Abstract:
A system, apparatus and method of controlling the flow of a fluid are provided. In accordance with one embodiment of the present invention, a flow control device includes a valve having a flow path defined therethrough and a valve seat in communication with the flow path with a valve stem disposed in the valve seat. The valve stem and valve seat are cooperatively configured to cause mutual relative linear displacement thereof in response to rotation of the valve stem. A gear member is coupled with the rotary stem and a linear positioning member includes a portion which complementarily engages the gear member. Upon displacement of the linear positioning member along a first axis, the gear member and rotary valve stem are rotated about a second axis and the valve stem and valve seat are mutually linearly displaced to alter the flow of fluid through the valve.

Description:
STATEMENT OF GOVERNMENT RIGHTS  
       [0001]     The present invention was made with United States Government support under Department of Energy Contract No. DE-AC07-99ID13727. The Federal Government has certain rights in this invention. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates generally to fluid flow control and, more particularly, to high resolution flow control of, for example, high pressure compressible fluids including supercritical fluids.  
         [0004]     2. State of the Art  
         [0005]     Control of fluid flow is important in numerous applications. For example, fluid flow control is involved in hydraulic applications, in the operation of various semiconductor fabrication systems such as chemical vapor deposition (CVD) and atomic layer deposition (ALD) equipment, in the operation of autoclaves and similar equipment, and in the performance of various laboratory experiments.  
         [0006]     In all of the above-listed applications, as well as numerous others, the ability to control fluid flow, whether according to pressure or flow rate (either mass or volume), is important to the success of the operation or process being performed. For example, in regard to various laboratory experiments, fluid flow control often needs to be precise and repeatable so as to ensure that certain input conditions are actually what was intended and the integrity of the experiment&#39;s outcome is not in question. It becomes even more important to control the fluid flow, and also more difficult to accurately do so, when the fluid being handled is supercritical and there is a potential of effecting a phase change within the fluid as it flows through a flow control device. While various fluid control devices have been designed in an attempt to provide high resolution flow control, such devices have been lacking in their ability to consistently provide accurate control of fluids including high pressure, compressible fluids.  
         [0007]     For example, referring to  FIG. 1 , a prior art flow control device  10  is shown. The flow control device  10  includes a valve  12  with a flow path  14  defined therethrough. The valve includes an inlet  16  configured to be coupled with a fluid source (not shown) and an outlet  18  configured to be coupled with a conduit or some other device to which fluid is to be delivered (none shown). A linearly positionable valve stem  20  is disposed within the valve and configured to control the flow of fluid passing through the defined flow path  14 . Packing  22  or some other seal arrangement may be disposed about a portion of the valve stem  20  to prevent leaking of the fluid around the valve stem  20 . The valve stem  20  is coupled with a linear positioning actuator  24  which displaces the valve stem along a linear path as indicated by directional arrow  26 .  
         [0008]     While the flow control device  10  may provide adequate fluid flow control for some applications, it is desirable to improve on such an arrangement. For example, a flow control device configured substantially as described with respect to  FIG. 1  may exhibit a flow coefficient of approximately 0.03 C v , wherein C v  may be defined, as it relates to valves, as a quantity relating a flow rate, in gallons per minute (gpm), of a fluid with a known specific gravity to the pressure drop experience across the valve as measured in pounds per square inch (psi). It may be noted that the flow coefficient is not dimensionally homogenous (as illustrated in the following equations) and is specifically limited to English units.  
         [0009]     For incompressible fluids the flow coefficient C v  may be expressed by the following equation:  
         C   v     =     Q         Δ   ⁢           ⁢   p       S   ⁢           ⁢   G               
 
         [0010]     Wherein Q is the flow rate in gallons per minute, Δp is the change in pressure across the valve in pounds per square inch, and SG is the specific gravity of the fluid flowing through the valve.  
         [0011]     For compressible fluids, the determination of the flow coefficient becomes more complex. For example, if the inlet pressure is twice that of the outlet pressure (what may be termed as critical flow) or greater, the flow coefficient may be expressed by the following equation:  
         C   v     =       Q   G     ⁢         S   ⁢           ⁢   G   ×   T         816   ×     P   inlet               
 
         [0012]     If the inlet pressure is less than twice the outlet pressure (what may be termed subcritical flow) the flow coefficient may be expressed by the following equation:  
         C   v     =         Q   G     962     ⁢         S   ⁢           ⁢   G   ×   T         P   inlet   2     -     P   outlet   2                 
 
         [0013]     Wherein Q G  is the flow rate of the fluid in standard cubic feet per minute (scfm), T is the absolute temperature in degrees Rankin, P inlet  and P outlet  are the inlet and outlet pressures of the valve, respectively, in pounds per square inch absolute (psia), and SG is the specific gravity of the fluid flowing through the valve.  
