Abstract:
A high pressure pump and delivery system mating to LNG storage and suited for natural gas powered trucks and buses, but also suitable for other cryogenic liquid fuels. The reciprocating pump is comprised of a liquid pumping portion and a vapor compressing portion, operating in concert so that it is possible to locate the pump above a source of saturated LNG and to reliably supply high pressure LNG. The delivery system provides a method of utilizing both the pumped LNG and the compressed NG in a Diesel type fuel injection system, and also to scavenge NG vapor from the LNG storage container so as to extend it&#39;s storage life. While especially useful for trucks and buses, the present invention is not limited thereto, as it is also useful for locomotives, automobiles and other vehicles designed to operate through combustion of natural gas, as well as stationary applications.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Not Applicable 
     STATEMENT OF FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
     Not Applicable 
     SEQUENCE LISTING 
     Not Applicable 
     BACKGROUND 
     Field of the Invention 
     This invention relates to the apparatus and methods suitable for very low Net Positive Suction Head (NPSH) cryogenic (and other low temperature boiling liquids) pump systems, either mobile or stationary, able to operate under a wide variety of liquid supply conditions. These conditions include where the pump is above, at or below the source of liquid; whether pumping to low or medium or high pressures; start-stop against discharge pressure; and from zero to low to high NPSH at the pump&#39;s intake. Thus it can operate under conditions including where NPSH varies during use from none, to little, to much while pumping. One example of such zero NPSH difficult pumping applications is where the pump is located above a saturated or near saturated cryogenic liquid source carried in a small tank located on a vehicle (the vibration of the vehicle/motor tending to destroy any liquid stratification or pressure building result), thus providing near zero Net Positive Suction Head (NPSH) or less at the intake of the pump&#39;s inlet conduit, a condition under which most known cryogenic pumps cannot reliably operate, especially as the tank becomes nearly empty. Furthermore, for many reasons, it may not be desirable to vent to the atmosphere vapor from the cryogenic or liquefied gas storage system; accordingly many traditional methods/techniques utilized in the cryogenic pump industry incorporating pressure building or similar techniques to provide prime or NPSH to a pump are not appropriate. A still further problem is that many such cryogenic systems are self-refrigerating, depending upon the repetitive delivery of cold liquid cryogen to provide the system&#39;s refrigeration needs, thus such pressure building methods are undesirable, as they add heat to the system. 
     One specific application where all these pumping abilities would be desirable is when using LNG (liquefied natural gas) as an on-board fuel for large trucks or buses (or other large mobile powered units), using a LNG fueled engine. Typically the LNG must be delivered by a LNG tank truck or rail car from the producing point to a bulk dispensing station having a large LNG storage vessel; from which the LNG is transferred into each truck&#39;s on-board fuel tank. Low pressure fuel storage tanks are desired so as to minimize their weight and costs. Then, as the truck&#39;s engine requires fuel, the LNG is vaporized and supplied to the engine at a pre-determined pressure, with the desired pressure being a function of the engine&#39;s specific design. Some engines are designed to operate at pressures below about 200 psig while others above about 2,000 psig, and still others at an intermediate pressure. One special difficulty presented at a LNG bulk station is that it is frequently desired for safety reasons to locate the LNG storage vessel underground and thus it is very inconvenient to locate a transfer pump underneath it, as is normal practice with many cryogens when stored in aboveground vessels. Depending upon a number of individual operational factors (and vessel design), the LNG in the underground vessel can be sub-cooled and/or pressurized and the vessel nearly full, thus offering substantial NPSH to an above-ground pump (once primed); or the opposite—at equilibrium conditions and an almost empty vessel, thus offering no NPSH to an above-ground pump; and accordingly the pump is subject to a variety of constantly changing, but normal, operating conditions. 
     Almost similar type difficulties and conditions are presented on the LNG fueled truck itself in providing NG to the engine. The most favored location on the truck or bus for the on-board fuel (LNG) tank(s) is low, and it would be inconvenient and unsafe to position a pump below the tank in an attempt to provide NPSH to the pump. In addition, the almost constant movement of a truck or bus (and of consequence the LNG fuel tank) causes the LNG throughout the tank to be at near equilibrium conditions, again making the provision of NPSH difficult. 
     Furthermore, it is desirable to be able to utilize as fuel nearly all the LNG in the tank, thus the ability to pump from a near empty fuel tank is desirable. A special difficulty of cryogenic and liquefied gas systems is that it is desirable to conserve the refrigeration potential of the stored liquid to the greatest extent possible, so that no venting of the cryogen or liquefied gas occurs, either when fuel is being used or when the truck is at rest; accordingly any heat conductive connections to the pump should be such that the heat leak caused by the pump is minimized. A still further difficulty is the wide range of fuel (LNG) supply rates required by trucks or buses and thus pumping capabilities required as the vehicle&#39;s engine goes from no use to idle to mid speed and to high speed in highly variable sequences on an as-needed basis. Different engines have different desired supply/injection pressures, but one current desire is to favor injection at higher pressures because of increased efficiency and reduced pollutants in the engine&#39;s exhaust gas. While it is theoretically possible to inject the LNG into the engine while in the liquid state (as with diesel fuel), the problems of variable volumetric efficiency associated with cryogenic pumps and the variation in LNG&#39;s density associated with its saturation pressure have made this unfeasible. Accordingly, designers have favored vaporizing the LNG after pumping it to the desired pressure and then supplying/injecting the natural gas (NG) to the engine as compressed natural gas (CNG). This typically requires a vaporizer (using the atmosphere and/or waste engine heat or other heat source) for warming the now pressurized LNG thus forming CNG, which is then stored in a small pressure vessel maintained between two pressures, the lower pressure of which is the minimum supply/injection pressure and the upper pressure of which is determined by system capabilities or other factors and delivered through a pressure regulator at the desired pressure; all controlled by a device to monitor the pressures and cause the pump to operate. 
