BACKGROUND OF THE INVENTION  
       [0001]     The field of the present invention is reciprocating air driven devices and specifically the air valves therefor.  
         [0002]     Reciprocating air driven devices have long had the advantage that they can be employed in circumstances and environments where motors and engines are inappropriate. One area of concern with engines and motors is their use in an environment with combustibles. Sparks and hot manifolds can potentially cause ignition of such combustibles with engines and motors.  
         [0003]     Even with air driven devices, as with any operating mechanism, sparks resulting from static charges cannot be ruled out under all conditions. Some of the smaller versions of such air driven mechanisms are now made of engineering plastics rather than conductive metal. Such plastics are typically not conductive and cannot be grounded. Therefore, a mechanism may be warranted to avoid static charge buildup and provide an ability to ground the device.  
         [0004]     One mechanism for avoiding the buildup of static charge is to blend a conductive filler into the structural plastic. Carbon and metal fibers are typically considered as fillers for the transformation of plastics from statically insulative to statically dissipative. However, such fillers have been determined to adversely effect the longevity of sealing members required to slide on the filled plastic such as in air valves for driving and controlling such devices.  
         [0005]     One such application of plastic for reciprocating air driven devices is for air operated double diaphragm pumps which include reciprocating air valves for the control and driving of the pumps. Valve elements having annular seals thereabout sliding within valve bodies are typically used in such air valves. Such arrangements can encounter the aforementioned seal longevity problem. The following patents illustrate a long line of pumps, air valves therefor and details in the construction thereof, the disclosures of which are incorporated herein by reference:  
                                                           RE 38,239   6,142,749   5,607,290           6,435,845   6,102,363   5,538,042           6,357,723   5,957,670   5,441,281           6,257,845   5,927,954   5,362,212           6,168,394   5,746,170   4,549,467           6,158,982   5,619,786           6,152,705   5,611,678                      
 
       SUMMARY OF THE INVENTION  
       [0006]     The present invention is directed to a statically dissipative body for reciprocating air driven devices such as an air valve. A statically insulative liner is located in the bore of the statically dissipative body to provide an advantageous surface upon which sealing components can slide.  
         [0007]     In a first separate aspect of the present invention, the statically dissipative body further includes a closure in the bore which is also statically dissipative. The statically insulative liner is fully enclosed by the statically dissipative body and closure. In this way, static charge resulting from the use of statically insulative plastic is shielded or dissipated by the body. Further, an air valve element having annular seals thereabout and other similar elements can advantageously slide against the statically insulative liner. The air valve may be part of an air operated double diaphragm pump.  
         [0008]     In a second separate aspect of the present invention, the statically insulative liner in the bore of the statically dissipative body is in locking engagement therewith. The engagement is arranged between laterally extending passages to isolate the passages from one another. The engagement may include annular tenon and mortise structures about the liner.  
         [0009]     A third separate aspect of the present invention contemplates the combination of the above separate aspects to greater advantage.  
         [0010]     Accordingly, it is an object of the present invention to provide an improved air valve. Other and further objects and advantages will appear hereinafter. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a cross-sectional elevation of an exemplar air driven double diaphragm pump.  
         [0012]      FIG. 2  is a cross-sectional elevation of an air valve and center section of an air driven double diaphragm pump.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]     Turning in detail the drawings,  FIG. 1  illustrates an air driven double diaphragm pump shown in cross section for clarity. The pump structure includes two pump chamber housings  20 ,  22 . These pump chamber housings  20 ,  22  each include a concave inner side forming pumping cavities through which the pumped material passes. One-way ball valves  24 ,  26  are at the lower end of the pump chamber housings  20 ,  22 , respectively, to provide pump inlet valving. An inlet manifold  28  distributes material to be pumped to both of the one-way inlet valves  24 ,  26 . One-way ball valves  30 ,  32  are positioned above the pump chambers  20 ,  22 , respectively, and are configured to provide one-way flow in the same direction as valves  24 ,  26  to provide pump outlet valving. An outlet manifold  34  is associated with the one-way outlet valves  30 ,  32 .  
