Abstract:
A cryogen pump, including: a pump section that includes: a bellow with an inlet opening at a first end and an exit opening, the inlet opening in direct fluid communication with a volume of a cryogen, the exit opening at least in fluid communication with a second end of the bellow opposing the first end, a pair of plugs configured to sealingly close the opposing ends of the bellow, the pair of plugs cooperating so that when one plug sealingly closes one of the ends, the other end of the bellow is open; and a drive section configured to drive the pump section in a reciprocating manner so as to move the plugs.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    Embodiments of the present invention relate generally to cryogenic pumps and, more particularly, to submerged or insulated cryogenic pumps. 
         [0003]    2. Description of Related Art 
         [0004]    Handling cryogen fluid at, or slightly below its boiling temperature, which is well below room temperature, can be cumbersome due to the creation of two-phase Condition with any heat absorbed from the environment. Liquid nitrogen, as a cryogen, has additional handling difficulties associated with the Leidenfrost effect and the 700 fold volume expansion from liquid to gas. 
         [0005]    As is conventionally known, liquid nitrogen has characteristics that make it difficult to fill a volume. This difficulty is due to the Lindenfrost effect, by which a cushion of vapor results whenever the liquid comes into contact with a surface with a temperature higher than the boiling temperature. 
         [0006]    The change of pressure may be another source of difficulties related to the physical state of the fluid. First, it makes it difficult to press the fluid since gaseous phase is compressible. Second, other effect is behavior of liquid nitrogen under vacuum condition. It is very difficult to suck liquid nitrogen. Under vacuum conditions, the boiling temperature decreases, which make the surface temperature higher than the boiling temperature and the above-mentioned effect, come again into play. 
         [0007]    One approach to compensate for these issues is the strategic selection of components for fluid cryogenic system. 
         [0008]    Applying bellows for several fluid systems components is known. 
         [0009]    For example, bellow valves are disclosed in U.S. Patent Publication No. 2011/0067879 A1 and U.S. Pat. No. 4,838,462. Dispensing fluid from a bottle or container is disclosed in International Patent Publication Nos. WO 94/07113, and WO 97/15223. 
         [0010]    The application of a bellow for pumping liquid is disclosed in, for example, the following U.S. Pat. Nos. 3,598,505; 4,310,104; 4,817,688; 4,902,206; 5,165,866; 5,308,230; and 5,655,893. The application of a bellow for pumping liquid is also disclosed in, for example, the following U.S. Patent Publications: US2004/0265149 A1; US 2005/0031475 A1; 2006/0165541 A1; and 2011/0318207 A1, as well as International Patent Publication WO 01/91911 A1. 
         [0011]    Further, submerged pumps are disclosed in, for example, U.S. Pat. Nos. 4,472,946, and 4,860,545. A bellow submerged pump is disclosed in, for example, U.S. Pat. No. 7,192,426 B2. 
         [0012]    A vacuum bellows is disclosed in U.S. Patent Application No. 6,268,995 B1. 
         [0013]    In these examples of related art, the main emphasis was on the mechanisms for pumping force and efficiency of the motion. However the application of simple check valves for controlling the inlet and outlet fluid is common. 
         [0014]    The foregoing is intended to be illustrative discussion rather an exhaustive one. 
       BRIEF SUMMARY 
       [0015]    Embodiments of the present invention provide an approach by which the inlet valve and suction condition are eliminated. Filling of a cylinder or a bellow with the pumped cryogenic liquid such as liquid nitrogen is done by creating conditions of communicating vessels, i.e. by gravitational force, without suction, or the need to lower pressure in the cylinder or the bellow, bellow the atmospheric pressure, or the pressure of the filling tank. Additionally, embodiments of the present invention reduce or eliminate the effect of the ambient temperature by vacuum insulating the cylinder or the bellow, thus eliminating the need to submerge the pumping unit into the cryogenic liquid. 
