B illustrating fluid flow through the valve assembly at a first flow rate;

[0015] Figure 4C illustrating fluid flow through the valve assembly at a second flow rate greater than the first flow rate;

[0016] Figure 5 It is along Figure 2 Another cross-sectional view of the valve assembly taken along line 5-5;

[0017] Fig. 6A It is along Figure 5 a cross-sectional view of the valve assembly taken along line 6A-6A of , wherein the flexible flow control member is in a relaxed position;

[0018] Figure 6B and Fig. 6A the same, but the flexible flow control member flexes inwardly due to increased fluid flow through the valve assembly;

[0019] Figure 7 Shown in detail Figure 4A Region 7;

[0020] Fig. 8A Shown in detail Figure 4A Area 8A;

[0021] Figure 8B Similar to Fig. 8A , but the flexible flow control member bends inwardly to reduce the flow rate of the fluid through the valve assembly;

[0022] Fig. 9 Shown in detail Figure 5 Area 9;

[0023] Fig.10 is a cross-sectional view of another valve assembly according to the present disclosure;

[0024] Fig.11 Shown in detail Fig.10 Region 11;

[0025] Fig.12 is a cross-sectional view of yet another valve assembly according to the present disclosure; and

[0026] Fig.13 yes Fig.12 Exploded view of the valve assembly.

[0027] Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. DETAILED DESCRIPTION

[0028] Example embodiments will now be described more fully with reference to the accompanying drawings.

[0029] Initial reference Figures 1 to 3 , a valve assembly according to the present disclosure is shown at reference numeral 10. The valve assembly 10 advantageously regulates the flow of fluid therethrough to provide a constant flow, regardless of pressure changes experienced in the system to which the valve assembly 10 is connected, as explained in detail herein. The valve assembly 10 may be used in any suitable application in which a constant fluid flow is advantageous. For example, the valve assembly 10 may be used to provide a constant fluid flow in the treatment of idiopathic normal pressure hydrocephalus (iNPH) and during chemotherapy. Although the valve assembly 10 is discussed in the context of hydrocephalus applications, the valve assembly 10 may be used to control fluid in any other application having varying pressure and / or fluid flow, such as any suitable non-medical application.

[0030] Hydrocephalus is most common in infants and the elderly, and is usually caused by obstruction of cerebrospinal fluid (CSF) circulation caused by trauma, tumors, congenital malformations, intracerebral hemorrhage, etc. Hydrocephalus often causes increased intracranial ventricular pressure, and patient symptoms usually include headaches, nausea, drowsiness, poor balance, visual impairment and / or loss of motor function. Current shunt technology includes the use of a differential pressure valve that regulates intracranial pressure and is driven by intracranial pressure. In contrast, the valve assembly 10 according to the present invention regulates excess fluid (such as excess CSF) by diverting the fluid at a constant flow rate.

[0031] exist Figure 1In an exemplary configuration, the valve assembly 10 is attached to a subject 510 to drain fluid from a brain 512. The valve assembly 10 is disposed on a skull 514 beneath a dermis 516 of the subject 510. The valve assembly 10 includes a housing or body 20 positioned between an inlet connector 22 and an outlet connector 26. The inlet connector 22 defines an inlet port 24. The outlet connector 26 defines an outlet port 28. Fluid enters the inlet port 24 at an inlet flow rate and leaves the outlet port 28 at an outlet flow rate. Advantageously, the valve assembly 10 is configured such that the outlet flow rate remains constant regardless of changes in the inlet flow rate and changes in pressure.

[0032] The inlet connector 22 is connected to a first conduit or catheter 520 extending from the brain 512. The outlet connector 26 is connected to a second conduit or catheter 522. The second conduit 522 extends to any suitable discharge location. With respect to excess CSF, for example, it is shunted from the intracranial ventricles to the peritoneal cavity or atria, and ultimately absorbed by the lymphatic system and / or blood circulation of the subject 510. Although the valve assembly 10 is shown as being arranged on the skull 54, the valve assembly 10 can be arranged at any other suitable location, such as behind the ear of the subject 510, on a bony skull plate of the subject 510, etc. Therefore, due to, for example, having an in-line opening and an integrated adjustment and opening mechanism, the valve assembly 10 is advantageously miniaturized and has a very low profile.

