Abstract:
A positive displacement pump comprising a cam for driving a piston assembly. The cam having an odd number of lobes, a first face, a second opposing face, and a peripheral surface extending between the first face and the second face. Each of the first face and the second face having a shoulder formed thereon conforming to the contour of the peripheral surface. The piston assemblies having at least two connector members extending from a piston in a spaced apart, parallel relationship to one another. A compression stroke bearing extends between the connector members in rolling contact with the peripheral surface, a first retraction bearing extends inwardly from one of the connector members and is rollingly positioned in contact with the shoulder of the first face, and a second retraction bearing extends inwardly from another one of the connector members and is rollingly positioned in contact with the shoulder of the second face.

Description:
INCORPORATION BY REFERENCE 
       [0001]    This application claims priority to U.S. Provisional Application Ser. No. 62/212,907, filed Sep. 1, 2015, the entire contents of which is hereby expressly incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    Natural gas is widely used to heat homes, generate electricity, and as a basic material used in the manufacture of many types of chemicals. Natural gas, like petroleum oil, is found in large reservoirs underground and must be extracted from these underground reservoirs and transported to processing plants and then to distribution centers for final delivery to the end user. Natural gas is moved with the use of many types and sizes of positive displacement pumps, commonly termed compressors, that collect, pressurize, and push the gas though the distribution pipes to the various processing centers and points of use. These compressors may be located in ships and drilling fields, in chemical and process plants, and in the huge maze of pipes that makeup the distribution network, which brings gas to the market in a pure, useable form. 
         [0003]    For transportation and storage, natural gas is compressed to save space. Gas pressures in pipelines used to transport natural gas are typically maintained at 1000 to 1500 psig. To assure that these pressures are maintained, compressing stations are placed approximately 40 to 100 miles apart along the pipeline. This application requires compressors (positive displacement pumps) specifically designed to compress natural gas and occupy a minimal area. 
         [0004]    The most common type of positive displacement natural gas compressor is the reciprocating compressor. Reciprocating compressors utilize a pump action that compresses gas by physically reducing the volume of gas contained in a cylinder using a piston. As the cylinder volume filled with gas is decreased through movement of an internal piston, there is a corresponding increase in pressure of the gas in the cylinder. 
         [0005]    Reciprocating compressors and fluid pumps benefit from their ease of availability and their modular nature; however, there are limitations that make them less desirable. For instance, compressors and fluid pumps of this type must either be large in size or operate at higher speeds, i.e., rotations per minute (RPM), to produce the necessary pressure and/or volume desired. The increase in size has obvious drawbacks and may preclude use in space limited situations. The increased RPM necessary in physically smaller compressors and fluid pumps produces unwanted side effects such as increased noise as well as increased cost in the form of more expensive parts and/or increased maintenance. Therefore, a need exists for a pump and compressor assembly having a smaller physical footprint that is able to produce the desired pressure and volume while operating at lower RPM. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0006]      FIG. 1  is a side elevational view of a compressor unit employing a positive displacement pump constructed in accordance with the inventive concepts disclosed herein. 
           [0007]      FIG. 2  is a front elevational view of the pump of  FIG. 1   
           [0008]      FIG. 3  is sectional view taken along line  3 - 3  of  FIG. 2 . 
           [0009]      FIG. 4A  is a partially exploded, side elevational view of a piston assembly of the pump. 
           [0010]      FIG. 4B  is a front elevational view of the piston assembly of  FIG. 4A . 
           [0011]      FIG. 4C  is an exploded, perspective view of an exemplary embodiment of a connector member. 
           [0012]      FIG. 4D  is an assembled, perspective view of the connector member of  FIG. 4C . 
           [0013]      FIG. 5A  is an elevational view of a cam constructed in accordance with the inventive concepts disclosed herein. 
           [0014]      FIG. 5B  is an elevational view of another embodiment of a cam constructed in accordance with the inventive concepts disclosed herein. 
           [0015]      FIG. 6A  is a sectional view of the pump illustrated in a first position. 
           [0016]      FIG. 6B  is a sectional view of the pump of  FIG. 6A  illustrated in a second position. 
           [0017]      FIG. 7  is an elevational view of a multi-stage multi-cylinder pump constructed in accordance with the inventive concepts disclosed herein. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0018]    Before explaining at least one embodiment of the presently disclosed and claimed inventive concepts in detail, it is to be understood that the presently disclosed and claimed inventive concepts are not limited in their application to the details of construction, experiments, exemplary data, and/or the arrangement of the components set forth in the following description or illustrated in the drawings. The presently disclosed and claimed inventive concepts are capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for purpose of description and should not be regarded as limiting. 
         [0019]    In the following detailed description of embodiments of the inventive concepts, numerous specific details are set forth in order to provide a more thorough understanding of the inventive concepts. However, it will be apparent to one of ordinary skill in the art that the inventive concepts within the disclosure may be practiced without these specific details. In other instances, certain well-known features may not be described in detail to avoid unnecessarily complicating the instant disclosure. 
         [0020]    As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having,” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherently present therein. 
         [0021]    Unless expressly stated to the contrary, “or” refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by anyone of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present). 
         [0022]    The term “and combinations thereof” as used herein refers to all permutations or combinations of the listed items preceding the term. For example, “A, B, C, and combinations thereof” is intended to include at least one of: A, B, C, AB, AC, BC, or ABC, and if order is important in a particular context, also BA, CA, CB, CBA, BCA, ACB, BAC, or CAB. Continuing with this example, expressly included are combinations that contain repeats of one or more item or term, such as BB, AAA, AAB, BBC, AAABCCCC, CBBAAA, CABABB, and so forth. A person of ordinary skill in the art will understand that typically there is no limit on the number of items or terms in any combination, unless otherwise apparent from the context. 