         [0016]    An aspect of the present invention provides a cryogen pump having: a pump section that includes: a bellow with an inlet opening at a first end and an exit opening, the inlet opening in direct fluid communication with a volume of a cryogen, the exit opening at least in fluid communication with a second end of the bellow opposing the first end, a pair of plugs configured to sealingly close the opposing ends of the bellow, the pair of plugs cooperating so that when one plug sealingly closes one of the ends, the other end of the bellow is open; and a drive section configured to drive the pump section in a reciprocating manner so as to move the plugs. 
         [0017]    Another aspect of the present invention provides a cryogen pump having: a pump section that includes a cylinder having an inlet opening in communication with a cryogen and an exit valve, a piston configured to travel reciprocally in the cylinder along a travel axis therein between a load condition in which the piston is at a position of minimum displacement and the cryogen flows into the cylinder via the inlet opening and a compressing condition in which the piston is at a position of maximum displacement, cryogen does not flow into the cylinder, and cryogen in the cylinder is compressed and pressed out of the exit valve; and a drive section configured to drive the pump section in a reciprocating manner so as to move the piston. 
         [0018]    This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is neither intended to identify key features or essential features of the claimed subject matter, nor should it be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantage noted in any part of this application. 
         [0019]    The aforementioned and/or other features, aspects, details, utilities, and advantages of the present invention are: set forth in the detailed description which follows and/or illustrated in the accompanying drawings; possibly inferable from the detailed description and/or illustrated in the accompanying drawings; and/or learnable by practice of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The present invention will be more readily understood from the detailed description of embodiments thereof made in conjunction with the accompanying drawings of which: 
           [0021]      FIG. 1 . is a schematic cross-sectional view of a pumping unit consistent with an exemplary embodiment of the present invention; 
           [0022]      FIG. 2 . is a schematic cross-sectional view of a pumping unit consistent with another exemplary embodiment of the present invention; 
           [0023]      FIG. 3 . is a schematic cross-sectional view of a pumping unit consistent with another embodiment of the present invention; 
           [0024]      FIG. 4A  is a schematic cross-sectional view of a pumping unit consistent with an embodiment of the present invention; and 
           [0025]      FIG. 4B  is detailed schematic cross-section view of the piston seen in  FIG. 4A ; 
           [0026]      FIG. 5A  is a schematic cross-sectional view of a pumping unit consistent with another embodiment of the present invention; and 
           [0027]      FIG. 5B  is detailed schematic cross-section view of the piston seen in  FIG. 5A ; 
           [0028]      FIG. 6A  is a schematic illustration of a piston optionally usable in any of the pumping units of  FIGS. 4A and 5A ; and 
           [0029]      FIG. 6B  is detailed schematic cross-section view of the piston seen in  FIG. 6A ; 
           [0030]      FIG. 7  is a schematic cross-sectional view of an alternative driving section that is optionally usable in any of the pumping units of  FIGS. 1-3 ,  4 A and  5 A; and 
           [0031]      FIG. 8  is a schematic cross-sectional view of yet another alternative drive section that is optionally usable in any of the pumping units of  FIGS. 1-3 ,  4 A and  5 A. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present invention by referring to the figures. 
         [0033]    The drawings are generally not to scale. For drawing clarity, non-essential elements may have been omitted from some of the drawings. 
         [0034]    Although the following text sets forth a detailed description of at least one embodiment or implementation, it is to be understood that the legal scope of protection of this application is defined by the words of the claims set forth at the end of this disclosure. The detailed description is to be construed as exemplary only and does not describe every possible embodiment since describing every possible embodiment would be impractical, if not impossible. Numerous alternative embodiments and/or implementations are both contemplated and possible, using either current technology or technology developed after the filing date of this patent, which would still fall within the scope of the claims. 
         [0035]    It is to be understood that, unless a term is expressly defined in this application using the sentence “As used herein, the term ‘ ’ is hereby defined to mean . . . ” or a similar sentence, there is no intent to limit the meaning of that term, either expressly or by implication, beyond its plain or ordinary meaning, and such term should not be interpreted to be limited in scope based on any statement made in any section of this patent (other than the language of the claims). To the extent that any term recited in the claims at the end of this patent is referred to in this patent in a manner consistent with a single meaning, that is done for sake of clarity only so as to not confuse the reader, and it is not intended that such claim term be limited, by implication or otherwise, to that single meaning. Finally, unless a claim element is defined by reciting the word “means” and a function without the recital of any structure, it is not intended that the scope of any claim element be interpreted based on the application of 35 U.S.C. §112, sixth paragraph. 
