BACKGROUND OF THE INVENTION Fluid valves are used extensively in industry. An example is the use of fluid valves in heat exchanging systems in buildings for heating or cooling purposes. In many applications, it is often desirable to maintain a constant flow rate through a fluid valve despite fluctuations that may occur in the pressure of the upstream or downstream fluid.

In order to provide a constant flow rate through a fluid valve, one type of prior device utilizes an aperture in a valve that changes in size as the pressure differential between the upstream and downstream fluid changes. In at least one such system, an inlet aperture that receives fluid from the upstream side of the valve decreases in size as the pressure differential between the upstream and downstream regions increases. Fluid flow is regulated in prior devices by offsetting increasing pressure differential, which tends to produce more flow through the valve with decreasing aperture size, which tends to produce less flow through the valve. Decreasing

the size of the inlet aperture as the pressure differential across the upstream and downstream sides increases is accomplished in prior devices by covering increasing portions of the inlet aperture as the pressure differential across the upstream and downstream sides increases, thereby selectively decreasing the size of the aperture through which fluid may flow.

A disadvantage of such devices is that they require exact dimensioning of the inlet aperture. The flow of fluid through such a device is very sensitive to the size of the aperture through which fluid is allowed to flow, and therefore, the amount of fluid flow through such a valve at any particular pressure differential is extremely sensitive to the shape of the inlet aperture in the valve. Because portions of the inlet aperture are covered as the pressure differential between the upstream and downstream regions increases, the shape of the inlet aperture affects the size of aperture through which fluid is allowed to flow. Thus, care must be taken to machine an aperture to exact dimensions that allow the desired amount of fluid flow for a range of pressure differentials. Exact dimensioning and manufacture of an inlet aperture is both expensive and difficult. Therefore such a requirement increases the cost of manufacturing a fluid valve and decreases the repeatability of producing mass quantities of acceptable valves.

Even if an inlet aperture can be repeatably manufactured, prior devices also suffer from variations in flow rate. Leakage of fluid around the valve, rather than through the inlet aperture, produces a component of flow that is unregulated that increases with increasing pressure differential, causing fluid flow through the valve to be non-constant.

Other types of devices that provide"feedback"from the downstream fluid allow the downstream fluid pressure to

act upon a moving portion of the valve, and therefore help regulate fluid flow through the device. A device claiming to operate in such a manner is described in U. S. Patent No.

4,080,993, entitled In-Line Flow-Control Valve, to Charles F. Lind. Such devices suffer from a phenomena known as "sag"that causes fluid flow through a valve to decrease as pressure differential increases, further contributing to a non-constant flow rate over a wide range of pressure differentials.

SUMMARY OF THE INVENTION Accordingly, a need has arisen for an improved method and apparatus for regulating fluid flow. The present invention provides a method and apparatus that addresses shortcomings of prior fluid regulation devices and methods.

According to one aspect of the invention, a fluid valve for controlling the flow of a fluid from an upstream region to a downstream region includes a housing and a piston slidably disposed within the housing. The piston includes a fluid inlet for receiving a fluid from an upstream region and a fluid outlet. The fluid valve also includes an elastic member for opposing displacement of the piston within the housing. In addition, a restriction enclosure having a restriction section receives the fluid outlet. The restriction enclosure includes a fluid exit for allowing fluid to flow to the downstream region.

According to another aspect of the invention, a method for controlling the flow of fluid from an upstream region to a downstream region includes providing a moveable surface for hindering flow of fluid from the upstream region. The moveable surface is moveable in response to changes in the pressure difference between the upstream region and the downstream region. The method also includes opposing movement of the moveable surface with increasing force as the pressure differential increases. The method

also includes providing a first passageway for fluid to flow from the upstream region past the moveable surface to a restriction enclosure. The restriction enclosure has a fluid exit for allowing fluid to flow to the downstream region and also includes a portion having a decreasing cross-sectional area. The method also includes providing a second passageway for fluid to flow within the restriction enclosure to the fluid exit and constricting the second passageway in response to increases in the pressure differential.

The invention provides several technical advantages.

For example, the invention increases the pressure differential range over which a fairly constant flow rate may be maintained. According to one embodiment of the invention, a fairly constant fluid rate is attainable over a 60 to 70-fold increase in pressure differential.

Conventional designs allow fairly constant fluid flow over pressure differential increases of approximately 16-fold.

