Submersible balanced piston pump

Abstract

A balanced piston pump (300) for a submarine vehicle, e.g., a variable buoyancy engine, includes an inlet (321), an outlet (325), and at least one fluid path between the inlet and the outlet. A piston arrangement within the fluid path includes a stepped piston (330) having a large end (333) and a small end (331). The piston steps (336) cooperate with the pump body (310) to form a piston chamber (320). Each of the piston ends (332, 334) are exposed to ambient pressure. The force required to drive the pump is dependent on the difference in cross-sectional area of ​​the piston ends.

Description

Technical Field

[0001] This application generally relates to submersible vehicles, and more particularly to pumps used in manned or unmanned submersible vehicles, particularly underwater gliders.

Background Art

[0002] Submersible vehicles such as gliders have the function of moving underwater to a considerable depth. Gliders are relatively quiet and can move long distances with minimal fuel. Due to these advantages, gliders can be used in various applications such as ocean surveys and military defense.

[0003] Pumps for underwater gliders have specific requirements due to their extreme operating depths. These pumps are required to be efficient and reliable despite the harsh operating environment.

[0004] Therefore, an improved pump for underwater vehicles is desired.

Summary of the Invention

Means for Solving the Problems

[0005] A pump according to one aspect of the present disclosure includes a pump body, at least one inlet, at least one outlet, a fluid path between the at least one inlet and the at least one outlet, and at least one piston configuration disposed in the fluid path and configured to pump fluid from the at least one inlet through the fluid path to the at least one outlet, the piston configuration including a piston chamber, an inlet valve, an outlet valve, a piston disposed to move within the piston chamber and including a first outer end face at a first end and a second outer end face at a second end, and a piston drive that drives the piston within the piston chamber and is operably attached to the first end of the piston. At least one of the first outer end face and the second outer end face of the piston is exposed to ambient pressure. Since the surface area of ​​the first outer end face is smaller than the surface area of ​​the second outer end face, the force due to ambient pressure at the second end is greater than the force due to ambient pressure at the first end.

[0006] A two-stage pumping system for deep-sea vessels according to one aspect of this disclosure is: pressure vessel and The system includes a main pump positioned to pump fluid from inside the pressure vessel, The aforementioned main pump comprises the pump body and At least one entrance, At least one exit, A fluid path between the at least one inlet and the at least one outlet, A piston configuration comprising: a piston chamber; an inlet valve; an outlet valve; a piston disposed to move within the piston chamber and having a first outer end face at a first end and a second outer end face at a second end; and a piston drive operably mounted to the first end of the piston for driving the piston within the piston chamber; At least one of the first outer end face and the second outer end face of the piston is exposed to ambient pressure. Since the surface area of ​​the first outer end face is smaller than the surface area of ​​the second outer end face, the force due to ambient pressure at the second end is greater than the force due to ambient pressure at the first end.

[0007] In a deep-sea vessel including a variable buoyancy engine according to one embodiment, the variable buoyancy engine is: pressure vessel and The system includes a main pump positioned to pump fluid from inside the pressure vessel, The aforementioned main pump comprises the pump body and At least one entrance, At least one exit, A fluid path between the at least one inlet and the at least one outlet, A piston configuration comprising: a piston chamber; an inlet valve; an outlet valve; a piston disposed to move within the piston chamber and having a first outer end face at a first end and a second outer end face at a second end; and a piston drive operably mounted to the first end of the piston for driving the piston within the piston chamber; At least one of the first outer end face and the second outer end face of the piston is exposed to ambient pressure. Since the surface area of ​​the first outer end face is smaller than the surface area of ​​the second outer end face, the force due to ambient pressure at the second end is greater than the force due to ambient pressure at the first end. [Brief explanation of the drawing]

[0008] The following examples only refer to specific embodiments and attached drawings.

