Abstract:
This invention pertains generally to valve lift spacers that determine the travel distance of a valve member, such as movement between upper and lower seats. In the case of pressure switching valves, such as those used in the fuel injection industry, valve travel distance is often relatively small. Because of realistic machining tolerances, it is often difficult to mass produce valves that consistently exhibit comparable travel distances, especially when those distances are on the order of microns. The present invention addresses this issue by providing valve lift spacers with a variety of thicknesses in order to compensate for the inevitable variation that would otherwise be produced due to the various valve components having realistic geometrical tolerances. The valve lift spacer and a valve using the same finds a principal use in fast response pressure switching valves, such as those utilized in electro-hydraulic actuator portion of a fuel injector.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates generally to valves with a predetermined travel distance, and more particularly to a valve lift spacer for adjusting the travel distance of a valve member.  
         BACKGROUND  
         [0002]    In one class of valves, a valve member&#39;s travel distance is determined by a thickness of a valve lift spacer, through which the valve member moves. The valve lift spacer typically separates two valve body components, such as an upper seat component and a lower seat component in the case of a three way valve. In some instances, consistent valve performance can be sensitive to variations in valve travel distance. For instance, relatively small fast acting pressure switching valves in fuel injection applications sometimes require consistent travel distances from one valve to another in order to produce consistent performance from one fuel injector to another. If the travel distances vary too substantially from one valve to another, the response time of the same can exceed acceptable variances, causing unacceptable deviations in performance from one fuel injector to another. Another problem associated with valves relates to routing passages through the valve in an effective and efficient manner.  
           [0003]    Efficiency could relate to decreasing valve leakage, whereas effectiveness could relate to ensuring a particular flow characteristic through the valve.  
           [0004]    The present invention is directed to this and other problems associated with valve lift spacers and valves using the same.  
         SUMMARY OF THE INVENTION  
         [0005]    A valve lift spacer comprises a metallic plate with a side surface separating the top surface from a bottom surface. The top surface includes a planar portion oriented parallel to a planar portion of the bottom surface. A valve travel bore extends between the top surface and the bottom surface. At least one of an inlet passage and an outlet passage extends between the top surface and the bottom surface. The plate belongs to one of a plurality of thickness groups.  
           [0006]    In another aspect, a collection of valve lift spacers includes a plurality of plates, each belonging to one of a plurality of thickness groups. Each of the thickness groups span a range of thicknesses, and each of the range of thicknesses has a width less than about 10 microns. Each of the plates has a circumferential side surface separating an at least partially planar top surface from an at least partially planar bottom surface. Each plate also includes a valve travel bore, an inlet passage and an outlet passage extending between the top surface and the bottom surface.  
           [0007]    In still another aspect, a valve includes an upper seat component separated from an lower seat component by a valve lift spacer. A valve member is moveable a predetermined travel distance between contact with the upper seat component and the lower seat component. An inlet passage is closed to a control volume when the valve member is in contact with the upper seat. An outlet passage is closed to the control volume when the valve member is in contact with the lower seat. At least one of the inlet passage and the outlet passage includes a segment extending through a top surface and a bottom surface of the valve lift spacer. The travel distance of the valve member is determined at least in part by a thickness of the valve lift spacer. The valve lift spacer belongs to one of a plurality of thickness groups.  
           [0008]    In still another aspect, a method of constructing a valve includes a step of trapping a valve member between an upper seat component and a lower seat component. The upper seat component is separated from the lower seat component by a nominal valve lift spacer having a predetermined thickness. The travel distance of the valve member between contact with the upper seat and the lower seat is measured. If the measured travel distance deviates from a predetermined travel distance by more than a predetermined amount, then a different valve lift spacer is substituted for the nominal valve lift spacer. The different valve lift spacer belongs to one of a plurality of thickness groups. At least one of an inlet passage and an outlet passage are located to extend between a top surface and a bottom surface of the valve lift spacer.  