[0033] A substrate 30 may be included to facilitate placement of the valve assembly 10, such as at an external bone surface. The housing 20 may be secured to the substrate 30 in any suitable manner, such as using any suitable adhesive. The substrate 30 may be made of woven silicone or any other suitable material. The housing 20 may be made of plastic or any other suitable material.

[0034] Continue to refer Figures 1 to 3 , and additionally refer to Figure 4A , the outlet connector 26 defines an outlet passage 40 that extends from the outlet port 28 into the housing 20. The outlet connector 26 is seated in the body outlet aperture 32 of the housing 20. The outlet passage 40 extends from the outlet port 28, through the body outlet aperture 32, and into the housing 20.

[0035] A first outlet opening 42A and a second outlet opening 42B of the outlet passage 40 are defined within the housing 20. Extending from the first outlet opening 42A and the second outlet opening 42B is a support 44 that extends further into the housing 20 toward the inlet connector 22. At one end of the support 44 near the inlet passage 48 is a knob 46. The inlet connector 22 defines an inlet passage 48 that extends from the inlet port 24 to the housing 20.

[0036] A flexible flow control member 50 is disposed on the support 44. In the example shown, the flexible flow control member 50 has a generally tubular configuration. The flexible flow control member 50 may be made of any suitable flexible material, such as silicone, polysiloxane, or any other suitable polymer. The flexible flow control member 50 may also be made of any suitable rubber material, such as ethylene propylene diene monomer (EDPM) or Viton. TM , which is available from the Chemours Company of Wilmington, Delaware.

[0037] The flexible flow control member 50 defines a hole 52 at its downstream end through which the outlet passage 40 extends. Near the upstream end of the flexible flow control member 50 are one or more inlet openings 56. For example, the flexible flow control member 50 may define four inlet openings 56, a pair of inlet openings 56 on the top and bottom, and a pair of inlet openings 56 on opposite sides of the flexible flow control member 50. The top and bottom inlet openings 56 may be smaller than the side inlet openings 56.

[0038] The flexible flow control member 50 defines an inner fluid cavity 90 therein. An outer fluid cavity 92 is defined between the flexible flow control member 50 and the inner surface 74 of the housing 20. The inlet opening 56 provides fluid communication between the outer fluid cavity 92 and the inner fluid cavity 90.

[0039] A check valve 70 is located at the upstream end of the flexible flow control member 50. In the example shown, the check valve 70 includes a flexible flap 72 and is integral with the remainder of the flexible flow control member 50. The check valve 70 is seated on the support 44 at the knob 46 so that when the flexible flap 72 is in a relaxed position, the flexible flap 72 abuts an inner surface 74 of the housing 20 near the inlet passage 48. The flexible flap 72 can move from the relaxed position to a bent or folded position to allow fluid to flow from the inlet passage 48 through the check valve 70 when the fluid is large enough to bend the flap 72. The flexible flap 72 restricts fluid flow in the opposite direction. Figure 4B and Figure 4C Exemplary fluid flow through the check valve 70 into the outer fluid cavity 92 and the inner fluid cavity 90 is shown and will be described in detail herein. Figure 7 Shown in detail Figure 4A 7 and illustrates the interaction between the flexible flap 72 of the check valve 70 and the inner surface 74 of the housing 20 .

[0040] like Figure 5 , Fig. 6A and Figure 6B4. As shown, the support member 44 has a generally rectangular cross-section such that the height of the support member 44 is less than the width of the support member 44. The width of the support member 44 generally spans the internal fluid cavity 90. Thus, the areas of the internal fluid cavity 90 into which fluid can flow are generally on the top and bottom sides of the support member 44. On the exterior of the flexible flow control member 50 are concave outer surfaces 120 located on the top, bottom, and sides of the flexible flow control member 50. The concave outer surfaces 120 facilitate fluid flow into the inlet opening 56. In the relaxed position, the internal fluid cavity 90 has a generally circular cross-sectional shape ( Fig. 6A When the flexible flow control member 50 bends inwardly in response to increased fluid flow as further described herein, the cross-section of the internal fluid cavity 90 becomes elliptical ( Figure 6B ).