[0009] [Figure 1] A schematic diagram of a submersible with an open-loop two-stage pumping system is shown. [Figure 2] A schematic diagram of a double-closed-loop, two-stage pumping system for a submersible is shown. [Figure 3] A schematic diagram of a balanced piston pump used as the main pump in a submersible is shown. [Figure 4] Figure 3 schematically shows the suction stage of the pump's operation. [Figure 5] Figure 3 schematically shows the pressurization stage of the pump's operation. [Figure 6] This is a schematic perspective view of a balance piston pump according to one embodiment of the present invention. [Figure 7] Figure 6 shows a pump with the outer housing components transparent. [Figure 8] Figure 6 shows a cross-section of the pump. [Figure 9]Shows the inlet plate. [Figure 10] Shows the bottom view of the small end plate. [Figure 11] Shows the top view of the small end plate. [Figure 12] Shows the bottom view of the large end plate. [Figure 13] Shows the top view of the large end plate. [Figure 14] Shows the bottom view of the outlet plate. [Figure 15] Shows the top view of the outlet plate. [Figure 16] Shows the end cap. [Figure 17] Shows the lower part of the pump in FIG. 6. [Figure 18] Shows the shaft that engages with the piston of the pump in FIG. 6. [Figure 19] Shows the top view of the transmission housing. [Figure 20] Schematically shows maintaining the ambient pressure within the oil filling pressure volume part of the pump.

Embodiments for Carrying Out the Invention

[0010] Since a submersible often generates forward thrust using a variable buoyancy engine, it can operate independently of a surface boat for a long period of time. In a variable buoyancy engine, the buoyancy of the submersible can be changed. By pumping water, for example, seawater, which enters and exits the pressure vessel within the submersible, to the outside of the submersible in what can be considered an open loop system, the buoyancy can be absolutely changed. Alternatively, the buoyancy distribution within the submersible may be changed by pumping fluid from the pressure vessel to different regions of the submersible or by changing the fluid amount to affect the density and buoyancy within the submersible. In a closed loop system, the fluid may be fresh water, oil, or other types of fluids and is pumped into a flexible reservoir that is acted upon by the ambient pressure.

[0011] Since the inside of the pressure vessel may approach a vacuum, a two-stage system may be provided, with an internal pump mounted inside the pressure vessel to function as a primary pump for the external main pump. The primary pump may be any simple type of pump, such as a vane pump, impeller pump, or piston pump.

[0012] Figure 1 shows a schematic diagram of one embodiment of an open-loop system. The submersible 100 has an internal pressure vessel 102. In the open-loop system, an inlet valve 104, such as a solenoid valve, can control the flow of external seawater into the pressure vessel. A two-stage pump can be used to empty the pressure vessel 102. A main pump 108 can pump water from the pressure vessel 102 to the outside of the submersible 100. A primary pump 106 located inside the pressure vessel 102 can be used to ensure that sufficient pressure is supplied to the main pump 108 in the line. The main pump can be operated by a motor 110, for example, a fluid-filled brushless DC motor. A battery 112 can supply power to the motor 110.

[0013] Figure 2 shows a schematic diagram of one embodiment of a closed-loop system. The submersible 200 includes two pressure vessels 202 and 203, primary pumps 206 and 207 for each of the pressure vessels, and main pumps 208 and 209 coupled to each of the primary pumps. However, instead of pumping fluid from outside the submersible, the pressure vessels 202 and 203 are filled with fluid via inlet solenoid valves 204 and 205 from an internal flexible reservoir 214, such as a bag, which is acted upon by the external ambient pressure. The main pumps 208 and 209 pump fluid back from each of the pressure vessels 202 and 203 to the flexible reservoir 214, against the ambient pressure acting on the reservoir 214. Since the fluid can enter and exit the bag 214 and independently enter and exit the pressure vessels, the displacement between the pressure vessels and the displacement between the pressure vessels and the bag can be changed, thereby affecting the buoyancy of the submersible.

[0014] Figures 1 and 2 show a two-stage pumping system in which a primary pump pressurizes fluid from a pressure vessel and supplies it to a main pump. In an alternative configuration, the primary pump may be omitted if sufficient pressure to operate the main pump can be obtained from the pressure vessel. For example, the pressure vessel may be partially filled by pumping fluid inside, rather than being filled with fluid in a free flow due to ambient pressure.

