Patent Publication Number: US-2015078942-A1

Title: Positive Displacement Injection Pump

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. patent application Ser. No. 12/104,883, filed on Apr. 17, 2008, which claims the benefit under 35 USC §119(e) of U.S. provisional application No. 60/914,559 filed Apr. 27, 2007, both of which are incorporated by reference herein in their entirety. 
    
    
     FIELD OF INVENTION 
     The present invention relates to reciprocating drive mechanisms and control valves for the same. Particular embodiments relate to pilot valves for controlling reciprocating tools, such as reciprocating pumps. 
     BACKGROUND OF INVENTION 
     There are various prior art devices known for controlling reciprocating pumps. Many prior art devices use a mechanical control mechanism to drive the piston of the reciprocating pump, but these mechanisms have been unreliable either because they require a number of failure- and/or wear-prone components or because they can stall or vary in stroke frequency in response to varying operating conditions frequently encountered in practical usage. 
     The pilot control valve disclosed in U.S. Pat. No. 6,183,217 B1 changes the directional flow of control fluid to a piston coupled to the pilot control valve to drive a reciprocating device. U.S. Pat. No. 6,183,217 B1 attempts to improve reliability by controlling the communication of control fluid to a piston included with a reciprocating device using pneumatic valve control rather than a mechanical control mechanism. U.S. Pat. No. 6,736,046 utilizes a slide valve member shiftable within a valve body between a first or “downstroke” position and a second or “upstroke” position. When in its first position, slide valves allow communication of control fluid supplied to the valve body to the lower surface of the piston. As the slide valves move to their second position, they allow communication of pressurized control fluid to the upper surface of the piston causing the piston to return to its first position. Nevertheless, there remain advantages in providing new reciprocating devices which offer still further improvements. 
     SUMMARY OF SELECTED EMBODIMENTS 
     One embodiment of the present invention is a reciprocating drive mechanism having a housing with upper and lower internal chambers. A spool is slidably positioned inside the upper internal chamber and at least one fluid inlet and fluid exhaust communicates with the upper internal chamber. At least one slide valve is positioned within the upper internal chamber and travels with the spool. A piston is positioned in the lower internal chamber and divides the lower internal chamber into an upper and lower cylinder space. There is further at least one fluid conduit communicating between the upper internal chamber and an upper cylinder space and at least one fluid conduit communicating between the upper internal chamber and a lower cylinder space. A valve stem is connected to the piston and includes a bore communicating with the upper internal chamber. There are two side passages formed in the valve stem: a first side passage connecting to a center bore in the valve stem; and a second side passage formed by second and third bores in the valve stem, resulting in the second side passage being spaced vertically apart from the first side passage; and the second and third bores spaced vertically apart from one another and fluidly connected with one another. 
     Another embodiment is a reciprocating drive mechanism having a housing with upper and lower internal chambers. A spool is slidably positioned inside the upper internal chamber and the spool has an internal passage which is less than the length of the spool. There is at least one fluid inlet and fluid exhaust communicating with the upper internal chamber and at least one slide valve positioned within the upper internal chamber travels with the spool. A piston is positioned in the lower internal chamber and divides the lower internal chamber into an upper and lower cylinder space. There is further at least one fluid conduit communicating between the upper internal chamber and the upper cylinder space and at least one fluid conduit communicating between the upper internal chamber and the lower cylinder space. A valve stem is connected to the piston, extends into the upper internal chamber, and has first and second side passages formed therein. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIGS. 1A to 1D  are top views of one embodiment illustrating where various cross-sections are taken in the following figures. 
         FIG. 2  is a cross-section along line A-A seen in  FIG. 1A . 
         FIG. 3  is a cross-section along line B-B seen in  FIG. 1B . 
         FIG. 4  is the same view as  FIG. 3 , but with the spool in the down position. 
         FIG. 5  is a cross-section along line C-C seen in  FIG. 1C . 
         FIG. 6  is the same view as  FIG. 5 , but with the spool in the down position. 
         FIG. 7  is a cross-section along line D-D seen in  FIG. 1D . 
