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BACKGROUND OF THE INVENTION 
     This invention relates to a portable, power operated post driving apparatus that can be operated by a single person to drive a steel fence post, or other kinds of posts, into the ground in an expeditious manner. 
     Posts, particularly steel fence posts, have been driven into the ground in a number of different ways. 
     Originally, such posts were manually driven into the ground by using a sledge hammer. Other manually operated post drivers are described in U.S. Pat. Nos. 3,712,389 and 5,020,605. 
     Power driven post drivers of various sorts appear in the prior art. Examples include cam driven post drivers where an electric powered cam drives the hammer directly (U.S. Pat. No. 2,703,479) or where an electric or gas powered cam lifts the hammer and drops it (U.S. Pat. No. 4,984,640). 
     Various other power driven post drivers have been suggested by the prior art. These drivers use either compressed air or hydraulics to operate a fluid operated power cylinder arrangement wherein a weight assembly is lifted and lowered. One such device is described in U.S. Pat. No. 4,665,994 wherein the weight assembly comprises a metal disc and two solid metal bars. Such devices, although technically portable, are still very heavy because the combination of the weight of the weight assembly and the weight of the remainder of the apparatus. Such pneumatic post drivers use large amounts of compressed air, typically from 25 cubic feet per minute up to 125 cubic feet per minute. Such drivers require a relatively large air compressor to supply compressed air to the driver. 
     U.S. Pat. No. 5,819,857, issued to the inventor of the present apparatus, describes a vastly improved portable power driven post driver. The entire contents of U.S. Pat. No. 5,819,857 are hereby incorporated by reference. 
     The post driver of the &#39;857 patent has an inner hollow cylinder open at both ends and adapted to receive a post through a lock clamp located at its lower end. An outer hollow cylinder having a closed upper end, and slightly larger in diameter than the inner cylinder, is located in sliding engagement over the inner cylinder. First and second power cylinders are attached to upper and lower surfaces of the outer cylinder in alignment with each other. A common piston rod connects the pistons of the power cylinders. A stationary fastening pin extends through a slot in the wall of the outer cylinder and is attached to the wall of the inner cylinder. A valve and conduit means communicate the two power cylinders to a source of fluid under pressure. 
     During operation of the post driver of the &#39;857 patent, a post is inserted through the lock clamp in the lower end of the inner cylinder until it abuts the closed upper end of the outer cylinder and is locked in place. The valve alternately communicates the fluid under pressure with the first and second power cylinders to alternately raise the outer cylinder above the inner cylinder and then to drive the outer cylinder downward until the closed end thereof forcefully contacts the upper end of the post. The outer cylinder has handle means attached thereto to permit an operator to carry and hold the driver during operation. The post driver is thus configured to cause all of the weight of the driver, except for the weight of the inner cylinder, to drivingly engage a post to be driven. 
     The valve employed in the post driver of the &#39;857 patent is a four way spool valve, such as Model No. 422CS011K manufactured by Parker. It has been found that although this valve functions to properly operate the post driver, it is expensive and difficult to perform maintenance thereon. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a valve for the post driver described in the &#39;857 patent which is simple, inexpensive, and easy to perform maintenance thereon. 
     The valve of the present invention has a front wall, rear wall, top wall, bottom wall and right and left side walls. 
     A central bore passes through the valve from the top wall to the bottom wall. 
     A cylindrical valve piston is located within the central bore. The valve piston has at least two spaced apart O-rings circumferentially attached thereto and adapted to come into sliding and sealing contact with the wall of the central bore. 
     A primary fluid supply passageway extends from the left side wall into the central bore and is adapted to communicate the central bore with a supply of pressurized fluid. 
     A first secondary fluid passageway extends from the central bore to the exterior of the valve body and is adapted to communicate with the first fluid powered cylinder of the post driver. 
     A second secondary fluid passageway extends from the central bore to the exterior of the valve body and is adapted to communicate with the second fluid powered cylinder of the post driver. 
