Abstract:
The present invention provides adjustable flow control valves  10  for controlling flow of a fluid from a fluid supply. The valves of the present invention can accurately regulate a wide range of flow rates and require a relatively small amount of torque to adjust the flow rate of the valve during operation. The valves of the present invention include a flow control component  12  and a pressure control component  14.  The adjustable flow control valves of the present invention are capable of accurately regulating a wide range of fluid flow rates. The valves of the present invention possess a very high turndown ratio, preferably up to about 200:1.

Description:
RELATED APPLICATIONS 
     This application claims benefit of priority from U.S. Provisional Application Ser. No. 60/097,736, filed Aug. 24, 1998, which is expressly incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to fluid transfer and metering, and particularly to adjustable valves for controlling the rate of fluid flow. 
     BACKGROUND OF THE INVENTION 
     Many types of equipment and industrial processes require accurate control of the flow of liquid and gaseous fluids over a broad range of fluid pressure and flow rates. It is particularly important that flow controllers for such equipment and processes be able to accurately meter fluid flow over a broad range of flow rates. One problem with many prior art valves is that the amount of torque required to adjust the valve to alter the flow rate increases proportionally to fluid pressure within the valve. This is because the fluid pressure is operating in the valve components that must be rotated during valve adjustment. As a result, adjustment can be difficult to accomplish at high pressures. 
     Many conventional flow control valves utilize a piston carrying a needle that acts against a spring set contained between the piston and the bottom wall of the valve chamber in which the valve seat is formed. To adjust the valve, the bias force of the piston spring set can only be adjusted from an external source, or an adjustable valve seat has to be provided. An improvement on such valves is provided in the metering valve of U.S. Pat. No. 5,427,139 to Hilton, the disclosure of which is hereby incorporated by reference. This valve overcomes some shortcomings of conventional valves by including an adjustable floating piston and needle assembly that provides for adjustment against internal differential pressure independent of the total system pressure. 
     While representing an advance in adjustability and metering accuracy, the Hilton &#39;139 metering valve maintains its highest degree of accuracy of flow regulation only in a narrow range. Hardware modifications are required to operate in other ranges with the same degree of accuracy. 
     An industry-recognized measure of the ability of a valve to control flow rate over a range of flow rates is the “turndown ratio”. Thus, if a valve has a “turndown ratio” of  10 : 1  and is capable of accurately regulating a maximum flow rate of 100 liters per hour, then the smallest flow rate that the valve can accurately regulate is 10 liters per hour (i.e., one tenth of the maximum flow rate). Typically, the “turndown ratio” of prior art valves is from about 4:1 to about 10:1. Thus, there is a need for a valve that can accurately regulate a wide range of fluid flow rates and that requires a relatively small amount of torque to adjust the flow rate of the valve during operation. 
     It is also desired to have a metering valve that is not unduly sensitive to pressure fluctuations in the system. This is particularly the case for downstream pressure fluctuations that may induce a sinusoidal flow rate fluctuations in conventional valves. 