           [0009]    In still another aspect of the present invention, a method of making a fluid passage in a metallic valve component with a predetermined flow characteristic includes a step of opening a passage between opposing surfaces of a metallic valve component at least in part by machining a hole through the component. The hole is enlarged at least in part by flowing an abrasive slurry through the hole. A flow characteristic of the passage is measured. At least one of the enlarging step and the measuring step are performed a plurality of times until the measured flow characteristic is about equal to a desired flow characteristic. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a sectioned side diagrammatic view of an electro-hydraulic actuator utilizing a valve lift spacer according to one aspect of the present invention;  
         [0011]    [0011]FIG. 2 is a top diagrammatic view of the valve portion of the electro-hydraulic actuator of FIG. 1;  
         [0012]    [0012]FIG. 3 is a sectioned side diagrammatic view of the valve of FIG. 2 as viewed along section line A-A;  
         [0013]    [0013]FIG. 4 is a bottom view of a valve lift spacer according to one aspect of the present invention;  
         [0014]    [0014]FIG. 5 is a sectioned side view of the valve lift spacer of FIG. 4 as viewed along section lines A-A;  
         [0015]    [0015]FIG. 6 is a top view of the valve lift spacer of FIG. 4;  
         [0016]    [0016]FIG. 7 is an enlarged section view of a passage through valve lift spacer as viewed along section lines D-D of FIG. 6;  
         [0017]    [0017]FIG. 8 is an enlarged sectioned side view of another passage through the valve lift spacer as viewed along section lines C-C of FIG. 4;  
         [0018]    [0018]FIG. 9 is a sectioned side view of the valve lift spacer as viewed along section lines B-B of FIG. 4;  
         [0019]    [0019]FIG. 10 is a schematic view of a hole enlargement apparatus according to another aspect of the present invention; and  
         [0020]    [0020]FIG. 11 is a graphical illustration of a collection of valve lift spacers according to still another aspect of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0021]    Referring to FIG. 1, electro-hydraulic actuator  12  is shown apart from a fuel injector (not shown) within which it could be used in relation to a direct control needle valve. In addition, FIGS.  2 - 3  show the three way valve assembly that makes up a portion of electro-hydraulic actuator  12  of FIG. 1.  
         [0022]    Three way control valve  14  is preferably positioned in close proximity to piston portion  32  so that the volume of needle control chamber  37  is made relatively small. Those skilled in the art will appreciate that pressure changes in needle control chamber  37  can be hastened by reducing its volume. This issue is addressed by actuator  12  in at least two ways. First, three way valve  14  is positioned in close proximity to the closing hydraulic surface  33  of piston portion  32 . In addition, needle control chamber  37  is preferably designed to be defined at least in part by volume reducing surface features. Thus, those skilled in the art will recognize that some measurable amount of improved performance can be achieved by paying attention to what surface features, which define needle control chamber, can be changed in order to reduce the volume of needle control chamber  37  without otherwise undermining performance. In many instances, it will be desirable to make any flow areas associated with needle control chamber  37  less restrictive than the flow areas associated with high pressure passage  40 , low pressure passage  41 , or the flow areas across seats  50  and  51 . When valve member  42  is in contact with lower seat  51 , as shown, needle control chamber  37  is fluidly connected across high pressure seat  50  to supply passage  24  via high pressure passage  40 . Supply passage  24  is fluidly connected to a source of high pressure liquid  18  via a high pressure supply line  19 . When valve member  42  is lifted upward into contact with high pressure seat  50 , needle control chamber  37  is fluidly connected to a low pressure area that surrounds actuator  12  across low pressure seat  51  via low pressure passage  41 . Low pressure passage  41  is fluidly connected to a low pressure reservoir  20  via drain vent  21 . Thus, valve member  42  can be thought of as being trapped between upper seat  50  and lower seat  51 . In order to reduce the influence of hydraulic forces on opposite ends of valve member  42 , a vent passage  83  vents armature cavity  82  to low pressure, and a vent passage  81  connects vented chamber  80  to low pressure.  