         FIGS. 8A and 8B  illustrate alternative valve stem passages. 
         FIGS. 9A to 9D  illustrate a still further alternative embodiment. 
     
    
    
     DETAILED DESCRIPTION OF SELECTED EMBODIMENTS 
       FIGS. 2-7  illustrate one embodiment of the reciprocating drive mechanism of the present invention.  FIG. 2  shows a cross-section of this embodiment of drive mechanism  1  taken along the section line A-A seen in  FIG. 1A . The drive mechanism  1  generally comprises a housing  2  which includes an upper internal chamber  15  and a lower internal chamber  16 . In this particular embodiment, the upper internal chamber  15  forms part of a pilot valve  3  and the lower internal chamber  16  forms part of a piston and cylinder assembly or drive assembly  4 . A reciprocating tool  100  is attached to and powered by drive mechanism  1 . A driving fluid supply line  55  and a fluid exhaust line  56  (see  FIG. 3 ) communicate with pilot valve  3 . 
     Nonlimiting examples of reciprocating tools  100  may include a single or double-acting liquid pumps utilizing a reciprocating plunger, diaphragm, or bellows. In one embodiment, the pilot valve  3  drives piston and cylinder assembly  4  using compressible, non-compressible, or dual-phase pressurized control fluid. The control fluid is typically a liquid or gas or some combination of both and will depend on the nature of the application. In certain embodiments, the control fluid may be air and is generally maintained at a pressure ranging anywhere from about 20 psi to about 1,500 psi (or any range therebetween) or more commonly between about 45 psi to about 250 psi, but higher or lower pressures are well within the scope of the invention depending on seals and piston materials employed. As further described below, the illustrated embodiment of pilot valve  3  achieves a continuous and consistent pumping rate for the reciprocating device  100  using only pneumatic valve control. 
     Viewing  FIG. 2 , it can be seen this embodiment of pilot valve  3  includes valve housing  2   a  with the upper internal chamber  15  formed therein. Fluid inlet  8  connecting to fluid supply line  55  and exhaust outlet  9  (see  FIG. 3 ) connecting to exhaust line  56  will be formed in housing  2   a.  In certain embodiments, the exhaust will be to atmospheric pressure. However, there may be embodiments where the exhaust is to a pressure greater or lesser than atmospheric. Generally, the exhaust pressure should be sufficiently less than the inlet fluid pressure so the reciprocating drive mechanism may operate at the desired efficiency. The embodiment of  FIG. 3  also illustrates variable orifice  175  which allows the velocity of drive fluid escaping from exhaust lines  56  to be regulated, thus controlling the speed of the reciprocating action of the drive mechanism. It will be understood that other ways of controlling the speed of the reciprocating mechanism exist, including the insertion of a variable orifice anywhere within fluid conduits  11  or  12 . There is further a top aperture  22  in housing  2   a  which may communicate with the atmosphere or alternatively connect to exhaust line  56 . In alternate embodiments top aperture  22  may be eliminated by increasing the “dead volume” located above spool  5 , as long as this dead volume is sufficient in size to maintain the pressure therein at a magnitude significantly less than the pressure at the fluid inlet. 