     SUMMARY OF THE INVENTION 
     The present invention provides adjustable flow control valves for controlling flow of a fluid from a fluid supply. The valves of the present invention can accurately regulate a wide range of flow rates and require a relatively small amount of torque to adjust the flow rate of the valve during operation. The valves of the present invention include a flow control component and a pressure control component. The flow control component includes (I) a housing defining a valve chamber having a first end and a second end, an inlet port opening into the first end of the valve chamber for placing a fluid supply in fluid communication with the valve chamber, and an outlet port for fluid flow to exit from the second end of the valve chamber; (II) a floating piston slidably mounted within the valve chamber between the inlet and outlet ports; (III) a passage connecting the valve chamber first end and valve chamber second end; (IV) a valve seat disposed within the housing in the second end of the valve chamber, upstream of the outlet port; and (V) a valve member carried by the floating piston. Preferably the valve member is selectively positionable relative to the piston and to the valve seat in order to restrict or facilitate fluid flow through the outlet port. The flow control component preferably includes a biasing spring disposed within the valve chamber second end to bias the floating piston toward the valve chamber first end. The pressure control component includes: (I) a housing defining a valve chamber having a first end and a second end, a first inlet port opening into the first end of the valve chamber for placing a fluid supply in fluid communication with the valve chamber, a second inlet port for placing the valve chamber second end in fluid communication with the outlet port in the valve chamber second end of the flow control component, and an outlet port for fluid flow to exit from the second end of the valve chamber to a downstream fluid destination; (II) a floating piston slidably mounted within the valve chamber between the first inlet port and the outlet port; (III) a valve seat included in the housing in the second end of the valve chamber, upstream of the outlet port; and (IV) a valve member carried by the floating piston. The pressure control component preferably includes a biasing spring disposed within the valve chamber second end to bias the floating piston toward the valve chamber first end. 
     In a first preferred embodiment of the adjustable flow control valve of the present invention, the valve member of the flow control component is mounted within an internal passage of the piston for selective advancement within the internal passage relative to the piston. Advancement of the valve member within the piston determines the position of the valve member relative to the valve seat to control the rate of flow of fluid through the valve chamber. A rotatable valve shaft has a work end external of the housing and a keyed engaging end passing through the housing into the first end of the valve chamber. The keyed engaging end of the valve shaft is slidably engaged with a keyed engaging surface defined by the valve member. The valve shaft rotates within the housing, and drives rotation of the valve member to translate the valve member within the piston. Selective rotation of the valve shaft causes advancement of the valve member within the internal passage of the piston to adjust the rate of flow of fluid through the valve chamber. The passage connecting the valve chamber first end and the valve chamber second end is defined through the piston, radially offset from the valve member. An orifice assembly is mounted within this passage. Alternately, the passage connecting the first and second ends of the valve chamber can be formed axially through the valve member, or can be formed in the wall of the valve housing. 
     In a second preferred embodiment, the piston in the flow control component carries a non-adjustable valve member and the orifice assembly. The valve member carried in the piston of the pressure control section is adjustable with a valve shaft. 
     In a third preferred embodiment, neither the piston in the flow control section nor the piston in the pressure control section includes an adjustable valve member. Rather than being carried in the piston of the flow control section, an external orifice is provided in a passage placing the first and second ends of the chamber of the flow control section in fluid communication. This orifice, which may be placed in a passage within the chamber housing or externally thereof, is adjustable. 
     In a fourth preferred embodiment, the valve members carried in the pistons of both the flow control and pressure control sections are adjustable. 
     The adjustable flow control valves of the present invention are capable of accurately regulating fluid flow rates of from about two liters per hour to about 1000 gallons per day for the first preferred embodiment summarized above, and up to 15,000 gallons per day for the third preferred embodiment summarized above. These flow rates are provided for illustration only, and values in accordance with the present invention may be scaled up or down to handle other flow rates. Preferably, once a valve of the present invention has been adjusted to permit a desired flow rate, the valve is capable of maintaining the flow rate with an accuracy of plus or minus about 7%, preferably plus or minus about  3 %, more preferably plus or minus about 1%. 
     Thus, the valves of the present invention are capable of accurately controlling flow rate over a wide range of flow rates. It is a feature of the valves of the present invention that they possess a very high turndown ratio, preferably up to about 100:1, more preferably up to about 200:1. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 shows a schematic view of a first preferred embodiment of the adjustable flow control valves of the present invention. 
     FIG. 2 shows a schematic view of a second preferred embodiment of the adjustable flow control valves of the present invention. 
     FIG. 3 shows a schematic view of a third preferred embodiment of the adjustable flow control valves of the present invention. 
     FIG. 4 shows a schematic view of a fourth preferred embodiment of an adjustable flow control valve of the present invention. 