[0041] Fig. 8A Shows Figure 4A Area 8A. Fig. 8A As shown, the first slot 140A is defined between the flexible flow control member 50 and the first outlet opening 42A (and the portion of the outlet connector 26 that defines the first outlet opening 42A). The second slot 140B is defined between the flexible flow control member 50 and the second outlet opening 42B (and the portion of the outlet connector 26 that defines the second outlet opening 42B). Fig. 8A In the relaxed position, fluid from the internal fluid cavity 90 can flow through the first and second slots 140A, 140B and into the outlet passage 40 through the first and second outlet openings 42A, 42B to exit the valve assembly 10 at a first flow rate.

[0042] When the pressure within the outlet passage 40 drops relative to the pressure within the internal fluid chamber 90, a negative static hydraulic pressure condition may occur within the outlet passage 40 which may result in a siphon effect that draws fluid through the valve assembly 10. Figure 8B During such negative static hydraulic pressure conditions, the flexible flow control member 50 is configured to flex inwardly toward the first outlet opening 42A and the second outlet opening 42B, thereby reducing the size of the first slot 140A and the second slot 140B and reducing fluid flow through the valve assembly 10 to ensure that fluid flows out at a constant rate. In this manner, the flexible flow control member 50 advantageously resists a siphon effect that could excessively drain fluid through the valve assembly 10. Figure 8B The inward bending structure can be Figure 4C The inward curvature of the Figure 4C An inwardly curved configuration occurs, which will be further described in this article.

[0043] Special References Figure 5 and show Figure 5 Area 9 Fig. 9 , a leakage channel 110 is defined by the flexible flow control member 50. The leakage channel 110 provides fluid communication between the external fluid chamber 92 and the outlet channel 40. The leakage channel 110 allows a small amount of fluid to flow directly from the external fluid chamber 92 into the outlet channel 40 at a low rate without flowing through the internal fluid chamber 90. The flow of fluid through the leakage channel 110 advantageously reduces the pressure in the external fluid chamber 92 and prevents fluid from being trapped in the external fluid chamber 92, which can "lock" the flexible flow control member 50 in place. Figure 4C or Fig. 8A The leakage channel 110 can also reduce "dead space" in the external fluid cavity 92, which can otherwise retain fluid and accumulate particles from the cerebrospinal fluid inside the intracranial ventricles (thereby advantageously reducing any possibility of infection during the shunt process). In some applications, for example, about 10% to 20% (such as about 14%) of the fluid flows through the leakage channel 110 to reduce the pressure in the external fluid cavity 92 by about 80% to 90% (such as about 85%). The amount of pressure drop in the external fluid cavity 92 depends on, for example, the pressure difference between the external fluid cavity 92 and the internal fluid cavity 90. The larger the difference, the greater the pressure drive, and therefore the greater the pressure drop in the external fluid cavity 92.

[0044] Re-reference Figure 4B and Figure 4C , when the pressure and flow rate of the fluid are sufficient to bend the flexible flap 72, the fluid from the inlet passage 48 flows through the check valve 70 and into the external fluid chamber 92. Some of the fluid remains in the external fluid chamber 92, and some of the fluid flows through the inlet opening 56 of the flexible flow control member 50 into the internal fluid chamber 90. The fluid flows from the internal fluid chamber 90 through the first slot 140A and the second slot 140B, and flows through the first outlet opening 42A and the second outlet opening 42B into the outlet passage 40. The fluid exits the valve assembly 10 from the outlet passage 40 through the outlet port 28. Some of the fluid in the external fluid chamber 92 flows through the leakage passage 110 into the outlet passage 40 without flowing through the internal fluid chamber 90.

[0045] As fluid flow through the inlet passage 48 increases, a higher flow velocity within the inner fluid cavity 90 relative to the outer fluid cavity 92 can be expected where the opening / diameter at the inlet opening 56 is larger than the leakage passage 110. Thus, as the fluid flows from the inlet opening 56 toward the first and second outlet openings 42A and 42B, more pressure / momentum losses will occur, which results in a pressure drop within the inner fluid cavity 90 relative to the outer fluid cavity 92.