         [0023]    In addition, use of the “a” or “an” are employed to describe elements and components of the embodiments herein. This is done merely for convenience and to give a general sense of the inventive concepts. This description should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise. 
         [0024]    The use of the terms “at least one” and “one or more” will be understood to include one as well as any quantity more than one, including but not limited to each of, 2, 3, 4, 5, 10, 15, 20, 30, 40, 50, 100, and all integers and fractions, if applicable, therebetween. The terms “at least one” and “one or more” may extend up to 100 or 1000 or more, depending on the term to which it is attached; in addition, the quantities of 100/1000 are not to be considered limiting, as higher limits may also produce satisfactory results. 
         [0025]    Further, as used herein any reference to “one embodiment” or “an embodiment” means that a particular element, feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment. 
         [0026]    As used herein qualifiers such as “about,” “approximately,” and “substantially” are intended to signify that the item being qualified is not limited to the exact value specified, but includes some slight variations or deviations therefrom, caused by measuring error, manufacturing tolerances, stress exerted on various parts, wear and tear, and combinations thereof, for example. 
         [0027]    Referring now to the drawings, and more particularly to  FIG. 1 , a compressor unit  10  constructed in accordance with the inventive concepts disclosed herein, is illustrated. The compressor unit  10  is particularly adapted for receiving natural gas from a well  22  and compressing the natural gas for facilitating the delivery of the natural gas to a gas gathering network  36 . The compressor unit  10  may be mounted on a skid  13  and may comprise a pump  11 , a compressor assembly  12 , a liquid separator  14 , a radiator  18 , an aftercooler  20 , a radiator fan  33 , and a prime mover  38 . 
         [0028]    Fluid produced from the well  22  is introduced into the liquid separator  14  via a separator inlet  24 . The liquid separator  14  separates the fluid into a gas portion and a liquid portion. The liquid portion is discharged from the liquid separator  14  via a liquid outlet  26  and is disposed of or further processed in a conventional manner depending on the makeup of the liquid portion. The gas portion separated in the liquid separator  14  is discharged from the liquid separator  14  via a gas outlet  28 . The gas is passed to the compressor assembly  12  of the pump  11  via conduit  30 . The gas is compressed in the compressor assembly  12  and thereafter discharged from the compressor assembly  12  via conduit  32 . 
         [0029]    During the compression process, the gas is heated. Therefore, the compressed gas is passed from the compressor assembly  12  to the aftercooler  20  via conduit  32 . The aftercooler  20 , which functions to cool the gas, may be a finned tube type and is mounted adjacent to the radiator  18  so as to take advantage of the fan  33  of the radiator  18 . The fan  33  of the radiator  18  pulls air through the aftercooler  20  to help it cool the compressed gas. The cooled gas is discharged from the aftercooler  20  and passed to a gas gathering network  36  via a conduit  34 . 
         [0030]    The pump  11  may further comprise a coolant pump  42  operably connected to a drive member  40  extending from and rotatably connected to the prime mover  38 . The coolant pump  42  is configured to circulate a cooling liquid from the radiator  18  through the compressor assembly  12 . The cooling liquid is drawn from the radiator  18  through an inlet hose  44  and pumped through a conduit  46  to the compressor assembly  12 . The cooling liquid is discharged from the compressor assembly  12  and passed to the radiator via conduit  48  where it is cooled and may be again circulated by the cooling pump  42 . 
         [0031]    In a field installation of the compressor unit  10 , the pump  11  may be coupled to the prime mover  38 . In this instance, the prime mover  38  is illustrated as an electric motor as is well known in the art. In another embodiment (not shown) the prime mover  38  may be an internal combustion engine fueled by gas from the well  22 , the practice of which is also well known in the art. A control panel  43  may be provided for controlling and monitoring the operation of the prime mover  38  and the pump  11 . It will be appreciated that the control panel  43  contains conventional switches and gauges well known in the art. 
         [0032]    Referring now to  FIGS. 2 and 3 , the pump  11  is illustrated as a two cylinder positive displacement pump wherein the compressor assembly  12  is a first compressor assembly, and the pump  11  further comprises a second compressor assembly  12   a . The pump  11  may further comprise a case  70 , a case cover  72 , outlet covers  74   a ,  74   b ,  74   c , and  74   d , an oil pan  76 , a bearing cover  78 , a drive member seal cover  80 , a drive member seal  82 , a main bearing  84 , a keyway  86 , a cooling inlet conduit  88 , a cooling outlet  92 , a cooling bridge  94 , a cooling inlet  96 , a cooling outlet conduit  100 , a gas inlet conduit  102 , an outlet port  106 , a belt pulley  107 , a pulley bolt  109 , a gas bridge  108 , an inlet port  110 , a bearing cover receiving bore  111 , a gas outlet hose  114 , case cover bolts  115  (only one of which is labeled in  FIG. 2 ), bearing cover bolts  116  (only one of which is labeled in  FIG. 2 ), drive member seal cover bolts  117  (only one of which is labeled in  FIG. 2 ), outlet cover bolts  118  (only one of which is labeled in  FIG. 2 ), cylinder block bolts  119  (only one of which is labeled in  FIG. 2 ), compressor valve assembly cover bolts  120  (only one of which is labeled in  FIG. 2 ), a drain valve  101 , a key  121 . 
         [0033]    The drive member  40  of the pump  11  is formed of a suitable material such as aluminum or steel, and is characterized as having a predetermined length and an outer surface  113  having a predetermined diameter. To facilitate secure connection components, the drive member  40  may be provided with the keyway  86  and a central keyway  364 . 