     Still viewing  FIG. 2 , positioned within upper internal chamber  15  is spool  5  which has upper seal  30  and lower seal  31 . In this embodiment, seals  30  and  31  are annular cup seals set in a groove formed in the outer surface of spool  5  and engage the inner surface of internal chamber  15  in order to prevent the escape of control fluid past seals  30  and  31 . However seals  30  and/or  31  could also be many other types of conventional or future developed seals which would function as required by the present invention. It will be understood that internal chamber  15  is annular in nature between the internal wall of upper housing  2   a  and the outer wall of spool  5 , and that fluid may freely flow all around spool  5  (thereby making the pressure equal) between upper seal  30  and lower seal  31 . Spool  5  also has lower pressure surface  33  and upper pressure surface  32  formed on its lower end. Although the embodiment shown in the figures illustrates the pressure surfaces  32  and  33  formed on the lower end of spool  5 , alternate embodiments could form the pressure surfaces elsewhere on spool  5 . In  FIG. 2 , the area of lower pressure surface  33  is greater than the area of upper pressure surface  32  and in one embodiment, lower pressure surface  33  is approximately twice as large as the upper pressure surface  32  and may be more than twice as large in still further embodiments. However, this area difference may vary depending as desired operating parameters as explained below. Spool  5  also includes an internal passage or central bore  29  extending from the bottom to approximately the mid-level of spool  5 . In the embodiment shown, central bore  29  does not extend through to the top of spool  5  and only need be sufficiently long to accommodate valve stem  10 , but the exact length of central bore  29  could vary from embodiment to embodiment. Contiguous with central bore  29  and formed between bottom pressure surface  33  and the top cylinder flange  40  is void space  36  (see  FIG. 2  insert). Spool  5  will also have a guide slot  34  which is engaged by alignment screw  23 . Alignment screw  23  allows spool  5  move in the vertical direction, but prevents rotation of spool  5  within internal chamber  15 . 
     Spool  5  will further include a slide valve slot  35  ( FIG. 3 ) for retaining slide valve  7 . In  FIG. 3 , slide valve  7  is shown tightly fitting within slide valve slot  35 . However, in other embodiments, slide valve slot  35  may be sized somewhat larger than slide valve  7  such as seen in U.S. Pat. No. 6,736,046 which is incorporated by reference herein in its entirety. In either instance, slide valve  7  should be considered as traveling with spool  5  as spool  5  moves up and down. The embodiment of slide valve  7  seen in  FIG. 3  is formed by a “d-slide” which completely encloses an internal valve space  37  between the inner surface of slide valve  7  and the inner surface of upper chamber  15  covered by slide valve  7 . This example of slide valve  7  has a curvature matching the internal curvature of internal chamber  15  and the slide valve  7  has an arc which sweeps about 120°. In the embodiment shown in the Figures, there are two slide valves  7 , but other embodiments could contain just one slide valve  7  or possibly more than two slide valves  7 . The smaller the arc, the more slide valves which may be accommodated. The drive mechanism size (i.e., housing and cylinder diameters) may also be parameters considered in the determination of slide valve arc length and number, since more slide valves enable greater control fluid flow rates. All such variations are within the scope of the present invention. 
     As will be explained in more detail below, slide valve  7  has a length which allows internal valve space  37  to cover exhaust port  9  and port  13   a  (but not block port  14   a ) while in the position seen in  FIG. 4 , and alternatively to cover exhaust port  9  and port  14   a  (but not block port  13   a ) while in the position seen in  FIG. 3 . Thus it can be seen that slide valve  7  partially interrupts the continuous annular space formed in upper chamber  15  between the inner side surface of housing  2 A and the outer side surface of spool  5 . 
       FIG. 3  also illustrates how port  13   a  communicates with fluid conduit  11  (shown in segments  11   a - 11   d ), which forms a continuous passage from upper internal chamber  15  to port  13   b,  which communicates with the lower cylinder space  49  (i.e., the portion of the cylinder space below piston  6 ) of lower internal chamber  16 . In the particular embodiment of  FIG. 3 , conduit section  11   c  is formed by external lines connecting conduit sections  11   b  and  11   d.  However, alternative embodiments could form conduit section  11   c  as a passage through a flange fixed to the external surface of cylinder sidewall  42  or form a conduit in any manner which connects upper internal chamber  15  with lower cylinder space  49 . Briefly turning to  FIG. 7 , a similar conduit  12  can be seen running from port  14   a  in upper internal chamber  15  to the port  14   b  opening to the upper cylinder space  48  (i.e., the portion above piston  6 ) of lower internal chamber  16 . Conduit  12  may also be external or internal to the mechanism housing or some combination thereof. The ports  13   a  and  14   a  may be spaced or offset from one another along the internal circumference of upper internal chamber  15  as suggested by the section B-B seen in  FIG. 3  (e.g., ports  13   a  are bisected by the cross-section cut while ports  14   a  are positioned further back along the internal wall of pilot valve housing  2   a ). In one exemplary embodiment, there are two passages  11  and four passages  12 . However, the specific arrangement and number of passages  11  and  12  (and corresponding ports  13   a / 13   b  and  14   a / 14   b ) may vary depending on space available for forming passages in the walls of housing  2  or other relevant design considerations. 