     The valve piston is adapted to reciprocate between a first position wherein the space between the spaced apart O-rings communicates the primary fluid supply passageway with the first secondary fluid passageway to a second position wherein the space between the spaced apart O-rings communicates the primary fluid passageway with the second secondary fluid passageway. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are elevation views of the post driver of the present invention; 
         FIG. 2  is an elevation view, partially in section, of the power cylinders and valve; 
         FIG. 3  is a front elevation view of the valve of the present invention; 
         FIG. 4  is a top plan view of the valve of the present invention; 
         FIG. 5  is a side elevation view of the valve of the present invention; 
         FIG. 6  is a front elevation in cross-section of the valve of the present invention; 
         FIG. 7  is a side elevation view of the valve piston of the valve of the present invention; 
         FIG. 8  is a side elevation view of the control lever of the valve of the present invention; 
         FIG. 9  is a top plan view of the control lever of the valve of the present invention; 
         FIG. 10  is a side elevation view of the valve and valve piston shown in its up (off) position; and 
         FIG. 11  is a side elevation view of the valve and valve piston shown in its down position 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     As seen in  FIGS. 1A and 1B , post driver  10  has an inner hollow cylinder  12  open at its upper (inner) end. Attached to the lower (outer) end of inner cylinder  12  is a clamp sleeve  16  having threaded clamp pin  18  extending there through, clamp pin  18  having a clamp handle  20  attached to its outer end. 
     Post driver  10  has an outer hollow cylinder  30  closed at its upper end  32  and open at lower end  34 . The inner diameter of outer cylinder  30  is slightly larger than the outer diameter of inner cylinder  12  to permit inner cylinder to be nested inside outer cylinder  30  in sliding engagement. An operator&#39;s handle  36  is attached to the exterior of outer cylinder  30 . 
     A first (upper) fluid powered cylinder  40  is fixedly attached to an upper outer surface of outer cylinder  30 , such as by welding. Inside upper power cylinder  40 , as seen in  FIG. 2 , is a piston  42  attached to the upper end of piston rod  44 . Piston rod  44  has a thick shoulder portion  45  at its mid-portion. The upper end of power cylinder  40  is threaded and has a screw cap  46  securely attached thereto. Threaded hollow fitting  48  communicates the inside of upper power cylinder  40  with the outside thereof and is located in screw cap  46 . Threaded hollow fitting  48  is connected to the upper end of first rigid air conduit  85 . 
     A second (lower) fluid powered cylinder  50  is fixedly attached to a lower outer surface of outer cylinder  30 , such as by welding. Inside lower power cylinder  50 , as best seen in  FIG. 2 , is a piston  52 . The longitudinal axes of upper power cylinder  40  and lower power cylinder  50  are in alignment with each other, and piston rod  44  is attached at its lower end to piston  52 . The bottom  56  of lower power cylinder  50  is closed. Threaded hollow fitting  58  communicates the inside of lower power cylinder  50  with the outside thereof in a location between bottom  56  and piston  52  at the closest approach of piston  52  to bottom  56 . Threaded hollow fitting  58  is attached to the lower end of second rigid air conduit  94 . 
     Piston rod  44  is attached to inner cylinder  12  by attachment means extending through a vertical slot in the wall of outer cylinder  30  in the manner described in U.S. Pat. No. 5,819,857. 
     A deactivation pin  70  extends through an arm  72  which is attached to piston rod  44  as described in greater detail in U.S. Pat. No. 5,819,857. A spring  78  surrounding the stem portion of deactivation pin  70  keeps it in a normally fully extended position, but permits it to retract upon application of a force to the enlarged head portion thereof. 
     As best seen in  FIGS. 3 and 4 , valve  100  is attached to a plate  105  attached to the lower outer surface of outer cylinder  30  by any suitable means, such as bolts  101  passing through openings  103  and nuts (not shown). 
     As best seen in  FIGS. 3-5 , valve  100  has a generally rectangular-shaped body with front wall  102 , rear wall  104 , upper wall  106 , lower wall  108 , and side walls  110  and  112 . Ears  114  and  116  extend upwardly from the upper wall  106  thereof adjacent side wall  110 . Ears  114  and  116  have central openings  115  and  117 , respectively, passing there through. Openings  115  and  117  have a common central axis. 
     As best seen in  FIG. 6 , a central bore  120  extends through a mid-portion of valve  100  between the upper wall  106  and lower wall  108 . 
     A primary pressurized fluid (e.g., pressurized air) supply passageway  122  communicates central bore  120  with the exterior of valve  100  through side wall  112 . That portion of primary pressurized fluid supply passageway  122  adjacent side wall  112  is enlarged and internally threaded in order to receive a threaded quick release fitting  83  ( FIG. 2 ). 
