SUBMERGIBLE CRYOGENIC PUMP WITH LINEAR ELECTROMAGNETIC MOTOR DRIVE

A fully submergible dual-action cryogenic pump has a housing configured to receive a liquid into the interior compartment when submerged in the liquid. The housing includes an interior compartment having an inner peripheral surface, a first end, and a second end. A free piston having a first end, a second end, and an outer peripheral surface is contained within the interior compartment. A first compression chamber is formed between the first end of the free piston and the first end of the interior compartment. A second compression chamber is formed between the second end of the free piston and the second end of the interior compartment. An electromagnetic drive is configured to reciprocate the free piston. A sealing area is formed by the outer peripheral surface of the free piston sealing with the inner peripheral surface of the interior compartment.

TECHNICAL FIELD

The present disclosure relates generally to a pump and, more particularly, to a submergible cryogenic pump having a linear electromagnetic motor drive.

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. Stationary equipment may also use an engine powered by natural gas. Natural gas may be more abundant and, therefore, less expensive than diesel fuel. In addition, natural gas may burn cleaner in some applications, producing less greenhouse gas.

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, typically about −100° C. 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's engine. In some applications, the liquid fuel may be gasified prior to injection into the engine and/or mixed with diesel fuel (or another fuel) before combustion.

One problem associated with cryogenic pumps located external to the tank of liquid natural gas involves cooling the pump down before it can be started. To achieve this, external cryogenic pumps use expensive and complicated cool-down circuits and procedures. Additionally, leakage can cause problems for external pumps. External pumps require complicated and expensive seals and bearings to prevent or reduce leakage. External pumps additionally require expensive and complicated systems for the cold end of the pump handling the liquid fuel. For example, cold-end systems include ventilation, purging, and temperature monitoring.

To reduce cost and complexity, some cryogenic pumps are installed inside the tank and submerged in the liquid natural gas. Submerging an electric motor in high pressure liquid natural gas, however, creates other problems. For example, the pump and motor generate heat, boiling the immediately surrounding liquid natural gas. Additionally, the rotating components of electric motors and rotating pumps present additional problems. For example, rotating bearings are prone to wear, and because they are submerged in high pressure liquid at cryogenic temperatures, they are difficult to access for service or replacement. Rotating pumps also consume large amounts of energy and have complex and expensive components.

To address these issues, some pumping systems have used linear electromagnetic drives to reciprocate a piston partially disposed in liquid. An exemplary pump is disclosed in U.S. Pat. No. 6,506,030 which issued to Kottke on Jan. 14, 2003 (“the '030 patent”). The pump includes a piston assembly inside a cylinder. Bushings support the piston and a linear electromagnetic drive system forces the piston to reciprocate within the cylinder. At the cold end of the pump, the piston reciprocates in the dispensing chamber to pump liquid during the down stroke. At the warm end of the pump, the piston reciprocates in a reservoir chamber which stores energy during the upstroke to be used in the next down stroke. Sealing members fluidly separate the dispensing chamber from the reservoir chamber. Bushings support and guide the piston. Friction between the piston and each of the sealing members and bushings generate heat. To minimize undesirable heat transfer into the liquid fuel, an adaptive plate insulates the cold end of the pump submerged in the fluid from the warm end which is not submerged. Additionally, the cold end is insulated by a thermal jacket.

While the pump of the '030 patent may help address some of the difficulties associated with using a linear electromagnetic drive to reciprocate a pump piston in a high pressure cryogenic tank, it presents additional problems. For example, the bushings and sealing member add undesirable complexity and cost because they are prone to wear and require frequent and expensive maintenance. Additionally, they generate unwanted heat, making submerging the pump completely in the liquid undesirable for this design.

The disclosed pump is directed to overcoming one or more of the problems set forth above and/or elsewhere in the prior art.

SUMMARY

In one aspect, the present disclosure is directed to a fully submergible dual-action cryogenic pump. The cryogenic pump includes a housing having an interior compartment, and the interior compartment has an inner peripheral surface, a first end, and a second end. The housing is configured to receive a liquid into the interior compartment when submerged in the liquid. A free piston is contained within the interior compartment of the housing, and the free piston includes an axis, a first end, a second end, and an outer peripheral surface. A first compression chamber is formed between the first end of the free piston and the first end of the interior compartment. A second compression chamber is formed between the second end of the free piston and the second end of the interior compartment. An electromagnetic drive is configured to reciprocate the free piston along the axis. A sealing area is formed by the outer peripheral surface of the free piston sealing with the inner peripheral surface of the interior compartment between the first compression chamber and the second compression chamber.

