Patent Publication Number: US-2016222949-A1

Title: Pumping mechanism with plunger

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to a pumping mechanism, and more particularly, to a pumping mechanism with a plunger. 
     BACKGROUND 
     Gaseous fuel powered engines are common in many applications. For example, the engine of a locomotive can be powered by natural gas (or another gaseous fuel) alone or by a mixture of natural gas and diesel fuel. Natural gas may be more abundant and, therefore, less expensive than diesel fuel. In addition, natural gas may burn cleaner in some applications. 
     Natural gas, when used in a mobile application, may be stored in a liquid state onboard the associated machine. This may require the natural gas to be stored at cold temperatures, e.g., about −100 to −162° C. The liquefied natural gas is then drawn from the tank by gravity and/or by a boost pump, and directed to a high-pressure pump. The high-pressure pump further increases a pressure of the fuel and directs the fuel to the machine&#39;s engine. In some applications, the liquid fuel may be gasified prior to injection into the engine and/or ignited by diesel fuel (or another fuel or ignition source) before combustion. 
     One problem associated with pumps operating at cryogenic temperatures involves heat transfer to the fuel while inside the pump. In particular, moving components of the pump create heat through friction, and this heat (as well as ambient heat and/or heat from lubrication inside the pump) can be conducted to the fuel. If the fuel absorbs too much heat while in the pump, the fuel may gasify too early, thereby disrupting desired operation of the pump and/or the engine. 
     One attempt to improve pumping of a cryogenic liquid is disclosed in U.S. Pat. No. 2,837,898 (the &#39;898 patent) that issued to Ahistrand on Jun. 10, 1958. In particular, the &#39;898 patent discloses a swashplate type system having three pumping elements disposed within a container. The container is divided into a liquid chamber and a gas chamber. Connecting rods extend through a neck of the container and the gas chamber to each of the three pumping elements to reciprocatingly drive the pumping elements. A storage tank feeds liquid fuel to a bottom of the liquid chamber. The liquid chamber is connected to the gas chamber via a connecting line, and a gas return line returns vapors and/or liquid fuel from the gas chamber to a top of the storage tank. The level of liquid fuel in the gas chamber is self-adjusting, and remains above the three pumping elements. 
     While the system of the &#39;898 patent may reduce some heat transfer to the liquid fuel by positioning the gas chamber above the pumping elements, it may still be less than optimal. In particular, the &#39;898 patent may require a large container to accommodate both of the liquid and gas chambers, which may be difficult to package in some applications and also expensive. Further, the pumping elements themselves may generate heat that is still conducted into the liquid. 
     The disclosed fluid system is directed to overcoming one or more of the problems set forth above. 
     SUMMARY 
     In one aspect, the present disclosure is directed to a pumping mechanism including a barrel assembly having a plunger bore. The plunger bore has a longitudinal axis. The pumping mechanism also includes a plunger configured to slide within the plunger bore parallel to the longitudinal axis. The pumping mechanism further includes a push rod separate from the plunger. The push rod is configured to move away from the plunger to be spaced from the plunger, and the push rod is further configured plunger. 
     In another aspect, the present disclosure is directed to a pump including a reservoir configured to store a fluid and at least one pumping mechanism at least partially disposed in the reservoir. The at least one pumping mechanism includes a barrel assembly having a plunger bore. The plunger bore has a longitudinal axis and is fluidly connected to the reservoir. The at least one pumping mechanism also includes a plunger configured to slide within the plunger bore along the longitudinal axis in a first direction and in a second direction opposite the first direction. The at least one pumping mechanism further includes a push rod separate from the plunger, and the push rod is configured to move away from the plunger to allow the plunger to move in the first direction. The push rod is further configured to move within the plunger bore to push the plunger in the second direction to direct the fluid to a discharge passage of the pump. 
     In another aspect, the present disclosure is directed to a fluid system including a storage tank configured to store a fluid, a pump fluidly connected to the storage tank to receive the fluid, and a boost pump configured to pressurize the fluid to communicate the fluid from the storage tank into the pump. The pump includes a reservoir configured to store the fluid pressurized by the boost pump and at least one pumping mechanism at least partially disposed in the reservoir. The at least one pumping mechanism includes a barrel assembly including a plunger bore. The plunger bore has a longitudinal axis and is fluidly connected to the reservoir. The at least one pumping mechanism also includes a plunger configured to slide within the plunger bore along the longitudinal axis in a first direction and in a second direction opposite the first direction, and a push rod separate from the plunger. The push rod is configured to move away from the plunger to allow the plunger to move in the first direction due to a pressure from the fluid pressurized by the boost pump. The push rod is also configured to move within the plunger bore to push the plunger in the second direction to direct the fluid to a discharge passage of the pump. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of a fluid system including a pump, according to an exemplary embodiment; 
         FIG. 2  is a perspective view of a manifold of the pump of  FIG. 1 ; 
         FIG. 3  is a top view of the manifold of the pump of  FIG. 1 ; 
         FIG. 4  is a cross-sectional view of the pump of  FIG. 1 ; 
         FIG. 5  is a cross-sectional view of a pumping mechanism of the pump of  FIG. 1 ; and 
         FIG. 6  is another cross-sectional view of the pump of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now he made in detail to exemplary embodiments, which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
       FIG. 1  illustrates a fluid system  10  that may be used to supply a pressurized fluid. In an embodiment, the fluid system  10  may be a fuel system used to provide a pressurized fuel, such as a cryogenic fluid, to a power source, such as an engine  12 , which may be a gaseous fuel powered internal combustion engine. It is understood, however, that the disclosed embodiments may apply to other engines that utilize gaseous fuel. 
     In an embodiment, the fluid system  10  may include a storage tank  14 , a boost pump  16 , and a pump  100 . The storage tank  14  may store fuel as a fluid, e.g., a liquid fuel (LNG) and/or gaseous fuel. The boost pump  16  may pump the fuel, e.g., LNG, from the storage tank  14  to the pump  100  and may generate a low-pressure fluid discharge for supplying to the pump  100 . The pump  100  may be mechanically driven by an external source of power (e.g., a combustion engine, such as the engine  12 , or an electric motor) to generate a high-pressure fluid discharge for supplying to the engine  12 . Thus, the boost pump  16  may be a low-pressure pump, and the pump  100  may be a high-pressure pump. The pump  100  may discharge the fuel, e.g., LNG, intended to be consumed by the engine  12 . It is contemplated, however, that the pump  100  may alternatively or additionally be configured to pressurize and discharge a different fluid, such as a different cryogenic fluid, if desired. For example, the cryogenic fluid may be liquefied helium, hydrogen, nitrogen, oxygen, or another fluid known in the art. 