One reason for such advantages over conventional systems that employ feedback is the present invention addresses the deleterious effects of the downstream pressure on the control of the fluid flow rate. Such an effect is known conventionally as"sag"or"edge effect." The"edge effect"is minimized at least in part by preventing the downstream pressure from acting upon portions of the control valve. In addition, the present invention addresses leakage flow that may tend to cause the flow rate to vary.

In addition to providing greater pressure differential ranges in which a constant flow rate may be obtained, the present invention also provides a more easily manufactured device than prior designs because the geometry of the inlet and exit apertures is not critical. The invention also overcomes the effects of friction, which tend to produce different flow rates depending on whether pressure is being

increased or decreased. The effects of friction are avoided, at least in part, by providing a relatively high spring force, which also contributes to overcoming the effects of the downstream pressure on flow rate.

Furthermore, a device is provided that begins regulating flow of a fluid at relatively low pressures.

Early regulation of fluid flow is accomplished, at least in part, by providing a piston having a relatively large surface area facing the upstream flow as part of a valve.

In addition, the present invention provides constant flow rates for changes in pressure differential for both gases and liquids. In addition, one embodiment of the present invention provides shock-absorbing capability that retards any sudden pressure wave or pulse received by the device.

Other technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following descriptions taken in connection with the accompanying drawings in which: FIGURE 1 is a cross-sectional drawing illustrating a side view of a portion of a fluid valve according to an embodiment of the present invention; FIGURE 2 is a perspective drawing of a piston used as a portion of a fluid valve according to an embodiment of the present invention; FIGURE 3 is a cross-sectional drawing illustrating a side view of a fluid valve in a first position according to one embodiment of the present invention; FIGURE 4 is a cross-sectional drawing illustrating a side view of the fluid valve of FIGURE 3 in a second position;

FIGURE 5 is a schematic drawing illustrating a side view of portions of the fluid valve illustrated in FIGURES 3 and 4, illustrating alternative pressure regions within a restriction enclosure of the fluid valve in FIGURES 3 and 4; FIGURE 6 is a graph of flow rate versus pressure differential for one embodiment of the present invention; FIGURE 7 is a graph of flow rate versus pressure differential for one embodiment of the present invention; FIGURE 8 is a perspective drawing illustrating two opposing disks for regulating flow to the fluid valve of FIGURES 3 and 4; FIGURE 9 is a cross-sectional drawing illustrating an adjustable fluid valve according to the teachings of the present invention incorporating the opposing disks illustrated in FIGURE 8; FIGURE 10 is a drawing illustrating a side view of an adjustable valve according to another embodiment of the present invention; FIGURE 11 is a schematic drawing illustrating a side view of a Y-housing, showing use of the valve shown in FIGURES 3 and 4 in the Y-housing; FIGURE 12 is a schematic drawing showing the use of the valve as shown in FIGURES 3 and 4 with an alternative housing configuration; FIGURE 13 is a cross-sectional drawing illustrating a side view of a fluid valve according to yet another embodiment of the present invention that incorporates a wiper seal; FIGURE 14 shows an enlarged view of the embodiment of the invention illustrated in FIGURE 13, showing additional details of the wiper seal; FIGURE 15 is a graph of flow rate versus pressure differential for several example fluid valves according tot he embodiment of FIGURE 13; and

FIGURE 16 is a graph of flow rate versus pressure differential for the same example fluid valves used for FIGURE 15, but without the use of a wiper seal.

DETAILED DESCRIPTION OF THE INVENTION Embodiments of the present invention and its advantages are best understood by referring to FIGURES 1 through 12 of the drawings, like numerals being used for like and corresponding parts of the various drawings.

FIGURE 1 is a cross-sectional drawing illustrating a side view of a portion of a fluid valve according to one embodiment of the present invention. Illustrated in FIGURE 1 is a housing 10 disposed within a pipe 12.

Housing 10 has an inside diameter 11 and an interior length 13. A restriction enclosure 14 is attached to housing 10.

Although restriction enclosure 14 is shown as formed integral with housing 10, restriction enclosure 14 may be formed separately from housing 10. Housing 10 and restriction enclosure 14 form a portion of a fluid valve according to the present invention that provides a relatively constant flow rate despite fluctuations in fluid pressure. Housing 10 is formed to receive a piston, which is described in greater detail below in conjunction with FIGURES 2 through 4. As illustrated, housing 10 is generally cylindrical; however, other suitable configurations may be used. Housing 10 includes a lip 15 for retaining a lock ring 46. Lock ring 46 is described in greater detail in conjunction with FIGURE 3. An 0-ring 16 may be disposed between housing 10 and pipe 12 to resist unwanted passage of fluid between housing 10 and pipe 12.