     A first (lower) fluid exit passageway is comprised of fluid exit passageway portion  124  and fluid exit passageway portion  126 . Fluid exit passageway portion  124  of first fluid exit passageway communicates with central bore  120  at its inner end and extends into communication with internally threaded lower fluid exit passageway portion  126  at its outer end. Fluid exit passageway portion  126  of first fluid exit passageway is substantially perpendicular to fluid exit passageway portion  124  and extends through front wall  102 , thereby communicating central bore  120  with the exterior of valve  100 . That part of fluid exit passageway portion  126  adjacent front wall  102  is internally threaded and adapted to receive a threaded hollow fitting  127  ( FIGS. 1B ,  2  and  5 ) which is connected to the lower end of rigid air tubing  85 . 
     A second (upper) fluid exit passageway  130  extends from central bore  120  through side wall  110  and communicates central bore  120  with the exterior of valve  100 . That portion of upper fluid exit passageway  130  adjacent side wall  110  is internally threaded and adapted to receive a threaded hollow fitting  131  ( FIGS. 1B and 2 ) which is connected to the upper end of rigid air tubing  94 . 
     First exhaust conduits  224 ,  224 ′ and second exhaust conduit  230  allow fluid to be exhausted from first and second fluid powered cylinders  40  and  50  in a manner to be described below. 
     A hollow cylindrical valve piston  140  ( FIG. 7 ) is adapted to be received within central bore  120  of valve  100  ( FIGS. 10 and 11 ). Valve piston  140  has a central cylindrical portion  142  having a diameter slightly smaller than the diameter of central bore  120 . O-ring receiving flanges  144  extend outwardly from cylindrical portion  142  and retain O-rings  146 . Upper portion  244  of valve piston  140  contains adjacent circumferential grooves which retain O-rings  246 ,  246 ′. The lower end  344  of valve piston  140  retains O-ring  346 . 
     The upper end of valve piston  140  terminates in shoulder  150 . Piston ears  152  and  154  are attached to or integral with shoulder  150  and extend upwardly therefrom. Piston ears  152  and  154  having circular openings  153  and  155  extending there through, openings  153  and  155  having a common central axis. A cylindrical handle  156 , made of plastic, has a cylindrical stem portion  158  made of steel press fit therein which extends outwardly therefrom. Stem  158  extends through openings  153  and  155  in piston ears  152  and  154  and is removably attached thereto by cotter pin  159 . 
     A pivoting control lever  160  ( FIG. 8 ), having a substantially rectangular cross-section, has an inner end  162  and a forked outer end  164 . The space between the tines  165 ,  165 ′ of forked outer end  164  receive stem  158  of handle  156  there through. An opening  166  passes through control lever  160  slightly forward of the middle thereof. Control lever  160  is pivotally attached to valve ears  114  and  116  by means of a pivot pin  168  having an enlarged head passing through opening  166  in control lever  160  and openings  115  and  117  in valve ears  114  and  116 . The outer end of pivot pin  168  is held in place by a cotter pin  169  or other suitable means. 
     Valve piston  140  is movable within central bore  120  between an “up” position shown in  FIG. 10  to a “down” position shown in  FIG. 11 . 
     In operation valve  100  is connected to a source of pressurized fluid, such as a compressed air source, via flexible hose  81  having a quick release fitting connection  82  at its outer end. Quick release fitting  82  is connected to a corresponding quick release fitting  83  located in threaded opening  122  of valve  100 . Control lever 160  is in the up (off) position shown in  FIG. 10 . A post (not shown), such as a conventional steel fence post having a T-shaped cross section, is inserted into inner cylinder through a T-shaped opening in clamp sleeve  16  while the driver  10  is in a substantially horizontal position, i.e., laying on the ground. The lower (outer) end of the post is placed at the location on the ground where the post is to be driven, driver  10  raised to a substantially vertical position, and the post caused to slide into inner cylinder  12  and through the open upper end thereof until the upper end firmly contacts closed end  32  of outer cylinder  30 . The post is then locked into place by turning clamp handle  20  attached to threaded clamp pin  18  clockwise until the inner end of clamp pin firmly contacts the post. 
     During start-up, control lever  160  of valve  100  is in its up (off) mode shown in  FIG. 10 , thereby causing compressed air to flow from valve  100  via upper fluid bore  130  to lower power cylinder  50  through rigid air tubing  94 , which keeps outer cylinder  30  in its retracted position. 