     An inlet line  30  may fluidly connect the boost pump  16  to the pump  100  to direct fuel, e.g., LNG, pressurized by the boost pump  16  to the pump  100 . One or more devices for controlling the flow of fuel may be disposed in the inlet line  30 , such as a shut-off valve  32  to stop the flow of fuel to the pump  100 . A filter  34  may be disposed in the inlet line  30  to filter the fuel directed to the pump  100 . One or more sensors  36  or monitoring devices may be disposed in the inlet line  30  to determine at least one parameter relating to the fuel directed to the pump  100 , such as temperature and/or pressure, e.g., to control the fluid system  10 . For example, the sensor  36  may monitor the pressure of the fuel to control the boost pump  16  to ensure that the boost pump  16  is pressurizing the fuel to a desired pressure or range of pressures. A vent valve  38  may be disposed in the inlet line  30  to permit the removal of fuel from the inlet line  30 , e.g., after shutting down the fluid system  10  and/or the engine  12 . The shut-off valve  32  and the vent valve  38  may be manually operated by an operator. 
     A discharge line  40  may fluidly connect the pump  100  to the engine  12  to direct fuel pressurized by the pump  100  to the engine  12 . One or more devices for controlling the flow of fuel to the engine  12  may be disposed in the discharge line  40 . In addition, a heater  42  may be disposed in the discharge line  40  to convert the fuel, e.g., LNG, to a gaseous state. An accumulator  44  may be disposed in the discharge line  40  downstream of the heater  42  to store the gaseous fuel, e.g., before starting the engine and/or when priming the pump  100 . The accumulator  44  may serve as a reservoir to ensure that fuel of adequate pressure is available to the engine  12 . In addition, an injection system. (not shown) may deliver the gaseous fuel to the engine  12 . 
     A leakage line  50  and a bypass line  60  may also fluidly connect the pump  100  to the storage tank  14  to direct fuel from the pump  100  to the storage tank  14 , as described below. As shown in  FIG. 1 , the leakage line  50  and the bypass line  60  may combine before connecting to the storage tank  14 . A regulating valve  62  may be disposed in the bypass line  60  to control an amount of fuel, e.g., liquid and/or gaseous fuel, directed from the pump  100  to the storage tank  14 . In an embodiment, the regulating valve  62  may control the amount of fuel based on a pressure of the fuel in the storage tank  14 , e.g., to be within a range of the pressure of the fuel in the storage tank  14 , such as within approximately 5 to 1,000 kPa. Alternatively, in place of the regulating valve  62 , the bypass line  60  may include an orifice of a fixed size for controlling the amount of fuel directed from the pump  100  to the storage tank  14  via the bypass line  60 . One or more sensors  64  or monitoring devices may be disposed in the bypass line  60  to determine at least one parameter relating to the fuel in the bypass line  60 , such as temperature and/or pressure, e.g., to control the fluid system  10 . For example, the sensor  64  may monitor the temperature of the fuel in the bypass line  60  to control when to start and/or stop priming the pump  100 . 
     A pressure relief valve  66  may be fluidly connected to the bypass line  60  to release pressure to the atmosphere in the event that the pressure of the fuel in the bypass line  60  exceeds a threshold. For example, when a component in the fluid system  10  fails (e.g., if the regulating valve  62  gets stuck in the closed position), then the pressure may increase high enough to break a component in the fluid system  10  and/or cause a failure in the fluid system  10 . Also, if the fluid system  10  is shut off when there is liquid fuel present in the bypass line  60  and the liquid fuel is heated, the pressure in the bypass line  60  may increase high enough to break a component in the fluid system  10  and/or cause a failure in the fluid system  10 . 
     The pump  100  may be generally cylindrical and divided into two ends. For example, the pump  100  may be divided into an input or warm end  102 , in which a driveshaft  104  is supported, and an output or cold end  106 . The cold end  106  may be further divided into a reservoir section  120  and a manifold  200 . Each of these sections may be generally aligned with the driveshaft  104  along a common axis  110 , and connected end-to-end. With this configuration, a mechanical input may be provided to the pump  100  at the warm end  102  (i.e., via the driveshaft  104 ), and used to generate a high-pressure fluid discharge at the opposing cold end  106 . In most applications, the pump  100  will be mounted and used in the orientation shown in  FIG. 1  (i.e., with the reservoir section  120  being located gravitationally lower than the manifold  200 ). 
     The warm end  102  may be relatively warmer than the cold end  106 . Specifically, the warm end  102  may house multiple moving components that generate heat through friction during operation. In addition, the warm end  102  may be connected to the power source, and therefore may result in heat being conducted from the power source into the pump  100 . Further, if the pump  100  and the engine  12  are located in close proximity to each other, air currents may beat the warm end  102  via convection. Finally, fluids (e.g., oil) used to lubricate the pump  100  may be warm and thereby transfer heat to the warm end  102 . In contrast, the cold end  106  may continuously receive a supply of fluid having an extremely low temperature. For example, LNG may be supplied to the pump  100  from an associated storage tank storing LNG at temperatures of, e,g., about −100 to −162° C. In some embodiments, LNG may be supplied to the pump  100  at less than about −140° C. or less than about −120° C. This continuous supply of cold fluid to the cold end  106  may cause the cold end  106  to be significantly cooler than the warm end  102 . If too much heat is transferred to the fluid within the pump  100  from the warm end  102 , the fluid may gasify within the cold end  106  prior to discharge from the pump  100 , thereby reducing an efficiency of the pump  100 . 
     The pump  100  may be an axial plunger type of pump. In particular, the driveshaft  104  may be rotatably supported within a housing (not shown), and connected at an internal end to a load plate  112 . The load plate  112  may be oriented at an oblique angle relative to the axis  110 , such that an input rotation of the driveshaft  104  may be converted into a corresponding undulating motion of the load plate  112 . A plurality of tappets (not shown) may slide along a lower face of the load plate  112 , and a push rod  114  may be associated with each tappet. In this way, the undulating motion of the load plate  112  may be transferred through the tappets to the push rods  114  and used to pressurize the fluid passing through the pump  100 . A resilient member (not shown), for example a coil spring, may be associated with each push rod  114  and configured to bias the associated tappet into engagement with the load plate  112 . Each push rod  114  may be a single-piece component or, alternatively, comprised of multiple pieces, as desired. Many different shaft/load plate configurations may be possible, and the oblique angle of the driveshaft  104  may be fixed or variable, as desired. 