Restriction enclosure 14 includes an interior surface 18 and an exterior surface 20. Restriction enclosure 14 includes a restriction section 22 having a diminishing interior cross section. As illustrated, restriction section 22 has an interior having a conical shape; however,

other diminishing cross-sectional shapes may be utilized, including the frustoconical shape illustrated in FIGURE 9.

Restriction section 22 has an interior length 25, an interior height 27, and an angle 29. As illustrated, angle 29 is 60°, which has been found to be particularly useful in the present invention; however, restriction section 22 may be formed with other dimensions. Restriction enclosure 14 also includes a cylindrical section 23 having fluid exits 24. Cylindrical section 23 has an inner diameter 31 and a length 33. Fluid exits 24 allow fluid to flow from an upstream region 26 of pipe 12 to a downstream region 28 of pipe 12.

FIGURE 2 is a perspective drawing of a piston 30 for placement in housing 10 and restriction enclosure 14.

Piston 30 includes a disk portion 32 and a stem portion 34.

Stem portion 34 has a length 37, an outside diameter 35, and an inside diameter 41. Disk portion 32 is formed with a fluid inlet 36, and stem portion 34 is formed with a fluid outlet 38. Stem portion 34 may also include a beveled end 39. The use of beveled end 39 for stem portion 34 is described in greater detail below in conjunction with FIGURE 5. Stem portion 34 is hollow and provides a fluid passageway 40 for fluid to flow from fluid inlet 36 to fluid outlet 38. Stem portion 34 also includes a plurality of equalization apertures 42 positioned near disk portion 32. Equalization apertures 42 are described in greater detail below in conjunction with FIGURES 3 and 4.

Interaction between restriction enclosure 14 and piston 30 assists in regulating flow of fluid from upstream region 26 to downstream region 28 to provide a fairly constant flow rate that is independent of the difference in fluid pressures between upstream region 26 and downstream region 28. The difference between the fluid pressure in upstream region 26 and the fluid pressure in downstream region 28 is referred to as pressure differential.

FIGURE 3 is a cross-sectional drawing illustrating a side view of a fluid valve 44 in a first position according to one embodiment of the present invention. Piston 30 is shown inserted within housing 10 and restriction enclosure 14. As illustrated, stem portion 34 protrudes into restriction enclosure 14.

Lock ring 46 is positioned against lip 15 of housing 10. Lock ring 46 retains disk portion 32 and therefore piston 30 within housing 10. Opposite lock ring 46, a shear plate 48 is disposed within housing 10. Shear plate 48 separates an intermediate region 49 of valve 44 from restriction enclosure 14. Fluid in intermediate region 49 has a fluid pressure P2. An 0-ring 50 is disposed between shear plate 48 and portions of housing 10 to prevent unwanted leakage of fluid past shear plate 48. A bias member 52 is disposed between disk portion 32 and shear plate 48. Bias member 52 may be an elastic member such as a spring, shown in FIGURE 3, or other suitable bias member.

0-ring 50 may be compressed both by bias member 52, and in addition, by a pressure force from fluid within intermediate region 49 at pressure P2. Bias member 52 provides a resistant force against disk portion 32 in response to a force from a fluid pressure Pi in upstream region 26 applied against disk portion 32 of piston 30. In the embodiment illustrated in FIGURE 3, a force against disk portion 32 due to fluid pressure P1 in upstream region 26 increases as the pressure differential between upstream region 26 and downstream region 28 increases. This force against disk portion 32 causes bias member 52 to compress and also displaces piston 30 in the direction of restriction enclosure 14, as illustrated in FIGURE 4.

Fluid pressure P2 in intermediate region 49 is less than fluid pressure P1 in upstream region 26 due to a pressure drop associated with fluid flowing through fluid inlet 36 and leaking between lock ring 46 and housing 10

near reference numeral 56. Intermediate region 49 and fluid passageway 40 are both maintained at pressure P2 through equalization apertures 42 formed in stem portion 34. As illustrated in FIGURE 3, fluid outlet 38 does not extend into restriction section 22 of restriction enclosure 14. In the present embodiment, this configuration corresponds to a minimum pressure differential condition.