     FIG. 5 shows an isometric view of the presently most preferred embodiment of the adjustable flow control valves of the present invention viewed from the lower end. 
     FIG. 6 shows an isometric view of the presently most preferred embodiment of the adjustable flow control valves of the present invention viewed from the upper end. 
     FIG. 7 shows an upper end view of the valve shown in FIGS. 5 and 6, and shows the planes of the longitudinal cross-sectional views shown in FIGS. 8-11. 
     FIGS. 8-11 show longitudinal cross-sectional views of the presently most preferred embodiment of FIGS.  1  and  5 - 7 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As shown schematically in FIG. 1, a first preferred embodiment of the adjustable flow control valve  10  of the present invention includes a flow control component  12  and a pressure control component  14 . Flow control component  12  includes a housing  16  that defines a valve chamber  18  including an upper portion  20  and a lower portion  22 . Valve chamber  18  receives a floating piston  24  that defines a central bore  26  for receiving a valve member  28  selectively positioned by a rotatable adjustment handle  30 . The adjustable handle  30  includes a keyed shaft  32  that slidably engages a keyed aperture in the valve member  28  to threadedly advance the valve member  28  within the piston  24 , thereby longitudinally repositioning a needle  34  carried on the end of the valve member  28  needle. Piston  24  also defines a jet  36  that places valve chamber upper portion  20  in fluid communication with valve chamber lower portion  22 . Spring  38 , such as a stack of belleville washers, is disposed within valve chamber lower portion  22 . Flow control component housing  16  also defines a fluid inlet port  40  and a fluid outlet port  42 . 
     Pressure control component  14  includes a housing  44  that defines a valve chamber  46  including an upper portion  48  and a lower portion  50 . The term “upper” is used to refer to the end proximate handle  30 , and “lower” to the opposite end, for ease of understanding. However, it should be understood that the valve of the present invention can be used in any orientation. Pressure control component valve chamber  46  receives a floating piston  52  that includes a needle  54 . Spring  56 , such as a stack of belleville washers, is disposed within valve chamber lower portion  50 . Pressure control component housing  44  also defines a first fluid inlet port  58 , a second fluid inlet port  60  and a fluid outlet port  62 . A bifurcated fluid inlet conduit 64  is connected to both flow control component fluid inlet port 40  and pressure control component fluid inlet port  58 . A connecting fluid conduit  66  connects flow control component fluid outlet port  42  with pressure control component second fluid inlet port  60 . 
     Briefly, in operation fluid enters bifurcated fluid inlet conduit  64  from a fluid supply source, and fluid flow is directed to both valve chamber upper portion  20  of flow control component  12  and to valve chamber upper portion  48  of pressure control component  14 . Fluid flows from valve chamber upper portion  20  of flow control component  12  to valve chamber lower portion  18  of flow control component  12  through orifice passage  36 . The force of the fluid entering valve chamber  18  and valve chamber  46  applies fluid pressure to floating piston  24  and to floating piston  52  which are pushed downwardly to compress spring  38  and  56 , respectively, thereby carrying needles  34  and  54  closer to complementary seats defined in fluid outlet port  42  and fluid outlet port  62 , respectively. The degree of slidable movement downward of floating piston  24  and floating piston  52  is proportional to the fluid pressure applied thereto. Higher pressures result in more movement of floating piston  24  and floating piston  52 , and thus a decrease in the gap between valve needle  34  and the seat defined in fluid outlet port  42 , and between valve needle  54  and the seat defined in fluid outlet port  62 , while lower pressures result in a larger gap, thereby regulating fluid flow through fluid outlet port  42  and fluid outlet port  62  at a constant level. Fluid flows from valve chamber lower portion  22  of flow control component  12  to valve chamber lower portion  50  of pressure control component  14  through connecting fluid conduit  66 . 