     The reservoir section  120  may include a close-ended jacket  122  connected to the manifold  200  (e.g., to a side of the manifold  200  opposite the warm end  102 ), by way of a gasket  126  and/or pressure-assisted seal, to form an internal enclosure or reservoir  124 . The reservoir  124  may be in fluid communication with the inlet line  30  via the manifold  200 , as described below. In the disclosed embodiment, the jacket  122  may be insulated, if desired, to inhibit heat from transferring inward to the fluid contained therein. 
     The manifold  200  may perform several different functions. In particular, the manifold  200  may function as a guide for the push rods  114 , as a mounting pad for one or more pumping mechanisms  300 , and as a distributor/collector of fluids for the pumping mechanism(s)  300 . In the exemplary embodiment, the pump  100  has five pumping mechanisms  300 , but it is understood that there may be more or fewer than five pumping mechanisms  300 . The pumping mechanisms  300  may be connected to the manifold  200  and extend into the reservoir  124 . 
       FIGS. 2 and 3  illustrate the manifold  200 , according to an exemplary embodiment. The manifold  200  may include a first side  202  and a second side  210  opposite the first side  202 . A peripheral surface  220  of the manifold  200  may extend between the first side  202  and a second side  210 . In the embodiment shown, the manifold  200  has a circular profile when viewed from the top view of  FIG. 3 , but it is understood that the manifold  200  may have a non-circular profile, such as a square, rectangular, polygonal, or irregular profile. 
     The second side  210  may include a base  212  connected to the warm end  102 , and the first side  202  may include a raised portion  204  extending from the base  212 . The raised portion  204  may be at least partially inserted into the open end of the jacket  122 , as shown in  FIGS. 1, 4, and 5 , to assist in providing a seal between the jacket  122  and the manifold  200 . 
     The raised portion  204  may include a surface  205  that faces the reservoir  124  when the manifold  200  is connected to the reservoir section  120 . On the side of the base  212  opposite the raised portion  204 , the base  212  may include a surface  214  facing the warm end  102  of the pump  100 . Surfaces  205  and  214  may be located on opposite sides of the manifold  200  relative to the axis  110  when disposed in the pump  100 . 
     The base  212  may also form a flange that extends outward from a periphery of the raised portion  204 . One or more mounting bores  216 , e.g., twelve mounting bores  216  as shown in  FIGS. 2 and 3 , may be formed on the flange and may receive one or more fasteners  218 . The flange of the base  212  may be connected to a flange of the jacket  122  using fasteners  218 , with the gasket  126  sandwiched between the flanges. 
     The manifold  200  may include a plurality of push rod guide bores  206  configured to receive the respective push rods  114 . The push rod guide bores  206  may extend through surface  205 , and may extend between surfaces  205  and  214  of the manifold  200 . As shown in  FIG. 3 , the push rod guide bores  206  may be disposed radially around the center of surface  205 , e.g., radially spaced at generally equal intervals. 
     The manifold  200  may include a plurality of passages configured to fluidly communicate fuel between the storage tank  14 , the pump  100 , and the engine  12 . In an embodiment, the manifold  200  may have formed therein a common inlet passage  230 , a high-pressure discharge passage  240 , a leakage passage  250 , and a bypass passage  260 . It should be noted that the inlet passage  230 , the discharge passage  240 , the leakage passage  250 , and the bypass passage  260  are not shown in any particular orientation in  FIGS. 1-3 . 
     The inlet passage  230  may include an inlet  232  that may be fluidly connected to the inlet line  30  so that the inlet  232  may receive fuel pumped from the storage tank  14  using the boost pump  16 . The inlet  232  may be disposed on the peripheral surface  220  of the manifold  200 , as shown in  FIGS. 2, 3, and 6 . Alternatively, the inlet  232  may be disposed on any surface of the manifold  200  outside surface  205 , such as surface  214 . The inlet passage  230  may also include an outlet  234  that may extend through surface  205  so that the fuel pumped from the storage tank  14  may be supplied to the reservoir  124 . In an embodiment, surface  205  may include a recess  208  located near or adjacent a center of the surface  205 , and the outlet  234  may be disposed in the recess  208 . Alternatively, the inlet passage  230  may be disposed in the jacket  122  rather than the manifold  200 , and may fluidly connect to the inlet line  30  to direct fluid from the inlet line  30  to the reservoir  124  contained in the jacket  122 . 
     The inlet passage  230  may be formed by one or more linear bores (e.g., extending along a generally straight line). For example, the inlet passage  230  may be formed by drilling a first linear bore to a desired length into the base  212  starting at the desired location of the inlet  232  and drilling a second linear bore into the raised portion  204  starting at the desired location of the outlet  234  until the second linear bore intersects the first linear bore. The first linear bore that forms the inlet  232  may extend radially toward the center of the base  212  and between a pair of adjacent mounting bores  216 . Alternatively, the second linear bore may be drilled to a desired length and then the first linear bore may be drilled until the first linear bore intersects the second linear bore. By drilling the linear bores until they intersect, the inlet passage  230  may be formed without creating extra holes in the outer surface of the manifold  200 , which may need to be plugged. As a result, the time and cost to form the manifold  200  may be reduced. 
     The discharge passage  240  may include one or more inlets  242  that may be fluidly connected to the pumping mechanisms  300  so that the inlet(s)  242  may receive fuel pumped from the pumping mechanisms  300 . In the exemplary embodiment, the discharge passage  240  has five inlets  242  corresponding to the number of pumping mechanisms  300 , but it is understood that there may be more or fewer than five inlets  242 , depending on the number of pumping mechanisms  300  in the pump  100 . The inlets  242  may be disposed in surface  205  as described below to receive fuel pumped by the pumping mechanisms  300 , which are mounted onto surface  205 . The inlets  242  may be disposed farther from the center of surface  205  (and/or the center of the raised portion  204 ) than the outlet  234  of the inlet passage  230 . As shown in  FIG. 3 , the inlets  242  may also be disposed radially around the recess  208  and/or the center of the surface  205  (and/or the center of the raised portion  204 ), e.g., radially spaced at generally equal intervals. 
     The discharge passage  240  may also include a common outlet  244  fluidly connected to discharge the high-pressure fuel received from the inlets  242  out of the pump  100 . The outlet  244  may be fluidly connected to the discharge line  40  so that the outlet  244  may direct the pumped fuel to the engine  12 . In the embodiment shown in  FIGS. 2 and 3 , the outlet  244  may be disposed on the peripheral surface  220  of the manifold  200 . Alternatively, the outlet  244  may be disposed on any surface of the manifold  200  outside surface  205 , such as surface  214 . 