FIGURE 4 is a cross-sectional drawing illustrating a side view of fluid valve 44 in a second position. As illustrated, fluid outlet 38 protrudes into restriction section 22 of restriction enclosure 14. This second position corresponds to a fluid pressure differential between upstream region 26 and downstream region 28 that is greater than the pressure differential associated with the first position of valve 44 illustrated in FIGURE 3.

In operation, fluid flows through valve 44 at a relatively constant mass flow rate that is independent of the pressure differential between upstream region 26 and downstream region 28. Fluid in upstream region 26 flows through fluid inlet 36 in disk portion 32, illustrated by arrow 57. This flow constitutes the primary fluid flow through valve 44. The primary flow continues through fluid passageway 40 in stem portion 34, illustrated by arrow 58, and exits fluid passageway 40 at fluid outlet 38. As shown, fluid outlet 38 protrudes into restriction section 22 of restriction enclosure 14. Fluid reaching restriction section 22 then flows through an annulus 60 defined by interior surface 18 of restriction section 22 and fluid outlet 38 of stem portion 34. Annulus 60 is best illustrated in FIGURE 5. Flow through annulus 60 is illustrated by arrows 62. Fluid then exits valve 44 by flowing through fluid exits 24 to downstream region 28, illustrated by arrows 64.

A relatively constant flow rate is achieved by the interaction of piston 30 with restriction enclosure 14 in response to changes in pressure differential between upstream region 26 and downstream region 28. Without regulation of the primary flow by the interaction of piston 30 with restriction enclosure 14, increases in the pressure differential between upstream region 26 and downstream region 28 would tend to increase the flow rate through valve 44. However, as the pressure differential between upstream region 26 and downstream region 28 increases, a resultant fluid pressure force increases on disk portion 32. The resultant pressure force causes deflection of piston 30 and, therefore, deflection of fluid outlet 38 in the direction of decreasing cross section of restriction section 22 of restriction enclosure 14. The deflection causes restriction of annulus 60. Restriction of annulus 60 counteracts the effect of increasing pressure differential between upstream region 28 and downstream region 26, which would otherwise tend to increase flow rate. Therefore, a relatively constant flow rate may be achieved due to the balancing of increasing pressure in upstream region 26 with decreasing flow area through annulus 60 caused by the deflection of stem portion 34 into restriction section 22 of restriction enclosure 14. In contrast to prior devices, a relatively constant flow rate over a wide range of pressure differentials may be attained without exact dimensioning of fluid inlet 36. The size and shape of fluid inlet 36 does not affect the constancy of the flow rate through valve 44, but rather affects only the magnitude of flow at which the flow rate is constant.

In addition to regulating flow through fluid inlet 36, the invention additionally regulates some leakage flow between housing 10 and disk portion 32 near reference numeral 56. This regulation of leakage flow is effected through equalization apertures 42. Equalization apertures

42 receive some leakage flow between housing 10 and disk portion 32 that reaches intermediate region 49 for combination with the primary flow denoted by arrow 58, which is then regulated as described above. This regulated leakage flow does not affect the constant nature of the flow rate through valve 44, but rather changes the magnitude of the flow at which the flow rate through valve 44 is constant. Regulation of leakage flow is beneficial because such regulation assists in maintaining the rate of fluid flow through valve 44 at a fairly constant level.

Because increases in pressure differential would otherwise tend to increase the rate of leakage flow, regulation of leakage flow according to the invention helps maintain the flow rate through valve 44 at a relatively constant level over a relatively wide range of pressure differentials. In one embodiment, equalization apertures 42 are placed near disk portion 32 so they are not reversed by shear plate 48 as piston 30 moves toward downstream region 28.

Forming piston 30 with disk portion 32 and stem portion 34 allows low startup pressures and facilitates overcoming the deleterious effects of friction. Because disk portion 32 provides a large surface area over which P of upstream region 26 may act, a sufficient force to displace piston 30 toward restriction enclosure 14 occurs at relatively low pressure differentials. Therefore, fluid may be regulated at relatively low pressure differentials.

The fluid pressure P1 of upstream region 26 provides a relatively large force that requires a relatively strong bias member 52. Because bias member 52 is relatively strong, friction effects are minimal. Friction provides a force opposing motion and therefore, if the forces due to friction are significant, can create different flow rates depending on the direction of motion of piston 30, resulting in a hysteretic-like flow rate versus pressure differential curve. In the present embodiment, piston 30

moves away from downstream region 28 when the pressure differential is decreasing and moves toward downstream region 28 when the pressure differential is increasing.