         [0023]    Valve member  42  is preferably operably coupled in a known manner to the moveable portion of an electrical actuator. In the illustrated embodiment, valve member  42  is attached to an armature  62  via a nut  63  that is threaded onto one end of valve member  42 . In particular, an armature washer  63  rests upon an annular shoulder  58  (FIG. 6), upon which armature  62  is supported. Next, a nut washer  64  is placed in contact with the other side of armature  62  followed by a spacer  65 , against which nut  66  bears. Armature  62  and hence valve member  42  are biased downward to close low pressure seat  51  by a suitable biaser, such as biasing spring  67 . Those skilled in the art will appreciate that a hydraulic biaser could be an alternative to the mechanical biaser shown. In addition, while electrical actuator  16  has been shown as a solenoid, those skilled in the art will appreciate that any other suitable electrical actuator, such as a piezo or a voice coil could be substituted in its place. A stator assembly  17  is preferably positioned within a carrier assembly  70  such that there respective bottom surfaces lie flush in a common plane. By doing so, a solenoid spacer  71  having an appropriate thickness can be chosen to provide a desired air gap between armature  62  and stator  61 . Thus, solenoid spacer  71  is preferably a categorized part that comes in variety of slightly different thicknesses that allow different valves to perform similarly by choosing an appropriate thickness to provide some uniformity in the armature air gap from one actuator to another.  
         [0024]    In order to aid in concentrically aligning upper seat  50  with lower seat  51  along common centerline  38 , valve member  42  includes an upper guide portion  54  with a close diametrical clearance (i.e. a guide clearance) with an upper guide bore  55  located in upper seat component  43 . In addition, valve member  42  also preferably includes a lower guide portion  56  having a relatively close diametrical clearance with a lower guide bore  57  located in lower seat component  45 . Thus, these guide regions tend to aid in concentrically aligning upper and lower seats  50  and  51  during the assembly of three way valve  15  (FIG. 5) as well as substantially fluidly isolating needle control chamber  37  from vented chamber  80  and/or armature cavity  82 , regardless of the position of valve member  42 . Because it is difficult to be certain, before assembly, the depth into seats  50  and  51  that valve member  42  will penetrate before coming in contact in closing that particular seat, three way valve  15  preferably employs a valve lift spacer  44  that is also a category part, and is preferably categorized in a plurality of different thickness groups. Thus, the distance that valve member  42  travels between upper and lower seats  50  and  51  is adjustable by choosing an appropriate thickness for valve lift spacer  44 .  
         [0025]    In order to reduce the influence of fluid flow forces on the movement of valve member  42 , high pressure passage  40  and low pressure passage  41  preferably include flow restrictions that are restrictive relative to a flow area across respective seats  50  and  51 . While these flow restrictions could be located in upper seat component  43  and/or lower seat component  45 , they are preferably located in valve lift spacer  44  as shown in FIG. 2. In particular, the flow characteristics through high pressure passage  40  can be relatively tightly controlled by including a cylindrical segment  47  having a predetermined length and flow area. Furthermore, cylindrical segment  47  is relatively restrictive to flow relative to that across upper seat  50 . Those skilled in the art will appreciate that it is easier to control, and consistently machine, a flow characteristic via a cylindrical segment as opposed to attempting to consistently control a flow area between a stationary seat component and moveable valve member  42 . Likewise, low pressure passage  41  preferably includes a cylindrical segment  48  that is located in valve lift spacer  44 . In order to differentiate the rate at which pressure changes can occur in needle control chamber  37 , cylindrical segment  48  preferably has a different flow area relative to cylindrical segment  47 . This feature is present in the illustrated example as a strategy by which the opening rate of the direct control needle valve is slowed relative to the closure rate of the same. In other words, when piston  32  is moved fluid is displaced from needle control chamber  37  through the flow restriction defined by cylindrical segment  48 . When direct control needle valve  11  is closed, high pressure fluid flows into needle control chamber  37  from high pressure passage  40  through the flow restriction defined by cylindrical segment  47 . Since cylindrical segment  48  has a smaller flow area than cylindrical segment  47 , in the illustrated embodiment, the movement rate of piston portion  32  is one direction can be made slower than its opposite movement rate. Although piston  32  could be located in a common body as lower seat component  45 , it is preferably separated from the same by a relatively thin separator  75  and housed in its own piston guide body  76 , as shown in FIGS. 1 and 2.  
         [0026]    In order to accommodate for the possibility of a slight angular misalignment between the centerline of valve member  42  and the respective centerlines of upper and lower seats  50  and  51 , valve member  42  preferably includes spherical valve surfaces  52  and  53 . Those skilled in the art will appreciate that spherical valve seats  52  and  53  can contact and close valve seats  50  and  51  even in the event of some minor angular misalignment between valve member  42  and its respective seats. In order to insure that the respective passageways, such as supply passage  24 , provide the proper fluid connection as shown in FIG. 1, the stationary components of three way valve  15  preferably include dowel bores  58  (FIGS.  2 - 3 ), which are present to prevent the valve from being misassembled. In order to hold three way valve  15  together, it preferably includes a plurality of fasteners  46  that are threadably received in fastener bores  49  located in upper seat component  43 . Nevertheless, those skilled in the art will appreciate that numerous other strategies could be employed for clamping three way valve  15  together.  