         [0014]     Returning to the prior art flow control device  10  described with respect to  FIG. 1 , while in absolute terms, a flow coefficient of 0.03 C v  would appear to provide fluid control at what might be consider a “high” resolution, such a flow coefficient may not be considered adequate for a number of applications including. For example, in some applications, such as various laboratory experiments, it may be desired to provide flow control with a resolution which is approximately an order of magnitude finer than such a prior art flow control device. Additionally, such a flow control device  10  has, in the past, only provided adequate pressure control of a fluid within, for example, 50 to 100 psi in some cases. It is desirable to obtain more exact pressure control of the fluid for numerous applications.  
         [0015]     An additional problem with the flow control device  10  shown and described with respect to  FIG. 1  is that the linear motion of the valve stem  20  makes the valve  12  vulnerable to contamination from grit or small particulates which may be present in the fluid flowing therethrough. For example, in the past, such a valve  12  has had small particulates become lodged or wedged between the valve stem  20  and the valve stem seat  28 . When lodged between the valve stem  20  and valve stem seat  28 , the particulates have interfered with the actuation of the valve stem  20  and the precise positioning thereof. Furthermore, the presence of particulates between the valve stem  20  and the valve stem seat  28  has, in the past, resulted in the galling of the two components thereby causing the valve  12 , initially, to operate imprecisely and, ultimately, to fail. In some particular cases, the valve  12  associated with a flow control device such as described with respect to  FIG. 1  has failed within approximately fifteen to twenty minutes of use because of the presence of such particulates in the fluid.  
         [0016]     In view of the shortcomings in the art, it would be advantageous to provide a method and apparatus for consistently and repeatedly controlling the flow of high pressure, compressible fluids at a relatively high resolution. It would further be desirable to provide a method and apparatus of controlling fluid flow which is not susceptible to fouling or galling due to the presence of particulates within a fluid being processed thereby.  
       BRIEF SUMMARY OF THE INVENTION  
       [0017]     In accordance with one aspect of the invention, a fluid flow control device is provided. The fluid flow control device includes a valve having a fluid inlet, a fluid outlet and a flow path defined therebetween. The valve further includes a valve stem disposed within a valve seat in communication with the flow path. A gear member is coupled to the valve stem, which is cooperatively configured with the valve seat to cause the valve stem to advance or back off within the valve seat responsive to rotation of the valve stem about a first axis. A linear positioning member is disposed adjacent the gear member wherein at least a portion of the linear positioning member is configured to complementarily engage the gear member. The linear positioning member is configured to be displaced along a second axis to cause rotation of the gear member and valve stem about the first axis and the attendant displacement of the valve stem along the first axis. In one embodiment, the portion of the linear positioning member which complementarily engages the gear member may be configured as substantially helically cut worm gear.  
         [0018]     In accordance with another aspect of the present invention, a fluid flow control system is provided. The fluid flow control system includes a controller and at least one fluid flow control device operably coupled with the controller. The fluid flow control device includes a valve having a fluid inlet, a fluid outlet and a flow path defined therebetween. The valve further includes a valve stem disposed within a valve seat in communication with the flow path. A gear member is coupled to the valve stem, which is cooperatively configured with the valve seat to cause the valve stem to advance or back off within the valve seat responsive to rotation of the valve stem about a first axis. A linear positioning member is disposed adjacent the gear member wherein at least a portion of the linear positioning member is configured to complementarily engage the gear member. The linear positioning member is configured to be displaced along a second axis to cause rotation of the gear member and valve stem about the first axis and the attendant displacement of the valve stem along the first axis.  