[0046] This pressure differential between the inner fluid chamber 90 and the outer fluid chamber 92 causes the flexible flow control member 50 to flex inwardly and cause the inner fluid chamber 90 to contract, as shown in FIG. Figure 4C As shown. The pressure differential is greatest at the portion of the internal fluid cavity 90 near the first outlet opening 42A and the second outlet opening 42B. When the fluid flow rate through the inlet passage 48 decreases, the pressure within the internal fluid cavity 90 increases toward or returns to the same pressure as the external fluid cavity 92, which moves the flexible flow control member 50 toward Figure 4B The relaxed position of the flexible flow control member 50 moves backward or returns to the relaxed position (or allows the flexible flow control member 50 to move toward Figure 4B The flexible flow control member 50 may bend backward or bend back to the relaxed position, such as when the flexible flow control member 50 is made of any suitable shape memory material. In this manner, the flexible flow control member 50 regulates the flow of fluid through the housing 20 to provide a constant fluid flow.

[0047] For example, when the fluid flow rate through inlet passage 48 increases from 5 cc / hr to 50 cc / hr, inner fluid cavity 90 experiences an exemplary pressure drop of approximately 0.056 psi, thus resulting in a pressure differential of approximately 0.050 psi between inner fluid cavity 90 and outer fluid cavity 92. Inner fluid cavity 90 then curves inwardly to reduce the fluid flow rate therethrough.

[0048] Figure 4B and Figure 4C The bending of the flexible flow control member 50 shown in FIG. 5 can be independent of or in combination with Fig. 8A and Figure 8B , thereby reducing the size of the first slot 140A and the second slot 140B to reduce the siphon effect caused by the negative static hydraulic pressure state. Similarly, Fig. 8A and Figure 8B The bends shown in can be independent of or combined with Figure 4B and Figure 4C This occurs due to the bending of the flexible flow control member 50 shown in FIG.

[0049] refer to Fig.10 and Fig.11 , the check valve 70 may be replaced by a check valve 210 that is spaced apart from the flexible flow control member 50. The check valve 210 is disposed on the support 44 between the knob 46 and the inner knob 46'. The check valve 210 is substantially similar to the check valve 70 except that it is spaced apart from the flexible flow control member 50. For example, the check valve 210 includes a flexible flap 212 that abuts the inner surface 74 of the housing 20 like the flexible flap 72. When the fluid flow through the inlet passage 48 exceeds a sufficient pressure and rate, the flow will cause the flap 212 to fold back and allow the fluid to flow into the outer fluid chamber 92.

[0050] Fig.12 and Fig.13 The check valve is shown as a spring ball valve including a ball 310, a spring 312, and a spring seat 314. The spring seat 314 defines a passage 316 for fluid to flow therethrough. The spring seat 314 is supported by the support 44. The spring 312 is configured so that when fluid flow through the inlet passage 48 increases above a certain rate and pressure, the spring 312 will compress. When the spring 312 compresses, the ball 310 moves inwardly and away from the inner surface 74, thereby allowing fluid to flow through the spring seat 314 and into the outer fluid cavity 92.

[0051] Thus, the present invention advantageously provides a valve assembly 10 that regulates a fluid, such as CSF, by providing a substantially constant flow rate through the valve assembly 10, regardless of overall system pressure, such as changes in intracranial pressure. Those skilled in the art will appreciate that the present disclosure also provides numerous additional advantages and unexpected results.

[0052] For the purpose of illustration and description, the foregoing description of the embodiments has been provided. The foregoing description is not intended to be exhaustive or to limit the present disclosure. The individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but are interchangeable and may also be used in selected embodiments, where applicable, even if not specifically shown or described. The same element or feature may be varied in a variety of ways. Such variations should not be considered as departing from the present disclosure, and all such modifications are intended to be included within the scope of the present disclosure.

[0053] Exemplary embodiments are provided so that the present disclosure will be thorough and will fully convey the scope of the present disclosure to those skilled in the art. Many specific details, such as examples of specific components, devices, and methods, are set forth to provide a thorough understanding of the embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that the exemplary embodiments may be embodied in many different forms, and should not be construed as limiting the scope of the present disclosure. In some exemplary embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.