         [0027]    Referring to FIGS.  4 - 9 , valve lift spacer  44  is shown in a variety of views that illustrate some of its more subtle features. In particular, valve lift spacer  44  preferably has a circumferential side surface  36  separating a mostly planar top surface  34  from a mostly planar bottom surface  35 . Preferably, the planar portion of the top surface is oriented substantially parallel to the planar portion of bottom surface  35 . As illustrated in FIGS. 1 and 3, valve lift spacer  44  includes a valve travel bore  39  within which valve member  42  moves when travelling between its upper and lower seats. Although not necessary in every application of the invention, this embodiment includes both an inlet passage  40  and an outlet passage  41  that extend between top surface  34  and bottom surface  35 . Inlet passage  40  and outlet passage  41  include cylindrical segments  47  and  48 , respectively, that exhibit predetermined flow characteristics. Preferably, both of these cylindrical segments are more restrictive to flow than flow across either of the respective high pressure seat  50  or low pressure seat  51 , as discussed earlier.  
         [0028]    Because cylindrical segments  47  and  48  are relatively small in diameter (less than a millimeter in the case of the illustrated embodiment), they are preferably machined in any suitable manner, such as via an EDM process. The holes are then enlarged by any suitable manner. For instance, the holes are preferably enlarged by flowing an abrasive slurry through the holes until each flow passage exhibits a predetermined flow characteristic, which is preferably correlated to some predetermined flow characteristic of a liquid used when the valve is in its intended use. For instance, in the illustrated embodiment, the flow characteristic of the abrasive slurry is correlated to a flow characteristic of fuel at some predetermined pressure differential, such as a pressure differential existing in a fuel injector between fuel at injection pressure levels and fuel at relatively low supply pressure levels. The abrasive slurry is preferably flowed through the passages  40  and  41  at a predetermined pressure differential. The progress of the enlargement process is preferably monitored by continuously monitoring the flow rate of the abrasive slurry through the respective passages. One could expect that the flow rate will continue to grow as the holes are enlarged, assuming that the pressure differential remains constant. When that flow rate rises to some predetermined flow rate that has been correlated to some flow characteristic of fuel, the passage is ready, and the individual valve lift spacer is advanced for further processing.  
         [0029]    In order to protect against misassembly of valve  14 , valve lift spacer preferably includes at least one dowel bore  58  that align with like bores in upper seat component  43  and lower seat component  45 . A dowel in these bores insures that various passages in the various components  43 - 45 , such as supply passage  24 , align with one another when the valve is assembled as shown in FIG. 3. In addition, valve lift spacer  44  preferably includes at least one, in this case four, fastener bores  49  through which fasteners  46  extend through as shown in FIG. 3, in order to hold the valve in an assembled condition. In order for dowel bores  58  to function as locating surfaces, the bore walls preferably extend parallel to a centerline  38  of valve lift spacer  44 . Of worthy mention with regard to FIGS.  1 - 9  is the inclusion on valve lift spacer  44  of at least one valve limiting surface  31 . In this case, the portion of control volume  37  extending through lower seat component  45  terminates about half way through valve lift spacer  44  where it opens into valve travel bore  39 . By making this portion of volume  37  penetrate only partially through valve lift spacer, its volume has been reduced relative to having that passage extend completely through valve lift spacer  44 . By paying attention to surface details in order to reduce the overall volume of control volume  37 , the response of electro hydraulic actuator  12  can be hastened since pressure changes in volume  37  can occur more quickly if its volume is small rather than being relatively large.  