     The discharge passage  240  may also include a plurality of connecting branches  246  that fluidly connect the inlets  242  to a common outlet branch  248  in a tree-shaped configuration. The inlets  242  and the connecting branches  246  may connect in parallel to the outlet branch  248 . The outlet branch  248  may combine the flow of fuel from the connecting branches  246  and direct the combined flow to the outlet  244 . Each of the connecting branches  246  and the outlet branch  248  may be formed by linear bores. For example, the outlet branch  248  may be formed by drilling a linear bore into the base  212  of the manifold  200  starting at the desired location of the outlet  244  on the peripheral surface  220  until reaching a desired length of the outlet branch  248 . The linear bore forming the outlet branch  248  may extend radially toward the center of the base  212  and between a pair of adjacent mounting bores  216 . Each of the connecting branches  246  may be formed by drilling a linear bore into the raised portion  204  starting at the desired location of the respective inlet  242  on surface  205  until the linear bore intersects the outlet branch  248 . Alternatively, the connecting branches  246  may be drilled to a desired length and then the outlet branch  248  may be drilled until the bore intersects each connecting branch  246 . By drilling the linear bores until they intersect, the discharge passage  240  may be formed without creating extra holes in the outer surface of the manifold  200 , which may need to be plugged. In addition, the connecting branches  246  may be formed perpendicular to the outlet branch  248  when viewed from the top view of  FIG. 3 . As a result, the time and cost to form the manifold  200  may be reduced, and the flow path for the high-pressure fuel may be relatively more direct and less complex. 
     The leakage passage  250  may fluidly connect to the push rod guide bores  206  to receive fuel, e.g., liquid and/or gaseous fuel, leaking from the pumping mechanisms  300  mounted to the manifold  200 . The leakage passage  250  may include a common outlet  254  that may be fluidly connected to the leakage line  50  to direct the leaked fuel from the pumping mechanisms  300  back to the storage tank  14 . In the embodiment shown in  FIGS. 2 and 3 , the outlet  254  may be disposed on the peripheral surface  220  of the manifold  200 . Alternatively, the outlet  254  may be disposed on any surface of the manifold  200  outside surface  205 , such as surface  214 . 
     The leakage passage  250  may include connecting branches  256  that fluidly connect the push rod guide bores  206  in a daisy chain configuration to form a loop. The connecting branches  256  may include inlets that fluidly connect to the respective push rod guide bores  206 . The push rod guide bores  206  and the connecting branches  256  may be disposed farther from the center of surface  205  (and/or the center of the raised portion  204 ) than the outlet  234  of the inlet passage  230  and/or the inlets  242  of the discharge passage  240 . As shown in  FIG. 3 , the push rod guide bores  206  may also be disposed radially around recess  208 , the center of surface  205  (and/or the center of the raised portion  204 ), and/or the inlets  242 , e.g., radially spaced at generally equal intervals. In the exemplary embodiment, the leakage passage  250  has five connecting branches  256  corresponding to the five push rod guide bores  206 , which corresponds to the number of pumping mechanisms  300 , but it is understood that there may be more or fewer than five connecting branches  256 , depending on the number of pumping mechanisms  300  in the pump  100 . 
     The leakage passage  250  may also include an outlet branch  258  that fluidly connects to one of the connecting branches  256  forming the loop. The outlet branch  258  may direct the flow of leaked fuel from the loop of connecting branches  256  to the outlet  254 . Each of the connecting branches  256  and the outlet branch  258  may be formed by linear bores. For example, each of the connecting branches  256  may be formed by drilling a first linear bore to a desired length into the raised portion  204  starting at one of the push rod guide bores  206  and drilling a second linear bore into the raised portion  204  starting at the adjacent push rod guide bore  206  until the second linear bore intersects the first linear bore. Each push rod guide bore  206 , or at least the end thereof, may have a sufficient width to allow the first and second linear bores to be drilled at an angle so that the first and second linear bores intersect to form an apex in the middle of the connecting branch  256 . The outlet branch  258  may be formed by drilling a linear bore into the base  212  of the manifold  200  starting at the desired location of the outlet  254  on the peripheral surface  220  until intersecting one of the connecting branches  256 . The linear bore forming the outlet branch  258  may extend radially toward the center of the base  212  and between a pair of adjacent mounting bores  216 . Alternatively, the outlet branch  258  may be drilled to a desired length and then the connecting branches  256  may be drilled such that one of the connecting branches  256  intersects the outlet branch  258 . By drilling the linear bores until they intersect, the leakage passage  250  may be formed without creating extra holes in the outer surface of the manifold  200 , which may need to be plugged. As a result, the time and cost to form the manifold  200  may be reduced. 
     The bypass passage  260  may include an inlet  262  that may extend through surface  205  so that fuel, e.g., liquid fuel, may be directed from the reservoir  124  back to the storage tank  14 , as will be described below. The inlet  262  may extend through surface  205  and may be located farther from the center of surface  205  (and/or the center of the raised portion  204 ) than the outlet  234  of the inlet passage  230 , the inlets  242  of the discharge passage  240 , the push rod guide bores  206 , and/or the connecting branches  256  of the leakage passage  250 . 
     The bypass passage  260  may also include an outlet  264  that may be fluidly connected to the bypass line  60  to direct the fuel from the reservoir  125  to the storage tank  14 . The outlet  264  may be disposed on the peripheral surface  220  of the manifold  200 , as shown in  FIGS. 2, 3, and 5 . Alternatively, the outlet  264  may be disposed on any surface of the manifold  200  outside surface  205 , such as surface  214 . 
     The bypass passage  260  may be formed by one or more linear bores. For example, the bypass passage  260  may be formed by drilling a first linear bore to a desired length into the base  212  starting at the desired location of the outlet  264  and drilling a second linear bore into the raised portion  204  starting at the desired location of the inlet  262  until the second linear bore intersects the first linear bore. The first linear bore that forms the outlet  264  may extend radially toward the center of the base  212  and between a pair of adjacent mounting bores  216 . Alternatively, the second linear bore may be drilled to a desired length and then the first linear bore may be drilled until the first linear bore intersects the second linear bore. By drilling the linear bores until they intersect, the bypass passage  260  may be formed without creating extra holes in the outer surface of the manifold  200 , which may need to be plugged. As a result, the time and cost to form the manifold  200  may be reduced. 
     The linear bores that form the inlet  232  of the inlet passage  230 , the outlet  254  of the leakage passage  250 , the outlet  264  of the bypass passage  260 , and the outlet  244  of the discharge passage  240  may extend between different pairs of the plurality of mounting bores  216 . 
     As shown in  FIGS. 4-6 , each pumping mechanism  300  may include a barrel assembly  310  including a base or proximal end  312  and a distal end  314  opposite the proximal end  312 . The terms “proximal” and “distal” are used herein to refer to the relative positions of the components of the exemplary barrel assembly  310 . When used herein, “proximal” refers to a position relatively closer to the end of the barrel assembly  310  that connects to the manifold  200 . In contrast, “distal” refers to a position relatively further away from the end of the barrel assembly  310  that connects to the manifold  200 . 