[0054] The terms used herein are for the purpose of describing specific example examples only and are not intended to be limiting. As used herein, the singular forms "a", "an", and "said" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprise", "comprising", "including", and "having" are inclusive, thus specifying the presence of the features, integers, steps, operations, elements, and / or parts described, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, parts, and / or groups thereof. The method steps, processes, and operations described herein should not be interpreted as requiring their execution in the specific order discussed or shown, unless explicitly determined as an execution order. It should also be understood that additional or alternative steps may be adopted.

[0055] When an element or layer is referred to as being "on," "engaged to," or "connected to," or "coupled to," another element or layer, it may be directly on, directly engaged to, connected to, or coupled to, or there may be intervening elements or layers. Conversely, when an element is referred to as being "directly on," "directly engaged to," "directly connected to," or "directly coupled to," another element or layer, there may be no intervening elements or layers. Other words used to describe relationships between elements (e.g., "between" versus "directly between," "adjacent" versus "directly adjacent," etc.) should be interpreted in a similar manner. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0056] Although the term first, second, third etc. can be used in the text to describe various elements, components, regions, layers and / or parts, these elements, components, regions, layers and / or parts should not be limited by these terms. These terms can only be used to distinguish an element, component, region, layer or part from another region, layer or part. Unless the context clearly indicates, the terms used herein such as "first", "second" and other numerical terms do not imply order or sequence. Therefore, without departing from the teaching of exemplary embodiments, the first element, component, region, layer or part discussed below can be referred to as the second element, component, region, layer or part.

[0057] Spatially relative terms such as "inside," "outside," "under," "below," "lower," "above," "upper," and the like may be used herein for ease of description to describe the relationship of one element or feature shown in the figures to another element or feature. Spatially relative terms may also be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the accompanying drawings. For example, if the device in the accompanying drawings is flipped, an element described as being "under" or "beneath" other elements or features would then be oriented to be "above" the other elements or features. Thus, the example term "below" may encompass both the above and below orientations. The device may be oriented in other ways (rotated 90 degrees or in other orientations), and the spatially relative descriptors used herein may be interpreted accordingly.

Claims

1. A valve assembly, the valve assembly being configured to control the flow of a fluid therethrough, the valve assembly comprising: a housing, an inlet passage, and an outlet passage, wherein a fluid enters the housing at an inlet flow rate through the inlet passage, and the fluid leaves the housing at an outlet flow rate through the outlet passage; a flexible flow control member within the housing, the flexible flow control member having a generally tubular configuration and defining an internal fluid cavity within the flexible flow control member and an inlet opening to the internal fluid cavity, the inlet passage and the outlet passage being in fluid communication with the internal fluid cavity; and an external fluid chamber defined between the flexible flow control member and an inner surface of the housing; wherein the valve assembly is configured to allow fluid to flow from the inlet passage into the outer fluid chamber, from the outer fluid chamber through the inlet opening defined by the flexible flow control member into the inner fluid chamber, and out of the inner fluid chamber through the outlet passage; and The flexible flow control member is configured to flex inwardly and contract the inner fluid cavity in response to a decrease in pressure of the inner fluid cavity relative to the outer fluid cavity due to an increase in the inlet flow rate to maintain the outlet flow rate at a constant rate.

2. The valve assembly according to claim 1, wherein the flexible flow control member is disposed on a support member, the support member defines an outlet opening leading to the outlet channel, and a narrow groove for fluid to flow out of the internal fluid cavity into the outlet channel is defined between the outlet opening and the flexible flow control member.

3. A valve assembly according to claim 2, wherein in response to an increase in negative static hydraulic pressure within the outlet passage relative to the pressure of the internal fluid chamber, the flexible flow control member is configured to bend toward the outlet opening to reduce fluid flow out of the internal fluid chamber to maintain the outlet flow rate at a constant rate.

4. The valve assembly of claim 1 , further comprising a check valve at an upstream end of the housing relative to fluid flow therethrough, the check valve being configured to allow fluid to flow from the inlet passage into the external fluid cavity and to restrict fluid from flowing out of the external fluid cavity into the inlet passage.