         [0019]     In accordance with yet another embodiment of the present invention, a method of controlling the flow of a fluid is provided. The method includes providing a valve having a flow path defined therethrough. A valve stem is disposed within a valve seat in communication with the flow path and is coupled with a gear member. The gear member is engaged with a complementary surface of a linear positioning member and the fluid is passed through the flow path. The linear positioning member is displaced along a first axis to rotate the gear member and valve stem about a second axis and displace the valve stem along the second axis. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0020]     The foregoing and other advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings in which:  
         [0021]      FIG. 1  shows a prior art fluid flow control device;  
         [0022]      FIG. 2  shows a fluid flow control device in accordance with an embodiment of the present invention;  
         [0023]      FIG. 3  shows an enlarged view of a portion of the device of  FIG. 2 ; and  
         [0024]      FIG. 4  is a schematic of a fluid flow control system in accordance with an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]     Referring to  FIG. 2 , a fluid flow control device  100  is shown. The flow control device includes a valve  102  with a flow path  104  defined therethrough. The valve  102  includes an inlet  106  configured to be coupled with a fluid source (not shown in  FIG. 2 ) and an outlet  108  configured to be coupled with a conduit or some other device to which fluid is to be delivered. A valve stem  110  is disposed within the valve  102  and configured to control the flow of fluid passing through the defined flow path  104 . Packing  112  or some other seal assembly may be disposed about a portion of the valve stem  110  to prevent leaking of the fluid around the valve stem  110 .  
         [0026]     The valve stem  110  is configured and oriented to be displaced within the valve along a defined axis  114  relative to an associated valve seat  116  upon the rotation of the valve stem  110  about the defined axis  114 . Thus, the valve stem  110  and a component of the valve  100 , such as the packing gland  113  or some other appropriate structure, may include mating or complimentarily engaged threads  118  to enable the displacement of the valve stem  110  relative to the valve  100  along the axis  114  in response to the rotation of the valve stem  110 . The pitch of the threads  118  may be selected to control the magnitude of displacement of the valve stem  110  relative to the valve  100  upon rotation of the valve stem  110 . An exemplary valve may include Micro Metering valve Part # 10VRMM2812 commercially available from Autoclave Engineers of Eerie Pa., although other valves may be used in practicing the present invention.  
         [0027]     A linear positioning actuator  120  is coupled with a positioning member  122  such as a shaft or other structural member. The actuator  120  may include, for example, a high resolution linear positioning stepper motor configured to displace the positioning member  122  along an axis  124  as indicated by directional arrow  126 . An exemplary actuator may include a model EVA-1 electronic valve actuator commercially available from Badger Meter, Inc., of Tulsa, Okla. Such an actuator  120  may include a transformer  128  coupled to a 120 VAC power supply  130  which is configured to provide DC power to the actuator  120 . Another exemplary actuator might include a pneumatic actuator which utilizes a current to pressure (I/P) converter for controlling the linear position of the positioning member  122 . It is noted, however, that other actuators  120  may be used in conjunction with the present invention.  
         [0028]     A portion of the positioning member  122 , such as at the distal end  132  thereof, is configured to matingly engage a gear  134 . The gear  134  is coupled with the valve stem  110  and configured to rotate the valve stem  110 . As shown, the gear  134  is disposed about valve stem  110  in perpendicular orientation thereto. Thus, as the positioning member  122  is displaced linearly along axis  124 , the portion of the positioning member  122  engaged with the gear  134  causes rotation of the gear  134  about axis  114  as indicated by directional arrow  136 , advancing or backing off the valve stem  110  within the valve seat  116 , depending upon the direction of displacement of positioning member  122 . The diameter of the gear  134  may be selected to provide a desired gear reduction and thereby improve the resolution provided by the linear actuator  120 . As will be appreciated by those of ordinary skill in the art, a larger diameter gear  134  will provide a greater amount of reduction such that a larger linear displacement of the positioning member  122  will be required to effect a full turn of the valve stem  110 .  
         [0029]     In one embodiment, the distal end  130  of the positioning member  122  may be configured as a toothed rack and the gear  134  may be configured as a mating pinion gear thereby providing a rack and pinion assembly. However, in another embodiment, as specifically shown in  FIG. 3 , (while also still referring to  FIG. 2 ) the distal end  130  of the positioning member  122  may be configured as a substantially helically cut worm gear  138  wherein gear  134  is configured to mate therewith. With conventional worm gear arrangements, the worm gear  138  acts as a driving gear by rotating about its axis  124  and driving or rotating the associated driven gear  134 . However, the worm gear  138  of the present invention is not configured to rotate about its axis  124  but, rather, remains rotationally fixed and is linearly displaced along its axis  124  by the actuator  120 .  
         [0030]     It has been determined that the use of a worm gear  138  with a mating gear  134 , wherein the worm gear  138  is rotationally fixed but linearly displaced, provides a configuration which may be designed with a minimum of backlash between intermeshed gear teeth (e.g., teeth  134 A,  138 A and  138 B). The minimization of backlash between the gear  134  and worm gear  138  enables more precise rotational control of the valve stem  110 . For example, if backlash exists between the gear  134  and complementarily engaging portion of the linear positioning member  120 , there will be a small displacement of the positioning member  122 , as the positioning member  122  reverses directions, which does not result in the rotation of the associated gear  134  and valve stem  110  coupled therewith. While the gear  134  and worm gear  138  may be formed from any of a number of suitable materials, in one exemplary embodiment the gear  134  is formed of a brass material while the worm gear  138  is formed of a carbon steel material.  