         [0014]     Inwardly of the pump chambers  20 ,  22 , a center section, generally designated  36 , includes air chambers  38 ,  40  to either side of an actuator housing  42 . There are two pump diaphragms  44 ,  46  arranged in a conventional manner between the pump chambers  20 ,  22  and the air chambers  38 ,  40 , respectively. The pump diaphragms are retained about their periphery between the corresponding peripheries of the pump chambers  20 ,  22  and the air chambers  38 ,  40 . These pump components, if made of engineering plastic, are preferably statically dissipative through the extensive use of plastic with conductive filler to facilitate grounding of the pump.  
         [0015]     The actuator housing  42  provides a first guideway  48  which is concentric with the coincident axis of the air chambers  38 ,  40  and extends to each air chamber. A shaft  50  is positioned within the first guideway  48 . The actuator housing  42  provides annular channels for O-rings  52 ,  54  as a mechanism for sealing the air chambers  38 ,  40 , one from another along the guideway  48 . The shaft  50  includes piston components  56 ,  58  on each end thereof. These components  56 ,  58  capture the centers of each of the pump diaphragms  44 ,  46 . The shaft  50  causes the pump diaphragms  44 ,  46  to operate together to reciprocate within the pump.  
         [0016]     Also located within the actuator housing  42  is a second guideway  60  within which a pilot shifting shaft  62  is positioned. The guideway extends fully through the center section to the air chambers  38 ,  40 . The pilot shifting shaft  62  extending through the second guideway  60  also extends beyond the actuator housing  42  to intersect with the travel of the piston components  56 . The pilot shifting shaft  62  extends into the path of travel of the inner piston components  56 . Thus, as the shaft  50  reciprocates, the pilot shifting shaft  62  is driven back and forth to effect shifting of an air valve element.  
         [0017]     The guideway  60  is shown to be defined by a bushing  64 . A plurality of O-rings  66  in annular channels in the bushing  64  provide seals between the air chambers  38 ,  40  as well as between pilot control passages  68 ,  70 ,  72 . The pilot shifting shaft  62  also employs O-rings  74  to seal along the guideway  60 .  
         [0018]     Turning to  FIG. 2 , an air valve, generally designated  76 , is associated with the actuator housing  42 . The air valve  76  includes a valve cylinder  78 . The valve cylinder  78  has a cylindrical bore  80  extending partially therethrough such that the bore  80  is closed at one end by the body of the valve cylinder  78 . The cylindrical bore  80  may be divided into two sections, section  82  is of a smaller diameter than section  84 . The cylindrical bore  80  is closed at the end of the large section  84  by an end cap  86 . The end cap  86  includes a cylindrical plug  88  which extends into the large section  84  of the cylindrical bore  80  and is statically dissipative. An O-ring  90  is arranged about the plug  88  to seal with the cylindrical bore  80 .  
         [0019]     The air valve  76  includes a valve element, generally designated  104 , which is positioned within the valve cylinder  78  in the cylindrical bore  80 . The valve element  104  includes a large element end  106  having an annular seal  108  in a receiving channel. The large element end  106  fits closely within the large section  84  of the cylindrical bore  80 . A small raised portion  110  ensures an annular space between the end of the valve element  104  and the plug  88  with the valve element  104  positioned toward the large end  106 .  
         [0020]     The valve element  104  also includes an element body  112  which is smaller in diameter than the large element end  106 . The element body  112  includes five annular seals  113 ,  114 ,  115 ,  116  and  117 . Between the seals  114  and  115 , the element body  112  is reduced in diameter to provide an axial passage  118  for flow of air. The element body  112  includes another axial passage  119  where the diameter is also reduced between the seals  115  and  116 . A small element end  120  is defined at the end of the element body  112 . The seals  117  seals the bore around the element end  120 . A small raised portion  121  on the small element end  120  ensures an annular space at that end with the valve element  104  positioned toward the small end of the cylindrical bore  80 .  
         [0021]     Several common passages  122 ,  124 ,  126  extend from the cylindrical bore  80 , the central passage  124  is an inlet and the end passages  122 ,  126  extend through the center section to the air chambers  38 ,  40 . On the opposite side of the bore  80 , exhaust ports  128 ,  130  extend through the valve cylinder  78 . The exhaust ports  128 ,  130  are tapered to expand to resist ice buildup. A muffler plate  131  defines an expansion chamber and an attachment for a muffler. Each of the passages  122  through  130  extend laterally of the longitudinal direction of the bore. There may be three each of the ports associated with passages  122 - 130  at the surface of the bore  80 .  