         [0034]    The case  70  of the pump  11  is formed of a suitable material such as aluminum or steel, and is characterized as having a first side  85 , a second side  89 , an outer surface  91 , a central bore  93 , a cylinder sleeve receiving bore  95 , a first seating shoulder  101 , and a second seating shoulder  103 . 
         [0035]    The first and second sides  85  and  89  of the case  70  form a substantially planar surface to facilitate a secure, sealable connection between the case  70  and the case cover  72 . The case cover  72  may be secured to the case  70  via connecting members such as case cover bolts  115  or other suitable connecting member. A sealing member, such as a gasket (not shown), may be positioned between the case cover  72  and first and second sides  85  and  89  of the case  70  to provide a fluid tight seal between the case cover  72  and the case  70 . 
         [0036]    The outer surface  91  of the case  70  is characterized as having planar surfaces  105  (only one of which is designated) which are formed having a predetermined width along the outer surface  91  and extending from the first side  85  to the second side  89  of the case  70 . The planar surfaces  105  of the outer surface  91  of the case  70  are formed to facilitate a secure, sealable connection between the case  70  and the piston assemblies  12  and  12   a , and the oil pan  76 . 
         [0037]    The first and second seating shoulders  101  and  103  of the case  70  are formed a predetermined distance from the first and second sides  85  and  89 . 
         [0038]    The cylinder sleeve receiving bore  95  of the case  70  extends from the outer surface  91  to the central bore  93  of the case  70 . Each of the planar surfaces  105  of the case designed to secure the piston assemblies  12  and  12   a  may have a cylinder sleeve receiving bore  95 . As illustrated in  FIG. 2 , not all of the planar surfaces  105  designed to accommodate piston assemblies will be fitted with a piston assembly. The planar surfaces  105  that are not fitted with a piston assembly  12  and  12   a  are sealed with the outlet covers  74   a ,  74   b ,  74   c , and  74   d . The outlet covers  74   a ,  74   b ,  74   c , and  74   d  are provided with a plurality of bolt holes (not shown) which extend through the outlet convers  74   a ,  74   b ,  74   c , and  74   d  and are designed to slidably receive connecting members such as outlet cover bolts  118  or other suitable connecting members for securing the outlet covers  74   a ,  74   b ,  74   c , and  74   d  to the case  70 . A sealing member, such as a gasket (not shown), may be positioned between the outlet covers  74   a ,  74   b ,  74   c , and  74   d  and the case  70  to provide a fluid tight seal therebetween. 
         [0039]    The components associated with the first side  85  and second side  89  of the case  70  of the pump  11  are substantially the same, therefore, in the interest of brevity, only the components associated with the first side  85  have been designated and will be described herein. However, for the sake of clarity, when referring to components associated with both the first and second sides  85  and  89 , the designator “a” will be added to the components of the first side  85 , and the designator “b” will be added to the components of the second side  89 . 
         [0040]    The case cover  72  of the pump  11  is formed of a suitable material such as aluminum or steel, and is characterized as having the bearing cover receiving bore  111  which extends through the case cover  72 . 
         [0041]    The bearing cover  78  may be formed of a suitable material, such as aluminum or steel, and is formed having a first side  123 , a second side  124 , cover seating shoulder  125 , a seal seating shoulder  126 , a seal cover seating shoulder  127 , and a drive member bore  128 . 
         [0042]    The cover seating shoulder  125  is formed on the second side  124  of the bearing cover  78  and extends a predetermined distance from the second side  124  of the bearing cover  78 . The seal seating shoulder  126  is formed on the first side  123  of the bearing cover  78  and extends a predetermined distance from the first side  123  of the bearing cover  78 . The seal seating shoulder  126  is dimensioned to receive the drive member seal  82 . The seal cover seating shoulder  127  is formed on the first side  123  of the bearing cover  78  and extends a predetermined distance from the first side  123  of the bearing cover  78 . 
         [0043]    The bearing cover receiving bore  111  of the case cover  72  is dimensioned to receive at least a portion of the cover seating shoulder  125  of the bearing cover  78 . The bearing cover  78  may be secured to the case cover  72  via connecting members, such as bearing cover bolt  116  or other suitable connector members. A sealing member, such as a gasket (not shown), may be disposed between the bearing cover  78  and the case cover  72  to effect a fluid tight seal therebetween. 
         [0044]    The drive member seal cover  80  is formed of a suitable material such as aluminum or steel, and is characterized as having a seal cover drive member bore  129 . The seal cover drive member bore  129  extends through the drive member seal cover  80  and is dimensioned to allow the drive member  40  to extend through the drive member seal cover  80 . The drive member seal cover  80  is provided having a plurality of bolt holes (not shown) designed to slidably receive connecting members such as drive member seal cover bolts  117  or other suitable connector members. 
         [0045]    The seal seating shoulder  126  of the bearing cover  78  is dimensioned to receive the drive member seal  82  such that the drive member seal  82  is disposed on the seal seating shoulder  126  of the bearing cover  78 . The drive member seal cover  80  is configured for abutting engagement with the drive member seal  82  for maintaining the drive member seal  82  in the seating shoulder  126  of the bearing cover  78 . 
         [0046]    The drive member seal  82  is constructed of a suitable material such as rubber, and is designed for sealing engagement with the outer surface  113  of the drive member  40 . The drive member seal  82  is constructed as is well known in the art, and similar seals are commercially available. Thus, no further explanation of the design and operation of the drive member seal  82  should be necessary to enable a person of skill in the art to understand the pump  11  of the present disclosure. 