[0015] Three-piston axial-driven pumps are known to be used as main pumps. However, such pumps are generally not designed to operate under the high ambient pressures (outside the pressure vessel) encountered in deep sea environments. The pumps need to discharge fluid to the outside or into a reservoir against the pressure of the surrounding environment.

[0016] To counteract the high ambient pressures encountered at the operating depths of underwater vessels, a main pump according to one embodiment of the present invention, hereafter referred to as a balanced piston pump, can be provided. Figure 3 shows a schematic diagram of a balanced piston pump according to one embodiment of the present invention. The pump 300 in Figure 3 includes a body 310 that defines a piston chamber 320. A stepped piston 330 is arranged to reciprocate within the piston chamber 320.

[0017] The piston chamber 320 is substantially toroidal and has an inlet 321 with an inlet check valve 322 and an outlet 325 with an outlet check valve 326. The piston chamber 320 receives fluid through the inlet 321 from a pressure vessel (or partially filled pressure vessel) that is initially pressurized by a primary pump (not shown in Figure 3) and discharges the fluid through the outlet 325.

[0018] The stepped piston 330 is substantially longitudinal in shape and has a first end 331 (small end) and a second end 333 (large end) at the longitudinal end opposite the first end 331 of the piston 330. The first end 331 has a smaller diameter than the second end 333. The stepped portion 336 of the piston 330 changes the diameter of the piston 330 between the first end 331 and the second end 333. The stepped portion 336 is located within the piston chamber 320. The first end 331 has a first outer end face 332, and the second end 333 has a second outer end face 334. Each outer end face 332, 334 is located outside the piston chamber 320 and is exposed to ambient pressure. A piston drive or motor (not shown) drives the reciprocating motion of the piston 330. The piston drive may be attached to the first end 331 of the piston.

[0019] The seals 342 and 344 abut against the main body 310, respectively, sealing the first and second ends of the piston 330, thereby isolating the piston chamber 320 from ambient pressure.

[0020] During operation, the motor drives the large-diameter portion of the piston 330 outside the piston chamber 320 (Figure 4) by driving the first end 331 into the piston chamber 320 (Figure 4) in the direction of arrow 352, thereby increasing the available volume of the piston chamber (suction stroke). Fluid is drawn into the piston chamber 320 through the inlet 321, as indicated by the inlet arrow 354. In the return stroke (pressurization stroke in Figure 5), the large end of the piston returns to the piston chamber (directional arrow 356), thereby decreasing the volume of the piston chamber 320 and pushing the fluid out from the outlet 325, as indicated by arrow 358.

[0021] Because the surface area of ​​the first outer end face 332 is smaller than that of the second outer end face 334, the force due to ambient pressure at the second end is greater than the force due to ambient pressure at the first end. Since the forces acting on the piston end faces 332 and 334 generated by ambient pressure are almost canceled out, the pump can be designed to operate at any depth. Although not constrained by theory, the force that the piston drive should act on the first end face 331 (small end) of the piston to pump the fluid is equal to the difference in cross-sectional areas between the small end face 332 and the large end face 334 (in the shown embodiment, the cylinder chamber is donut-shaped) multiplied by the ambient pressure (ignoring friction, valve springs and other losses, and assuming no input pressure assists).

[0022] In one embodiment, the end of the piston is subjected to the pressure of the ambient environment through an oil-filled compartment. This may be called a “balancing” operation. In one embodiment, one end of the piston is exposed to the ambient environment, while in an alternative embodiment, both ends of the piston are subjected to the ambient environment. The compartments may be separated from each other or connected.

[0023] Figure 6 shows a perspective view of a balance piston pump 600 according to one embodiment of the present invention. Figure 7 shows a perspective view of Figure 6 in which the outer body elements are transparent to allow the internal components of the pump to be seen. The pump 600 is a multi-piston pump with five pistons arranged around its circumference. Fluid is supplied into the pump through a fluid inlet 621 and pumped out through an outlet on the top surface of the pump. Oil is supplied from an oil reservoir (not shown) to an oil chamber inside the pump through an oil inlet 623 and can be discharged through an outlet 627.