     A majority of the outer surface of the barrel assembly  310  may be generally cylindrical and may have a longitudinal axis  316  extending between the proximal end  312  and the distal end  314 . The barrel assembly  310  may include a generally hollow barrel  318  formed at the proximal end  312  and a head  340  formed at the distal end  314 . The head  340  may be attached to the barrel  318  to close off the barrel  318 . Alternatively, the barrel assembly  310 , including the barrel  318  and the head  340 , may be formed integrally as a single component. 
     A plunger bore  320  may extend through the barrel  318  and may be configured to receive a plunger  330  for sliding within the plunger bore  320 . A distal end of the plunger bore  320  may form a chamber  322 , which may extend into the head  340 . A proximal end of the plunger bore  320  may also align with the push rod guide bores  206  in the manifold  200  such that the plungers  330  may slide proximally into at least a portion of the push rod guide bores  206 . The plunger bore  320  may extend generally parallel to the axis  316  of the barrel assembly  310 . The plunger bore  320  may have an axis that is collinear with the axis  316  of the barrel assembly  310 , which may be collinear with an axis of the barrel  318 . 
     The plunger  330  may include a main portion  332 , a distal portion  334 , and may form a shoulder  336  at the transition between the main portion  332  and the distal portion  334 . The shoulder  336  may be angled as shown in  FIG. 5 , or may form a step, curve, or other shape. The cross-section of the main portion  332  may be sized with respect to the cross-section of the plunger bore  320  such that the main portion  332  may slide within the plunger bore  320  without damaging the plunger bore  320  or the plunger  330 . In the embodiment shown in  FIG. 5 , the chamber  322  at the distal end of the plunger bore  320  may have a lateral dimension (e.g., an inner diameter or width) that is smaller than a lateral dimension of the proximal end of the plunger bore  320  through which the main portion  332  slides. The plunger bore  320  may form a transition portion  324  ( FIG. 5 ) at the transition between the smaller lateral dimension of the chamber  322  and the larger lateral dimension of the proximal end of the plunger bore  320 . As shown in  FIG. 5 , the transition portion  324  may be formed with a chamfer or angled edge to correspond to the angled shoulder  336  of the plunger  330 , or alternatively may form a step, curve, or other shape. In an embodiment, the chamber  322  having the smaller lateral dimension may be disposed in the head  340 , and the proximal end of the plunger bore  320  having the larger lateral dimension may be disposed in the barrel  318 . 
     The angled edge of the transition portion  324  of the plunger bore  320  may have an angle α ( FIG. 5 ) that is different from an angle β of the shoulder  336  of the plunger  330 . The difference in angles (angle differential) may be approximately 3° to 6°. For example, in an embodiment, the angled edge of the transition portion  324  of the plunger bore  320  may be formed at an angle α of approximately 40° relative to the axis  316  of the barrel assembly  310 , and the shoulder  336  of the plunger  330  may be formed at an angle β of approximately 45° relative to the axis of the plunger  330  (which may be collinear with the axis  316  of the barrel assembly  310 ), thereby resulting in an angle differential (e.g., the difference between angle a and angle β) of approximately 5°. Providing the angle differential may assist in preventing the plunger  330  from wedging into and sticking in the plunger bore  320  if the distal portion  334  of the plunger  330  slides into the chamber  322 . Alternatively, the angle α of the angled edge of the transition portion  324  may be substantially equal to the angle β of the shoulder  336 . 
     The cross-section of the distal portion  334  of the plunger  330  may be sized with respect to the cross-section of the chamber  322  such that the distal portion  334  may slide within the chamber  322  without damaging the plunger bore  320  or the plunger  330 . The distal portion  334  may have a lateral dimension (e.g., outer diameter or width) that is smaller than a lateral dimension of the main portion  332 . Alternatively, the chamber  322  and the distal portion  334  of the plunger  330  may have the same size and cross-section as the proximal end of the plunger bore  320  and the main portion  332  of the plunger  330 , respectively. 
     The head  340  may include at least one inlet passage  342  fluidly connected to the plunger bore  320  and configured to receive fuel from the reservoir  124 . In the exemplary embodiment, the head  340  has four inlet passages  342  disposed radially around the axis  316 , e.g., radially spaced at generally equal intervals, but it is understood that there may be more or fewer than four inlet passages  342 . Each inlet passage  342  may include an inlet adjacent to the distal end  314  and an outlet fluidly connected to the plunger bore  320  so that the plunger bore  320  receives fuel from the reservoir  124  via the inlet passages  342 . For example, the inlet of each inlet passage  342  may extend through the distal end  314 . 
     The reservoir  124  may receive fuel pressurized by the boost pump  16  via the inlet line  30  and the inlet passage  230  in the manifold  200 . The reservoir  124  may be completely or nearly completely filled with liquid fuel during a pumping operation. Accordingly, the outer surface of the barrel assembly  310 , e.g., the outer surfaces of the barrel.  318  and the head  340 , may be at least partially submerged within the liquid fuel during operation. Fuel may surround at least a portion of the outer surface of the barrel assembly  310  at the distal end  314 . For example, at least the distal end of the head  340  (e.g., at least the inlets of the inlet passages  342 ) may be located a distance below a liquid surface inside the reservoir  124 . The pump  100  may normally be packaged for use in the orientation shown in  FIGS. 1 and 4-6 , such that the manifold  200  may cover an opening of the jacket  122  to form the reservoir  124 . Therefore, the manifold  200  may form a ceiling of the reservoir  124 , and the jacket  122  may constitute a floor and walls thereof. 
     Each push rod  114  may extend through the push rod guide bores  206  in the manifold  200  into a corresponding barrel  318 . For example, each push rod  114  may include a distal end  116  that may contact and push the plunger  330  distally within the plunger bore  320 . The push rod  114  may separate and move away from the plunger  330 , as will be described below. 
     The barrel  31 $ and the head  340  may also form an outlet passage  350  fluidly connected to the plunger bore  320  and configured to receive fuel from the plunger bore  320 . The inlet passages  342  and the outlet passage  350  may open into the chamber  322  such that flow into and out of the chamber  322  may be controlled by an inlet check valve  344  and an outlet check valve  352  described below. 