         [0036]    Referring now to  FIG. 1 , there is shown a pumping unit  100  consistent with an embodiment of the present invention. The pumping unit  100  includes: a driving section  190 , a container  107  and pumping element  180 . Generally, pumping unit  100  is used for pumping cryogen to a cryosurgical device such as, by way of non-limiting example, a cryogenic medical treatment probe (not shown) which is connected to its outlet  110 . 
         [0037]    The driving section  190  is a crank-follower mechanism that includes: a rotating wheel  105  connected to a link  115  via a bearing  106  at an end of the link; and a follower  111  connected to another end of the link  115  via a bearing  116 . 
         [0038]    The pumping section  180  includes: inlet plug  104 , valve seat  102 , bellow  101 , valve seat  103 , and outlet plug  112  and is driven by the back and forth motion of follower  111 . 
         [0039]    The bellow  101  includes an inlet valve seat  102  and is submerged in a cryogen  108 . The inlet valve seat  102  is below the surface  130  of the cryogen  108  so that when inlet plug  104  travels away from the inlet seat  102  (upward as illustrated in  FIG. 1 ), cryogen  108  flows  131  into the bellow  101 . It should be noted that surface  130  of the cryogen  108  may be well above inlet plug  104 . At the other end of the bellow  101 , opposing the end with inlet opening  102  is an outlet valve seat  103  that is not in direct fluid communication with the cryogen  108 . Bellow  101  is mechanically connected to container  107  at or near outlet valve seat  103 . Relief valve  109  allows evaporation of the cryogenic fluid  108 , and maintains atmospheric pressure (or pressure slightly above atmospheric pressure) in the container  107 . Preferably, container  107  is thermally insulated as known in the art of cryogenics. 
         [0040]    When outlet plug  112  travels away from outlet opening  103  of bellow  101  (downward as illustrated in  FIG. 1 ), fluid in bellow  101  may exits through outlet opening  103 . 
         [0041]    In operation, as the wheel  105  turns, for example in direction  117 , such that bearing  106  is moving up, for example, the link  115  which is connected to wheel  105  via bearing  106 , forces the follower  111 , which is connected to link  115  via bearing  116 , to move up. Follower  111  pulls both inlet plug  104  and outlet plug  112  upwards such that inlet opening  102  is opened and cryogen  108  enters  131  bellows  101  by gravitational force due to the condition of communicating vessels created between inner volume of bellows  101  and container  107 . 
         [0042]    As wheel  105  continues to turn such that bearing  106  reaches its highest position and starts to descend, follower  111  pushes down inlet plug  104  and outlet plug  112 , closing inlet opening  102  and opening outlet opening  103 . As follower  111  continues to descend, bellows  101  is compressed under the pressure of inlet plug  104  and the cryogen in the bellows is forced through the now opened outlet valve seat  103  and flows  133  through outlet  110 . 
         [0043]    As wheel  105  continues to turn such that bearing  106  reaches its lowest position and starts to ascend, the refilling of bellows  101  is repeated as disclosed above. During the ascent of inlet plug  104  bellows  101  expand due to its flexibility to accept the inflow  131  of cryogen  108 . 
         [0044]    Keeping driving section  190  out of container  107 , and specifically keeping the motor (not seen in these figures) that rotates wheel  105  outside the cold environment may reduce heat leaks into the container and heat generation inside the container, thus reducing evaporation and waste of the cryogen. 
         [0045]    Referring now to  FIG. 2 , there is shown a pumping unit  200  consistent with an embodiment of the present invention. The pumping unit  200  includes driving section  290 , a container  207 , and pumping section  280 . Relief valve  209  allows evaporation of the cryogenic fluid  208 , and maintains atmospheric pressure (or pressure slightly above atmospheric pressure) in the container  207 . 
         [0046]    The driving section  290  is similar or identical to driving section  190  that was depicted in  FIG. 1 . 