     The downward motion of flow control component piston  24  is resisted by spring  38  and by a back pressure, within lower portion  22  of flow control component valve chamber  18 , that is generated by the downward motion of pressure control component floating piston  52 . As pressure control component floating piston  52  moves downwards under the force of fluid entering pressure control component valve chamber upper portion  48 , fluid within pressure control component valve chamber lower portion  50  is compressed, thereby generating a back pressure that is transmitted to valve chamber lower portion  22  of flow control component  12  through connecting fluid conduit  66 . Similarly, spring  56  and the force of fluid entering valve chamber lower portion  50  of pressure control component  14  combine to resist the downward motion of pressure control component piston  52 . 
     The pressure range within which valve  10  operates can be determined by appropriately selecting spring  38  and  56  that offer a desired amount of resistance to the downward motion of pistons  24  and  52 . For example, spring washers having desired spring constants can be utilized as spring  38  and  56 . Pressure control component  14  serves as the principal pressure regulator, while flow control component  12  permits fine adjustments to be made to the operable pressure range. 
     Fine adjustment of the operable pressure range of valve  10  is made by means of valve member  28 . Valve member  28  is advanceable within floating piston  24  by rotation of rotatable handle  30  and shaft  32 , thereby repositioning valve member  28  within piston  24  to adjust the gap between needle  34  and the seat defined in fluid outlet port  42  thus controlling the rate of fluid flow therethrough. 
     Additionally, pressure control component  14  serves to substantially isolate flow control component  14  from changes in pressure transmitted to valve  10  from a downstream component of a fluid flow system that includes valve  10 . Consequently, valve  10  is capable of accurately controlling fluid flow even in the presence of downstream system perturbations. 
     Valve  10  is a differential pressure regulator, maintaining a substantially constant differential between the inlet pressure (at conduit  64 ) and the intermediate system pressure (at conduit  66 ), i.e., between the flow control section and the pressure control section. A momentary change in inlet pressure will result in only a short duration change in fluid flow rate through valve  10 , which is rapidly equalized. 
     The pressure control component  14  acts as a dampener to compensate substantially for pressure changes isolating the flow control piston  24  from such changes and maintaining a constant intermediate system pressure. Sinusoidal flow variations due to downstream pressure perturbations are avoided. Pressure drop across the orifice passage  36  is accurately controlled, enabling use of a simple drilled orifice rather than more expensive traditional control orifices, although conventional orifices can be utilized if desired. 
     FIG. 2 shows a schematic representation of second preferred embodiment of adjustable flow control valve  10  of the present invention. The second preferred embodiment is identical to the first preferred embodiment, except that adjustable valve member  28  is disposed within floating piston  52  of pressure control component  14   35  instead of being disposed within floating piston  24  of flow control component  12 . While suitable over a smaller flow rate range, this embodiment is not as preferred as the first embodiment, which is useful over a larger flow rate range. 
     FIG. 3 shows a schematic representation of a third preferred embodiment of the adjustable flow control valve  10  of the present invention. The third preferred embodiment is similar to the first and second preferred embodiments except that flow control component  12  includes an external adjustable orifice valve  68 , connecting valve chamber upper portion  20  and valve chamber lower portion  22 , located external to housing  16  of flow control component  12 . ° Che external adjustable orifice valve  68  serves the function of the orifice passage  36  of the first preferred embodiment. This arrangement is not as accurate as the first preferred embodiment at low flow rates, but allows operation at higher flow rates. 
     FIG. 4 illustrates a fourth preferred embodiment of the present invention, which combines the features of the first three embodiments. Thus each of the pistons,  24 ,  52  of the flow control component  14  and pressure control component  12 , respectively, carries an adjustable valve member operated on by a handle  30 . In addition, an external flow adjustment valve  69  is provided. Thus coarse flow control, fine flow control, and dampening pressure differential can all be selectively adjusted. 
     A gauge  71  monitors differential pressure in the system. Other combinations of the first three embodiments may likewise to configured in accordance with the present invention. 