     The U.S. Dept. of Energy (DOE) in a Small Business Innovation Research Program Solicitation No. DOE/ER0686 identified “Liquid Natural Gas Storage for Heavy Vehicles” as a technical topic in which DOE has a R &amp; D mission. In this Solicitation, on-board medium pressure (about 500 psig) and high pressure (about 3,000 psig) cryogenic pumps for LNG fueled vehicles were identified as specific areas where innovation was specifically desired. A related pump use is where it is desired to also be able to provide CNG or LNG at the bulk dispensing station for charging the truck&#39;s small pressure vessel or similar uses, thus a high pressure transfer pump is needed capable of pumping from a LNG source lower than itself (underground). 
     While LNG in mobile applications is used as an example herein, almost every cryogenic liquid being pumped from storage under conditions wherein a reduction in pressure below the liquid&#39;s equilibrium pressure or where the incursion of heat into the liquid, causes part of the intake liquid to vaporize would present similar difficulties. This includes cryogens which vaporize easily from heat incursion, and also liquefied gases, which while less sensitive to heat incursion, vaporize readily from a reduction in pressure. 
     These problems have generally been addressed by pumps characterized by the term “low NPSH” pumps. Included in previous low NPSH designs are U.S. Pat. No. 3,011,450 issued Dec. 5, 1961; U.S. Pat. No. 3,023,710 issued Mar. 6, 1962; U.S. Pat. No. 3,263,622 issued Aug. 2, 1966; U.S. Pat. No. 3,277,797 issued Oct. 11, 1966; and U.S. Pat. No. 6,006,525 issued Dec. 28, 1999—all to the present inventor. Also U.S. Pat. No. 5,188,519 issued Feb. 23, 1993 to I. S. Spulgis. In particular, these patents illustrate a type of reciprocating pumping mechanism where the intake valve is caused to open by the mechanical action of the piston rod retracting from a center opening in a hollow piston, a type of action commonly referred to as a “lost motion” action, as the piston does not move as far as does the piston rod. This mechanical opening of the intake valve reduces one principal need for NPSH, that of causing the intake valve to open by a reduction in pressure across it. In addition, if the intake valve is located above the compression chamber, vapor in the compression chamber can escape backwards by rising through the open intake valve. These designs require that the pumping chamber be located even with or lower than the source of liquid for optimum low NPSH service. 
     U.S. Pat. No. 5,411,374 issued May 2, 1999 to A. Gram represents a pump design able to be located above the supply container and able to pump saturated liquid from the container&#39;s bottom, a condition described by Gram as “negative feed pressure”. The pump essentially has a double acting piston removing vapor in the pump&#39;s inlet conduit at a rate sufficiently fast that liquid rises into the pump; as Gram states “by removing vapor from liquid in an inlet conduit faster than the liquid therein can vaporize by absorbing heat. . . ” However, absorbing heat is but one element in the source of vapor, as equilibrium liquid almost instantaneously releases vapor (and cools itself by evaporative cooling) as its pressure is reduced. In any event, the Gram pump is essentially a pump and/or compressor, handling intermittently under the different conditions that are encountered when pumping such liquids: all vapor, or vapor and liquid mixed, or all liquid. When handling all vapor it becomes a single stage compressor, with all the limitations—when compared to a single stage pump—of a single stage compressor, i.e.: greatly increased power; greatly increased heat generation (heat of compression); greatly reduced capacity; and greatly reduced possible pressure differentials. When handling vapor and liquid mixed (and at low NPSH or “negative feed pressure”), cavitation occurs and the pump&#39;s volumetric efficiency (and output) become unpredictably reduced, sometimes to the extent that vapor locking and pumping failure results, especially so when operating at compression ratios of about 10 or more. 
     U.S. Pat. No. 5,575,626 issued Nov. 19, 1996 to Brown et al is a pump submerged from the top into a container to the bottom. However, the mechanisms represent a serious and constant heat leak and the pump requires positive NPSH to open its spring loaded inlet valve. 
     U.S. Pat. No. 5,787,940 issued Aug. 4, 1998 to Bonn et al is a pump submerged from the top to the bottom of a separate sump attached to the storage vessel, so that the sump can be flooded with liquid when the pump is in use or not flooded when not in use, so as to reduce the heat leak when not operating. However, the heat gain to the system is substantial due to the heat leak to the sump and pump, even when not filled with liquid; and due to both the sump&#39;s and the pump&#39;s thermal masses, and the consequent warming of the liquid when it is desired to return the sump and pump to the proper operating temperatures. 
     U.S. Pat. No. 5,860,798 issued Jan. 19, 1999 to Tschopp is representative of a more common type of cryogenic pump having both spring loaded inlet and outlet valves. The pump is located below its supply container and two connections to the supply container allow liquid to flow down to the pump and vapor to flow back, due to gravity. However, this type of pump cannot pump from a liquid source that is lower than itself, and is not satisfactory at very low NPSH conditions. 