         [0047]    In contrast to pumping section  180  of  FIG. 1 , wherein outlet plug  112  is connected to, and operated by follower  111 , controlling plug  212  which is capable of closing outlet valve seat  203  is not operated by follower  211  but instead it is responding to differences in cryogen pressures within bellows  201  and outlet  210 . Alternatively, controlling plug  212  is operated electrically in synchronization with the rotation of wheel  205 . 
         [0048]    In operation, as the wheel  205  turns, for example in direction  217 , such that bearing  206  is moving up, the link  215  which is connected to wheel  205  via bearing  206 , forces the follower  211 , which is connected to ling  215  via bearing  216 , to move up. Follower  211  pulls inlet plug  204  upwards such that inlet opening  202  is opened and cryogen  208  having level  230  above inlet opening  202  enters  231  bellows  201  by gravitational force due to the condition of communicating vessels created between inner volume of bellows  201  and container  207 . During this refilling stage of the pumping cycle, controlling plug  212  closes exit opening  203  due to one or combination of the following:
   1) The cryogen pressure in outlet  210  is greater than the pressure in the container  207 . This may be caused by flow resistance in the path of the pumped cryoliquid exiting outlet  210 , or by evaporation of cryogen in the cryosurgical device connected to outlet  210 . The difference in pressures forces controlling plug  212  against outlet valve seat  203 ;   2) A spring (not seen in this figure) may be used for overcoming gravity and forcing controlling plug  212  against outlet opening  203 ;   3) Controlling plug  212  may be made such that its specific gravity is lower than the cryoliquid such that it floats on cryogen in outlet  210  and is pushed against outlet opening  203 ; and   4) Controlling plug  212  may be electrically operated, for example using a solenoid (not shown), in synchronization with the rotation of  205 .   
 
         [0053]    As wheel  205  continues to turn such that bearing  206  reaches its highest position and starts to descend, follower  211  pushes down inlet plug  204 , closing inlet valve seat  202 . As follower  211  continues to descend, bellows  201  is compressed under the pressure of inlet plug  204  and the cryogen the bellows forces open controlling plug  212  and flows  133  through outlet  210 . Alternatively, controlling plug  212  is electrically opens to allow cryogen flow  133  through outlet  210 . 
         [0054]    As wheel  205  continues to turn such that bearing  206  reaches its lowest position and starts to ascend, the refilling of bellows  201  is repeated. During the ascent of inlet plug  204  bellows  201  expand due to its flexibility to accept the inflow  231  of cryogen  208 . 
         [0055]    Referring now to  FIG. 3 , there is illustrated a pumping unit  300  consistent with an embodiment of the present invention. 
         [0056]    The driving section  390 , which is similar or identical to driving sections  190  and  290  disclosed above includes: a rotating wheel  305  connected to a link  315  via a bearing  306  at an end of the link; and a follower  311  connected to another end of the link  315  via a bearing  316 . 
         [0057]    The pumping section  380  includes: an inlet plug  304 , an inner bellow  301 , an outer bellow  321 , and an outlet plug  312  and is driven by the reciprocal motion of follower  311 . 
         [0058]    The pumping unit  300  differs from the pumping units  100  and  200  of  FIGS. 1 and 2 , respectively, in that the pumping unit  300  includes a double bellows (i.e., inner bellow  301  and outer bellow  321 , with vacuum in the space  331  between them to thermally insulate the cryogen in the inner bellows  301  from the environment. In this case, the bellows  301  and  321  are not immersed in the container  307  filled with cryogen  308 . Relief valve  309  allows evaporation of the cryogenic fluid  308 , and maintains atmospheric pressure (or pressure slightly above atmospheric pressure) in the container  307 . The filling of the inner bellow by the law of communicating vessels is permitted by fluid connection  341 . The flexible connection  342  permits the relative motion of the valve seat  302  which is connected to the bellows  301 , and  321 , and the cryogen container  307 , while container  307 , and outlet  310  with outlet valve seat  303 , and driving section  390  are fixed to the body of pumping unit  300 . 