     During normal operation of the pump  100 , the plunger  330  may slide between a Bottom-Dead-Center position (BDC) and a Top-Dead-Center (TDC) position within the plunger bore  320 . The head  340  may house valve elements that facilitate fuel pumping during the movement of the plunger  330  between BDC and TDC positions. In an embodiment, the head  340  may include the inlet check valve  344  associated with the inlet flow from the inlet passages  342 , and the outlet check valve  352  associated with outlet flow to the outlet passage  350 . Thus, the inlet passages  342  are fluidly connected to the plunger bore  320  via the inlet check valve  344 . 
     Due to the undulation of the load plate  112  during normal operation of the pump  100 , the push rod  114  may move away and be spaced from the plunger  330  (upward movement in  FIGS. 4 and 5 ). Due to the difference in pressure between the distal and proximal ends of the plunger  330 , the plunger may move from TDC to BDC (upward movement in  FIGS. 4 and 5 ). Specifically, pressurized fuel from the boost pump  16  (via the inlet line  30  and the reservoir  124 ) may unseat an element of the inlet check valve  344 , allowing the fuel to be directed into the plunger bore  320 . The pressure acting on the distal end of the plunger  330  is generally equal to the boost pressure of the pressurized fuel pumped from the boost pump  16  (via the inlet line  30 ), and the pressure acting on the proximal end of the plunger  330  is generally equal to the relatively lower tank pressure of the fuel stored in the storage tank  14  (via the leakage line  50 ). The pressure differential causes the plunger to move from TDC to BDC. Thus, the boost pump  16  provides pressure sufficient to lift the plunger  330 . 
     The undulation of the load plate  112  may also cause the push rod  114  to move toward and push against the proximal end of the plunger  330  (downward movement in  FIGS. 4 and 5 ). During the ensuing plunger movement from BDC to TDC (downward movement in  FIGS. 4 and 5 ), high pressure may be generated within the plunger bore  320  by the volume contracting inside the plunger bore  320 . This high pressure may function to reseat the element of the inlet check valve  344  and unseat an element of the outlet check valve  352 , allowing fuel from within the plunger bore  320  to be pushed out through the outlet passage  350 . Then during the next plunger movement from TDC to BDC, the element of the outlet check valve  352  may be reseated. One or both of the elements of the inlet check valve  344  and the outlet check valve  352  may be spring-biased to a particular position, if desired (e.g., toward their seated and closed positions). The fuel may be discharged from the plunger bore  320  through the outlet passage  350 , and the pressurized fuel from the outlet passages  350  of all of the pumping mechanisms  300  may be combined in the discharge passage  240  in the manifold  200  for discharge from the pump  100  via discharge line  40 . 
     During normal operation of the pump  100 , the plunger  330  and/or the plunger bore  320  may be configured so that the plunger  330  does not slide far enough within the plunger bore  320  to contact the transition portion  324  when the plunger  330  moves from BDC to TDC. If the plunger  330  does slide far enough to contact the transition portion  324 , the transition portion  324  may prevent the plunger  330  from contacting the inlet check valve  344 . The shoulder  336  of the plunger  330  may abut against the transition portion  324  to prevent the plunger  330  from sliding too far into the chamber  322 . 
     Further, the length of the distal portion  334  of the plunger  330  along the axis  316  and the length of the chamber  322  along the axis  316  may be configured so that the distal portion  334  and the inlet check valve  344  are far enough away from each other to avoid overlap between the normal ranges of motion of the plunger  330  and the inlet cheek valve  344 . The respective lengths of the distal portion  334  and the chamber  322  may also be configured so that the distal portion  334  and the inlet check valve  344  are close enough to each other to minimize the volume in the chamber  322 . For each stroke of the plunger  330  during normal operation of the pump  100 , the chamber  322  may contain an amount of fuel that is pressurized by the pumping mechanism  300 , but is not discharged through the outlet check valve  352  into the outlet passage  350 . The energy used to pump the fuel contained in the chamber  322  may be wasted. Therefore, minimizing the volume of the chamber  322  may minimize the amount of energy wasted by the pump  100 . Also, the fuel in the chamber  322  may be warmer and may transfer heat to the fuel in the next stroke. Warmer fuel may be less viscous, which may then result in more fuel leaking into the leakage passage  250  and a reduction in pump efficiency. Warmer fuel may also be less dense, which may also result in a reduction in pump efficiency. 
     Fuel may leak past the plungers  330  into the proximal ends of the respective plunger bores  320  due to the pressure differential between the pressure acting on the distal end of the plunger  330  and the pressure acting on the proximal end of the plunger  330 . The proximal ends of the plunger bores  320  may be fluidly connected to the respective push rod guide bores  206 , which may direct the leaked fluid to the leakage passage  250  in the manifold  200 . The leaked fuel from each of the pumping mechanisms  300  may be combined in the leakage passage  250  and directed back to the storage tank  14  via leakage line  50 , as described above. 
     The outlet passage  350  may be separate from the plunger bore  320  such that the plunger bore  320  and the outlet passage  350  form separate openings in the proximal end  312  of the barrel assembly  310 . In an embodiment, the outlet passage  350  may include a first portion  354  and a second portion  356 . The outlet check valve  352  may be disposed in the first portion  354 , and the second portion  356  may receive fuel from the first portion  354  via the outlet check valve  352 . The first portion  354  may extend from the plunger bore  320  toward the distal end  314  of the barrel assembly  310  at an acute angle with respect to axis  316 . The second portion  356  may be generally parallel to the plunger bore  320  and may form the opening of the outlet passage  350  adjacent to the proximal end  312  of the barrel  318 . For example, the opening of the outlet passage  350  may form the outlet of the outlet passage  350  and may extend through the proximal end  312  of the barrel  318 . The second portion  356  may be located closer to the outer surface of the barrel assembly  310  (e.g., the outer surface of the barrel  318  and the head  340 ) than the plunger bore  320 . 
     The pumping mechanisms  300  may be mounted in a radial configuration on the manifold  200 , e.g., radially spaced with respect to axis  110 . For example, the barrel assemblies  310  may be spaced at generally equal intervals around axis  110  and at a radial distance R ( FIG. 4 ) with respect to axis  110 . To mount each pumping mechanism  300  to the manifold  200 , the barrel assembly  310  may include one or more mounting bores  360  configured to receive one or more fasteners  362 . In the exemplary embodiment, the barrel assembly  310  has five mounting bores  360  configured to receive five fasteners  362 , but it is understood that there may be more or fewer than five mounting bores  360  and fasteners  362 . The mounting bores  360  may extend from the proximal end  312  to the distal end  314  of the barrel assembly  310 , and may be generally parallel to the plunger bore  320  and the second portion  356  of the outlet passage  350 . Each barrel assembly  310  may include a boss or other protrusion in which the outlet check valve  352  is disposed, and which extends from the head  340 , as shown in  FIGS. 1 and 4-6 . The boss may extend generally radially outward from the axis  316  of the barrel assembly  310  and distally from the distal end  314 . Also, to reduce the possibility for interference, each barrel assembly  310  may be rotated by about 15° or less so that the bosses may extend at an angle with respect to the line, connecting the axes  110  and  316  instead of pointing directly toward axis  110  of the pump  100 . 