     The detailed construction of the first preferred embodiment will now be described, with it being understood that the remaining embodiments use similarly constructed components. As shown in FIG.  5  and FIG. 6, the presently most preferred embodiment of the adjustable flow control valve  10  of the present invention includes an upper housing  70 , a lower housing  72  and an intermediate housing  74  that cooperatively house flow control component  12  and pressure control component  14 . 
     Upper housing  70  and lower housing  72  each define a plurality of bolt holes  76  for receiving bolts  77  for securing upper housing  70  and lower housing  72  to intermediate housing  74 . Intermediate housing  74  is penetrated by first access port  78  and second access port  80 . Intermediate housing  74  is also provided with an inlet port  82  (shown in FIG.  9 ). An outlet port  84  is defined by lower housing  72  and penetrates lower housing  72  at an angle of approximately 90° relative to the direction of penetration of inlet port  82 . Valve  10  further includes a manually operable knob  86  secured to a rotatable adjustment shaft  88  (shown in FIG. 8) that opens through upper housing  70  into the interior of valve  10 . Lower housing  72  is provided with an access cover  90  for providing access to pressure control component  14 . 
     As used herein throughout, the terms “lower” and “bottom” refer to the end of valve  10  closest in proximity to outlet port  84 , while the terms “upper” and “top” refer to the opposite end of valve  10  closest to manually adjustable knob  86 . These identifiers are used for convenience in aid of understanding the disclosures contained herein; however, it should be apparent to those skilled in the art that valve  10  can be used in any physical orientation. 
     FIG. 7 shows an upper end view of the presently most preferred embodiment of the adjustable flow control valve  10  of the present invention. 
     FIG. 7 shows the planes of the longitudinal cross-sectional views shown in FIGS. 8-11. 
     Referring now to FIG. 8, upper housing  70  includes a neck portion  92  having an externally threaded surface  94  for threadedly engaging mount ring  96  used to securely mount valve  10  to a support surface. Upper housing neck portion  92  defines a retainer chamber  98 , having an internally threaded surface  100 , that receives externally threaded retainer  102  which is mounted around rotatable adjustment shaft  88 . Retainer  102  defines indentations  104  useful for threadedly inserting or withdrawing retainer  102  into or from retainer chamber  98 . Upper housing  70 , and the upper portion of intermediate housing  74 , cooperatively define a flow control component valve chamber  106  including a head portion  108 , a neck portion  110  and a body portion  112 . Rotatable adjustment shaft  88  includes a first end  114 , fixedly attached to manually operable knob  86 , and a second end  116 . Rotatable adjustment shaft  88  extends perpendicularly from manually operable knob  86  and penetrates valve chamber neck portion  110  through an upper housing bore  118 . A rotatable adjustment shaft first seal  120  is disposed around rotatable adjustment shaft  88  immediately above bore  118 , and a rotatable adjustment shaft second seal  122  is disposed around rotatable adjustment shaft  88  immediately below bore  118 . 
     Disposed within flow control component valve chamber  106  are flow control component floating piston  124  and needle assembly  126 . The needle assembly  126  serves as the aforementioned valve member  28 . Rotatable adjustment shaft second end  116  is fixedly inserted within needle assembly  126  which includes a body  128 , including an upper body  130  and a lower body  132 . Upper body  130  bears an externally-threaded surface  134  for threadedly engaging an internally threaded surface  136  of piston  124 . Lower body  132  defines spring cavity  138  which houses coil spring  140 . Needle assembly lower body  132  bears an externally threaded surface  142  which threadedly engages an internally threaded surface  144  of a needle carrier sleeve  146 . Needle carrier sleeve  146  defines a needle cavity  148  that houses a needle  150 . Needle  150  includes a needle head  152  and a pointed tip  154 . Needle head  152  is disposed within needle cavity  148 . 