         [0059]    In the exemplary embodiment depicted in  FIG. 3 , outlet plug  312  is connected to, and operated by follower  311  to allow flow  133  of cryogen through outlet  310 . This operation is a similar to the operation of outlet plug  112  depicted in  FIG. 1 . Alternatively, outlet plug  312  may operate similarly to the operation of plug  212  depicted in  FIG. 2 , that is: outlet plug  312  may be operated electrically in synchronization with the rotation of wheel  305 ; or outlet plug  312  may be responding to differences in cryogen pressures within bellows  301  and outlet  310 . 
         [0060]      FIG. 4A  schematically illustrates a cross sectional view of a pumping unit  400  consistent with an exemplary embodiment of the present invention. 
         [0061]    The pumping unit  400  includes: a driving section  490 ; a container  407 ; and a pumping section  480 . Relief valve  409  maintains atmospheric pressure in the container  407  filled with cryogenic fluid  408 , to permit the filling of the bellow by the law of communicating vessels. 
         [0062]    The driving section  490  includes: a rotating wheel  405  connected to a link  415  via a bearing  406  at an end of the link; and a follower  411  connected to another end of the link  415  via a bearing  416 . 
         [0063]    The pumping section  480  includes a piston  401  that travels reciprocally within a cylinder  410  and that is driven by the reciprocal motion of follower  411 . 
         [0064]    In operation, as the wheel  405  turns in direction  417 , the link  415  forces the follower  411  to move cyclically in up and down directions. As piston  401 , which is connected to follower  411  moves down from its upmost position, it closes the opening  402  in cylinder  410 , stopping the filling of the cylinder  410  with cryogen  408  through opening  402  which is below the level  430  of cryogen  408  in container  407 , by law of communicating vessels. As the follower continues to move downwards toward a position of maximum displacement, the piston presses the cryogen in the cylinder  410  to exit through the check valve  403 . 
         [0065]    After the follower has reached its lowest position and is moving up, valve  442  in piston  401  opens, letting air flow through tunnel  441  in piston  401 , and compensate for the low pressure created by the movement, i.e. preventing vacuum pressure to be generated in cylinder  410  under piston  401 . 
         [0066]    Alternatively, the tunnel  442  and valve  441  may be omitted and the small gap between piston  401  and cylinder  410  may be configured to allow some gas flow into the cylinder  410 . Same small gap between piston  401  and cylinder  410  is small enough to prevent excessive escape of cryogenic liquid during the down motion of the piston due to the higher viscosity of liquid in relation to the viscosity of gas. Additionally or alternatively, partial vacuum is generated in the cylinder  410  below piston  401  when piston  401  is moving up. This partial vacuum is partially filled with vapor of cryogenic left in the bottom of cylinder  410  and near check valve  403 . 
         [0067]    When piston  401  moves up, the inlet  402  is exposed to the cryogen  408  in the container  407  allowing the fluid to fill the cylinder through inlet opening  402 , replacing any air that enter the cylinder  410 , or vapor generated in it during the first part of the movement upwards. 
         [0068]      FIG. 4B  schematically illustrates enlarged cross sectional view of piston  401  showing tunnel  441 , valve  442 , and part of follower  411  according to the exemplary embodiment of the present invention depicted in  FIG. 4A . 
         [0069]      FIG. 5A , schematically illustrates a pumping unit  500  consistent with an exemplary embodiment of the present invention. The pumping unit  500  includes driving mechanism  590  and a pumping element  580 . 
         [0070]    The driving section  590  includes: a rotating wheel  505  connected to a link  515  via a bearing  506  at an end of the link; and a follower  511  connected to another end of the link  515  via a bearing  516 . 
         [0071]    The pumping section  580  includes a piston  501  that travels reciprocally within a cylinder  510  and that is driven by the reciprocal motion of follower  511 . Cylinder  510  is a double walled cylinder with an outer wall  507  and an inner wall  521 . The two walls  507  and  521  of cylinder  510  are separated by vacuum space  531  for thermal insulation. 
         [0072]    Opening  502  in cylinder  510  is connected to a container (not shown) with cryogen. 