     INDUSTRIAL APPLICABILITY 
     The disclosed fluid system and pump finds potential application in any fluid system where heat transfer to the fluid is undesirable and where priming of the pump is desired. The disclosed pump finds particular applicability in cryogenic applications, for example power system applications having engines that burn LNG fuel. One skilled in the art will recognize, however, that the disclosed pump could be utilized in relation to other fluid systems that may or may not be associated with a power system. Operation of the fluid system  10  and the pump  100  will now be explained. 
     Priming of the pump  100  may occur when the engine  12  is stopped or operating in a mode that does not depend on high-pressure fuel from the pump  100 , such as a diesel-only operating mode or a low-pressure gas spark-ignited operating mode. Priming of the pump  100  may be desired, for example, when the pump  100  is started after being inactive for an extended period of time. Due to the inactivity, the pump  1 . 00  may warm to temperatures that are less desirable for operation of the pump  100 , e.g., up to ambient temperatures. Therefore, priming of the pump  100  may be desirable to cool the pump  100  to a desirable operating temperature before the pump  100  may be started at normal operation to supply high-pressure fuel to the engine  12 . As a result, the likelihood of a pump failure due to thermal gradients in the pump  100  may be reduced. Also, the pump  100  may not operate as efficiently or at all if one or more of the components in the pump  100  are too hot. The heat may cause fuel in the pump  100  to vaporize and prevent the build-up of pressure in the chamber  322 . 
     The pump  100  may be cooled by allowing flow to circulate through the pump  100  using the inlet line  30 , the discharge line  40 , the leakage line  50 , and the bypass line  60 . To begin priming the pump  100 , the boost pump  16  may be started. Referring to  FIG. 1 , the boost pump  16  may supply fuel pressurized to a boost pressure from the storage tank  14  into the reservoir  124  via the inlet line  30 . During priming, the power source (e.g., the electric motor) for rotating the driveshaft  104  may remain shut down and inactive. As a result, the push rods  114  may also be inactive and held in position so that they do not push the plungers  330 , thereby causing the plungers  330  to be inactive. 
     Fuel pressurized by the boost pump  16  may flow from the reservoir  124  (e.g., through the inlet passages  342  and past the inlet check valves  344  in the barrel assemblies  310 ) into the barrel assemblies  310 . The fuel may then flow from the barrel assemblies  310  (e.g., past the outlet check valves  352  and through the outlet passages  350  in the barrel assemblies  310 ) to the discharge passage  240  in the manifold  200  and then to the discharge line  40 . As a result, fuel (including relatively colder fuel from the storage tank  14  via the inlet line  30  and the reservoir  124 ) may flow through the inlet passages  342  via the inlet check valves  344  and through the outlet passages  350  via the outlet check valves  352  in the barrel assemblies  310  to assist in cooling the inside of the barrel assemblies  310 . 
     Further, because relatively colder fuel from the storage tank  14  is entering the reservoir  124  via the inlet line  30 , the colder fuel may flow around the barrel assemblies  310  to cool the outside of the barrel assemblies  310 . Also, the second portions  356  of the outlet passages  350  may be located closer to the outer surfaces of the respective barrel assemblies  310  than the plunger bore  320 . As a result, the colder fuel flowing around the barrel assemblies  310  may cool the second portions  356  of the outlet passages  350 . 
     In the discharge line  40 , the heater  42  may beat the liquid to gaseous fuel, which may be stored in the accumulator  44 . The gaseous fuel may be stored in the accumulator  44 , and a valve (not shown) in the discharge line  40  may be closed to prevent the gaseous fuel from being supplied to the engine  12 . 
     When priming begins the pressure in the outlet passages  350  of the barrel assemblies  310  may be less than the boost pressure of the fuel supplied by the boost pump  16 . As fuel flows from the reservoir  124  through the barrel assemblies  310  during priming, the pump  100  may direct fuel to the accumulator  44  until the pressure in the outlet passage  350  and/or the discharge passage  240  in the barrel assemblies  310  is substantially equal to the boost pressure, e.g., the pressure of the fluid in the reservoir  124 . The pressures may be substantially equal when enough fuel accumulates downstream of the pump  100  to limit or stop additional fuel from flowing into the outlet passage  350 . The fuel may accumulate in lines or passages downstream from the outlet passage  350 , such as the discharge passage  240 , lines or passages fluidly connecting the pump  100  to the engine  12  (e.g., the discharge line  40  and/or the accumulator  44 , if included in the fluid system  10 ), and/or lines or passages in the engine  12 . The range of pressures that are considered “substantially equal” to the boost pressure may include pressures that are slightly less than the boost pressure and that result in stopping fuel flow into the outlet passage  350 . When the pressures are substantially equal, the outlet check valves  352  in the barrel assemblies  310  may close, thereby limiting or preventing fuel from flowing into the outlet passages  350 . 
     Excess liquid and/or vapor inside the reservoir  124  may be returned to the storage tank  14  via the bypass passage  260  in the manifold  200  and the bypass line  60 , e.g., to maintain a desired pressure within the reservoir  124 , as shown in  FIG. 6 . In this way, regardless of the usage rate of the fluid from the reservoir  124  and/or the supply rate of fluid to the reservoir  124 , the reservoir  124  may not be overfilled with fluid and the resulting pressure may be maintained at a desired level. The regulating valve  62  (or orifice) in the bypass line  60  may control the amount of flow directed to the storage tank  14  from the reservoir  124 . For example, the regulating valve  62  may maintain a certain difference in pressure between the storage tank  14  and the reservoir  124 . Therefore, the regulating valve  62  may adjust the pressure in the bypass line  60  based on the pressure of the fuel in the storage tank  14 . The fuel may flow into the reservoir  124  via the inlet line  30  and out of the reservoir  124  via bypass line  60 . As a result, fuel (including relatively colder fuel from the storage tank  14  via the inlet line  30  and the reservoir  124 ) may flow around the barrel assemblies  310  and cool the outside of the barrel assemblies  310 . 
     Thus, when priming the pump  100 , a first flow of fuel may be directed from the reservoir  124  into the discharge passage  240  of via the inlet passages  342  and the outlet passages  350  in the barrel assemblies  310 ) without pumping the first flow of fuel until the pressure in the outlet passage  350  and/or the discharge passage  240  is substantially equal to the boost pressure. Also, when priming the pump  100 , a second flow of fuel may be directed from the reservoir  124  into the bypass passage  260  and then returned to the storage tank  14 . 