[0024] Figure 8 shows a cross-section of the pump 600 as inverted in Figure 6. The labeled components of the pump 600 are as follows:

[0025] [Table 1]

[0026] Pump 600, having five pistons, has a body formed by the integral joining of several circular plates, these circular plates defining five individual fluid passages that penetrate the body from a single inlet 621 to a single outlet 625. The piston configuration is positioned in each of the fluid passages. In the following description, the outlet 625 and the big end are shown at the top, and the small end or drive end is shown at the bottom, as shown in the orientation of Figure 6. The term orientation is for illustrative purposes only and is not intended to limit the scope of the present invention to these orientations.

[0027] Figure 9 shows a top view of the inlet plate 900. Five piston guide holes 902 are formed radially distributed in the inlet plate, extending longitudinally through the plate. The guide holes 902 are configured to accommodate the small end of a stepped piston. A radial hole 904 receives the inlet 621 and extends from the periphery 906 of the plate to a central vertical hole 908, which extends downward from the top surface 910 of the plate 900 so as to abut against the radial hole 904. The vertical hole 908 is closed off by the bottom surface of the plate 900.

[0028] The upper surface 910 of the inlet plate 900 is in contact with the back surface (Figure 10) of the small end plate 1000. The small end plate 1000 is the piston guide of the inlet plate 900. hole It includes a piston guide 1002 aligned with 902 and extending longitudinally through plate 1000. The back surface 1004 of the small end plate has a central longitudinal hole 1008 that extends inward through the plate and is closed at the top surface 1010. A series of (five) flow channels 1012 extend radially from the central hole 1008 to the outer flow channel ends 1014. Each outer flow channel end 1014 has a hole formed therein that extends longitudinally through plate 1000 to the top surface.

[0029] The upper part of the small end plate 1000 is shown in Figure 11. Five recesses 1018 are distributed around the plate. Each recess 1018 contains an inlet poppet valve seat 1020. Within the poppet valve seat, a flow hole 1016 is formed, aligned with the outer flow end 1014 of the flow path 1012 and extending through the plate. The inlet poppet valve seat 1020 is configured to receive the end of an inlet poppet valve that seals the flow hole 1016. A single poppet valve 1022 is shown in Figure 11, and the remaining poppet valves are omitted in the drawing for simplification. The recesses 1018 extend to the piston guide 1002. The piston guide has a stepped portion 1024 that defines the lower end of the piston chamber. The stepped portion 1024 is aligned with the stepped portion of the piston 1030. and define the piston seat The piston guide is configured to receive the stepped portion of the piston and provide a seat. A single piston 1030 adjacent to the inlet poppet valve 1022 is shown. The remaining pistons are omitted in the drawing for simplification.

[0030] Figure 10 shows that each piston guide 1002 is stepped 1017 This indicates that it has the following: The upper part of the piston guide is sized to fit snugly onto the small end of the stepped piston. Below the step, the width of the piston guide increases. Sealing ring 1019 It is inserted into the piston guide 1002 from below, and the stepped portion 1017 It is located there and seals the piston chamber above the sealing ring from the ambient pressure below the sealing ring.

[0031] Piston seat Step portion that defines Above 1024 is the piston chamber 1120 (described in more detail below). The inlet passage 1026 extends from the inlet poppet valve seat 1020 to the piston chamber 1120. The piston's lower structure is the piston to the seat Therefore, when fully seated, the body of the piston 1030 seals the inlet passage 1026, preventing any fluid from entering the piston chamber 1120. At this time, the poppet valve is biased to close the passage hole 1016. When the piston rises Piston seat?When moving away, the inlet passage 1026 is open to the piston chamber. At this time, the vacuum formed in the piston chamber 1026 and the pressure of the fluid from the inlet are sufficient to overcome the closing biasing force of the inlet poppet valve 1022. The poppet valve opens, and the fluid flows through the inlet plate 900 into the passage 1012 of the small end plate, and then through the passage holes 1016 and inlet passage 1026 of the respective open pistons into the piston chamber 1120.