         [0073]    Pumping unit  500  operates the same as system  400  seen in  FIG. 4A . The link  515  forces the follower  511  to move in up and down directions. A piston  501  connected to follower  511  closes the opening  502  as it moves down, stopping the filling of the cylinder  510  with cryogen through opening  502 , by law of communicating vessels. As the follower continues to move downwards, the piston presses the cryogen in the cylinder  510  to exit through the check valve  503 . When the follower is moving up, the inlet  502  is exposed to the cryogen allowing the cryogenic fluid to fill the cylinder  510  through inlet opening  502 . 
         [0074]    After the follower has reached its lowest position and is moving up, valve  542  in piston  401  opens, letting air flow through tunnel  541  in piston  501 , and compensate for the low pressure created by the movement (i.e. preventing vacuum pressure to be generated in cylinder  510  under piston  501 ). 
         [0075]    Alternatively tunnel  542  and valve  541  are missing. Instead, the small gap between piston  501  and cylinder  510  allows some gas flow into the cylinder  510 . Same small gap between piston  401  and cylinder  510  is small enough to prevent excessive escape of cryogenic liquid during the down motion of the piston  501  due to the higher viscosity of liquid in relation to the viscosity of gas. Additionally or alternatively, partial vacuum is generated in the cylinder  510  below piston  501  when piston  501  is moving up. This partial vacuum is partially filled with vapor of cryogenic left in the bottom of cylinder  510  and near check valve  503 . 
         [0076]    When piston  501  moves up, the inlet  502  is exposed to the cryogen in the container (not shown) allowing the fluid to fill the cylinder  510  through inlet opening  502 , replacing any air that enter the cylinder  510 , or vapor generated in it during the first part of the movement upwards. 
         [0077]      FIG. 5B  schematically illustrates an enlarged cross sectional view of piston  501  showing optional tunnel  541 , valve  542 , and part of follower  511  according to the exemplary embodiment of the present invention depicted in  FIG. 5A . 
         [0078]      FIG. 6A  schematically illustrates a cross sectional view of a pumping unit  600  using a piston  601  with a groove  652  according to an exemplary embodiment of the present invention. 
         [0079]    Pumping unit  600  using a piston  601  with a groove  652  is an optional configuration that may be used in pumping units  400  and  500  of  FIGS. 4A and 5A , respectively. The piston  601  is configured to include a groove  651  that permits, by rotating the piston  601  to select position of the piston in relationship with the opening  602 , in which opening  602  is closed as the piston moves down, thus selecting the amount of the cryogen that is pressed to the exit valve  603 . 
         [0080]    The orientation of piston  601  may be preset during manufacturing or calibrating or adjusting the pumping unit. Optionally, additionally or alternatively, the orientation of the piston may be changed by rotating follower  611 , which connected to the piston  611 . For example, follower  611  may comprise a manual or motorized actuator allowing changing the rotational orientation of the piston  601  relative to opening  602 , optionally while the pumping unit is assembled or in operation. 
         [0081]    After the follower has reached its lowest position and is moving up, valve  642  in piston  601  opens, letting air flow through tunnel  641  in piston  601 , and compensate for the low pressure created by the movement, i.e. preventing vacuum pressure to be generated in the cylinder  610  under piston  601 . 
         [0082]    Alternatively tunnel  642  and valve  641  are missing. Instead, the small gap between piston  601  and cylinder  620  allows some gas flow into the cylinder  510 . Same small gap between piston  401  and cylinder  610  is small enough to prevent excessive escape of cryogenic liquid during the down motion of the piston  501  due to the higher viscosity of liquid in relation to the viscosity of gas. Additionally or alternatively, partial vacuum is generated in the cylinder  610  below piston  601  when piston  601  is moving up. This partial vacuum is partially filled with vapor of cryogenic left in the bottom of cylinder  610  and near check valve  603 . 
         [0083]    When piston  601  moves up, the inlet  602  is exposed to the cryogen in the container (not shown) allowing the fluid to fill the cylinder  610  through inlet opening  602 , replacing any air that enter the cylinder  610 , or vapor generated in it during the first part of the movement upwards. 