       FIG. 2  illustrates how piston and cylinder assembly  4  generally comprises top cylinder flange  40 , bottom flange  41 , and cylinder side walls  42  with the assembly being secured together with cylinder bolts  45  to form lower internal chamber  16 . The piston  6  is positioned in assembly  4  and is attached to piston rod  44 , which in turn drives the reciprocating tool  100 . A lower piston seal  60  prevents fluid from escaping where piston rod  44  moves through bottom flange  41 . 
       FIG. 2  also illustrates the valve stem  10  attached to piston  6 . The bottom portion of valve stem  10  will be fixed to piston  6  such that valve stem  10  moves up and down in conjunction with piston  6 . As best seen in the detail of  FIG. 2 , valve stem  10  will pass through stem bore  47  formed in top cylinder flange  40 . Stem bore  47  will further include annular slots to accommodate a series of sealing or packing elements such as upper packing  53  and lower packings  54  in order to prevent the leakage of operating fluids between stem bore  47  and valve stem  10 . Packing elements  53  and  54  will be retained in the annular slots by snap rings  52 . Stem bore  47  will also include an annular cavity  50  which communicates with vent conduit or passage  51  (and vent line  57 ) forming a second fluid exhaust path leading to exhaust line  56  (although in the alternative this exhaust path could vent to the atmosphere). 
     The detail of  FIG. 2  further illustrates a series of passages formed in valve stem  10 . A first side passage  17  is formed in valve stem  10  and communicates with a vertical passage  20  traveling to the top of valve stem  10 . Although  FIG. 2  shows first side passage  17  formed as a horizontal bore through valve stem  10 , first side passage  17  could take on any number of different configurations as long as it communicates with vertical passage  20 . Positioned within vertical passage  20  is a one-way valve  21  which allows fluid to flow up vertical passage  20  (i.e., from side passage  17  to the top of valve stem  10  in the upward direction indicated by arrow A), but prevents fluid flow in the opposite or downward direction (indicated by arrow B). Although many alternative types of one-way valves may be used, the embodiment shown in  FIG. 2  employs a poppet valve similar to that seen in U.S. Pat. No. 6,736,046 as the one-way valve  21 . However, depending on the pressure of the control fluid and other operating conditions, a “rod ball” valve device, a vent opening or other one-way valve configurations may be an acceptable substitution for the “poppet.” Positioned below side passage  17  is a second side passage formed by side bores  18  and  19  drilled into valve stem  10  and connected within valve stem  10  by vertical bore  65 . As will become more apparent with the description of the reciprocating drive mechanism&#39;s operation below, the distance between first passage  17  and the second passage beginning at bore  18  is linearly related to the stroke length of piston  6 . The greater or shorter the distance between side passage  17  and side bore  18 , the greater or shorter respectively is the stroke length of piston  6 . In the embodiment of  FIG. 2 , side bores  18  and  19  are connected by vertical bore  65  such that fluid may flow between the two side bores. In this example, several horizontal bores  18  and  19  are made through valve stem  10  and vertical bore  65  connects bores  18  and  19  in order to form the second passage. In the example of  FIG. 2 , vertical bore  65  has been drilled through the bottom of valve stem  10  for ease of manufacturing. 
     As additional nonlimiting examples,  FIGS. 8A and 8B  illustrate alternative embodiments for valve stem  10 . In  FIG. 8A , a second side passage  66  is formed in place of the second and third side bores  18  and  19  previously described. Second side passage  66  may be any indention in valve stem  10  shaped to bridge the seal  53  (i.e., allow air to flow between annular cavity  50  and void space  36 ) in the same manner as the V-shape of bores  18  and  19  seen in  FIG. 2 . In  FIG. 8A , the indention forming side passage  66  is formed around the entire circumference of valve stem  10 . However, other embodiments could form the indention on only part of valve stem  10 &#39;s circumference, thereby adjusting the area of passage  66  through which fluid could flow. 