In another aspect, the present disclosure is directed to a fully submergible dual-action cryogenic pump system. The pump system includes a housing having an interior compartment. The interior compartment has an inner peripheral surface. The housing is configured to receive a liquid into the interior compartment when submerged in the liquid. A piston includes an outer peripheral surface, an axis, and a length along the axis. An electromagnetic drive is configured to reciprocate the piston when the piston is contained within the interior compartment. A sealing area is formed by the outer peripheral surface of the piston sealing with the inner peripheral surface of the interior compartment when the piston is contained within the interior compartment.

In another aspect, the present disclosure is directed to a method of pumping a cryogenic liquid using a pump submerged in the cryogenic liquid. The method includes electromagnetically reciprocating a free piston enclosed within a housing of the submerged pump along an axis of the free piston. The method also includes allowing the cryogenic liquid to alternately flow into a first compression chamber inside the housing and into a second compression chamber inside the housing. The method also includes alternating between discharging the cryogenic liquid from the first compression chamber and from the second compression chamber. The method also includes electromagnetically rotating the free piston about the axis of the free piston.

DETAILED DESCRIPTION

FIG. 1illustrates one embodiment of the cryogenic pump10. In this embodiment, the cryogenic pump10is installed in a tank8of liquid6such as a cryogenic fuel. The cryogenic fuel may be liquid natural gas, but, alternatively, the cryogenic pump10may be used to pump other liquid cryogenic fuel, such as helium, hydrogen, nitrogen, or oxygen, etc. The cryogenic pump10is fully submerged within the liquid6in the fuel tank8. In the embodiment illustrated inFIG. 1, the fuel tank8is drawn behind a locomotive14and provides fuel to the engine11of the locomotive14. A power source13is electrically connected to the cryogenic pump10. The cryogenic pump10is fluidly connected to a vaporizer15, where the liquid6is converted into a gas. The vaporizer15is connected through fuel line12to the engine11of the locomotive14, where the engine11burns the gaseous fuel. Alternatively, in other embodiments, however, the cryogenic pump10may be used in stationary equipment (not shown). The cryogenic pump10may be used in any suitable application for pumping liquid cryogenic fuel.

In one embodiment, illustrated inFIG. 2, the cryogenic pump10is fully submerged within the liquid6. The cryogenic pump10includes a housing16, and the housing16includes an interior compartment18having an inner peripheral surface20(best illustrated inFIG. 3). The interior compartment18also has a first end22and a second end24. The cryogenic pump10also includes a free piston26contained within the interior compartment18of the housing16. The free piston26has no linkages or rods attached to it. The free piston26has an axis28, a first end30, a second end32, and an outer peripheral surface34(best illustrated inFIG. 3). A first compression chamber36is formed between the first end30of the free piston26and the first end22of the interior compartment18. A second compression chamber38is formed between the second end32of the free piston26and the second end24of the interior compartment18.

An electromagnetic drive40is configured to reciprocate the free piston26along its axis28when the free piston26is contained inside the housing16. The free piston26includes a magnetic portion50responsive to electromagnetic fields. The electromagnetic drive40includes a plurality of electric coils42encircling the axis28of the free piston26. The electric coils42may be enclosed within a separate structure as shown inFIG. 1. Alternatively, the coils42may be disposed within an outer wall44of the housing16.

In the embodiment illustrated inFIG. 2, the ends30,32of the free piston26do not contact the respective ends22,24of the interior compartment18at each end of the stroke. Rather, at each end of the stroke, an over-stroke length76is defined as the distance between the ends30,32of the free piston26and the respective ends22,24of the interior compartment18.FIG. 2illustrates the free piston26at one end of its stroke, after having fully compressed the first compression chamber36. In this position, the over-stroke length76is shown as the distance between the first end22of the interior compartment18and first end30of the free piston26. Similarly, at the other end of the stroke (position not shown), the over-stroke length76is the distance between the second end24of the interior compartment18and the second end32of the free piston26. Thus, in this embodiment the over-stroke length76is the same at both ends of the stroke.