     To actuate driver  10  the operator pushes down on handle  156  of control lever  160  to place valve  100  into its on (operating) mode, as shown in  FIG. 11 . In its initial operating mode, the position of piston  140  causes air to flow via conduits  124  and  126  into upper power cylinder  40  via rigid hose  85 . Compressed air flowing into upper power cylinder  40  pushes downwardly on piston  42 . Since piston rod  44  is fixedly attached to inner cylinder  12 , downward pressure on piston  42  raises outer cylinder  30  together with everything attached to it, which is everything constituting driver  10  except inner cylinder  12 . 
     As outer cylinder  30  approaches its outermost vertical extension, the outer end  162  of control lever  160  contacts and is pushed down by spring loaded deactivation pin  70 . This raises the inner end  164  of control lever  160 , thereby raising valve piston  140  to the position shown in  FIG. 10  which shuts off communication of the compressed air to upper power cylinder  40  and opens communication between upper power cylinder  40  and the atmosphere via first exhaust conduits  224 ,  224 ′. At the same time, valve  100  opens communication between the compressed air source and lower power cylinder  50  via conduit  130 . Compressed air entering lower power cylinder  50  via rigid hose  94  pushes against piston  52 . This action drives outer cylinder  30  downwardly and into driving communication with the upper end of the post. Having two exhaust conduits  224 ,  224 ′ insures that any air within upper power cylinder  40  is allowed to exhaust freely and not impede the downward movement of outer cylinder  30  into driving contact with the post being driven. 
     As closed end  32  of outer cylinder  30  strikes the upper end of the post, the inertial forces generated causes the inner end  164  of control lever  160  to pivot downwardly, thereby pushing valve piston  140  downwardly to the position shown in  FIG. 11  which shuts off communication of the compressed air to lower power cylinder  50  and opens communication between lower power cylinder  50  and the atmosphere via third fluid exit passageway  130  and second exhaust conduit  230 . At the same time, communication between valve  100  and upper power cylinder  40  via conduits  124  and  126  is reopened, thereby once again raising the outer cylinder  30 . The inner end of third fluid exhaust conduit  230 , located adjacent central bore  120 , has a smaller diameter than the outer end thereof, the diameter of the inner end being of a size adapted to control the rate of exhaustion of air from lower fluid powered cylinder  50  to thereby dampen the velocity of outer cylinder  30  during its upward stroke to prevent “hammering” and a tendency to pull the post out of the ground. 
     The raising and driving cycle is automatically repeated until the post is driven to its desired depth. At that point the operator waits for a downward (driving) stroke of outer cylinder  30  and then raises handle  156  of control lever  160  upwardly to its off position. This causes compressed air to be fed to lower power cylinder  50  thus retaining outer cylinder  30  in its retracted position. 
     During driving of the post into the ground, outer cylinder  30  and everything attached to it, including the handle  36  held by the operator, reciprocates up and down, driving the post into the ground at the end of each downward or driving stroke of outer cylinder  30 . The stroke of piston  42  is not very great, about 7.5 inches, so that the reciprocating motion of the handle  36  is not bothersome to the operator. 
     Power cylinders  40  and  50  are relatively small, having a bore of about 1.0 inch in diameter. As a result, a lower air pressure of less than about 100 psi, preferably between about 70 psi and about 90 psi can be used. At a pressure of 85 psi driver  10  uses about 2 cfm of air. 
     In commercial embodiments of this invention, driver  10  would have a safety shield (not illustrated) placed over exposed piston rod  44 . 
     It will be obvious to those having skill in the art that many changes may be made to the details of the above-described embodiments of this invention without departing from the underlying principles thereof. The scope of the present invention should, therefore, be determined only by the following claims.

Summary:
An improved valve for a portable post driver. The post driver has an inner hollow cylinder open at both ends and adapted to receive a post through a lock clamp located at its lower end. An outer hollow cylinder having a closed upper end, and slightly larger in diameter than the inner cylinder, is located in sliding engagement over the inner cylinder. First and second power cylinders are attached to upper and lower surfaces of the outer cylinder in alignment with each other. A common piston rod connects the pistons of the power cylinders. A stationary fastening pin attached to the piston rod extends through a slot in the wall of the outer cylinder and is attached to the wall of the inner cylinder. The valve has a reciprocating valve piston which alternately communicates the two power cylinders to a source of fluid under pressure.