         [0031]     Referring back more particularly to  FIG. 2 , a frame member  140  may be used to couple the valve stem  110  and the actuator  120  to one another such that the valve stem  110 , with its associated gear  134 , may remain in a relatively fixed geometric position with respect to the positioning member  122 . In other words, the frame member  140  serves to maintain the geometrical relationship of the two axes  114  and  124 . Additionally, in one embodiment, other frame or guide members  142  and  144  may be used to maintain the alignment of the gear  134  with the positioning member  122 . For example, the gear  134  may be slidably coupled with the valve stem  110 , such as with mating splines  146 A (see also  146 B in  FIG. 3 ), such that the gear  134  may transfer rotational motion to the drive stem  110  while enabling the gear  134  to maintain alignment with the positioning member  122  along its axis  124  during displacement of the valve stem  110  along the defined axis  114 . Of course other arrangements may be utilized to accomplish such a slidable coupling between the gear  134  and drive stem  110 . It is also noted that in some circumstances, such as wherein expected rotation of the gear  134  and the resulting displacement of the valve stem  110  along the defined axis  114  is small, any misalignment between the gear  134  and drive stem  110  may be negligible. In such a circumstance, a coupling which enables the displacement of the gear  134  relative to the drive stem  110  along the axis  114  would not be necessary.  
         [0032]     The flow control device  120  of the present invention is configured to provide relatively high resolution fluid flow control for high pressure, compressible fluids. For example such a configuration may have an associated flow coefficient, C V  (as defined above herein), of approximately 0.004. Additionally, the flow control device may operate at pressures of up to 3,000 psi gauge (psig) while controlling the pressure of the fluid flow within approximately 3 psi. Fluid flow can be regulated to less than approximately 1 milliliter per minute (mL/min). Furthermore, such a flow control device  100  is capable of similarly controlling the flow of supercritical fluids, wherein the fluid changes phases due to a pressure drop across the valve  102 .  
         [0033]     Such high resolution of fluid flow control is largely a result of the precise control of the tip  110 A of the valve stem  110  relative to the valve seat  116 . As set forth above, the movement of the linear positioning member  122  turns the gear  134  which, in turn, causes rotation of the valve stem  110  relative to the body of the valve  102 . As the valve stem  110  turns, the mating threads  118  enable a linear movement of the valve stem tip  110 A relative to the valve seat  116 . The relatively small changes in rotational motion of the valve stem  110  result in even more minute changes in the linear position of the valve stem  110  and associated tip  110 A along defined the axis  114 . These precise, minute changes in linear position of the valve stem tip  110 A relative to the valve seat  116  enable precise changes in a pressure drop experienced across the valve  102 . Thus, the precision of the linear actuator  120  is enhanced through the implementation of the gear  134  and worm gear  138  as well as the rotary-type valve stem  110 .  
         [0034]     It is noted that the rotary-type valve stem  110  not only provides enhanced resolution of the fluid flow control, but also inhibits the lodging of particulates between the valve stem  110  and the valve seat  116  and the attendant galling that may result therefrom. For example, considering the prior art valve  12  shown in  FIG. 1 , such a linearly positionable valve stem  20  requires relatively tight machining tolerances for proper operation and control of fluid flow. However, because the valve  102  of the present invention utilizes a rotary-type valve stem  110 , broader or, relatively gross tolerances may be used with respect to the fit of the valve stem  110  and the valve seat  116  while still accomplishing a flow coefficient (C v ) which is similar to that of the prior art valve  12  described with respect to  FIG. 1 .  
         [0035]     Furthermore, when using a valve  12  configured as described with respect to  FIG. 1 , the close tolerances of the valve stem  20  with respect to the valve seat  28  cause the valve  12  to become prone to galling, particularly when solids are present in the fluid flow. Additionally, in situations where a substantial pressure drop and accompanying phase change occur across the valve  12 , heat is often applied to the fluid flow to prevent flash freezing of the fluid flow, which may lead to deposition and accumulation of solids within the valve  12  (or other portions of the fluid flow path), so as to prevent the plugging of the valve  12 . However, the addition of heat may also result in thermal expansion of various components including, for example, the body of the valve  12 , the valve stem  20  and valve seat  28 . Because tolerances between such components are already tight, any thermal expansion exhibited by these components is likely to result in increased friction therebetween. This results in an even greater likelihood of galling and failure of the valve  12 .  