Because the force of bias member 52 is relatively strong in comparison to the friction forces, the friction effects are minimal. Disk portion 32 also acts as a shock absorber that slows down any pressure wave or pulse that may occur due to a sudden fluid pressure change.

FIGURE 5 is a schematic drawing illustrating a side view of portions of fluid valve 44 shown in FIGURES 3 and 4, illustrating alternative pressure regions within restriction enclosure 14 of fluid valve 44. Additional advantages provided by the present invention may be more clearly understood with reference to FIGURE 5.

The present invention realizes that the phenomenon known as"sag,"which tends to decrease flow rate through a valve as the pressure differential across a valve increases, is caused by fluid pressure at the downstream side of a valve sucking on a moveable portion of the valve, such as stem portion 34. Such sucking tends to decrease flow through a valve as the pressure differential between the upstream and downstream regions increases. Therefore, the present invention not only utilizes an advantageous configuration for piston 30, but also is designed to alter the pressure forces that may be applied to piston 30.

As illustrated in FIGURE 5, the interior of restriction enclosure 14 is depicted as divided into two regions: an intermediate pressure region 68, which contains fluid at a pressure P2, and a downstream pressure region 70, which contains fluid at a downstream pressure P3.

The restricting nature of restriction enclosure 14 and particularly the conical shape of restriction section 22 helps overcome the phenomena known as"sag."The use of a conical shaped interior for restriction enclosure 14 pushes the interface between intermediate pressure region 68 and

downstream pressure region 70 to the line denoted by reference numeral 72. Interface 72 is a desirable interface because it provides no surface area on stem portion 34 for downstream pressure P3 to act upon, and thereby pull, piston 30 toward downstream region 28. In contrast, an undesirable interface, shown by the line denoted by reference numeral 74, allows downstream pressure P3 to act upon stem portion 34 of piston 30 and pull piston 30 toward downstream region 28, which causes the decrease in flow rate known as sag. Beveled end 39 of stem portion 34 provides additional protection against sag by reducing the effective surface area on which a pressure may act to pull piston 30 toward the downstream region 28. As described above, shear plate 48 separates intermediate region 49, which contains a fluid at a pressure of P2, from downstream region 28, which retains a fluid at a pressure <BR> <BR> <BR> <BR> P3. Therefore, shear plate 48 prevents the pressure P3 of downstream region 28 from acting on disk portion 32 to urge piston 30 toward downstream region 28, further addressing the effects of sag. Therefore, the invention further achieves a relatively constant flow rate through a fluid valve by additionally addressing both sag and leakage concerns.

FIGURE 6 is a graph of flow rate versus pressure differential for one embodiment of the present invention.

As illustrated, the flow rate through a valve, such as valve 44, is fairly constant over pressure differentials ranging from 2 pounds per square inch to 32 pounds per square inch. The dimensions for a valve, such as valve 44, for this test case are as follows: Disk Portion 32: 0.947 inches maximum diameter (reference numeral 33) Stem Portion 34: 0.66 inches length (reference numeral 34) 0.725 increase outside diameter (reference numeral 35)

0.173 inches inside diameter (reference numeral 41) Housing 10: 0.950 inches diameter (reference numeral 11) 0.63 inches length (reference numeral 13) Restriction Section 22: Interior length (reference numeral 25) = 0.298 inches Interior height (reference numeral 27) = 0.344 inches Angle (reference numeral 29) = 60° Cylindrical Section 23: Diameter (reference numeral 31) = 0.344 inches Length (reference numeral 33) = 0.238 inches Fluid Exits 24: Four at 90° apart and 0.136 inches diameter Fluid Inlet 36: 0.079 inches (reference numeral 37) Equalization Apertures 42: Four at 90° apart and 0.0625 inches diameter FIGURE 7 is another graph of flow rate versus pressure differential for an embodiment of the invention. The dimensions and configuration of the valve for this test case are the same as that described in conjunction with FIGURE 6. As illustrated, the flow rate through the valve remains acceptably constant for upstream pressure differentials in the range of 2 pounds per square inch to at least 120 pounds per square inch. The slightly decreasing magnitude of flow rate is considered acceptable by industry standards. As illustrated, a 60 to 70-fold increase in pressure differential may be effected through the teachings of the present invention with a fairly constant flow rate maintained. Conventional valves provide fairly constant flow rates for only a 16-fold increase in pressure differential.