       FIG. 8B  illustrates an alternative embodiment of valve stem  10  similar to that in  FIGS. 1 to 7 . In this embodiment, each of side bores  18  and  19  are V-shaped and extend through valve stem  10  to opposite sides. Although side bores  18  and  19  in the embodiment of  FIG. 8B  each have two openings on valve stem  10  and meet at the tips of their V-shapes in order to form an X-shaped configuration, many other configurations of side bores  18  and  19  are possible. Side bores  18  and  19  do not need to be slanted and do not need to communicate with two (or more) sides of valve stem  10 , although most embodiments of side bores  18  and  19  will have a vertical distance between them and the two side bores will communicate with one another within valve stem  10 . Although the drawings illustrate only three different embodiments of the second side passage, it will be understood that the present invention encompasses all manners of forming a passage on or through valve stem  10  to allow for the movement of fluid as needed in order for the valve to operate as contemplated. In the embodiment of  FIG. 2 , the vertical distance between side bores  18  and  19  is too short to allow communication between annular space  50  and the upper cylinder space  48  (i.e., the space formed between the bottom of top flange  40  and the top of piston  6 ). On the other hand, the vertical distance between side bores  18  and  19  is sufficiently long to allow communication between annular space  50  and void space  36  in upper internal chamber  15 . For convenience of explanation herein, side passage  17  with bore  20  may sometimes be referred to as a “first” passage while bores  18  and  19  may be referred to as a “second” passage, but this should not be understood as a particular limitation in how the side passages may be arranged in the many possible alternative embodiments (i.e.,  FIG. 8A ), or that there could not be additional passages beyond those shown in the Figures. 
     Operation of Illustrated Embodiment 
     The operation of the reciprocating drive mechanism may be described with continued reference to the Figures. As further described below, slide valves  7  are slideably shiftable in upper internal chamber  15  between a first position and a second position by means of pressure applied by control fluid supplied to upper internal chamber  15  through fluid inlet  8 . The movement of slide valve  7  between a first position and a second position further controls the communication of control fluid to either the upper cylinder space  48  or the lower cylinder space  49  in lower internal chamber  16  to drive the piston  6  between an upper and lower position. In this manner, reciprocating device  100  achieves a consistent cyclic rate. 
     This operation may be understood with reference to the sequence of figures described below.  FIG. 4  shows piston  6  traveling downward and spool  5  in the downward position. Because spool  5  and thus slide valves  7  are in the lower position, slide valves  7  cover and connect exhaust ports  9  and ports  13   a.  As piston  6  travels downward, fluid in lower cylinder space  49  escapes through fluid conduit  11  into the internal valve space  37  of slide valve  7 , and out of fluid exhaust  9 . Likewise, operating fluid entering upper internal chamber  15  through inlet  8  is able to enter ports  14   a  and upper cylinder space  48  via fluid conduits  12  (hidden from view in  FIG. 4  but seen in the section of  FIG. 7 ). It can be understood that backpressure valve  175  ( FIG. 3 ) is capable of controlling the rate of downward movement of piston  6  by restricting the rate at which fluid may escape lower cylinder space  49 . At the point of operation seen in  FIG. 4 , the side passage  17  on valve stem  10  has not yet entered upper cylinder space  48 . 