         [0036]     The use of a rotary-type valve  102  of the present invention is less prone to galling when fluid flow is heated because of the relatively gross tolerances between the valve stem  110  and mating components. Furthermore, if a particulate does become lodged between the valve stem  110  and the valve seat  116 , it has been determined that rotation of the valve stem to an open position, followed by reverse rotation of the valve stem  110  to a closed or reduced flow position, allows the particulate to be washed through the valve  102  and continued operation of the flow control device  100  may continue. Thus, the flow control device  100  of the present invention may require less filtering of a given fluid.  
         [0037]     Still referring to the  FIG. 2 , in many applications it may be desirable to utilize an actuator  120  which is configured to enable automatic control of the flow control device  100 . Thus, for example, the actuator  120  may include a control signal input I such as a 4-20 milliamp (mA) analog input from an associate controller (not shown in  FIG. 2 ). Furthermore, the actuator  120  may include span adjustment S and a zero adjustment Z to set limit of travel and the zero position of the positioning member  122  respectively. Additionally, a linear potentiometer P or other linear position sensor may be utilized to determine the position of the positioning member  122 , within its limits of travel, at any given time.  
         [0038]     Referring now to  FIG. 4 , a fluid flow control system  200  may include a flow control device  100  coupled with a controller  202 . The controller may include, for example, a PID (proportional, integral, derivative) controller or, it may include a computer having a central processing unit (CPU)  204 , or other microprocessor, and memory  206 . The controller  202  may be coupled to an input device  208  and an output device  210  such that, for example, commands or instructions may be provided to the controller  202  and so that actions taken or conditions monitored by the controller may be displayed or reported. The controller  202  may also be coupled with a pump  212  or other device configured to provide fluid flow from a fluid source  214  at a specified pressure and/or flow rate. An exemplary pump may include a high-pressure syringe pump commercially available from, for example, ISCO, Inc., of Lincoln, Nebr.  
         [0039]     One or more sensors  216 A and  216 B may be utilized to monitor one or more characteristics of the fluid flow. For example, the sensors  216 A and  216 B may include pressure transducers to monitor the pressure of the fluid flow at a desired location, or to determine the pressure drop experienced by the fluid as it flows through the valve  102 . In another embodiment, one or more of the sensors  216 A and  216 B may be configured to determine the flow rate of the fluid. Additionally, one or more of the sensors  216 A and  216 B may be configured to detect the temperature of the fluid flow at a given location along the flow path. It will be noted that the sensors  216 A and  216 B may be configured to determine other parameters or characteristics of the fluid flow and that multiple sensors may be employed to determine a combination of the above-listed parameters. As shown in  FIG. 4 , the sensors  216 A and  216 B may be located and configured to detect a characteristic of the fluid flow at a location upstream from the valve  102  (e.g., sensor  216 B) or downstream from the valve  102  (e.g., sensor  216 A) or both.  
         [0040]     In operation, the controller  202  may provide a signal to the pump  212  to provide fluid flow from the fluid source  214 . One or more of the sensors  216 A and  216 B may detect a specified parameter of the fluid flow. If the value of the detected parameter of the fluid flow differs from a desired value, the controller  202  may actuate the flow control device  100  to alter the setting of the valve and, thereby, alter one or more characteristics of the fluid flow in order to obtain the desired value of the parameter being monitored.  
         [0041]     As noted above, the present invention may be practiced in a variety of environments and in conjunction with numerous applications. For example, various laboratory experiments will benefit from the high level of fluid flow control achieved with the present invention. Other exemplary applications include, for example: extraction of carbon dioxide from soils; catalyst regeneration processes including an exemplary process set forth in U.S. Pat. No. 6,579,821 for METHOD FOR REACTIVATING SOLID CATALYSTS USED IN ALKYLATION REACTIONS, issued Jun. 17, 2003, the disclosure of which is incorporated, in its entirety, by reference herein; as well as a process set forth in copending U.S. patent application Ser. No. 09/554,708 for A PROCESS FOR THE REACTIONS OF GLYCERIDES AND FATTY ACIDS IN A CRITICAL FLUID MEDIUM, filed Jul. 31, 2000, the disclosure of which is incorporated, in its entirety, by reference herein. Of course, as stated above, such applications are exemplary only and, as will be appreciated by those of ordinary skill in the art, the present invention is useful in numerous other applications and processes.  
         [0042]     While the invention may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.