[0032] As shown in Figure 11, the poppet valve 1022 opens from the top and includes a hole 1023 located on the side of the body of the poppet valve 1022. At the top of the piston stroke when the piston chamber 1120 is filled with fluid and the pressure equals the inlet pressure, a spring or similar biasing mechanism located above the poppet valve may seal the flow path hole 1016 by pressing it to close the poppet valve.

[0033] Figure 12 shows a rear view of the large end plate 1200 seated on the small end plate 1000. The large end plate 1200 includes a piston guide 1202 that extends longitudinally through the plate 1200 and is aligned with the piston guide 1002 of the small end plate 1000. piston Guy D1 202 is configured to accommodate the large end of a stepped piston. An inlet poppet valve guide 1204 is formed on the lower surface 1201 of the large end plate 1200, aligned with the poppet valve seat 1020 on the small end plate 1000. Figure 12 shows a single inlet poppet valve 1022 positioned on the poppet valve guide 1204. The remaining inlet poppet valves are omitted in the drawing for simplification.

[0034] The inlet poppet valve guide has a diameter sufficient to accommodate the width of the inlet poppet valve and has space between it and the inlet poppet valve. The valve guide terminates through most of the large end plate 1200. The small outlet opening extends through the valve guide to the upper surface of the large end plate 1200. A spring or other biasing mechanism (39 in Figure 8) is provided on the valve guide 1204 to bias the inlet poppet valve downward toward the inlet poppet valve seat 1020. The base 1025 of the inlet poppet valve is narrower than the main body of the poppet valve but is sufficient to seal the flow passage hole 1016. However, if the base is sealed toward the flow passage hole 1016, fluid can flow around the inlet poppet valve and into the valve guide 1204. Therefore, when the piston is in the return stroke, the fluid flows through the passage 1026 of the hole 1023 on the side of the poppet valve 1022, through the donut-shaped cavity between the small end of the piston 1030 and the wall of the piston guide 1202. and (shown as shown) Piston chamber 1120 It is then pushed into the valve guide 1204.

[0035] Figure 13 shows the upper part 1210 of the big end plate 1200. Adjacent to each piston guide 1202 is an outlet opening 1206 aligned with the lower inlet poppet valve guide 1204. The outlet opening 1206 is sealed by an outlet poppet valve 1422. A single outlet poppet valve 1422 is shown in Figure 13. The remaining outlet poppet valves are omitted for simplification. Figure 13 shows that each piston guide 1202 has a stepped portion 1216. The lower part of the piston guide is sized to fit snugly onto the big end of the stepped piston. Above the stepped portion, the width of the piston guide increases. A sealing ring 1218 is located on the stepped portion 1216 to seal the piston chamber below the sealing ring from the ambient pressure above the sealing ring.

[0036] Figure 14 shows the back surface 1401 of the outlet plate 1400. The outlet plate seats on the big end plate 1200. The outlet plate 1400 includes a piston guide 1402 that extends longitudinally through the plate 1200 and is aligned with the piston guide 1202 of the big end plate 1200. piston Guy D1 402 is configured to house the large end of a stepped piston. Within surface 1401, an outlet poppet valve guide 1404 is embedded, aligned with the inlet poppet valve guide 1204 of the large end plate 1200. From each outlet poppet valve guide 1404, a radial flow path 1406 extends to abut against a central hole that axially penetrates the outlet plate 1400. Figure 14 shows a single outlet poppet valve 1422 positioned in a valve guide 1404. The remaining outlet poppet valves are omitted in the drawing for simplification.

[0037] Figure 15 shows the top surface 1410 of the outlet plate 1400. The top surface 1410 shows the piston guide 1402 and a single piston 1030 extending above the outlet plate. The remaining pistons are omitted in the drawing for simplification. A central hole 1408 communicating with the flow path 1406 located on the underside of the plate 1400 is shown penetrating the thickness of the plate 1400.