In another embodiment, however, the over-stroke length76at the first end22of the interior compartment18may be different from a second over-stroke length (not shown) at the second end24of the interior compartment18. And alternatively, in another embodiment, the ends30,32of the free piston26may contact the ends22,24of the interior compartment18at each end of the stroke of the free piston26. That is, the over-stroke length76may effectively be zero.

Referring again to the embodiment illustrated inFIGS. 2 and 3, the housing16is configured to be submerged in liquid6. The housing16includes a system of one-way valves52,56,58,60to allow fluid to flow into and out of the compression chambers36,38. A first one-way intake valve52fluidly connects the first compression chamber36to the liquid6surrounding the housing16. The system of one-way valves52includes a second one-way intake valve56fluidly connected to the second compression chamber38. The system of one-way valves52includes a first one-way exhaust valve58and a second one-way exhaust valve60fluidly connected to the first and second compression chambers36,38, respectively. The one-way exhaust valves58,60are configured to allow fluid to flow out of their respective compression chambers36,38during compression.

The one-way valves52,56,58,60may be any suitable type of one-way valve known in the art. Although the one-way valves52,56,58,60are shown as separate valves disposed outside of the housing16, alternatively, they may be integrally formed with the housing16. And although the intake valves52,56are illustrated near the ends22,24of the interior compartment18of the housing16, alternatively, the intake valves52,56may be disposed at any suitable location. Instead of separately formed valves, alternatively, the intake valves52,56may simply be formed as the intake fluid line55directly connected to the interior compartment18of the housing16at a location (not shown) that is intermittently sealed by the free piston26as the free piston26reciprocates.

A primer pump54fluidly connects the first and second compression chambers36,38to the liquid6surrounding the housing16. The primer pump54is fluidly connected with the first compression chamber36through the first one-way intake valve52and an intake line55. Similarly, the primer pump54is fluidly connected with the second compression chamber38through the second one-way intake valve56and the intake line55. Alternatively, in another embodiment, the one-way intake valves52,56may be directly fluidly connected (not shown) to the liquid6surrounding the housing16without a primer pump54and/or the intake line55.

In the embodiment illustrated inFIGS. 2 and 3, the free piston26is configured to create a sealing area62along its outer peripheral surface34without using a separate sealing element, such as a piston sealing ring. Various features may work together to create a low friction interface along the sealing area62. For example, these features may include solid dry lubricants, precision-manufactured surface smoothness and tolerances, and/or a gas layer around the free piston26. Each of these features is discussed in greater detail below.

The outer peripheral surface34of the free piston26is configured to seal with the inner peripheral surface20of the interior compartment18without a piston sealing ring. Other variations may include the use of sealing elements at other locations on the cryogenic pump10.

To form the sealing area62, the outer peripheral surface34of the free piston26and the inner peripheral surface20of the interior compartment18are formed to precise tolerances, and the surfaces20,34have smooth finishes. Preferably, the peripheral surfaces20,34are machined to have an average roughness measurement between 0.01 micrometers and 0.1 micrometers. In other embodiments, the average roughness measurement may be less than 0.01 micrometers. Preferably, the radius66of the outer peripheral surface34of the free piston26is between 0.01 micrometers and 2 micrometers less than the radius67of the inner peripheral surface20of the interior compartment18.

The sealing area62may prevent leakage between the first compression chamber36and the second compression chamber38at a high pressure differential, for example up to around 500 psi or more. In theory, however, some trace amounts of leakage are possible. Because the free piston26is enclosed within the housing16, any leakage from one compression chamber flows to the other compression chamber. For example, any leakage from the first compression chamber36flows to the second compression chamber38. Thus, the cryogenic pump10may prevent external (to the housing16) leakage.

In the embodiment illustrated inFIG. 2, the sealing area62is formed along all of the length64of the free piston26, measured from its first end30to its second end32. Alternatively, in another embodiment, the continuously smooth portions of the outer peripheral surface34of the free piston26may be disposed on less than the entire length64of the free piston26. In this embodiment, the sealing area62may be formed along less than the entire length64of the free piston26. For example, the continuously smooth portions of the outer peripheral surface34may be disposed along a majority of the length64of the free piston26. In addition, the free piston26may have various features interrupting the continuously smooth portions of the outer peripheral surface34. The free piston26may have one or more notches or recesses at various spacings and/or intervals along the outer peripheral surface34. Additionally or in the alternative, the free piston26may have one or more ends that are not necessarily flat or that do not necessarily lie in one or more planes perpendicular to the axis28of the free piston26. For example, end surfaces of the free piston26may be configured with various profiles resulting in the ends of the free piston26having a semispherical configuration, a frustoconical configuration, a triangular configuration, or other convex or concave configurations, and the interior compartment18may have complementary shaped ends (not shown).