     During priming, some of the fuel that flows from the reservoir  124  into the barrel assemblies  310  may leak past the plungers  330  in the plunger bores  320 . The leaked fuel may flow through the plunger bores  320  into the push rod guide bores  206  and the leakage passage  250  in the manifold  200 , and the leakage line  50  back to the storage tank  14 . As a result, the flow of fuel past the plungers  330  in the plunger bores  320  (including relatively colder fuel from the storage tank  14  via the inlet line  30  and the reservoir  124 ) may assist in cooling the inside of the barrel assemblies  310 . 
     After fuel stops flowing into the discharge passage  240  of the pump  100 , fuel may continue to flow into the reservoir  124  via the inlet line  30  and out of the reservoir  124  via bypass line  60  for a period of time, e.g., until the temperature of the fuel in the bypass line  60 , as measured by the sensor  64 , drops to a desired temperature, e.g., equal to or less than a threshold temperature. For example, the threshold may be approximately equal to or within an acceptable difference (e.g., 10° C. or less) from the temperature of the fuel in the storage tank  14 . For example, if LNG is stored in the storage tank  14  at about 140° C., the desired temperature may be about 130° C. or less. When the desired temperature is reached, priming of the pump  100  may end and normal operation of the pump  100  may begin. For example, during normal operation of the pump  100 , a pump controller (not shown) may start the power source (e.g., the electric motor), which may start up the drive mechanism (e.g., the driveshaft  104  and the load plate  112 ) configured to cause the plungers  330  to cyclically rise and fall within the barrel assemblies  310 , and then the pump  100  may pressurize fuel for directing to the engine  12 . The valve (not shown) in the discharge line  40  may be opened to allow the gaseous fuel to be injected into the engine  12 . 
     In an embodiment, flow may be directed from the reservoir  124  to the storage tank  14  continuously via the regulating valve  62  (or orifice) in the bypass line  60  during priming and normal operation of the pump  100 . Alternatively, the regulating valve  62  may be closed when priming ends (e.g., when the desired temperature is reached) and may remain closed during normal operation of the pump  100 . 
     During normal operation of the pump  100 , the driveshaft  104  may be rotated by the power source (e.g., the electric motor), which may cause the load plate  112  to undulate in an axial direction. This undulation may result in translational movement of the push rods  114 . As described above, the rotation of the driveshaft  104  in combination with the supply of fuel at boost pressure into the pumping mechanisms  300  may cause axial movement of the plungers  330  between TDC and BDC. Alternatively, other drive mechanisms may be provided, in place of the driveshaft  104  and the load plate  112 , to cause the push rods  114  to move translationally. 
     As the plungers  330  cyclically rise and fall within the barrel assemblies  310 , this reciprocating motion may function to allow liquid to flow from the reservoir  124  (e.g., through the inlet passages  342  and past the inlet check valves  344  in the barrel assemblies  310 ) into the barrel assemblies  310  and to push the fluid from the barrel assemblies  310  (e.g., past the outlet check valves  352  and through the outlet passages  350  in the barrel assemblies  310 ) at an elevated pressure. The high-pressure liquid may flow through the outlet passages  350  of the barrel assemblies  310 , the discharge passage  240  in the manifold  200 , and the discharge line  40  to be injected into the engine  12 . The pressure of the fluid that is output from the pump  100  via the discharge line  40  may be greater than the pressure of the fluid supplied from the boost pump  16 . 
     The manifold  200  may be formed as a single integral component that allows different paths of fluid flow to be routed between the reservoir  124 , the storage tank  14 , and the accumulator  44  or the engine  12  without individual lines, seals, clamps, or other components for forming the fluid connections during priming and normal operation of the pump  100 . The passages in the manifold  200 , such as the inlet passage  230 , the discharge passage  240 , the leakage passage  250 , and the bypass passage  260 , may be formed using intersecting linear bores that are positioned to avoid having to use plugs to prevent leakage from the passages, as described above. Also, the linear bores of the inlet passage  230 , the discharge passage  240 , the leakage passage  250 , and the bypass passage  260  may be positioned to avoid intersections between the different passages and to provide a design that may be easier to manufacture. Also, fuel flowing through the passages in the manifold  200  may assist in cooling the manifold and therefore the pump  100 . 
     The barrel assemblies  310  may be disposed in the pump  100  to provide a more compact design that may be less susceptible to failure due to thermal stresses. For example, flow may be discharged from the barrel assemblies  310  via the respective outlet passages  350 , which may be disposed in the barrel assemblies  310  parallel to the plunger bores  320 , instead of as individual lines or pipes that are external and connected to the barrel assemblies  310 . External pipes may have minimum bend radii requirements, which may cause the external pipes to take up more space. External pipes may also experience pressure waves, which may cause the pipes to vibrate and leak. Without external pipes, the barrel assemblies  310  may be formed with a lower overall number of connections and shorter routes for the fuel, and may provide a uniform and symmetric geometry that reduces thermal gradients. Also, the design of the barrel assemblies  310  may be relatively compact and may allow for a relatively smaller radial distance R for the barrel assemblies  310 . As a result, the overall size of the pump  100  may be smaller. 
     In addition, without external pipes, less surface area may be exposed to the fuel in the reservoir  124 , which may reduce heat transfer from the outlet passages  350  in the barrel assemblies  310  to the fuel in the reservoir  124 . The outlet passages  350  may receive fuel that may be relatively warmer during normal operation of the pump  100  than the fuel in the reservoir  124 . 
     The plungers  330  may be sealless, and at least the main portions  332  of the plungers  330  may have a uniform outer dimension (e.g., the outer diameter). The plungers  330  may also be formed as a single integral component, and a tight clearance may be formed between the plungers  330  and the respective plunger bores  320 . The plungers  330  may be formed without an external seal (e.g., a piston seal, such as a plastic or non-metallic component disposed on the outer surface of the plunger  330 ), which may wear and limit the life of the pump  100 . Alternatively, the plungers  330  may include the external seal or other type of seal. The plungers  330  may be connected to or disconnected from the distal ends  116  of the push rods  114 . When the plungers  330  are not connected to the push rods  114 , any side forces on the plungers  330  from the push rods  114  may be reduced or eliminated. This may reduce or eliminate wear, scuffing, and other damage on the plungers  330  and the plunger bores  320 . 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the pump of the present disclosure. Other embodiments of the fluid system and the pump will be apparent to those skilled in the art from consideration of the specification and practice of the fluid system and the pump disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.