     U.S. Pat. No. 3,430,576 issued Mar. 4, 1969 to the present inventor is for a low NPSH liquefied gas (liquid carbon dioxide) pump having a spring loaded inlet valve, but creates a temporary increase in suction pressure (NPSH) at the inlet valve during the intake stroke, so as to temporarily provide sufficient NPSH to open the spring loaded inlet valve. Variations of this are also found in the &#39;626, the &#39;940, and the &#39;798 patents. All require that the liquid be supplied to the pump. 
     U.S. Pat. No. 5,593,288 issued Jan. 14, 1997 to Kikutani is a liquefied gas pump shown in a mobile LNG application, top mounted and submerged to the bottom of the storage vessel; having a leakage path during the initial phase of the compression stroke back to the storage tank intended to allow vapor (bubbles in the liquid) to escape the compression chamber during the initial phase of the compression stroke, and thus avoid cavitation. However, the amount of vapor or bubbles can vary due to a number of factors, and thus excessive bubbles (and liquid) or insufficient bubbles can be allowed to escape, interfering with desirable pump operation. 
     A container for a cryogenic liquid that is stationary can be referred to as a vessel, and one that is mobile can be referred to as a tank, and tanks are considered to be smaller than vessels, but these terms can be used interchangeably. 
     The definition of a cryogenic liquid as used herein is one found in “Cryogenic Engineering” by R. B. Scott, Van Nostrand Co. 1959 which is that it is a liquid whose critical temperature is below terrestrial temperatures, taken as minus 70° F. Examples include nitrogen, oxygen, argon, methane, hydrogen and natural gas, when in the liquid condition. 
     The definition of a liquefied gas as used herein includes cryogens but also substances (gases) when stored under conditions where the gas is in the liquid phase and where the storage temperature is below the ambient conditions there/then present. It can be a saturated liquid if it is at both the saturation temperature and pressure; it can be a sub-cooled liquid if the temperature of the liquid is lower than the saturation temperature for the existing pressure; and can be a compressed liquid if the pressure is greater than the saturation pressure for the temperature it is at. Examples include carbon dioxide, ammonia, and other low temperature refrigerants. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides a system and method for reliably pumping cryogenic liquids to low, medium or high pressures when the pump is located even with, above or remote from, its source of liquid and the liquid may or may not be saturated. The low NPSH pumping system and method of the present invention provide the suction lift required to bring a saturated liquid (but also less demanding condition liquid) to the pump, and are equally capable of pumping under zero, very low, medium or high NPSH conditions or conditions where the NPSH varies during pumping. The system and method also are able to remove any vapor created by the pumping action, thereby preventing vapor locking or damaging cavitation of the pump. The system and method also offers a number of desirable options for utilizing the removed vapor. As such, they provide the unique versatility necessary to meet the varying conditions encountered in many pumping applications. Depending upon the needs of the entire system the pump is part of, the vapor can be returned to the source container, either below or above the liquid level in that container, or supplied to a vapor using need external to the tank or vessel (such as NG to an engine or other need). 
     One key element of this system is recognition that the amount of vapor encountered when bringing such liquids to the pump and filling the compression chamber of the pump with a cryogenic liquid or liquefied gas can vary greatly (either increase or decrease). This variation can result from a number of causes, even while pumping, as they are a function of many factors, some of which are: condition or available NPSH of the inlet liquid resulting from storage or flow characteristics of the inlet conduit or other reason, and incoming liquid vaporizing upon contact with warmed pumping chamber elements, the result of frictions. Another factor is residual liquid in the clearance volume expanding to vapor upon the depressurization accompanying the suction stroke as a result of the heat of compression (greater at higher discharge pressures), all resulting in vapor in the inlet side of the pump, which needs to be removed in order to effect reliable high pressure pumping of saturated cryogenic liquids. 
     Another key element is purposeful vapor removal from a saturated cryogen or liquefied gas located within the inlet conduit of a pump so as to provide suction lift, by causing the remaining cryogen or liquefied gas in the conduit to be cooled by evaporative cooling, thereby providing the differential pressure required for the suction liquid lift for a pump located above, alongside or remote from, the liquid source; and to essentially empty the liquid source. This process is progressive as the liquid in the inlet conduit continues to rise, and also is progressive as new liquid enters the inlet conduit. The cooled cryogen or liquefied gas can continue to be cooled and provided with lift so long as vapor is removed and the resultant evaporative cooling occurs faster than any warming of the evaporative cooled liquid in the conduit. The volume increase occurring when many of these liquids become gas is typically greater than about 40 to 1 under normal storage conditions, so a relatively small volume of liquid becoming vapor can result in a great volume of vapor. While it varies some for each liquid and storage conditions, a lift of over about 10 ft. for some saturated cryogens can result in a greater volume of vapor than liquid. 
     Accordingly, a pump system is provided that is able to satisfactory function under a wide variety of conditions; instead of the opposite situation, where the conditions must be correct for the pump to operate properly. This eliminates many special conditions and limitations faced in the past at pump installations for the cryogenic liquids and liquefied gases, especially the lower temperature cryogenic liquids. In addition, the dual compressing/pumping nature of this pump uniquely satisfies the requirements of mobile LNG fuel supply for dual injection pressure Diesel type engines and also has the capability to extend the storage life of the on-board LNG storage. 