     Next viewing  FIG. 6 , piston  6  has traveled to its lowest position and side passage  17  on valve stem  10  is just entering upper cylinder space  48 . The pressurized fluid in upper cylinder space  48  travels through side passages  17 , vertical passage  20 , and one-way valve  21  to act on the upper inside surface of spool bore  29  and spool lower pressure surface  33 . Because this surface area is greater than spool upper pressure surface  32  (with the pressure in upper chamber  15  and void space  36  being approximately equal at this point), spool  5  moves to the upward position seen in  FIG. 5 . Along with spool  5 , slide valves  7  move to their upward position, thus covering and connecting ports  14   a  and exhaust ports  9 . Likewise, ports  13   a  are now exposed to the pressurized fluid in upper internal chamber  15 . Therefore, pressurized fluid moves to the area below piston  6  via passages  11  while fluid in upper cylinder chamber  48  is forced through passages  12  ( FIG. 7 ) and escapes through exhaust ports  9  as piston  6  begins to rise. Thereafter, piston  6  will continue to move upward until in a position seen in  FIG. 2 . Naturally, backpressure valve  175  has the same control effect on piston  6  when fluid is exhausted from upper cylinder space  48 . From the foregoing, it can be seen how the difference in area of upper and lower pressure surfaces  32 / 33  is a factor in controlling how rapidly spool  5  changes positions and switches which of upper or lower cylinder spaces  48 / 49  is vented to the exhaust. 
     As piston  6  pushes valve stem  10  upward to the position of  FIG. 2 , side bore  18  will encounter void space  36 . Although the detail of  FIG. 2  shows side passage  18  at the level of snap ring  52 , it will be understood that fluid in space  36  may readily flow around snap ring  52  into side bore  18 . Because the vertical distance between side bores  18  and  19  is spaced to allow communication between void space  36  and annular space  50 , pressurized fluid in void space  36  is allowed to escape via annular space  50  and vent passage  51 . At this point, with no pressurized fluid in void space  36 , the pressurized fluid in upper internal chamber  15  acting on upper pressure surface  32  drives spool  5  to the downward position. Once again, slide valves  7  connect ports  13   a  with fluid exhausts  9  (as in  FIG. 4 ) and pressurized fluid in lower cylinder space  49  may travel through passages  11  and out fluid exhausts  9 . Likewise, pressurized fluid in upper internal chamber  15  now enters ports  14   a  and travels via passages  12  to upper cylinder space  48  and begins moving piston  6  downward to the position of  FIG. 6 , as the above described process begins again. 
     An alternate embodiment of the present invention is seen in  FIGS. 9A to 9D . For simplicity, several elements such as spool  5 , slide valves  7 , and valve stem  10  are omitted and only the housing is shown. However, it will be understood that in the completed mechanism, these elements would be present and function either as described above, or as seen in other mechanisms (nonlimiting examples of which include the spool, slide valves, etc. seen in U.S. Pat. Nos. 6,736,046, 5,468,127 and/or 4,776,773, which are incorporated by reference herein in their entirety). 
     Rather than two separate housings as shown in the previous embodiments, the  FIG. 9  embodiment is created from a single section of material forming a unitary housing  75 . In some embodiments, this unitary housing could include a single, uniform section of material. In other embodiments, a “unitary” housing could include multiple sections of material fixed together in various manners, including welding, threaded engagement, etc. In one embodiment, the material is hard anodized aluminum, but those skilled in the art will recognize enumerable other materials, including rigid plastic materials, steels, and/or base materials with coatings that may be suitable depending on the use and environment of the drive mechanism. In preferred plastic embodiments, the material will exhibit good abrasion resistance, high strength, little or no cold flow, and good resistance to UV and chemical attack. Non-limiting examples of such plastics could include UHMWPE, Delrin, polypropylene, Torlon, PEEK, PEI, and PVC.  FIG. 9A  is a top view illustrating the spacing of fluid inlet  8 , fluid exhausts  9 , and the position of passages  11  and  12  leading to ports  13   a  and  14   a.    
       FIG. 9B  is a section along line B-B showing the path of passage or conduit  11 , which may be referred to as “lower chamber conduit” because it travels from upper internal chamber  15  to the lower cylinder chamber  49 .  FIG. 9D  is a section along line C-C showing the path of passage or conduit  12 , which may be referred to as “upper chamber conduit” because it travels from upper internal chamber  15  to the upper cylinder chamber  48 . Also shown in  FIG. 9B  is a screw hole to accommodate an alignment screw (such as alignment screw  23  seen in  FIG. 2 ). 