     Needle assembly  126  is disposed within needle assembly cavity  156  defined by floating piston  124 . A seal is formed around needle assembly  126  by needle assembly sealing element  158  disposed within a groove  160  circumferentially disposed around needle assembly body  128 . 
     Flow control floating piston  124  is disposed within flow control valve chamber  106 . Floating piston  124  includes a first end  162 , a second end  164  and a body  166 . A seal is formed around floating piston body  166  by piston seal  168 . 
     Floating piston body  166  defines jet chamber  170  which houses jet  172  that fluidly connects valve chamber head portion  108  with valve chamber body portion  112 . Floating piston  124  is upwardly biased by spring washers  174  disposed within valve chamber body portion  112 . 
     Intermediate housing  74  defines a valve seat cavity  176  for receiving flow control valve seat assembly  178 . Valve seat assembly  178  includes a valve seat  180  positioned within a valve seat holder  182  which threadedly receives a valve seat retainer  184 . Valve seat retainer  184  defines an outlet orifice  186  and an outlet conduit  188 . A seal is formed around valve seat holder  182  by valve seat holder seal  190 . 
     Again with reference to FIG. 8, lower housing  72  and intermediate housing  74  cooperatively define a pressure control component valve chamber  192  including an upper portion  194  and a lower portion  196 . Upper portion  194  of pressure control component valve chamber  192  communicates (due to manufacturing considerations) with valve seat cavity  176  of fluid control component  12  through a bore  198 , which is sealed with threaded plug  200  in operation. Disposed within upper portion  194  of pressure control component valve chamber  192  is a pressure control floating piston  202 . Floating piston  202  includes a first end  204 , a second end  206  and a body  208 . A seal is formed around floating piston body  208  by floating piston seal  210 . Floating piston body  208  defines a spring cavity  212  that extends from floating piston first end  204  to floating piston second end  206 . The portion of spring cavity  212  proximate to floating piston first end  204  includes an internally-threaded surface  214  for threadedly receiving a plug  216  that seals spring cavity  212 , while tip  222  projects downwardly therefrom. Spring cavity  212  receives needle  218  which includes needle head  220  and pointed tip  222 . Needle head  220  is disposed within spring cavity  212 . A coil spring  224  is disposed within spring cavity  212  between needle head  220  and plug  216 . Pressure control component floating piston  202  is upwardly biased by a plurality of spring washers  226  disposed within valve chamber lower portion  196 . 
     Lower housing  72  defines a valve seat cavity  228  for receiving pressure control valve seat assembly  230 . Valve seat assembly  230  includes a valve seat  232  positioned within a valve seat holder  234  which threadedly receives a valve seat retainer  236 . Valve seat retainer  236  defines an outlet orifice  238  and an outlet conduit  240 . A seal is formed around valve seat holder  234  by valve seat holder seal  242 . Valve seat assembly  230  is secured within valve seat cavity  228  by an externally-threaded portion  244  of valve seat holder  234  which threadedly engages an internally-threaded portion  246  of valve seat cavity  228 . Valve seat cavity  228  is sealed at its lower end by a plug  248  which is secured in place by an end cap  250  bearing an internally threaded surface  252  that threadedly engages an externally threaded surface  254  of lower housing  72 . A seal is formed around plug  248  by plug seal  256 . A seal is formed around end cap  250  by end cap seal  258 . 
     Adjustable flow control valve  10  includes a plurality of fluid conduits that define a fluid path within adjustable flow control valve  10  and thereby fluidly connect valve inlet port  82  and valve outlet port  84 . As shown in FIG. 9, beginning at valve inlet port  82 , an inlet conduit  260  extends (which is an off-axis longitudinal cross section) to a transverse inlet conduit  262  oriented at a right angle with respect to inlet conduit  260 . Inlet conduit  260  opens into valve chamber upper portion  194  of pressure control component  14  through a first feeder conduit  264  and a second feeder conduit  266 . Transverse inlet conduit  262  opens into valve chamber  106  of flow control portion  12  through valve chamber feeder conduit  268  (shown in FIG.  10 ). 