     It should be understood that while the invention is described as especially useful for certain LNG applications, there are many other pumping applications involving LNG and other cryogenic liquids or liquefied gases where the dual path arrangement for supplying and pumping liquid and removing vapor from the intake side of the pump and the intake liquid container and other elements of the invention would find valuable use. 
    
    
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
     FIGS. 1A,  1 B,  1 C and  1 D are simplified diagrammatic/sectional views of the invention incorporating both a low, medium or high pressure, lost motion type reciprocating piston pump and a gas/vapor compressor arranged to remove any vapor occurring at the pump&#39;s inlet area and to return any compressed vapor to the source liquid container, or to a use outside the container. 
     FIGS. 2A,  2 B and  2 C are simplified diagrammatic/sectional views of the pump of FIGS. 1A,  1 B,  1 C and  1 D installed above the source of liquid, as at a bulk LNG station (where the bulk LNG storage tank may be below ground level), and illustrating the various locations the compressed vapor may be supplied to. 
     FIGS. 3A and 3B are a diagrammatic/sectional partial views of the pump of FIGS. 1A,  1 B,  1 C and  1 D; but modified so as to be able to remove vapor from the ullage volume of the source liquid container, as well as that occurring at the pump&#39;s inlet area and also able to supply the compressed vapor to a use outside the source liquid container. 
     FIGS. 4A and 4B are simplified diagrammatic/sectional views of pump, modified in accordance with FIGS. 3A and 3B, installed on a truck or bus (not shown) using LNG as a source for fuel, with the pump above or alongside the on-board LNG tank and the compressed vapor from the pump being supplied to an LNG fueled engine, along with the vaporized/pumped liquid for supplying NG either at a single or at dual pressures for supply to or injection into the truck or bus engine. 
    
    
     In the drawings that follow, an arrow  represents a cryogenic liquid (or liquefied gas), an arrow with a circle following the head  represents the vapor phase of the cryogenic liquid, a double headed arrow  represents a cooled cryogenic liquid, a double headed arrow with a circle following the heads  represents a mixture of vapor and the liquid it cooled, a triple headed arrow  represents a compressed liquid and a triple headed arrow with a circle following the heads  represents a compressed vapor. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Shown in FIGS. 1A,  1 B,  1 C and  1 D is the pump of the present invention  10 ; having a cryogenic pumping portion  11  of the reciprocating mechanically opened intake valve/ lost motion type (depicted as a double lost motion type), also incorporating a separate vapor removal compressing portion  12  connected to the intake side of pumping portion  11 , and a drive portion  13 , all making it possible to pump to high pressures near equilibrium or saturated condition cryogenic liquids or liquefied gases from a source lower than the pump, and also useful for any other liquid conditions and pump or storage locations. The embodiment of the present invention illustrated in FIGS. 1A and 1B incorporates as pumping portion  11  a pump of the type described in U.S. Pat. No. 6,006,525 to the present inventor. 
     As best shown on FIG. 1A, pump  10  is comprised of cylindrical casing  14 , mounted at one end to a warm end plate  15 , as could be installed on a typical insulated cryogenic liquid storage tank  16  (or vessel  16 ′), on which the reciprocating drive and drive controls  13  are mounted. The single acting pumping portion  11  is just past the beginning of the its suction stroke, and the double acting vapor removal compressing portion  12  is both just past the beginning of a suction stroke and just past the beginning of a discharge stroke. While various drive arrangements can be used with the invention, the depicted drive  13  is a typical reciprocating hydraulic type. Drive  13  is arranged to transmit its reciprocating motion to a piston rod  18 . Suitably mounted near plate  15  and between the inside of casing  14  and rod  18  are warm end packing  20  and warm end guide bushing  22 . At the opposite end of casing  14 , pumping cylinder housing  24  is so connected and contained within lower casing  26 , so as to form sump  28 . Liquid inlet ports  30  and vapor outlet ports  32  provide openings in cylinder  24  for flow of cryogenic liquid  34 , and its vapor phase  35  occupying the space above the liquid phase  34 , with ports  30  and ports  32  acting as conduits between sump  28  and pump intake chamber  36 . Cryogenic liquid  34  is depicted at the bottom of vessel  16 , in sump  28  and in chamber  36 , with it&#39;s vapor  35  above, with appropriate arrows indicating liquid and vapor flows as pump  10  operates. Pump  10  is generally mounted either vertically or inclined, with the warm end higher than the cold end, so that liquid  34  readily tends to flow from sump  28  down through ports  30  into chamber  36  and vapor  35  readily tends to flow up through ports  32  from chamber  36  into sump  28 , all due to gravity, once sump  28  contains liquid  34  to a level at least between ports  30  and  32 . 
     A first cylindrical and hollow pumping piston  37  loosely fits over the cold end of rod  18 , so as to form a conduit between the outside of rod  18  and the inside of piston  37 . Pin  38  which is secured to piston  37  slidably engages and passes through slot  39  of rod  18 . Bushing  40  is fastened to rod  18  so as to loosely guide piston  37 , and contains serrations  41  as illustrated in FIG. 1B so as to not impeded flow of vapor  35  or liquid  34  through the conduit between rod  18  and piston  37 . 