         [0047]    The pump  11  further comprises a bearing brace  330 . The bearing brace  330  is formed of a suitable material such as aluminum or steel, and is characterized as having a first side  332 , a second side  334 , an upper end  336 , a central bore  338 , a plurality of bolt holes  340  (only one of which is designated in  FIG. 3 ), and a plurality of bearing brace bolts  342  (only one of which is designated in  FIG. 3 ). The plurality of bolt holes  340  are formed through the bearing brace  330  from the first side  332  to the second side  334  and are sized to accommodate the heads of the plurality of bearing brace bolts  342 . 
         [0048]    The central bore  338  extends through the bearing brace  330  from the first side  332  to the second side  334 . The central bore  338  has a bearing seating shoulder  339  formed a predetermined distance from the second side  334  of the bearing brace  330 . The first seating shoulder  101  of the case  70  is dimensioned to receive the bearing brace  330  such that the bearing brace  330  is supported by the seating shoulder  101  of the case  70 . The bearing brace  330  is secured to the case  70  via connecting members, such as the bearing brace bolt  342  or other suitable connecting members. 
         [0049]    The main bearing  84  is formed as is well known in the art and is deployed in rolling contact with the outer surface  113  of the drive member  40 . The design and function of such main bearings is well known in the art, and many versions are commercially available. The central bore  338  of the bearing brace  330  is dimensioned to receive the main bearing  84  such that the main bearing  84  is supportingly disposed on the bearing seating shoulder  339 . The main bearing  84  is secured in the central bore  338  by the bearing cover  78 . 
         [0050]    As illustrated in  FIG. 3 , one embodiment of the pump  11  may be provided having the belt pulley  107  operably connected to the drive member  40 . The belt pulley  107  may be secured to the drive member  40  via the key  121  and a connecting member, such as pulley bolt  109  or other suitable connector members. The belt pulley  107  may be utilized to drive accessory devices such as, for instance, the coolant pump  44  ( FIG. 1 ). Other accessory devices may include, but are not limited to, an alternator, a generator, an air pump, or a fluid pump. 
         [0051]    In operation of the pump  11 , the drive member  40  extends from the prime mover  38  and through the width of the case  70  from the second side  89  to the first side  85 . The drive member  40  passes through the drive member seal cover bores  129   a  and  129   b , the drive member bores  128   a  and  128   b , and the central bores  338   a  and  338   b  at both the first and second sides  85  and  89  of the case  70 . The drive member  40  is supportingly deployed in rolling contact with the main bearings  84   a  and  84   b , and sealed by drive member seals  82   a  and  82   b.    
         [0052]    The first and second compressor assemblies  12  and  12   a  are substantially the same, therefore, in the interest of brevity, only the components of the first compressor assembly  12  will be described herein. However, for purposes of clarity, when referring to the features of multiple compressor assemblies, a designator, such as “a” for the features of compressor assembly  12   a  for instance, will be added. Broadly, the compressor assembly  12  comprises a cylinder block  60 , a compressor valve assembly  62 , and a compressor valve assembly cover  64 . 
         [0053]    As best illustrated in  FIG. 3 , the cylinder block  60  may be formed of a suitable material, such as, for instance, aluminum or steel, and is characterized as having an upper end  130 , a lower end  132 , a first side  134 , a second side  136  ( FIG. 2 ), a third side  138 , a fourth side  140  ( FIG. 2 ), a cylinder sleeve receiving bore  142 , a water chamber  144 , and a sleeve seating shoulder  146 . The lower end  132  is a substantially planar surface to facilitate seating of the cylinder block  60  to the case  70 . The cylinder block  60  is provided with a plurality of bolt holes  122  (only one of which is designated in  FIG. 3 ) which extend through the cylinder block  60  from an upper end  148  to a lower end  150  of a bolt notch  152  and which are adapted to slidably receive cylinder block bolts  119  or other suitable connecting members for securing the cylinder block  60  to the case  70 . A sealing member, such as a gasket  154 , may be positioned between the cylinder block  60  and the case  70  to provide a fluid tight seal between the cylinder block  60  and the case  70  when the cylinder block  60  is secured to the case  70 . 
         [0054]    To remove excess heat from the cylinder block  60 , the cylinder block  60  is provided with the water chamber  144  located between the first, second, third and fourth sides  134 ,  136 ,  138  and  140  and the cylinder sleeve receiving bore  142  of the cylinder block  60  extending a predetermined distance from the upper end  130 . The water chamber  144  interconnects a cooling inlet  90  formed through the third side  138  and the cooling outlet  92  formed through the first side  134  of the cylinder block  60 . The water chamber  144  is sealed with a gasket  156  which is secured between the upper end  130  of the cylinder block  60  and the compressor valve assembly  62 . 
         [0055]    In operation of the pump  11 , cooling fluid passes into the water chamber  144  from the coolant pump  42  ( FIG. 1 ) via the cooling inlet conduit  88  which is mechanically connected at one end to the cooling inlet  90 . After circulating through the water chamber  144 , the cooling fluid passes from the cooling outlet  92  of the water chamber  144  into the radiator  18  via conduit  100  which is mechanically connected at one end the cooling outlet  92 . 
         [0056]    The cylinder sleeve receiving bore  142  of the cylinder block  60  is formed having a predetermined circumference and extends through the cylinder block  60  from the upper end  130  to the lower end  132 . The cylinder block  60  is mounted to the case  70  such that the cylinder sleeve receiving bore  142  of the cylinder block  60  is aligned with the cylinder sleeve receiving bore  95  of the case  70 . The sleeve seating shoulder  146  of the cylinder block  60  is formed a predetermined distance from the upper end  130  of the cylinder block  60 . 