     As shown in FIG. 11, flow control component valve chamber  106  is placed in fluid communication with a first connecting conduit  270  by valve seat outlet orifice  186  and valve seat outlet conduit  188 . First connecting conduit  270  extends to a second connecting conduit  272  that is in fluid communication with valve chamber lower portion  196  of pressure control component  14  via a tripartite connecting conduit  274  including a first portion  276 , a second portion  278  and a third portion  280 . Valve chamber lower portion  196  of pressure control component  14  is connected to valve outlet port  84  by outlet orifice  238  and outlet conduit  240 . 
     In operation, fluid enters valve  10  through valve inlet port  82  where the fluid flow is directed to both flow control component  12  and pressure control component  14 . Fluid is directed to flow control component  12  through inlet conduit  260  and transverse inlet conduit  262 , and enters fluid control component valve chamber  106  through valve chamber feeder conduit  268 . Fluid is directed to pressure control component  14  through inlet conduit  260  and enters valve chamber upper portion  194  of pressure control component  14  through feeder conduits  264  and  266 . Fluid entering flow control portion valve chamber  106  passes through jet  172  and also applies fluid pressure to floating piston  124  which is pushed downwardly to compress spring washers  174 , thereby carrying needle  150  closer to valve seat  180 . The degree of slidable movement downward of floating piston  124  within valve chamber  106  is proportional to the fluid pressure applied to floating piston  124 . Higher pressures result in more movement of floating piston  124 , and thus a decrease in the gap between valve needle  150  and valve seat  180 , while lower pressures result in a larger gap. By selecting a spring with an appropriate spring constant, an increase in fluid pressure is balanced by a proportionally increased pressure drop through the resulting decreased gap between valve needle  150  and valve seat  180 . 
     Additionally, the downward motion of floating piston  124  within valve chamber  106  is upwardly biased by a back pressure within valve chamber body portion  112  which is generated by the downward motion of pressure control component floating piston  202 . As pressure control component floating piston  202  moves downwards under the force of fluid entering valve chamber upper portion  194 , fluid within valve chamber lower portion  196  of pressure control component  14  is compressed, thereby generating a back pressure that is transmitted to valve chamber body portion  112  of flow control component  12  through tripartite connecting conduit  274 , second connecting conduit  272  and first connecting conduit  270 . 
     Similarly, the portion of the fluid flow that is directed to valve chamber upper portion  194  of pressure control component  14 , through feeder conduits  264  and  266 , pushes floating piston  202  downward to compress spring washers  226 , thereby carrying valve needle  218  closer to valve seat  232 . Spring washers  226  and the force of fluid entering valve chamber lower portion  196  of pressure control component  14  combine to upwardly bias the downward motion of pressure control component piston  202 . 
     Thus, the movement of floating pistons  124  and  202  regulates the flow of fluid through valve  10  by increasing or decreasing the gap between needle tip  150  and valve seat  180 , and between needle tip  218  and valve seat  232 . The pressure range within which valve  10  operates can be determined by selecting spring washers  174  and spring washers  226  each having an appropriate spring constant. 
     Fine adjustment of the operable pressure range of valve  12  is made by means of needle assembly  126 . Needle assembly  126  is advanceable within floating piston  124  by rotation of manually operable knob  86  and rotatable adjustment shaft  88 , which rotatably and longitudinally advances needle assembly  126  within piston  14 , thereby adjusting the gap between needle tip  154  and valve seat  180 . Additionally, pressure control component  14  serves to substantially isolate flow control component  14  from changes in pressure transmitted to valve  10  from a downstream component of a fluid flow system that includes valve  10 . Consequently, valve  10  is capable of accurately controlling fluid flow even in the presence of downstream system perturbations. 
     While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.