     A second cylindrical and hollow pumping piston  42  fits loosely over piston  37  so as to form a conduit between the outside of piston  37  and the inside of piston  42 . Pin  44 , secured to piston  42  and slidably positioned in slots formed in piston  37  and bushing  40 , engages slot  46  of rod  18 . The cold end nose of rod  18  is tapered so as, when portion  11  is on it&#39;s compression stroke, it forms a seal with the also tapered inner nose section of piston  37  by compressing nose end seal  47 . The cold end outer nose of first piston  37  is similarly tapered so as, when pumping portion  11  is on it&#39;s compression stroke, it forms a seal by compressing nose end seal  48  with the tapered inner nose of piston  42 . These actions form the opening and closing of pumping portion  11 &#39;s intake valve mechanisms. 
     As the depicted liquid intake stroke begins, slot  39  and slot  46  are arranged so that pin  38  is engaged by slot  39  before pin  44  is engaged by slot  46 . Accordingly, the initial portion of the intake valve action to open is that located at seal  47 . This allows any vapor  35  in the pumping chamber  49  to escape by a dedicated path back to sump  28  before the principal liquid intake action begins through a separate path. Once pin  38  engages the bottom of slot  39 , rod  18  and piston  37  move simultaneously. This action causes piston  37  to rise with respect to piston  42 , so the next intake valve action to open is that located at seal  48 , Once both intake valve actions have occurred and pin  44  has engaged the bottom of slot  46 , piston  37  and piston  42  move as one unit through the remainder of the suction stroke. Liquid cryogen  34  then freely flows between pistons  37  and  42  and into chamber  49 , essentially unimpeded by vapor  35  egressing chamber  49  between piston  37  and rod  18 . As influenced by rod  18 , pins  38  and  44 , pistons  37  and  42  then move simultaneously to Top Dead Center, where the suction stroke ends and the compression stroke begins. 
     After Top Dead Center is passed, both intake valve mechanisms close in sequence, the first to close that formed by the tapered end of rod  18  and the tapered inner nose section of piston  37 , and then the second to close that formed by the tapered nose end of piston  37  and the tapered inner nose section of piston  42 , and then actual compression of liquid  34  and any attendant vapor  35  occurs in chamber  49 . Pumping chamber  49  is sealed along the exterior of piston  42  by combination bushing and high pressure sliding seals  50 . Upper discharge end plate  52  and lower discharge end plate  54  close chamber  49  and contain discharge check valve  56 . As rod  18 , pistons  37  and  42  then move simultaneously in the compressing stroke, pressurized liquid  34  flows through valve  56  and through discharge line  58 , which exits pump  10  through plate  15 , to use. 
     Vapor removal compressing portion  12  of pump  10  is comprised of a vapor removal piston  60 , which is slidably positioned within vapor removal housing  61 . Piston  60  features sliding seals  62  and is attached to rod  18  on both sides by retainer rings  63 , so that it, like the pumping portion  11 , also reciprocates in response to the action of drive  13 ; in one direction both a suction stroke for causing vapor to enter lower chamber  64 , and a compression stroke for discharging any vapor in upper chamber  65  (as depicted) and the reverse when moving in the other direction. Pump chamber  36  is separated from chamber  64  by lower chamber plate  66  and upper chamber plate  68  separates chamber  65  from the warm end of pump  10 . Lower chamber seals  69  are located in plate  66  and upper chamber seals  70  are located in plate  68 . Compression of vapor  35  by portion  12  occurs as controlled by lower suction check valve  71  and upper suction check valve  72  and lower discharge check valve  73  and upper discharge check valve  74 , all mounted to housing  61 . FIG. 1C depicts valves  71  and  72 , with clack  75  held against seat  76  by the action of spring  77  against retainer  78 . Retainer  78  is made of a material that is attracted by a magnet, and if retainer  78  is attracted sidewise by a magnet, clack  75  is held in a cocked position and is not able to close, thereby disabling (unloading) the compressing action of the chamber it serves (as depicted by the alternate center line). Other methods of unloading compressing portion  12  are well known in the compressor industry and can be substituted without departing from the present invention. 
     FIG. 1D is a simplified view along line A-A′ of FIG. 1A, showing the control elements and valves of vapor removal portion  12  of pump  10 ; at a time when sufficient liquid  34  is in sump  28 , but some vapor  35  is being released from chamber  49 . Valve  72  communicates with suction cavity  79 , which communicates with sump  28 . Valve  74  communicates with discharge cavity  80  and discharge vapor line  81  in turn. Accordingly, valve  72  communicates with the upper portion of sump  28 , containing float type level control  82 , which is equipped with magnet  84  that as control  82  rises, magnet  84  also rises and attracts suction valve  72  so that it is held open in the manner illustrated in FIG. 1C, by the magnetic action of control  82 . Magnet  84  is located so as to progressively disable the action of compressing portion  12  by disabling in turn, valve  71  and valve  72 , and thus compensate for the varying amounts of vapor  35  created in pumping portion  11  or arriving at sump  28  through seperator  88 , possibly from all vapor during pumping portion  11 &#39;s cool-down to no vapor when tank  16  (or vessel  16 ′) are full, or when there is NPSH available. If control  82  then rises to where the point that magnet  84  has attracted valve  71  so that it is cocked and remains open (disabled), but not valve  72 , thereby causing partial unloading of compressing portion  12 . If control  82  continues to rise, valve  72  is also attracted by magnet  84  so as to remain open, and no vapor  35  is removed from sump  28 . This condition results in compressing portion  12  becoming vapor trapped, so that no liquid  34  reaches valve  71  and valve  72 . If control  82  sinks, magnet  84  allows both valve  71  and valve  72  to function normally, and vapor  35  to be removed from sump  28  at the full capacity of compressing portion  12 . If desired, magnet  84  can be separated into two halves and each half so located in control  82  that the order in which valve  71  and valve  72  become disabled is reversed (not shown); or alternately valve  71  and valve  72  become disabled simultaneously (not shown). Other type known level controls can be substituted without departing from the present invention. 