     As best seen in  FIGS. 9A and 9B , in this embodiment the fluid inlet(s)  8 , the fluid exhaust(s)  9 , port(s)  14   a  (for the upper chamber conduits), and the port(s)  13   a  (for the lower chamber conduits) are all angularly offset from one another (i.e., are spaced apart from one another along the inner circumference of internal chamber  15 ). This allows for upper chamber conduits  12  and lower chamber conduits  11  to be formed through the side walls of unitary housing  75 , thereby eliminating the need for the external tubing described in the previous embodiments.  FIG. 9B  illustrates the various ports  13   a / 14   a,  inlets  8 , and exhausts  9  as being vertically spaced apart as well as angularly offset. However, other embodiments could form the ports, inlets, and exhausts on the same vertical level (i.e., all in the same horizontal line). 
     The present invention also includes a method of constructing the housing  75  seen in  FIGS. 9A to 9B . The method begins with providing a unitary section of material. In the example of  FIGS. 9A and 9B , the section of material has the shape of two solid cylinders joined at one of their ends, but the section of material could take on other shapes in other embodiments. One of the cylinders has an outside diameter larger than the other, but a difference in outside diameters between the cylinders is not necessary in all embodiments, and it is mainly advantageous for weight minimization. 
     An upper internal chamber  15  is bored into the upper (smaller diameter) solid cylinder and a larger diameter lower internal chamber  16  is bored in the lower solid cylinder portion. A stem bore  47  is formed between the upper and lower internal chambers  15  and  16 . In the embodiment of  FIG. 9D , the stem bore  47  has an insert to form the proper spacing for packing, retaining rings, etc. Then a first vertical passage or conduit  12   a  ( FIG. 9D ) is bored through a sidewall of the upper internal chamber  15  and into the upper cylinder chamber  48 . 
     A second vertical passage or conduit  11   a  ( FIG. 9B ) is bored through a sidewall of the upper internal chamber  15  at a position angularly offset from conduit(s)  12   a  (and inlet(s)  8  and exhaust(s)  9 ). A third vertical passage or conduit  11   c  is bored through a sidewall of the lower internal chamber  16 . Finally, the horizontal passage or conduit  11   b  is bored such that conduits  11   a  and  11   c  are connected. Thereafter, a bottom flange  41  may be positioned over the lower end of housing  75  and outer openings of the various drill bores may be capped to provide the configuration illustrated. Although the embodiment of  FIG. 9  illustrate a valve with offset passages formed in this manner from a unitary section of material, other embodiments could employ the offset passage concept in valves formed of multiple housing pieces such as in  FIGS. 1-7 . 
     Although the above description is in terms of selected embodiments, the present invention may include many modifications and variations of the present figures. For example, although  FIG. 2  shows the reciprocating drive mechanism  1  configured to drive a single reciprocating device  100 , it can be appreciated by one of ordinary skill in the art that multiple reciprocating devices  100  could be driven by the present invention in alternative embodiments. For example, additional reciprocating devices  100  could be cascaded below the piston and cylinder assembly  4  with each drawing its motion from the movement of piston  6  and piston rod  44 . Each reciprocating device  100  would be mechanically coupled in some fashion to piston rod  44 . Furthermore, a reciprocating device  100  could be located at other positions relative to pilot control valve  3  (i.e., above or to the side) and driven in accordance with the present invention by extending the motion of piston rod  44  by some type of mechanical coupling or linkage and such motion could be synchronized with the motion of other reciprocating devices  100  positioned around pilot control valve  3 . Likewise, the embodiments described in the above figures have many advantages over prior art devices such as requiring fewer seals, providing a more reliable switching system, and allowing for greater ease in adjusting stroke length. For example, in U.S. Pat. No. 6,736,046, adjustment of stroke length requires a different size pilot valve housing. On the other hand, selected embodiments of the present invention allow adjustment of stroke length merely by altering the distance between side passages in the valve stem. This allows for the use of a smaller, single pilot valve housing while providing greater versatility in stroke length. However, none of these advantages are necessarily critical to any particular embodiment and other embodiments not having such advantages are intended to fall within the scope of the present invention. All obvious modifications and variations of the embodiments described above are intended to come within the scope of the following claims.