FIGURE 8 is a perspective drawing illustrating portions of a fluid control apparatus 79 for regulating

flow of fluid from upstream region 26 to piston 34. In this embodiment, fluid control apparatus 79 includes two opposing disks 76,78 for regulating flow. The teachings of the present invention may be incorporated to produce valves having a fairly constant flow rate over a wide range of pressure differentials that may be adjusted to accommodate various magnitudes of constant flow rates.

First opposing disk 76 and second opposing disk 78 are illustrated in FIGURE 8 to effect this purpose. Each opposing disk includes a plurality of apertures 80.

Apertures 80 may be aligned to provide a variable flow rate through opposing disks 76 and 78.

FIGURE 9 is a cross-sectional drawing illustrating an adjustable fluid valve 144 according to the teachings of the present invention incorporating fluid control apparatus 79 illustrated in FIGURE 8. As illustrated in FIGURE 9, first opposing disk 76 and second opposing disk 78 may be aligned such that a selected number of apertures 80 may align with each other to provide a variable and easily adjusted flow rate from upstream region 26 to fluid inlet 36. Although one embodiment of fluid control apparatus 79 is particularly described, other devices that control the amount of fluid provided from upstream region 26 to piston 34 may also be incorporated in adjustable fluid valve 144.

Flow of fluid from upstream region 26 to fluid inlet 36 is illustrated by arrows 156. By regulating the amount of flow received at fluid inlet 36, the amount of flow through valve 144 may be adjusted. However, for a given alignment of opposing disks 76 and 78, a constant flow rate is achieved for varying pressure differentials between upstream region 26 and downstream region 28. FIGURE 9 also illustrates an alternative configuration for restriction section 22 of restriction enclosure 14. In this embodiment, interior surface 18 of restriction section 22 is formed in a frustoconical configuration. A similar

fluid control apparatus may alternatively be incorporated near downstream region 28 to regulate the amount of fluid exiting fluid exits 24 to downstream region 28, and therefore provide an adjustable valve.

FIGURE 10 is a drawing illustrating a side view of an adjustable valve 244 according to another embodiment of the present invention. Adjustable valve 244 incorporates the teachings of the present invention to provide a valve that produces a fairly constant flow rate over a wide range of pressure differentials, but for which a variety of flow rates at which the flow rate is constant may be specified.

Valve 244 is analogous to valve 44 except that restriction enclosure is formed with a fluid opening 206 at an end of a restriction section 222. An adjustment member 202 is provided for selectively constricting fluid opening 206.

For this purpose, fluid opening 206 is provided with a seat 208 for engagement with an engagement portion 204 of adjustment member 202. Valve 244 also differs from valve 44 in that no inlet aperture is provided in a disk portion 232 of a piston 230. A diaphragm (not explicitly shown) may also be provided over piston 230 to prevent leakage and to facilitate a zero-flow condition.

The operation of valve 244 is as follows. Fluid in an upstream region 226 flows through fluid opening 206 to a downstream region 228. Disk portion 232 of piston 230 is, however, exposed to fluid pressure due to the fluid within upstream region 226. Therefore, as the pressure differential between upstream region 226 and downstream region 228 increases, piston 230, including a stem portion 234, deflects into restriction section 222 of a restriction enclosure 214. Deflection of stem portion 234 into restriction section 222 constricts an annulus 260 formed between restriction section 222 and stem portion 234, thereby reducing the flow rate of fluid from upstream region 226 to downstream region 228 as the pressure

differential between upstream region 226 and 228 decreases.

Because increasing pressure differential is offset by decreasing the size of annulus 260 through which fluid may flow, a fairly constant flow rate for any given setting of adjustment member 202 may be achieved.

Adjustment of the flow rate may be achieved by displacing adjustment member 202 relative to fluid opening 206. Displacement of adjustment member 202 toward fluid opening 206 constricts fluid opening 206, thereby reducing the amount of fluid that may be transferred from upstream region 226 to downstream region 228. As described above, for any given setting of adjustment member 202, flow from upstream region 226 to downstream region 228 is regulated, and therefore fairly constant, by the offsetting effects of increasing pressure differential displacing stem portion 234 into restriction section 222 and therefore restricting annulus 260 and the increasing pressure differential.