     As shown in FIGS. 2A,  2 B and  2 C, discharge vapor line  81  can be extended, line  81   a  or line  81   b  or line  81   c , so as to direct any compressed vapor  35  to where it is most useful, depending upon the supply and use circumstances of the entire facility pump  10  is a part of. 
     FIG. 2A shows pump  10  as located above storage tank  16  (or vessel  16 ′), wherein pump  10  is inserted into tank  16  (or vessel  16 ′) through an opening in it&#39;s top, utilising plate  15  for mounting. A tank generally refers to a liquid container that in some fashion is (or can be) mobile, and vessel to a liquid container that is stationary. Line  58  takes the compressed liquid  34  to use (not shown). Inlet line  86  extends to near the bottom of tank  16  (or vessel  16 ′), so tank  16  (or vessel  16 ′) may be nearly emptied by pump  10 , and vapor return line  81   a  extends not quite as far as does line  86 , so that the returning vapor  35  does not unduly agitate the stored liquid  34  or dissipate any NPSH at the inlet of line  86 . When tank  16  (or vessel  16 ′) contains liquid  34  to a level above L-2, such as L-1, vapor  35  returning tends to be cooled as it bubbles up through liquid  34  so as to return to the vapor space in tank  16  (or vessel  16 ′). This action both reduces the volume of vapor  35  and warms liquid  34  as it bubbles through, as well as reducing any temperature related stratification of liquid  34  and consequent high pressure in tank  16  (or vessel  16 ′). Moreover, this warming of liquid  34  extends the fill life of tank  16  (or vessel  16 ′), as much of the heat gain of pump  10  and tank  16  (or vessel  16 ′) then tends to be removed with the pumped liquid  34 . When the level of liquid  34  falls to level L-2, such action would no longer occur. Pump  10  and tank  16  (or vessel  16 ′) are not shown to the same scale, as if tank  16  (or vessel  16 ′) is large, pump  10  benefits by being located in the ullage volume of tank  16  (or vessel  16 ′), thereby tending to remain cold during non-use, and not imposing as large a heat leak to the system. A small extension on the top of tank  16  (or vessel  16 ′) could be provided to accept pump  10  (not shown). 
     Turning next to FIG. 2B, typically used for larger vessels  16 ′, where it is frequently desired to mount a pump external to the vessel, pump  10  is connected in such a manner that pump  10  may be disconnected from vessel  16 ′ without depressurizing vessel  16 ′, even through liquid  34  may be in it. In this case, pump  10  can be mounted inclined (or vertical if preferred) inside an insulated enclosure  90 , and vapor line  81   b  may only extend partially below the safe fill line for vessel  16 ′. Line  58  takes the compressed liquid  34  to use (not shown). A spray header  92  is typically used during liquid replenishment, condensing vapor  35  with the cold, low pressure liquid  34  typically being supplied, so as to reduce the pressure of vessel  16 ′and thus prevent venting of vapor  35 . If desired, pump  10  could be remote from vessel  16 ′, including inlet line  86  being external to vessel  16 ′ and containing trap(s) (not shown). 
     Turning next to FIG. 2C, pump  10  is depicted as in FIG. 2A, except it is supplying both compressed vapor  35  with line  81   c , and pumped liquid  34  with line  58 , either to one use or to two uses, outside tank  16  or vessel  16 ′. 
     As can be seen from FIGS. 2A,  2 B and  2 C, the amount of lift, that is the distance from the point in tank  16  or vessel  16 ′ where the actual inlet of the line  86  occurs to the liquid level desired within sump  28  can vary with the dimensions of tank  16  or vessel  16 ′, as well as the method chosen to mount pump  10  to tank  16  or vessel  16 ′. For the same condition saturated or near saturated liquid, the greater this lift distance, the greater the capacity of compressing portion  12  of pump  10  should be. This occurs because the greater the lift, the higher the percentage of vapor formed in lifting saturated liquid by causing a reduced pressure, so as to produce the needed lift. Also, vapor is formed in the pump itself as caused by heat leak from pump  10 &#39;s surroundings and from residual heat caused by friction and from residual heats of compression, or other reasons. Thus the higher the discharge pressure of pumping portion  11  and to a lesser degree compressing portion  12 , the greater the quantity of vapor  35  formed. To accommodate such higher lifts and higher pressures, resulting in greater amounts of vapor  35  that is to be removed, the capacity of compressing portion  12  can be increased by increasing the diameters of chamber  64  and chamber  65 , piston  60  and casing  14 , and casing  26  to match. Vapor  35  returned to tank  16  or vessel  16 ′ by compressing portion  12  can be returned to about the top, about the middle, or about the bottom of tank  16  or vessel  16 ′ by line  81   a  or  81   b , as individual circumstances dictate as to any desired point of return inside tank  16  or vessel  16 ′ or outside tank  16  or vessel  16 ′ by line  81   c  to various uses (not shown). A foot valve (not shown) can be used with line  86 , if the dimensions and flow dynamics require such, so as to prevent back-flow of liquid  34  in line  86  when pump  10  is operating. 