         [0030]    Referring now to FIG. 10, an apparatus for enlarging cylindrical segment  47  of outlet passage  40  in valve lift spacer  44  is illustrated. In practice, a source of high pressure abrasive slurry  90  is connected to inlet passage  40  adjacent top face  35 . The abrasive slurry passes through cylindrical segment  47  and through bottom face  34 , and onto low pressure reservoir  93  via drain line  92 . A flow meter  94  is preferably located somewhere in supply line  91  and/or drain line  92 . By continuously monitoring the flow rate of the abrasive slurry through cylindrical segment  47 , while maintaining a predetermined pressure differential between high pressure source  90  and low pressure reservoir  93 , one can monitor the progress of the hole enlargement process. In addition, by correlating the abrasive slurry flow rate at that predetermined pressure differential to some predetermined flow characteristic corresponding to an intended use of the valve, the valve lift spacer can be made to produce predictable performance. Flow meter  94  could be, for the illustrated embodiment, a ______ flow meter of a type manufactured by ______ of ______ Japan.  
         [0031]    Referring to FIG. 1  1 , a collection of valve lift spacers  95  shows that each collection preferably includes a plurality of different thickness groups that correspond to a known probability distribution  98  about a nominal thickness. Probability distribution  98 , in the present example, preferably corresponds to a distribution of valve lift spacer thicknesses that will produce valves with roughly equal travel distances given the natural variation that will occur due to typical part dimensional tolerances. Each collection  95  preferably includes a nominal thickness group  96  and a plurality of other thickness groups  97  that each include numbers corresponding to the probability distribution  98 . In this way, when many valves of the type shown in FIGS. 2 and 3 are manufactured. One can manufacture valve lift spacers in a variety of thicknesses that will avoid over production of one or more thicknesses. In the illustrated example, the valve of FIGS.  1 - 3  preferably has a travel distance about equal to 30 microns plus or minus 5 microns. In order to accomplish this small and tight travel distance requirement, valve lift spacers are preferably divided into the thickness groups illustrated in FIG. 11. For the illustrated embodiment, each thickness group spans a range of thicknesses that is less than 10 microns. In the illustrated embodiment, each thickness group spans a range of about 6 microns. In other words, each valve lift spacer in a given group has a predetermined thickness, plus or minus about 3 microns.  
         [0032]    Industrial Applicability  
         [0033]    The present invention finds potential application in any valve whose performance characteristics must be relatively tightly controlled, while at the same time providing a structure that permits mass production and relatively consistent performance from one valve to another. In addition, the present invention preferably finds particular application in the case of relatively high speed valves that are required to accommodate relatively low flow volumes, such as pressure control valves employed in fuel injection systems.  
         [0034]    Shortly before the timing at which actuator  12  is activated via valve  14 , electrical actuator  16  is preferably energized by supplying an excessive current to coil  60 . Because the speed at which electrical actuator  16  operates is related to the current level supplied to coil  60 , one preferably supplies an excessive current, which can be substantially higher than an amount of current necessary to cause the armature to move against the action of the spring bias. When sufficient magnetic flux builds, armature  62  and valve member  42  are pulled upwards until spherical valve surface  52  contacts upper or high pressure seat  50 . When this occurs, needle control chamber  37  is fluidly connected to low pressure fuel reservoir  20  via low pressure passage  41 . In order for piston portion  32  to move, fluid must be displaced from needle control chamber  37  toward low pressure reservoir  20 . The rate at which piston  32  moves is slowed by restricting this flow through cylindrical segment  48 . Shortly before the desired end of an actuation event, current to electrical actuator  16  is reduced or terminated to a level that allows spring  67  to push armature  62  and valve member  42  downward until spherical seat  53  comes in contact with low pressure seat  51 . When this occurs, high pressure fluid originating in supply passage  24  flows through high pressure passage  40  past high pressure seat  50  and into needle control chamber  37 . The rate at which pressure builds in needle control chamber  37  and hence the response time from when current is terminated until piston  32  moves toward another position can be influenced by appropriately sizing cylindrical segment  47 .  
         [0035]    In order to produce electro-hydraulic actuators  12  that behave consistently, the present invention preferably includes a structure for three way valve  15  that alleviates some of the problems that have plagued past valves. By including flow restrictions (cylindrical segments  47  and  48 ) away from valve seats  50  and  51 , fluid flow forces that can interfere with movement of the valve member  42  are reduced since the pressure differentials often associated with valves are moved away from the valve seats. Furthermore, by locating these flow restrictions in the valve lift spacer, the flow restrictions can be more easily manufactured. This same strategy allows more consistency in performance among valves since their performance is desensitized from the flow areas across the respective seats of the valves. These flow areas will likely be different from one valve to another due at least in part to the fact that each component has geometrical tolerances that render them realistically manufacturable. Because the cylindrical segments formed in the valve lift spacers can be made with great consistency, the behavior of the respective valves can be made more consistent.  