[0038] Figure 16 shows the end cap 1600 of the pump. The end cap has a central hole 1608 that leads to the outlet 625. The central hole is aligned with the central hole 1408 of the outlet plate 1400. The end cap 1600 is substantially hollow and, together with the upper surface 1410 of the outlet plate 1400, defines an ambient pressure volume 1604. The large end of the piston extends into the volume 1604. A valve spring (e.g., valve spring 23 in Figure 8) can be seated in a spring recess 1606. department One of them goes through the end cap. Provides an opening 1612This provides a connection to the ambient pressure for the ambient pressure volume section 1604. In one embodiment, the opening 1612 (shown outside the end cap 1600 as the oil outlet 627 in Figure 6) can be used to introduce oil into the ambient pressure volume section 1604 or to discharge oil from the ambient pressure volume section 1604.

[0039] As described above, during the downward stroke of the piston 1030, the fluid is pushed into the valve guide 1204 of the inlet poppet valve. As the piston force increases during the downward stroke, the pressure of the outlet poppet valve 1422, which seals the outlet opening 1206 of the inlet poppet valve guide 1204, opens the outlet poppet valve, allowing the fluid to flow into the outlet poppet valve guide 1404, into the flow path 1406, through the axial hole 1408 of the outlet plate 1400, and out to the outlet 625 of the end cap 1600. This discharges the fluid from the pump.

[0040] At the lower end of the pump, the small end of the piston is the piston guide of the inlet plate 900. hole It passes through 902 and protrudes into the volume defined between the lower end of the inlet plate and the transmission housing 1700 (Figure 17).

[0041] Figure 18 shows the small end of the piston 1030 positioned on the shaft 1802 and the inclined swash plate 1804, also called an inclined plate or oblique plate. The shaft 1802 and the swash plate form a piston drive that generates the reciprocating motion of the piston. As the shaft 1802 rotates, the inclined swash plate 1804 provides the suction stroke for each piston chamber by sequentially raising each piston. After passing the highest point of the swash plate, the pressurizing stroke is performed by returning the piston to its original position due to the differential pressure of the ambient pressure acting on the large end of the piston and the small drive end of the piston.

[0042] The end of the shaft may be engaged with the transmission housing 1700 by the motor's crank to impart rotation to the shaft. Various crank motor connections will be apparent to those skilled in the art. The motor may be an electronically rectified fluid-filled brushless DC motor. The fluid filling makes the motor well-suited for operation at considerable depths underwater. As is known, a battery may be provided to power the motor.

[0043] The transmission housing 1700 is shown separately in Figure 19. Internally, the transmission housing comprises an ambient pressure volume 1704 provided through an inlet 623. Through the inlet 623, the volume 1704 may be exposed to ambient pressure. Alternatively, the volume 1704 may be filled with oil maintained at ambient pressure.

[0044] When the pump plates are joined together, they define a continuous piston housing from the small end to the large end. The plates may be joined together by appropriate bolts 630 extending through complementaryly aligned holes in each plate. O-ring seals may be provided between the plates to prevent water from entering the pump body. The inlet plate 900 (Figure 9) has a groove 914 on its upper surface to receive the O-ring seal. Similar grooves are provided in plates 1000, 1200, 1400, the transmission housing 1700, and the end caps 1600.

[0045] The piston balancing operation is performed by positioning the large and small ends of the stepped piston in the ambient pressure volume sections. The drawings show two ambient pressure volume sections 1604 and 1704 located at the large and small ends of the pump, respectively. The ambient pressure volume sections may be maintained independently through their respective openings 627 and 623. However, to ensure that each ambient pressure volume section is maintained at the same pressure, the volume sections may be connected via the pump plates. Thus, in the shown embodiment, the transmission case volume section 1704 is connected to the end cap volume section 1604 via aligned and connected holes in the inlet plate 900 (hole 950), the small end plate 1000 (hole 1050), the large end plate 1200 (hole 1250), and the outlet plate 1400 (hole 1450). Although one connection is shown in the drawings for simplification, multiple oil conduits penetrating the pump plates are shown.