     FIGS. 3A and 3B are simplified views of an alternate compressing portion  12 ′ of pump  10 ′, having an arrangement whereby vapor  35  is removed first from the sump  28  and then once sufficient vapor  35  has been removed from sump  28 , removes vapor  35  from the ullage volume of tank  16  (or vessel  16 ′), and the compressed vapor  35  is supplied to a use outside tank  16  (or vessel  16 ′), along with the pumped liquid  34 , with the discharge arrangements as depicted in FIG.  2 C. The removal of vapor  35  from the ullage volume of tank  16  or vessel  16 ′ has the desirable effect of extending the fill life of tank  16  or vessel  16 ′. 
     FIG. 3A depicts alternate float type liquid level control  96  arranged so as to change the source of vapor  35  supplying compressing portion  12 ′ from the top of sump  28  to the ullage volume of tank  16  (or vessel  16 ′), utilizing line  98  and valve  100 , which modulates the opening of line  98  in response to control  96 , so that whenever liquid  34  in sump  28  is at the desired level, compressing portion  12 ′ then removes vapor  35  from the ullage volume of tank  16  (or vessel  16 ′). Thus once the desired level of liquid  34  is present in sump  28 , the action of control  96  provides a conduit between the ullage volume of tank  16  or vessel  16 ′, and modulates the flow of vapor  35  through line  98  in response to the level of liquid  34  in sump  28  as sensed by control  96 , so as to provide sufficient vapor  35  to removal portion  12 ′. Should it be desired (not shown), a valve can be installed in line  98  so that flow of vapor from the ullage volume of tank  16  or vessel  16 ′ can be blocked and the functions of control  82  and control  96  combined so that valve  71  and valve  72  are disabled by the same means as described in FIGS. 1A,  1 C and  1 D in the event the flow of vapor  35  through line  98  is caused to cease. 
     FIG. 3B depicts valve  100  which modulates the size of the passageway in line  98  between sump  28  and the ullage volume of tank  16  (or vessel  16 ′). Sleeve  102  cooperates with control  96 , and is slidably attached to line  98 . Opening  104  in line  98  is closed by sleeve  102 , unless control  96  has risen, and caused sleeve  102  to also rise, to the extent that opening  106  in sleeve  102  is aligned with opening  104 , thereby allowing vapor  35  to flow through line  98  from the ullage volume of tank  16  (or vessel  16 ′) to sump  28 . 
     Turning next to FIGS. 4A and 4B, of special use when pump  10 ′ is utilized to supply the cryogen (LNG) as a gaseous fuel (NG) to engine  110  of truck  108 . The compressed vapor  35  and pressurized liquid  34  are warmed to about ambient temperature, either with waste heat from engine  110  or from ambient, then supplied to engine  110  of truck  108  as NG fuel. Tank  16  is shown mounted in saddle tank fashion from frame  112  to tractor type truck  108 , and between cab  114  and tire  116 . 
     FIG. 4A is a generalized view which depicts a case where engine  110  does not require NG fuel supplied at a pressure higher than about 500 psig. Pump  10 ′ is located above and mounted to tank  16  in a manner similar to that shown in FIG. 2C, with lines  58  and  81   c  exiting tank  16  through plate  15 . Pump  10 ′ is modified in accordance with FIGS. 3A and 3B and alternate control  96 , making it possible to also scavenge vapor  35  from the ullage volume of tank  16  through line  98 . After exiting tank  16 , lines  58  and  81   c  can be combined (not shown) or routed separately to vaporizers and use in engine  110  of truck  108 . In this case, fuel (NG) supply pressure required by engine  110  is less than about 500 psig, a pressure that compressing portion  12 ′ can readily provide if the pressure in tank  16  is above 50 psig, a normal condition. Accordingly, line  58  carrying pumped liquid  34  passes through vaporizer  120  to NG storage  122 , whose pressure is monitored by control  124 , which causes pump  10 ′ to operate when the pressure in storage  122  is below a pressure of about 750 psig and causes pump  10 ′ to cease operation when the storage pressure reaches a higher figure (about 1,000 psig), indicating engine  110  is requiring NG fuel at a slower rate than pump  10 ′ is supplying it. Pressure regulator  126  maintains line  128  at the desired supply pressure to engine fuel control  130 , which then supplies the NG fuel to engine  110 . Line  81   c  carrying compressed vapor  35  passes through vaporizer  132  to storage  134 , whose pressure is also monitored by control  124  and causes pump  10 ′ to cease operation if the pressure becomes excessive or will cause line  98  to close. Storage  134  utilizing line  136  by itself provides fuel (NG) to line  128  until the pressure in line  128  drops below the setting of pressure regulator  126 . When this ocurs, pressure regulator  126  opens so that NG fuel from storage  122  supplements the NG from storage  134   50  that the pressure in line  128  returns to the proper level. NG will be supplied to fuel control  130  through line  128  from both storage  134  and storage  122  until the pressure within storage  122  drops below approximately 750 psig. At that time, pump  10 ′ will be caused to operate so as to replenish both storage  134  and storage  122 . Storage  134  then returns to being the sole source of NG for line  128  after regulator  126  closes. Line  136  connects storage  134  with line  128 , so both the compressed vapor  35  and the pumped liquid  34  supply the fuel needs of engine  110 . Alternately, pump  10 ′ could be mounted to tank  16  in the manner illustrated