In one embodiment, reciprocation of the free piston26within the interior compartment18of the housing16may cause a small and controlled amount of friction-generated heat along the sealing area62. This heat vaporizes the immediately surrounding liquid6, creating a gas layer between the outer peripheral surface34of the free piston26and the inner peripheral surface20of the interior compartment18. The gas layer is disposed along the sealing area62and reduces friction thereby facilitating reciprocation of the free piston26. In this way, the gas layer may act like a linear gas bearing along the sealing area62.

Alternatively, in another embodiment, solid dry lubricants are used to reduce friction along the sealing area62. This may reduce friction-generated heat and prevent the gas layer from forming such that the outer peripheral surface34of the free piston26directly contacts and slides along the inner peripheral surface20of the interior compartment18. In this embodiment, one or more of the outer peripheral surface34of the free piston26and the inner peripheral surface20of the housing16may include solid dry lubricants. The solid dry lubricants may include, for example, molybdenum disulfide (MoS2), sintered silicon carbide (SiC), tungsten(IV) sulfide (WS2), graphite, or a combination thereof. The solid dry lubricants may be embedded, fused, or diffused into the free piston26and/or the interior compartment18. For example, thin film of the solid dry lubricants may be formed on one or more of the peripheral surfaces20,34, using any suitable technique, for example, conventional sputtering deposition or ion beam assisted deposition. In this embodiment, the solid dry lubricants help facilitate low friction reciprocation of the free piston26.

No bushings or separate support structure are necessary between the free piston26and the interior compartment18of the housing16. Rather, the inner peripheral surface20of the interior compartment18supports and guides the free piston26along its axis28during reciprocation. As explained above, low friction between the peripheral surfaces20,34generates minimal heat and reduces wear.

In one embodiment, the free piston26may be rotated to reduce wear along the sealing area62. For example, the electromagnetic drive40may be configured to rotate the free piston26about its axis28to reduce wear on the free piston26and housing16potentially caused by small variations in shape or surface finish. In the embodiment illustrated inFIG. 2, the free piston26includes a second magnetic portion68. The electromagnetic drive40may be configured to exert a force on the second magnetic portion68to rotate the free piston26. The second magnetic portion68may be eccentrically disposed with respect to the axis28as measured in a plane (not shown) orthogonal to the axis28.

Alternatively, the cryogenic pump10may use any suitable configuration to rotate the free piston26as known in the art to electromagnetically rotate a shaft. Although the second magnetic portion68is separate from the magnetic portion50in this embodiment, instead, in other embodiments, magnetic portion50and the second magnetic portion68may be formed together as one continuous magnetic portion. That is, the electromagnetic drive40may be configured to both reciprocate and rotate the free piston26by acting on the magnetic portion50.

In the embodiment illustrated inFIGS. 2 and 3, rotation of the free piston26helps prevent uneven wear. In another embodiment, rotation of the free piston26may also provide an additional flow of liquid6from the housing16. In this embodiment, the free piston26includes one or more recesses (not shown) forming rotational pumping chambers (not shown) with the interior compartment18of the housing16. The housing16includes additional ports and valves (not shown) fluidly connected with the rotational pumping chambers. The flow from the rotational pumping chambers provides an additional way to fine tune the total output of the cryogenic pump10. For example, the reciprocation rate of the free piston26may be held constant while the rotational rate is adjusted to fine tune the total output of the cryogenic pump10.

The cryogenic pump10may be manufactured using any suitable method. In some embodiments, the housing16is manufactured as two separate parts (not shown). The two parts (not shown) of the housing16are assembled with the free piston26disposed in the interior compartment18of the housing16. The two parts of the housing16may be sealed together using any suitable method. For example, they may be sealed using fasteners, adhesives, welding, etc. Alternatively, the housing16may be manufactured as a tube (not shown) with separate end caps (not shown). Once the free piston26is placed within the interior compartment18of the housing16, the end caps are attached to the tube to seal both ends of the tube. Any suitable method may be used to attach the end caps to the tube to enclose the free piston26within the housing16. For example, the end caps may be sealed to the housing16using fasteners, adhesives, welding etc. Additionally, any other suitable manufacturing technique for producing a housing16with an internally contained free piston26may be used.