[0046] Figure 20 schematically illustrates how oil is used to maintain ambient pressure at each end of the pump. In Figure 20, the stepped piston 1030 is shown with its large end protruding into the ambient pressure volume section 1604 and its small end protruding into the ambient pressure volume section 1704. A fluid conduit 1750 connects the volume sections 1604, 1704 via the pump. A flexible oil reservoir 1760 is connected to the inlet 621 of the transmission volume section 1704 and the outlet 625 of the end cap volume section 1604. The reservoir 1760 may be slightly pressurized for positive compensation by means of a spring acting on a bladder (bag). Initially, this system may be used to fill the pump with ambient fluid such as oil. The system may be deflated to remove any escaped air, and then the connection with the reservoir 1760 may be maintained. Because the storage section is subjected to ambient pressure, even if the fluid is compressed as the ambient pressure increases, the pressure in the volume sections 1604 and 1704 remains the same as the ambient pressure. Although oil has been described as the ambient pressure fluid, other fluids such as seawater in the case of an open-loop system or freshwater in the case of a closed-loop system may be used.

[0047] The embodiment, particularly the cross-sectional view in Figure 8, shows that the large end of the piston is seated via a spring, but the springs at one end or both ends of the piston may be considered arbitrary.

[0048] In the shown embodiment, the inlet and outlet poppet valves of the same fluid path are positioned directly above each other. In an alternative embodiment, cross-flow may be achieved by positioning the outlet poppet valve of one fluid path above the inlet poppet valve of an adjacent fluid path, providing an additional passage connecting the piston chamber and the outlet. Cross-flow may be advantageous in terms of operational efficiency.

[0049] The pump in the embodiments of this specification is described as the main pump of a two-stage pumping system. However, alternative uses of the pump will be obvious to those skilled in the art. For example, the pump may be used independently of the primary pump if sufficient inlet pressure is available.

[0050] While embodiments of the present invention are shown in the accompanying drawings and described above, it should be understood that the present invention is not limited to the disclosed embodiments and that numerous reconfigurations, modifications, and substitutions are possible without departing from the spirit of the invention as described and limited in the accompanying claims.

Claims

1. a. Pump body and b. At least one entrance, c, at least one outlet, d, a fluid path between the at least one inlet and the at least one outlet, e, at least one piston configuration arranged in the fluid path and configured to pump fluid from at least one inlet through the fluid path to at least one outlet, comprising i, a piston chamber, ii, an inlet valve, iii, an outlet valve, iv, a piston disposed to move within the piston chamber and having a first outer end face at a first end and a second outer end face at a second end, and v, a piston drive that drives the piston within the piston chamber and is operably mounted to the first end of the piston, f, the first outer end surface and the second outer end surface of the piston are each exposed to ambient pressure, g. A pump in which, because the surface area of ​​the first outer end face is smaller than the surface area of ​​the second outer end face, the force due to the ambient pressure at the second end is greater than the force due to the ambient pressure at the first end.

2. The pump according to claim 1, comprising at least one ambient pressure chamber, wherein at least one of the first and second outer end faces of the piston is located within the ambient pressure chamber.

3. The pump according to claim 2, wherein the at least one ambient pressure chamber includes a first ambient pressure chamber located at the first end of the pump and a second ambient pressure chamber located at the second end of the pump.

4. The pump according to claim 3, wherein the pump body includes one or more fluid conduits that penetrate the pump body and fluidly connect the first ambient pressure chamber and the second ambient pressure chamber.

5. The pump according to claim 2 or 3, wherein the at least one ambient pressure chamber includes an inlet connection for receiving ambient pressure fluid.

6. The pump according to any one of claims 1 to 5, wherein the at least one piston configuration is longitudinal, the inlet valve is arranged in a longitudinal line with the outlet valve, and the piston chamber is arranged adjacent to the inlet valve.