         [0022]     Looking to the structure of the valve cylinder  78 , a liner  132  is located within a valve body  134  to define the bore to receive the valve element  104 . The valve body  134  is statically dissipative and is typically of engineering thermoplastic resins, examples of which include polycarbonate, polyethylene, polypropylene, acetal, nylon and others. These thermoplastic resins are typically electrically insulative. To make the valve body  134  statically dissipative, the engineering thermoplastic resins are blended with conductive additives employed for such purposes. Among the possible additives are carbon fiber, carbon powder, stainless steel fiber and nickel fiber. These are conventionally known to be added to such engineering plastic resins in sufficient quantity to make the valve body  134  statically dissipative.  
         [0023]     The liner  132  may be made from one of the same engineering thermoplastic resins. However, the conductive fillers added to make the valve body  134  statically dissipative are not included in the liner  132 . Consequently, the liner  132  is statically insulative. Without the conductive filler materials, the longevity of the O-ring seals associated with the valve element  104  is greatly enhanced.  
         [0024]     The liner  132  of this embodiment conveniently has a wall thickness of 0.100″ inches. About the periphery of the liner, annular tenons extend from the liner surface. Three such tenons  136 ,  138 ,  140  are illustrated. These tenons  136 ,  138 ,  140  are conveniently about 0.065″ inches high and have an undercut surface to each side thereof which has an included angle of 60° with the surface of the liner. Conforming to the valve cylinder  78  to facilitate molding processes, the liner  132  may also include a closed end  142 . Further, the bore  80  defined by the interior surface of the liner  132  includes a smaller diameter at the closed end and a larger diameter at the open end. The liner  132  extends fully to the end of the bore in the valve body  134 . With the placement of at least the one end cap  86  on at least the larger of the two ends, the valve body  134  fully encloses the statically insulative liner  132  with statically dissipative material. As such, the statically insulative liner is shielded from any combustibles within the environment by grounded components of the air valve  76 .  
         [0025]     The valve cylinder  78  is made by first molding the liner  132 . The valve body  134  is then over-molded on the liner  132 . In this process, the tenons  136 ,  138 ,  140  allow for the molding of material thereabout to solidify into the valve body  134 . As such, annular mortises  146 ,  148 ,  150  are created through this over-molding process to snugly surround and join with the tenons  136 ,  138 ,  140 . These interlocking tenon and mortise engagements are presented between the common passages  122 ,  124 ,  126 . As such, the interocking engagements better seal the passages one from another. Thus, the common passages  122 ,  124 , 126  which extend through both the liner  132  and the valve body  134  are separated from one another.  
         [0026]     In the manufacture of the air valve  76 , the liner is created without the common passages  122 ,  124 ,  126  and positioned on a core for the over molding process. The over molding process of the valve body  134  includes core pins which extend to press against the liner and retain the liner in place on the core. Once removed from the molding process, the valve cylinder  78  is further machined to achieve the required surfacing for the bore of the liner and to port and debur the common passages  122 ,  124 ,  126  as well as the exhaust ports  128 ,  130 , pilot ports  152 ,  153  and relief port  154 .  
         [0027]     Thus, an improved air valve having a statically dissipative effect has been shown and described. All embodiments in the application of this invention have been shown and described, it would be apparent to those skilled in the art that many more modifications are possible without departing from the inventive concepts herein. The invention, therefore, is not to be restricted except in the spirit of the appended claims.
An air operated double diaphragm includes an air valve, air chambers, a center section between the air chambers, pump chambers and diaphragms between the air and pump chambers harnessed together with a piston rod. The air valve includes a statically dissipative body having a bore therein with a statically insulative liner in the bore. The statically insulative liner is fully enclosed within the statically dissipative body. A valve element is slidably positioned in the liner. The liner includes annular tenons to mate with annular mortises in the statically dissipative body and an end cap is used to close the valve cylinder.