The cryogenic pump10may be installed inside a tank8of cryogenic fuel. Installing the cryogenic pump10within the tank8may include directly mounting the housing16to the inside of the tank8to secure it therein. Alternatively, a mounting bracket (not shown) may be mounted to the tank8and the housing16may be mounted to the mounting bracket. The mounting bracket may isolate vibrations generated from the movement of the locomotive14or other machinery, to reduce wear on the cryogenic pump10. In some embodiments, the cryogenic pump10may be assembled during installation. For example, the steps described above for enclosing the free piston26inside the housing16may be performed during installation.

In the embodiment illustrated inFIG. 2, a single housing16has a single interior compartment18, and a single free piston26is disposed therein. Alternatively, a plurality of interior compartments and free pistons may form the cryogenic pump10. The plurality of interior compartments may be formed within one or more housings (not shown). Each housing may be manufactured as two parts which are sealed together to create the plurality of interior compartments with respective free pistons disposed therein.

In the embodiment illustrated inFIG. 2, the free piston26is hollow and has an outer wall70defining a cavity72inside. This reduces the weight of the free piston26. The cavity72may be filled with gas or may be evacuated to create a vacuum. Alternatively, in another embodiment, however, the free piston26may be solid throughout. In the embodiment illustrated inFIG. 2, the free piston26, housing16, and interior compartment18are generally cylindrical in shape. Alternatively, in other embodiments, free piston26, housing16, and interior compartment18, may have any other suitable shape.

The magnetic portion50of the free piston26is disposed within the outer wall70of the free piston26. Any suitable material responsive to magnetic fields may be used to form the magnetic portion50. For example, the magnetic portion50may be a permanent magnet. The magnetic portion50may disposed generally in the middle of the free piston26along the axis28. Each of the electromagnetic drive40and the magnetic portion50has a length measured along the axis28. As shown in the embodiment illustrated inFIG. 2, the lengths of the electromagnetic drive40and magnetic portion50may be roughly equal. Alternatively, in another embodiment, the length of the magnetic portion50is approximately two times the length of the electromagnetic drive40. This allows the electromagnetic drive40to fully engage the magnetic portion50along the entire stroke of the free piston26. Alternatively, the magnetic portion50may be disposed within the cavity72and attached to the inside of the outer wall70. The magnetic portion50may be disposed along the entire length64of the free piston26. For example, the free piston26may be a formed as a cylinder of metal with a coating forming the outer peripheral surface34of the free piston26. The coating may be made from ceramic, for example. The free piston26may be formed from any suitable material, however. For example, the free piston26may include a material that expands and contracts a relatively small amount over a wide range of temperatures, such as ceramic. That is, the material may have a low coefficient of thermal expansion.

The dimensions of the various parts of the cryogenic pump10are selected to optimize multiple design considerations. For example, the volumes of the compression chambers36,38determine the volume output of the cryogenic pump10per reciprocation cycle. The volumes of the compression chambers36,38, in turn, are a product of the stroke length74and the cross sectional area (not shown) of the free piston26in a plane orthogonal to its axis28. In one embodiment, the free piston26has a diameter between 15 mm and 25 mm, and the stroke length74of the free piston26is between 90 mm and 110 mm.

INDUSTRIAL APPLICABILITY

The disclosed cryogenic pump10finds potential application in any fluid system where high-pressurization of cryogenic fluids is required. For example, the disclosed cryogenic pump10may be used in mobile (e.g., locomotive) or stationary (e.g., power generation) applications having an internal combustion engine that consumes the fluid pressurized by the disclosed cryogenic pump10. Operation of the cryogenic pump10will now be explained.