         [0036]    Another feature of the three way valve  14  of the present invention that can provide for more consistent performance includes the use of a valve lift spacer  44  as a category part. In other words, in order for consistency to be maintained, the valve travel distance from one valve to another should be made as consistent as possible. In the case of the present valve, this is accomplished by choosing a valve lift spacer for each individual valve with a thickness that results in a relatively uniform travel distance from one valve to another. In other words, each valve should have relatively uniform travel distances, but this is accomplished by employing valve lift spacers of a variety of thicknesses in each of the different valves. In the case of the present invention, the valve travel distance is preferably on the order of about 30 microns, or between 25 and 35 microns. In any event, the strategy of the present invention can be employed to reliably produce valves with consistent lifts less than about 50 microns. This is accomplished by grouping valve lift spacers in a plurality of different thickness groups. Preferably, each of these groups contain valve lift spacers of a specific predetermined thickness, plus or minus about three microns.  
         [0037]    Another strategy employed by the present invention in order to improve response time includes defining the needle control chamber  37 , which is referred to in the claims as the “third passage”, at least in part with volume reducing features ordinarily, this will be accomplished by paying attention to machining the various components that make up needle control chamber  37  in order to reduce its volume. By reducing its volume, it can respond to pressure changes more quickly. For instance, in the present invention, this strategy is employed, for example, by making the vertical portion of needle control chamber  37  only extend a portion of the way into valve lift spacer  44 . Thus, the top surface of this segment could be considered a volume reducing surface feature.  
         [0038]    When manufacturing valve lift spacer  44 , it preferably starts as a cylindrically shaped disk without the inclusion of cylindrical segments  47  and  48 . These holes are then relatively roughly machined, such as by using an EDM process. This preferably takes the holes to a diameter that is some measurable amount smaller than its preferred end diameter. After the holes are “roughly” made through an appropriate process, the holes are preferably enlarged by flowing an abrasive slurry through the passage as illustrated in FIG. 10. This enlargement process is preferably continuously monitored with a flow meter  94 . When the flow rate of the abrasive slurry reaches a predetermined magnitude, the enlargement process is ended and the hole should have its desired flow characteristics. This desired flow characteristic flow rate of the abrasive slurry is preferably correlated to a flow rate of a predetermined fluid at a predetermined pressure differential. In the illustrated example, this predetermined fluid could be fuel, and the pressure differential could correspond to the pressure differential between fuel at injection pressures and fuel at low pressure circulation pressures. After the respective cylindrical segments  47  and  48  are machined and enlarged to their predetermined flow characteristic profiles, the bottom and top faces  34  and  35  are preferably ground in a conventional manner, such as by using double disks, to a predetermined thickness. Preferably, the thickness of valve lift spacers are machined to correspond to the thickness groups illustrated in FIG. 11. When the valve is manufactured, past experience will have shown that a nominal lift spacer from the nominal thickness group  96  of FIG. 11 has the highest probability of producing a valve with a predetermined travel distance. Thus, each valve is preferably first assembled using a nominal thickness valve lift spacer. Next, the travel distance of the valve is measured. If the measured travel distance deviates from the desired predetermined travel distance by more than a predetermined amount (about 5 microns in the illustrated embodiment) then a different valve lift spacer from one of the other thickness groups is chosen. In other words, a different valve lift spacer having a thickness that, when substituted for the nominal valve lift spacer, will give the valve the desired predetermined travel distance. This process is accomplished by first determining a valve spacer thickness that would provide the valve with a travel distance that is about equal to a desired travel distance. Next, a thickness group is identified that corresponds to the valve spacer thicknesses associated with the desired travel distance. Next, a valve lift spacer from the identified thickness group is retrieved and substituted for the nominal valve lift spacer. Next, the travel distance is preferably again measured to confirm that the valve now has a travel distance that corresponds to the desired travel distance. When this is confirmed, the fasteners  46  are preferably tightened to some predetermined torque to complete the assembly of valve  14  illustrated in FIGS. 2 and 3.  
         [0039]    Those skilled in the art will appreciate the other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.