         [0084]      FIG. 6B  schematically illustrates enlarged cross sectional view of piston  601  showing optional tunnel  641 , valve  642 , and part of follower  611  according to the exemplary embodiment of the present invention depicted in  FIG. 6A . 
         [0085]      FIG. 7  illustrates an alternative driving section  700  that may optionally replace the driving sections in any of pumping units  100 ,  200 ,  300 ,  400 , and  500  of  FIGS. 1-3 ,  4 A and  5 A, respectively. The driving section  700  includes a cam  705  instead of a wheel. The cam  705  rotates in direction  717  around its pivot  706  and, because of its shape, drives a follower  715  reciprocally toward and away from the cam resulting in translation of the rotational motion of the cam  705  into reciprocating linear motion of the follower  715 . The follower  715  is optionally connected to follower  711  via a pivot  716 . The follower  711 , in turn, may drive either a piston or a bellows. Followers  715  or  711  may act as followers  111 ,  211 ,  311 ,  411 ,  511  and  611  in  FIGS. 1-3 ,  4 A,  5 A, and  6 A, respectively. 
         [0086]      FIG. 8  illustrates pneumatic system, another alternative driving section  800 , which may optionally replace driving section  190 ,  290 ,  390 ,  490 ,  590  or driving section  700 . Pneumatic driving system  800  may optionally be used in any of pumping units  100 ,  200 ,  300 ,  400 , and  500  of  FIGS. 1-3 ,  4 A, and  5 A, respectively. The pneumatic driving section  800  includes a piston  850  instead of a wheel or cam. With this configuration, there is no need to translate rotational motion into reciprocating linear motion. The piston  850  moves up and down depending on the pneumatic pressure supplied at either opening  851  for motion downwards, or at opening  852  for motion upwards. In operation, a link  853 , which is attached to an end of piston  850  optionally, pushes the optional follower  811  through optional pivot  816 . Follower  811 , or link  853  in turn, drives the pumping section. Pneumatic pressure is supplied by a gas pressure source and controlling valves as known in the art, which are not seen in this figure. Alternatively, hydraulic power may be used. Follower  811  or link  853  may act as followers  111 ,  211 ,  311 ,  411 ,  511   611  and  711  (or  715 ) in  FIGS. 1-3 ,  4 A,  5 A,  6 A and  7 , respectively. 
         [0087]    As described above, embodiments of the present invention provide a cryogen pump with unique control of the inlet and outlet flow. The system includes either a bellow pump or piston pump. The pump is either submerged in cryogenic fluid, or vacuum insulated. The inlet of the fluid is applying the law of communicating vessels, eliminating the need for an inlet valve. 
         [0088]    Also, as described above, the cryogen pumps of embodiments of the present invention simplify the handling of the boiling fluid by either insulating it from the environment with vacuum insulation, or submerging the pumping unit in the bath of boiling fluid. In addition the inlet uses the natural law of communicating vessels, eliminating the need for a check valve and smoothing the operation. The motion distance of the connecting lever from the crank and the diameter of the crank position also can be used to make the pump metering pump. The pump can raise the pressure of the cryogens from atmospheric pressure or below to 40 at. The control of the pressure and the flow can be achieved by either changing the speed of the motion of the pump or change in the displacement of the pressing element. 
         [0089]    All the elements of the disclosed systems may be made from material suitable to withstand the low temperature and the function of the elements would not be compromised by the low temperature. The lowest design temperature is negative 220 degrees Celsius. 
         [0090]    Examples of various features/aspects/components/operations have been provided to facilitate understanding of the disclosed embodiments of the present invention. In addition, various preferences have been discussed to facilitate understanding of the disclosed embodiments of the present invention. It is to be understood that all examples and preferences disclosed herein are intended to be non-limiting. 
         [0091]    Although selected embodiments of the present invention have been shown and described individually, it is to be understood that at least aspects of the described embodiments may be combined. 
         [0092]    Although selected embodiments of the present invention have been shown and described, it is to be understood the present invention is not limited to the described embodiments. Instead, it is to be appreciated that changes may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and the equivalents thereof.