         [0057]    The cylinder sleeve receiving bore  142  of the cylinder block  60  is dimensioned to receive a cylinder sleeve  160 . The cylinder sleeve  160  is formed of a suitable material such as aluminum or steel, and is characterized as having an upper end  162 , a lower end  164 , an inner surface  166 , an outer surface  168 , and a seating shoulder  170 . The cylinder sleeve  160  is dimensioned such that the outer surface  168  is substantially the same diameter as the cylinder sleeve receiving bore  142  of the cylinder block  60 . The cylinder sleeve  160  may be removeably deployed in fluid communication with the cylinder sleeve receiving bore  142  of the cylinder block  60  with the upper end  162  of the cylinder sleeve  160  and the upper end  130  of the cylinder block  60  forming a substantially planar surface to facilitate a secure connection between the cylinder block  60 , the cylinder sleeve  160 , and the compressor valve assembly  62 . 
         [0058]    The seating shoulder  146  of the cylinder block  60  is dimensioned to receive the seating shoulder  170  of the cylinder sleeve  160  such that the seating shoulder  170  of the cylinder sleeve  160  is supportingly disposed in fluid contact with the seating shoulder  146  of the cylinder block  60 . 
         [0059]    The inner surface  166  of the cylinder sleeve  160  forms a cylinder bore  172  extending from the upper end  162  to the lower end  164  of the cylinder sleeve  160 . The cylinder bore  172  forms a substantially uniform circle having a predetermined diameter configured to concentrically surround at least a portion of a piston assembly  190 . 
         [0060]    The compressor valve assembly  62  of the pump  11  may be formed of a suitable material, such as, for instance, aluminum or steel, and is characterized as having an upper end  63 , a lower end  65 , a first side  66 , a second side  67  ( FIG. 2 ), a third side  68 , a fourth side  69  ( FIG. 2 ), a valve receiving bore  71 , a valve seating shoulder  73 , an inlet port  104 , and an outlet port  106 . The lower end  65  forms a substantially planar surface to facilitate seating of the compressor valve assembly  62  to the cylinder block  60 . The compressor valve assembly  62  is provided with a plurality of bolt holes (not shown) which extend through the compressor valve assembly  62  from the upper end  63  to a lower end  65  and which are adapted to slidably receive bolts (not shown) or other suitable connecting members for securing the compressor valve assembly  62  to the cylinder block  60 . A sealing member, such as the gasket  156 , may be positioned between the compressor valve assembly  62  and the cylinder block  60  to provide a fluid tight seal between the compressor valve assembly  62  and the cylinder block  60  when the compressor valve assembly  62  is secured to the cylinder block  60 . 
         [0061]    The valve receiving bore  71  extends from the upper end  63  to the lower end  65  of the compressor valve assembly  62 . The valve seating shoulder  73  is formed a predetermined distance from the lower end  65  of the compressor valve assembly and extends a predetermined distance into the valve receiving bore  71 . 
         [0062]    The gas inlet port  104  of the compressor valve assembly  62  forms an annular recess extending from the third side  68  of the compressor valve assembly  62  to the valve receiving bore  71 . At least a portion of the gas inlet port  104  may be threaded to facilitate threadingly receiving an end of the gas inlet conduit  102  or gas bridge  108 . 
         [0063]    The gas outlet port  106  of the compressor valve assembly  62  forms an annular recess extending from the first side  66  of the compressor valve assembly  62  to the valve receiving bore  71 . At least a portion of the gas outlet port  106  may be threaded to facilitate threadingly receiving an end of the gas outlet conduit  114  or the gas bridge  108 . 
         [0064]    As shown in  FIG. 3 , the valve receiving bore  71  is dimensioned to receive a compressor valve  75  such that the compressor valve  75  is concentrically surrounded by the valve receiving bore and supportingly disposed on the valve seating shoulder  73 . The compressor valve  75  shown herein is a concentric, plate-type valve having a central suction portion  77 , an outer discharge portion  79 , and a valve retainer  81  as disclosed, for instance, in U.S. Pat. No. 5,947,697, which is expressly incorporated herein by reference. The design and operation of concentric compressor valves as briefly described above are commercially available and well known in the art. Therefore, no further description of the various types of compressor valves, their components, or their operation is believed necessary in order to enable a person of skill in the art to understand the compressor valve assembly  62  of the present disclosure. 
         [0065]    The compressor valve  75  is secured in the valve receiving bore  71  of the compressor valve assembly  62  by the compressor valve assembly cover  64 . The compressor valve assembly cover  64  is formed of a suitable material such as aluminum or steel, and is characterized as having an upper surface  97  and a lower surface  99 . The lower surface  99  of the compressor valve assembly cover  64  forms a substantially planar surface designed to be secured to the upper end  63  of the compressor valve assembly  62  via bolts  120  (only one of which is designated in  FIG. 2 ). 
         [0066]    As illustrated in  FIGS. 3-4B , the piston assembly  190  is characterized as having a piston  192 , a first connector member  210   a , a second connector member  210   b , at least one compression stroke bearing  230 , a first retraction bearing  250 , and a second retraction bearing  260 . 
         [0067]    The piston  192  of the piston assembly  190  may be formed of a suitable material, such as aluminum or steel, and is characterized as having an upper end  194 , a lower end  196 , an outer surface  198 , a first mounting shoulder  200 , a second mounting shoulder  202 , and at least one piston ring  204  (only one of which is designated in  FIG. 4B ). The first and second mounting shoulders  200  and  202  may be formed a predetermined distance from the lower end  196  of the piston  192  and extending inward a predetermined distance from the outer surface  198 . The first and second mounting shoulders  200  and  202  are configured to provide a substantially planar surface to facilitate connection of the first and second connector members  210   a  and  210   b , respectively. 