7. a. Pressure vessel and b, a main pump arranged to pump fluid from inside the pressure vessel, The aforementioned main pump is i. Pump body and ii, at least one entrance, iii, at least one exit, iv, a fluid path between the at least one inlet and the at least one outlet, v, a piston configuration comprising: a piston chamber; an inlet valve; an outlet valve; a piston disposed to move within the piston chamber and having a first outer end face at a first end and a second outer end face at a second end; and a piston drive operably mounted to the first end of the piston for driving the piston within the piston chamber, vi. A pumping system for underwater vessels, wherein the first and second outer end faces of the piston are each exposed to ambient pressure, and the surface area of ​​the first outer end face is smaller than the surface area of ​​the second outer end face, so the force due to ambient pressure at the second end is greater than the force due to ambient pressure at the first end.

8. The pumping system according to claim 7, comprising a motor that operates the piston drive of the main pump to cause the piston of the at least one piston configuration to reciprocate.

9. The pumping system according to claim 7 or 8, comprising at least one ambient pressure chamber, wherein at least one of the first and second outer end faces of the piston is located within the ambient pressure chamber.

10. The pumping system according to claim 9, wherein the at least one ambient pressure chamber includes a first ambient pressure chamber located at the first end of the main pump and a second ambient pressure chamber located at the second end of the main pump.

11. The pumping system according to claim 10, wherein the pump body includes one or more fluid conduits that penetrate the pump body and fluidly connect the first ambient pressure chamber and the second ambient pressure chamber.

12. The pumping system according to any one of claims 9 to 11, wherein the at least one ambient pressure chamber includes an inlet connection for receiving ambient pressure fluid into the at least one ambient pressure chamber.

13. The pumping system according to claim 12, comprising an external flexible reservoir that is fluid-connected to the inlet connection and contains ambient pressure fluid, wherein the flexible reservoir is subjected to ambient pressure.

14. A pumping system according to any one of claims 7 to 13, comprising a primary pump arranged to pump fluid from inside the pressure vessel to the main pump.

15. An underwater vehicle including a variable buoyancy engine, wherein the variable buoyancy engine is a. Pressure vessel and b, a main pump arranged to pump fluid from inside the pressure vessel, The aforementioned main pump is i. Pump body and ii, at least one entrance, iii, at least one exit, iv, a fluid path between the at least one inlet and the at least one outlet, v, a piston configuration comprising: a piston chamber; an inlet valve; an outlet valve; a piston disposed to move within the piston chamber and having a first outer end face at a first end and a second outer end face at a second end; and a piston drive operably mounted to the first end of the piston for driving the piston within the piston chamber, vi, the first outer end surface and the second outer end surface of the piston are each exposed to ambient pressure, vii, a submersible vehicle in which the surface area of ​​the first outer end face is smaller than the surface area of ​​the second outer end face, and therefore the force due to the ambient pressure at the second end is greater than the force due to the ambient pressure at the first end.

16. The underwater vehicle according to claim 15, comprising a motor that operates the piston drive of the main pump to cause the piston of the at least one piston configuration to reciprocate.

17. The underwater vehicle according to claim 15 or 16, comprising at least one ambient pressure chamber, wherein at least one of the first and second outer end faces of the piston is located within the ambient pressure chamber.

18. The underwater vehicle according to claim 17, wherein the at least one ambient pressure chamber includes a first ambient pressure chamber located at the first end of the main pump and a second ambient pressure chamber located at the second end of the main pump.

19. The underwater vehicle according to claim 18, wherein the pump body includes one or more fluid conduits that penetrate the pump body and fluidly connect the first ambient pressure chamber and the second ambient pressure chamber.

20. The underwater vehicle according to any one of claims 17 to 19, wherein the at least one ambient pressure chamber includes an inlet connection for receiving ambient pressure fluid into the at least one ambient pressure chamber.

21. The underwater vehicle according to claim 20, comprising an external flexible reservoir that is fluidly connected to the inlet connection and contains ambient pressure fluid, wherein the flexible reservoir is subjected to ambient pressure.

22. The underwater vehicle according to any one of claims 15 to 21, further comprising a primary pump arranged to pump fluid from inside the pressure vessel to the main pump.

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