in FIG.  2 B. FIG. 4B depicts a specific application utilizing pressurized and vaporized LNG as an on-vehicle fuel, wherein the unique capabilities of the present invention are displayed. Pump  137 , tank  138 , pressure control  140 , fuel injection control  142  and engine  144 , are installed on a large heavy duty truck or tractor truck  108  or intra-city bus (not shown) making multiple stops in a large, densely populated metropolitan area, using expressways for a portion of its run, such as the grater Los Angeles area. Pump  137  is as described in FIGS. 3A and 3B; having the ability to both pump liquid  34  to high pressure from tank  138  and when desired, to scavenge vapor  35  from the ullage volume of tank  138  so as to provide extended hold time for the LNG therein, without requiring a very high pressure capability for tank  138 . Management of the internal pressure of tank  138  and of the supply pressures to engine  144  is by system gas (NG) storage and control  140 ; which can change the speed of pump  137  (if drive portion  13  is so equipped), or stop or stop pump  137 ; block line  98 , open line  81   a  or  81   b  (not shown), and store a small amount of NG in gas storage at a suitable pressure for instant use as fuel in engine  144 . For the purposes of this example, engine  144  is Diesel cycle, fuel injected requiring about 3,000 psig NG when the engine is under heavy load and about 500 psig NG when under light load or idling; and the response to the operator&#39;s input is to be immediate. Pump  137  can be mounted to tank  16  in a similar manner to that depicted in FIG. 4A; but for space convenience and thermal isolation, is located alongside tank  138 , utilizing a head end opening in tank  138  for connecting insulated sump  145  into the top of which pump  137  is inserted. Pump  137  is modified in accordance with FIG.  3 A and FIG.  3 B. After exiting sump  145 , line  58  carrying liquid  34  pumped to a high pressure, passes through vaporizer  120 ′ to NG storage  122 ′, whose pressure is monitored by control  140 , which causes pump  137  to operate when the pressure in storage  122 ′ is below about 110% of the minimum selected high injection pressure (about 3,300 psig) and causes pump  137  to cease operation when the pressure in storage  122 ′ reaches a pressure about 120% higher than the selected minimum high injection pressure (about 3,600 psig), indicating engine  144  is requiring fuel at a slower rate than pump  137  is supplying. Pressure regulator  126 ′ maintains line  128 ′ at the selected high injection pressure to engine fuel control  142 , which then supplies the high pressure NG fuel for injection into Diesel engine  144  when required. Line  81   c  carrying compressed vapor  35  passes through vaporizer  132 ′ to storage  134 ′, whose pressure is also monitored by by control  140 . Regulator  150  maintains line  151  at the selected low injection pressure, supplying control  142 . In the event that a greater quantity of low pressure NG fuel is required than that available in storage  134 ′, regulator  152 , located in line  153 , supplies low pressure NG fuel from storage  122 ′, should the supply of NG from storage  134 ′ be insufficient. 
     A gas intensifier, which uses a higher pressure stream to raise the pressure of a lower pressure stream, and then joins it, can be added in either line  136  between storage  134  and line  128 , with high pressure gas supply from storage  122  (FIG. 4A) should a higher pressure compressed NG be desired than pump  10 ′ provides (not shown). Similarly, an intensifier can be added in line  151  between storage  134 ′ and the junction of line  153 , with high pressure gas supply from storage  122 ′ (FIG.  4 B), should a higher pressure compressed NG be desired than pump  137  provides (not shown). 
     Single lost motion pumps, such as U.S. Pat. Nos. 3,023,710 and 3,263,622 to the present inventor, have similar characteristics to the depicted double lost motion pump except there is only one piston. A number of low NPSH reciprocating piston pumps are available which provide assistance in opening the intake valve by inertia of the intake valve or momentary creation of a higher pressure regime at the entrance to the intake valve or by magnetic force or by a combination of these. Such pumps are able to reliably pump low NPSH, or very low NPSH cryogenic liquids as long as the pump&#39;s intake is covered with liquid and any vapor there is able to escape; and for the purposes of this invention, are all considered as benefiting the same as the depicted double lost motion pump. 
     Cryogenic liquids and liquefied gases are characterized by being typically stored under pressure above atmospheric. Some, (the cryogens) are manufactured at pressures only slightly above atmospheric, but are allowed to increase in pressure (by warming) in steps as the cryogen progresses along the distribution and use chain. Accordingly, pump  10 ,  10 ′ or  137  can be operating at a varying number of intake pressures, as the pressure in sump  28  relates to the pressure of the liquid in tank  16 , vessel  16 ′ or tank  138 . 
     Although the invention has been described with regard to what is believed to be the preferred embodiment, changes and modifications as would be obvious to one having ordinary skill in both pump design, cryogenic and liquefied gas engineering and compressed gas use can be made to the invention without departing from its scope. Particular features are emphasized in the claims that follows. The term conduit in the following claims should be interpreted broadly to include pipe, tube, valve and other devices used in the transfer of liquid or vapor.