         [0068]    The outer surface  198  of the piston  192  forms a substantially uniform cylinder having a predetermined diameter matched to the diameter of the cylinder bore  172  in a manner that is well known and accepted in the art. The at least one piston ring  204  may include, for instance, a compression ring, a wipe ring, and an oil return ring as is well known in the art. The at least one piston ring  204  is designed to seal a predetermined gap between the diameter of the piston  192  and the cylinder bore  172  in a manner that is well known in the art. 
         [0069]    The piston  192  is characterized as having a predetermined height extending from the upper end  194  to the lower end  196  of the piston  192 . The predetermined height of the piston  192  is designed to distribute the reactive side forces on the piston, reducing the side wear on the piston  192  and the inner surface  166  of the cylinder sleeve  160 . 
         [0070]    The first and second connector members  210   a  and  210   b  of the piston assembly  190  are substantially the same; therefore, in the interest of brevity, only connector member  210   a  will be described herein. For the sake of clarity, when discussing both connector members  210   a  and  210   b , the designator “a” will be added to the features of connector member  210   a  and the designator “b” will be added to the features of connector member  210   b.    
         [0071]    Connector member  210   a  is formed of a suitable material, such as, for instance, aluminum or steel, and is characterized as having an upper end  212 , a lower end  214 , a first side  216 , and a second side  218 . The connector member  210   a  is provided having a plurality of bolt holes  220 ,  221 ,  222 , and  224  which extend through the connector member  210   a  from the first side  216  to the second side  218  and which are adapted to slidably receive bolts  226 ,  242 ,  244 , and  264  or other suitable connecting members for securing the connector member  210   a  to the piston  192 , the compression bearing  230 , and the first retraction bearing  250 , respectively. It should be noted for clarity, that bolt hole  224   b  of connector member  210   b  will be utilized to secure the second retraction bearing  260  to the connector member  210   b  via the bolt  264   b  or other suitable connecting members. 
         [0072]    The compression bearing  230  may be formed as is known in the art, and is characterized as having an outer surface  232 , a first side  234 , a second side  236 , a first shoulder  238 , and a second shoulder  240 . As illustrated in  FIG. 3 , the compression bearing  230  may be formed as a single bearing having a predetermined width extending between the second face  218   a  of connector member  210   a  to the second face  218   b  of connector member  210   b . The compression bearing  230  may be secured between the first and second connector members  210   a  and  210   b  via bolts  242  and  244  or other suitable members designed to allow the compression bearing  230  to freely rotate. 
         [0073]    As illustrated in  FIG. 4A , in one embodiment, the compression bearing  230  of the piston assembly  190  may comprise a plurality of bearings  230   a ,  230   b ,  230   c , and  230   d . Each of the plurality of compression bearings  230   a ,  230   b ,  230   c , and  230   d  is formed as is known in the art and is substantially the same, therefore, in the interest of brevity only compression bearing  230   a  will be described herein. It should be noted, however, that when describing more than one of the plurality of compression bearings  230   a ,  230   b ,  230   c , and  230   d  the designator “a”, “b”, “c”, or “d”, respectively, will be added for the sake of clarity. 
         [0074]    Compression bearing  230   a  is formed as is known in the art, and is configured having an outer surface  270 , a first side  272 , and a second side  274 . Compression bearing  230   a  is formed having a predetermined width from the first side  272  to the second side  274 . 
         [0075]    The outer surface  232  of compression bearing  230  and the outer surfaces  270   a ,  270   b ,  270   c , and  270   d  of the plurality of compression bearings  230   a ,  230   b ,  230   c , and  230   b  may be formed having substantially the same diameter. The combined width of the plurality of compression bearings  230   a ,  230   b ,  230   c , and  230   d  from the first side  272   a  of compression bearing  230   a  to the second side  274   d  of compression bearing  230   d  is substantially the same as the width of compression bearing  230  when measured from the first side  234  to the second side  236 . 
         [0076]    Compression bearings  230   a ,  230   b ,  230   c , and  230   b  may be secured between the first and second connector members  210   a  and  210   b  via bolts  242  and  244  or other suitable connector members designed to allow compression bearings  230   a ,  230   b ,  230   c , and  230   b  to freely rotate. 
         [0077]    The first and second retraction bearings  250  and  260  are formed as is known in the art, and are characterized as having an outer surface  252  and  262 , a first side  254  and  264 , and a second side  256  and  266 . The first and second retraction bearings  250  and  260  may be secured to the second sides  218   a  and  218   b  of connector members  210   a  and  210   b , respectively, with bolts  264   a  and  264   b  or other suitable connector members designed to allow the first and second retraction bearings  250  and  260  to freely rotate. 
         [0078]    Referring now to  FIGS. 4C and 4D , another embodiment of a connector member  210   c  for use in the piston assembly  190  is illustrated. It will be appreciated that the piston assembly  190  would employ a second connector member that would be a mirror image of the connector member  210   c . The connector member  210   c  is similar to the connector members  210   a  and  210   b  except the connector member  210   c  is configured to slidably support a retraction bearing assembly  250   a  in a way that a rotational axis of the retraction bearing assembly  250   a  is able to laterally shift in response to a lateral force applied to the retraction bearing assembly  250   a.    