As illustrated, adjustment member 202 may be positioned to completely close valve 244, resulting in a zero-flow condition. Because valve 244 may be completely closed, valve 244 may be particularly useful as a pressure- compensated automatic temperature control device in addition to an adjustable flow controller.

FIGURE 11 is a schematic drawing illustrating a side view of a Y-housing 302, showing use of valve 44 therein.

To facilitate insertion of a fluid valve according to the invention, such as fluid valve 44 shown in FIGURES 3 and 4, a Y-housing may be incorporated. As illustrated in FIGURE 11, valve 44 may be inserted easily within Y-housing 302 in order to regulate flow. The conical shape of an exterior portion 320 of a restriction enclosure 314 facilitates insertion of valve 44 within Y-housing 302.

FIGURE 12 is a schematic drawing showing the use of valve 44 shown in FIGURES 3 and 4 in an alternative configuration. As illustrated in FIGURE 12, valve 44 is

disposed transverse to the upstream and downstream regions, therefore, flow from an upstream region 426 to a downstream region 428 occurs as is shown by arrows 404. The operation of valve 44 shown in FIGURE 12 is analogous to that described in conjunction with FIGURES 3 and 4.

FIGURE 13 is a cross-sectional drawing illustrating a side view of a fluid valve according to yet another embodiment of the present invention that incorporates a wiper seal 53. As described above in connection with the description of FIGURE 4, leakage flow between disk portion 32 and housing 10 at, for example, reference numeral 56 in FIGURES 4 and 13 is regulated through equalization apertures 42. Therefore, regulated leakage flow between disk portion 32 and housing 10 does not affect the constant nature of the flow rate through valve 44 or valve 344; however, the amount of leakage flow between disk portion 32 and housing 10 does affect the magnitude of the flow at which the flow rate through valves 44 and 344 is constant.

It has been determined that in one embodiment, a clearance between disk portion 32 and housing 10 of approximately 0.0006 inches 0.0004 inches is sufficient to consistently produce fluid valves having a magnitude of flow at which the flow rates through the valves is constant that are within an acceptable range. One way to accomplish such a clearance is to manufacture disk portion 32 and housing 10 with machining tolerances of 0.0001 inches.

Alternatively, the clearance between disk portion 32 and housing 10 near reference numeral 56 may be sealed by, for example, the use of wiper seal 53. FIGURE 14 shows an enlarged view of the embodiment of the invention illustrated in FIGURE 13, showing additional details of wiper seal 53. As illustrated, wiper seal 53 seals any leakage flow between disk portion 32 and housing 10, thereby producing a consistently repeatably manufactured seal 344 that provides a constant flow rate at set constant

rate. As disk portion 32 deflects toward downstream region 28, a tip 55 of wiper seal 53 provides a seal between disk portion 32 and housing 10. The use of wiper seal 53 allows less stringent tolerances for disk portion 32 and housing 10 than would be required for optimal performance without wiper seal 53. Another advantage of wiper seal 53 is that as the pressure differential across fluid valve 344 increases, the greater the force applied by wiper seal 53 on housing 10, and thus the tighter the seal. Therefore, minimal friction is executed by wiper seal 53 for low pressure differentials, such as those occurring during start up. Although wiper seal 53 has been described as useful for sealing leakage flow between disk portion 32 and housing 10, other alternative sealing techniques may be used. For example, a diaphragm connecting disk portion 32 with housing 10 may be used as well as other alternative suitable sealing techniques. Benefits of the use of wiper seal 53 are illustrated in FIGURES 15 and 16.

FIGURE 15 is a graph of flow rate versus pressure differential for several examples of fluid valve 344 incorporating wiper seal 53, and FIGURE 16 is a graph of flow rate versus pressure differential for several examples of a fluid valve constructed according to the teachings of the present invention but without incorporating a wiper seal 53 or similar sealing device. In FIGURE 15, four fluid valves 344 having the same nominal dimensions were subjected to a range of pressure differentials. As shown, the resulting measured flow rates differ little between each other for most pressure differentials. Thus, the use of wiper seal 53 allow manufacture of fluid valves 344 that produce fairly repeatable flow rates.

By contrast, FIGURE 16 illustrates resulting flow rates for four fluid valves having the same nominal dimensions but without wiper seal 53. As shown, the magnitude at which the flow rates are constant differ

greatly from seal to seal. Thus, the inclusion of wiper seal 53 or similar sealing device provides additional advantages.

Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made therein without departing from the spirit and scope of the invention as defined by the appended claims.