5. The valve assembly of claim 4, wherein the check valve includes a flexible flap that is integral with the flexible flow control member or spaced apart from the flexible flow control member on a support that supports the flexible flow control member.

6. The valve assembly of claim 4, wherein the check valve is a ball valve.

7. The valve assembly of claim 1, wherein the flexible flow control member has a circular cross-section in a relaxed configuration and is configured to bend to an elliptical cross-section in response to the pressure of the inner fluid cavity relative to the outer fluid cavity decreasing.

8. The valve assembly of claim 1, further comprising a leakage passage defined by the flexible flow control member, the leakage passage providing fluid communication between the external fluid chamber and the outlet passage at the downstream end of the external fluid chamber to release pressure from within the external fluid chamber.

9. The valve assembly of claim 1, further comprising a substrate secured to a lower surface of the housing and configured to support the housing on a surface of an anatomical structure of a user.

10. A valve assembly configured to be disposed on a user to provide a constant flow rate of a fluid entering or leaving the user through the valve assembly, the valve assembly comprising: case; an inlet connector extending from an upstream end of the housing, the inlet connector being configured to connect to a first conduit that delivers the fluid into the housing at an inlet flow rate; an outlet connector extending from a downstream end of the housing, the outlet connector being configured to connect to a second conduit that conveys the fluid away from the housing at an outlet flow rate; a flexible flow control member within the housing, the flexible flow control member having a generally tubular configuration and defining an interior fluid cavity within the flexible flow control member and an inlet opening to the interior fluid cavity; a support within the housing, the flexible flow control member being mounted to the support, the support defining an outlet opening leading to the outlet connector, the outlet opening being within the internal fluid cavity; an external fluid chamber defined between the flexible flow control member and an inner surface of the housing; a check valve located at an upstream end of the housing, the check valve being configured to allow the fluid to flow from the inlet connector into the external fluid chamber and to restrict the fluid from flowing from the external fluid chamber back into the inlet connector; wherein the valve assembly is configured to allow the fluid to flow from the outer fluid cavity into the inner fluid cavity through the inlet opening defined by the flexible flow control member and out of the inner fluid cavity through the outlet opening and outlet passage; and Wherein in response to an increase in negative static hydraulic pressure within the outlet passage, the flexible flow control member is configured to flex toward the outlet opening to reduce flow of the fluid through the outlet opening and maintain the outlet flow rate at the constant flow rate.

11. The valve assembly of claim 10, wherein a slot for the fluid to flow out of the internal fluid cavity and into the outlet passage is defined between the outlet opening and the flexible flow control member; and Wherein in response to the increase in negative static hydraulic pressure, the flexible flow control member is configured to flex inwardly to make the slot smaller and reduce the outlet flow rate.

12. A valve assembly according to claim 11, wherein in response to a pressure drop within the internal fluid cavity relative to the external fluid cavity caused by an increase in the inlet flow rate of the fluid entering the housing, the flexible flow control member is configured to flex inwardly and cause the internal fluid cavity to contract to provide the constant flow rate of the fluid through the valve assembly.

13. The valve assembly of claim 10, wherein the check valve includes a flexible flap that is integral with the flexible flow control member or spaced apart from the flexible flow control member on the support.

14. The valve assembly of claim 10, wherein the check valve is a ball valve.

15. The valve assembly of claim 12, wherein the support extends through the internal fluid cavity and has a rectangular cross-section within the internal fluid cavity; and Wherein in response to the pressure drop within the internal fluid cavity, the cross-section of the internal fluid cavity changes from a circular shape to an elliptical shape.

16. The valve assembly of claim 10, further comprising a leakage passage defined by the flexible flow control member, the leakage passage being an opening providing fluid communication between the external fluid chamber and the outlet passage at the downstream end of the external fluid chamber to release pressure from within the external fluid chamber.

17. The valve assembly of claim 10, further comprising a substrate secured to a lower surface of the housing and configured to support the housing on a surface of the user's anatomy.

18. The valve assembly of claim 10, wherein the support is connected to the outlet connector.

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