         [0079]    In one embodiment, the connector member  210   c  has a slot  270  formed near a lower end thereof. The slot  270  is laterally oriented and shown to extend through the connector member  210   c  from a first side to a second side. The slot  270  is also shown to have a generally rectangular shape. However, it should be appreciated that the slot  270  may be configured in a variety of shapes so long as the retraction bearing assembly  250   a  is able to slide relative to the connector member  210   c.    
         [0080]    The retraction bearing assembly  250   a  has a bearing support  271  having one end  272  configured to receive a bearing  274  and a second end  276  configured to be slidably received in the slot  270  of the connector member  210   c . To this end, the second end  276  of the bearing support  271  is illustrated as a rectangularly shaped block. The bearing support  271  may be connected to the connector member  210   c  in any suitable fashion that permits the bearing support  271  to be retained in and slide through the slot  270 . In one version, the bearing support  270  may be connected to the connector member  210   c  with a fastener  278  and a washer  280 . 
         [0081]    In one embodiment, the bearing support  271  is biased to one end of the slot  270  by a spring  282 . The spring  282  is positioned in the slot  270  with one end engaging the bearing support  271  and another end engaging the connector member  210   c  and retained with a connector, such as a set screw  284 . While only one spring  282  has been illustrated, it should be understood that more than one spring may be utilized. For example, a spring may be installed on opposing sides of the bearing support  271 . 
         [0082]    Referring now to  FIGS. 3-5A , the pump  11  further comprises a cam  300  rotatably positioned in the case  70  and operably connected to the drive member  40 . The cam  300  is formed of a suitable material, such as aluminum or steel, and is characterized as having a first face  302 , a second face  304 , a peripheral surface  306 , a key  360 , a drive member bore  362 , and a keyway  364 . 
         [0083]    The first and second faces  302  and  304  of the cam  300  are substantially the same; therefore, in the interest of brevity only the features of the first face  302  will be described and labeled herein. For the sake of clarity, when describing both faces, the designator “a” will be added to features of the first face  302  and the designator “b” will be added to features of the second face  304 . 
         [0084]    The first face  302  of the cam  300  forms a substantially planar surface extending from the peripheral surface  306  to the drive member bore  362 , and comprises a first shoulder  308 , a first shoulder face  309 , a second shoulder  310 , a second shoulder face  311 , and a groove  312 . 
         [0085]    The first shoulder  308  of the cam  300  forms a substantially planar surface having a predetermined width along the first face  302  extending from the peripheral surface  306  to the first shoulder face  309 . The first shoulder face  309  is formed having a predetermined height extending perpendicularly inward from the first shoulder  308  of the first face  302 . 
         [0086]    The second shoulder  310  of the cam  300  forms a substantially planar surface extending from the second shoulder face  311  to the drive member bore  362  of the cam  300 . The second shoulder face  311  is formed having a predetermined height extending perpendicularly inward from the second shoulder  310  of the first face  302  of the cam  300 . 
         [0087]    The groove  312  of the cam  300  is formed having a predetermined width that is substantially the same along its entire length around the circumference of the cam  300  and has a predetermined offset length measured from the first shoulder face  309  to the second shoulder face  311 . The width of the groove  312  determines the maximum circumference of the outer surfaces  252  and  262  of the first and second retraction bearings  250  and  260 . 
         [0088]    The cam  300  comprises an odd number of at least 3 lobes which may be determined using the calculation 3+n where n is equal to 0 or an even-numbered integer. The axes of the lobes relative to each other can be calculated by dividing 360° by the number of lobes on the cam  300 . For instance, as illustrated in  FIG. 5A , in one embodiment of the compressor unit  10 , the cam  300  may be formed as a tri-lobe cam  365  having a first lobe  366 , a second lobe  368 , and a third lobe  370 . The first, second, and third lobes  366 ,  368 , and  370  are offset by a first angle  372 , a second angle  374 , and a third angle  376 . The first, second, and third angles  372 ,  374 , and  376  each equal an absolute angle calculated by dividing 360° by 3 which equals 120°. Or, in other words, each of the first, second, and third angles  372 ,  374 , and  376  are offset from one another by an absolute angle of substantially 120°. For the sake of clarity, as illustrated in  FIG. 5A , if the first lobe  366  is at an angle of 0°, the second lobe  368  would be at 120°, and the third lobe  370  would be at 240°. 
         [0089]    By way of further illustration, in one embodiment of the compressor unit  10  illustrated in  FIG. 5B , the cam  300  may be formed as a five-lobe cam  379  having a first lobe  380 , a second lobe  382 , a third lobe  384 , a fourth lobe  386 , and a fifth lobe  388 . The first, second, third, fourth, and fifth lobes  380 ,  382 ,  384 ,  386 , and  388  are offset by a first angle  390 , a second angle  392 , a third angle  394 , a fourth angle  396 , and a fifth angle  398 . Using the above calculation, dividing 360° by the number of lobes ( 5 ) we find that each of the first, second, third, fourth, and fifth angles  390 ,  392 ,  394 ,  396 , and  398  are offset from one another by an absolute angle of substantially 72°. For the sake of clarity, as illustrated in  FIG. 5B , if the first lobe  380  is at an angle of 0°, the second lobe  382  would be at 72°, the third lobe  384  would be at 144°, the fourth lobe  386  would be at 216°, and the fifth lobe  388  would be at 288°. 
         [0090]    Also illustrated in  FIG. 5B , in some embodiments, the cam  300  of the compressor unit  10  may be formed having only the first shoulder  308 . In such an embodiment, the first shoulder face  309  would have a predetermined height extending perpendicularly from the first face  302  to the first shoulder  308 . The first face  302  would form substantially planar surface extending from the first shoulder face  309  to the drive member bore  362 . In operation of such an embodiment, the outer surfaces  252  and  262  of the first and second retraction bearings  250  and  260  would be in rolling contact with the first shoulder face  309  of the cam  300 . 