FIG. 1illustrates an overview of one embodiment of the cryogenic pump10used in a locomotive application. In this embodiment, the cryogenic pump10provides pressurized cryogenic fuel in liquid form to the engine11of the locomotive14for combustion. The power source13provides electricity to the cryogenic pump10and the primer pump54. The primer pump54pumps the liquid6into the cryogenic pump10, which in turn, pumps the liquid6to the vaporizer15. The vaporizer15then converts the liquid6into a gas. From the vaporizer15, the gaseous fuel flows through the fuel line12to the engine11of the locomotive14, where the engine11burns the gaseous fuel.

Detailed operation of the cryogenic pump10will now be explained. In one embodiment illustrated inFIG. 2, the primer pump54pumps liquid6from the fuel tank8into the interior compartment18of the housing16of the cryogenic pump10. The liquid6travels from the primer pump54through the intake line55and through one-way intake valves52,56into the interior compartment18. Thus, the primer pump54delivers the liquid6into the interior compartment18of the housing16at a higher pressure than the liquid6surrounding the housing16.

Alternatively, however, in another embodiment, liquid6surrounding the housing16may flow directly into the interior compartment18without a primer pump54(not shown). In this embodiment, the movement of the free piston26draws the liquid6directly into the compression chambers36,38. Specifically, as the free piston26translates to the left as illustrated inFIG. 2, the free piston26compresses the first compression chamber36. Simultaneously, this translation expands the second compression chamber28. This pulls the liquid6surrounding the housing16directly into the second compression chamber38(configuration not shown). Next, the free piston26translates to the right as illustrated inFIG. 2, and compresses the second compression chamber38. Simultaneously, this translation expands the first compression chamber36. This pulls the liquid6surrounding the housing16directly into the first compression chamber36(configuration not shown). Thus, in this embodiment, the reciprocating movement of the free piston26causes the liquid6surrounding the housing16to alternately flow into each of the compression chambers26,28.

Referring again to the embodiment illustrated inFIG. 2, the electromagnetic drive40reciprocates the free piston26inside the housing16to pump the liquid6. The power source13(FIG. 1) provides an alternating electric current through an electric line9(FIG. 1) to the coils42(FIG. 2). By alternating the electric current through the electric coils42, the electromagnetic drive40produces an alternating magnetic field in the interior compartment18of the housing16. This magnetic field acts on the magnetic portion50of the free piston26, forcing the free piston26to reciprocate. Additionally, the electromagnetic drive40may also electromagnetically rotate the free piston26about the axis28of the free piston26by acting on the second magnetic portion68.

Reciprocation of the free piston26will now be explained in more detail.FIG. 2illustrates the free piston26after fully compressing the fluid in the first compression chamber36. In this position, the first end30of the free piston26remains the over-stroke length76from the first end22of the interior compartment18. From this position, the electromagnetic drive40forces the free piston26towards the second end24of the interior compartment18. The free piston26travels the stroke length74towards the second end24of the interior compartment18. This compresses the fluid in the second compression chamber38. The free piston26then stops when its second end32is the over-stroke length76away from the second end24of the interior compartment18. The electromagnetic drive40then forces the free piston26towards the first end22of the interior compartment18. The free piston26travels the stroke length74towards the first end22of the interior compartment18. This compresses the fluid in the first compression chamber36and returns the free piston26to the starting position shown inFIG. 2. Thus, alternating current through the electromagnetic drive40forces the free piston26to reciprocate the stroke length74.

A system of valves52,56,58,60facilitate the flow of liquid6into and out of the interior compartment18. The intake valves52,56allow the liquid6to alternately flow into the first compression chamber36and the second compression chamber38inside the housing16. The cryogenic pump10alternates between discharging the liquid6from the first compression chamber36and from the second compression chamber38through the exhaust valves58,60.

The disclosed cryogenic pump10may provide a high-pressure supply of fuel in a simple, low maintenance, and submergible configuration. The cryogenic pump10creates a sealing area62between the outer peripheral surface34of the free piston26and the inner peripheral surface20of the interior compartment18of the housing16. This may eliminate the need for piston sealing rings that are both prone to wear and generate undesirable heat from friction. Eliminating these sealing members may reduce maintenance costs, down time, and the amount of heat generated from friction. Thus, the cryogenic pump10may be completely submerged in a cryogenic fuel without introducing undesirably large amounts of heat to the liquid fuel. Completely submerging the cryogenic pump10may also eliminate costly and complicated systems associated with completely and partially external pumps.

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 pump will be apparent to those skilled in the art from consideration of the specification and practice of 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.