         [0091]    Referring now to  FIGS. 3-6B , in operation of the pump  11 , the prime mover  38  applies a rotational force to the drive member  40  causing it to rotate the cam  300  which is operably connected thereto. Rotation of the cam  300  imparts a reciprocating rectilinear motion to the diametrically opposed piston assemblies  190  and  190   a  in the compression assemblies  12  and  12   a , respectively. The outer surfaces  232  and  232   a  of compression bearings  230  and  230   a  of the piston assemblies  190  and  190   a  are in rolling contact with the peripheral surface  306  of the cam  300  and impart an up stroke, or compression stroke. The outer surfaces  252  and  262  of the first and second retraction bearings  250  and  260  are in rolling contact with the first shoulder faces  309   a  and  309   b  of the first and second faces  302  and  304 , respectively, of the cam  300  and impart a down stroke, or intake stroke on the piston assemblies  190  and  190   a.    
         [0092]    As illustrated in  FIGS. 6A and 6B , the odd number of lobes of the cam  300  allows opposed compressor assemblies  12  and  12   a  to operate together to produce a high pressure compressed gas. In operation, compressor assembly  12  intakes relatively low pressure gas via gas inlet conduit  102  on an intake stroke of piston assembly  190  (as illustrated in  FIG. 6B ). The relatively low pressure gas is compressed in compressor assembly  12  as the piston assembly  190  is pushed into a compression stroke by the rotation of the cam  300 . As illustrated in  FIG. 6A , when piston assembly  190  of compressor assembly  12  is at a top dead center (TDC), or in full compression, the gas now having an intermediate pressure is discharged via gas bridge  108 . The gas bridge  108  passes the intermediate pressure gas through aftercooler  20  before directing it to compressor assembly  12   a  wherein the piston assembly  190   a  will be at a bottom dead center (BDC), or at full intake. Further rotation of the cam  300  pushes piston assembly  190   a  into a compression stroke as piston assembly  190  is pulled into an intake stroke. As illustrated in  FIG. 6B , when piston assembly  190   a  reaches TDC high pressure compressed gas is discharged via gas outlet conduit  114 . At substantially the same time, piston assembly  190  reaches BDC intaking relatively low pressure gas via gas inlet conduit  102 . This phase pairing allows the pump  11  to reach the high pressure required in natural gas networks. 
         [0093]    The flow of gas through a reciprocating compressor inherently produces pulsation because the discharge valves are not open for the entire compression stroke. Interconnection of the compressor assemblies  12  and  12   a  as a single stage in the pump  11  of the present disclosure allows for greater pulsation and vibration control. 
         [0094]    To further facilitate heat reduction, in some embodiments of the pump  11  gas outlet conduit  114  may be routed through the intercooler  20  before discharging the compressed gas into pipeline  36  via piping assembly  34  as illustrated in  FIG. 1 . 
         [0095]    It will be recognized by one of skill in the art that the number of compression strokes for each compressor assembly per revolution of the pump  11  is equal to the number of lobes on the cam  300 . For instance, as illustrated in  FIG. 6A , one full rotation of the three-lobed cam  300  results in 3 full compression cycles of both compressor assembly  12  and  12   a . This greatly reduces the rotations per minute (RPM) required of the prime mover  38  when compared to conventional natural gas compressors. The lower RPM requirements of the pump  11  reduces emissions from the prime mover, and allows quieter operation of the compressor unit  10  when deployed in or near noise sensitive environments such as residential areas. 
         [0096]    As illustrated in  FIG. 7 , the pump  11  may be configured having multiple paired compression assemblies to form a multi-stage compressor  500  comprising compression assembly  12 , compression assembly  12   a , compression assembly  12   b , compression assembly  12   c , compression assembly  12   d , and compression assembly  12   e . Diametrically opposed compression assemblies  12  and  12   a ,  12   b  and  12   c , and  12   d  and  12   e  form a first stage  502 , a second stage  504 , and a third stage  506 , respectively. 
         [0097]    Referring now to  FIGS. 1 and 7 , in operation the multi-stage compressor  500  receives gas from the gas network or a well via conduit  30  connected to an intake manifold  508 . The intake manifold  508  distributes gas to the first stage  502 , higher pressure output from stage  502  is distributed to second stage  503  comprised of compressor assembly  12   b  and  12   c  via conduit  103   a , some embodiments will feed intercooler  20  via conduit  103   a  before returning flow to input of stage  503  via conduit  103   b . Higher pressure output from stage  503  is distributed to third stage  504  comprised of compressor assembly  12   d  and  12   e  via conduit  103   c . Some embodiments will feed intercooler  20  via conduit  103   c  before returning flow to input of stage  504  via conduit  103   d . High pressure output from stage  504  is distributed via discharge piping  32  to aftercooler  20  discharging into pipeline  36  via piping assembly  34 . 
         [0098]    From the above description, it is clear that the inventive concepts disclosed and claimed herein are well adapted to carry out the objects and to attain the advantages mentioned herein, as well as those inherent in the invention. While exemplary embodiments of the inventive concepts have been described for purposes of this disclosure, it will be understood that numerous changes may be made which will readily suggest themselves to those skilled in the art and which are accomplished within the spirit of the inventive concepts disclosed and/or defined in the appended claims. For example, while use of the pump  11  has been described for compression of gaseous state fluids, primarily natural gas, it should be understood that the pump  11  may also be employed to pump various liquids by installation of cylinder head systems designed for liquid transmission, as opposed to gaseous state fluids.