DOUBLE PISTON PUMPING DEVICE

Description

[0001] The present invention relates to a novel double piston pump device.

[0002] Piston pumps in various embodiments are known in the prior art, see e.g. Dubbel, Maschinenbau, Chapter H8.

[0003] The present invention aims to provide a piston pump that achieves a high efficiency, enables the most uniform possible delivery of the pumped fluid, and is easy and inexpensive to manufacture.

[0004] US 5 348 451 A relates to a pumping device with an electric linear motor that drives drive pistons which are hydraulically coupled to pump pistons or to coupling pistons which are mechanically connected to the pump pistons which move a fluid to be pumped.

[0005] The present invention therefore provides a novel double-piston pump device according to claim 1, comprising a first hydraulic cylinder and a second hydraulic cylinder, each completely filled with a fluid and in each of which a drive piston and a working piston are movably arranged, wherein the device is configured such that an external driving force can act on the drive pistons, causing the drive pistons to move in opposite directions, causing the working pistons to also move in opposite directions, and this opposite movement is supported by a mechanical coupling of the working pistons, and the device further comprising a first and a second pump unit for conveying a fluid, preferably a liquid, which is assigned to the first and second hydraulic cylinders respectively, wherein the rear sides of the working pistons of the first and second hydraulic cylinders are articulated.The second hydraulic cylinder is connected to the associated pump unit in such a way that fluid is alternately drawn in and expelled by the reciprocating movement of the working pistons in the associated pump unit, with the intake and discharge of the fluid to be pumped occurring at different times in the two pump units.

[0006] The pumping device according to the invention enables, on the one hand, the transmission of the force acting on the drive pistons to the working pistons by means of the hydraulic fluid located in the hydraulic cylinders, which in turn transmit the force to the pumping units that cause the delivery of the fluid to be delivered.

[0007] The pressure or force can be transmitted unchanged, or it can be amplified. This means that, for example, the pressure acting on the fluid being pumped can be equal to, greater than, or less than the pressure exerted by the piston on the hydraulic fluid in a hydraulic cylinder. Thus, for instance, increased pressure can be generated without changing the force.

[0008] This results in lower electricity costs, more power, and greater fluid displacement even at higher pressure.

[0009] The change in pressure can be achieved, for example, through the design of the drive and working pistons in the hydraulic cylinders in conjunction with the design of the pump units.

[0010] If the pump unit is designed, for example, to include a pump cylinder and a pump piston movable within it, a pressure change can be set by the ratio of the displacement volumes of the pump pistons and the associated drive or working pistons.

[0011] Furthermore, the pumping device according to the invention ensures that the fluid to be pumped is conveyed particularly evenly by means of the time-staggered intake and discharge cycles of the two pump units.

[0012] The pumping device of the present invention can be designed as a high-speed pump, e.g. the device can be designed so that it performs 1500 complete piston strokes of both drive pistons in the hydraulic cylinder per minute.

[0013] The advantages of the pumping device continue to be its self-priming capability, its good efficiency, and, especially in smaller units, its simple design and low investment costs.

[0014] The pump device functions as follows: the force acting upon it causes one of the drive pistons to move in the forward direction, i.e., in such a way that the hydraulic fluid in the cylinder is pushed into the cylinder interior, while the second drive piston moves in the opposite direction, i.e., in the return direction, in such a way that the hydraulic fluid is drawn out of the cylinder interior following the piston.

[0015] Forward and reverse directions are understood in relation to the movement of the piston in the respective cylinder, where "forward" refers to the direction into the cylinder and "reverse" refers to the direction out of the cylinder.

[0016] The hydraulic cylinders are designed in the area of ​​the stroke of the drive or working pistons in such a way that the pistons seal against the inner walls of the cylinders.

[0017] "Opposite movement" refers to a movement of the pistons relative to the respective cylinder, i.e., the opposite movement of, for example, the driving piston means that one moves in the direction of propulsion and the other in the direction of return with respect to the respective cylinder.

[0018] Following the movement of the drive pistons, and the resulting movement of the hydraulic fluid, in the respective hydraulic cylinders, the working piston in the first hydraulic cylinder, where the drive piston moves in the thrust direction, moves in the return direction, while the working piston in the second hydraulic cylinder, where the drive piston moves in the return direction, moves in the thrust direction. This means that the drive and working pistons in each of the hydraulic cylinders move in opposite directions, which in turn also causes the two working pistons to move in opposite directions. This opposing movement of the working pistons is supported by the mechanical coupling of the working pistons.

[0019] The movements of the working pistons are then transferred to the respective pump unit, which also operate "in opposite directions", i.e., when one pump unit is in suction mode, the other pump unit is in delivery mode, thus achieving an overall uniform delivery of the fluid to be delivered.

[0020] The "front of a piston" refers to the side of the piston facing the respective cylinder, and the "back of a piston" refers to the side of the piston facing away from the respective cylinder.

[0021] A liquid such as a mineral oil-based or water-based liquid is preferably used as the hydraulic fluid.

[0022] The two ensembles consisting of hydraulic cylinders and associated components and the associated pump unit are hereinafter also referred to as "units of the pumping device".

[0023] Preferably, the movement of the driving pistons is effected by means of a crankshaft. This can be achieved, for example, in a conventional manner by force transmission from the crankshaft to the respective driving piston via connecting rods, whereby the rotational movement of the crankshaft is converted into a translational movement of the driving pistons.

[0024] The crankshaft is preferably connected to a power unit that transmits torque to the crankshaft, thus setting it in rotation. An electric motor is typically used as the power unit, but depending on the application, an internal combustion engine can also be used.

[0025] Typically and preferably, the movement of the drive pistons and / or the working pistons in the respective hydraulic cylinder is linear; that is, the hydraulic cylinders are shaped in such a way that this movement occurs linearly. The pistons thus move back and forth in an oscillating manner along a straight line between a top dead center and a bottom dead center.

[0026] Preferably, the hydraulic cylinders are designed such that the movement of the drive pistons and the working pistons in the respective hydraulic cylinder is perpendicular to each other.

[0027] This means that the directions of the stroke paths of the drive and working pistons in the respective hydraulic cylinder are preferably perpendicular to each other, so that the hydraulic cylinders have a rectangular shape when viewed in cross-section.

[0028] Preferably, the opposing movement of the drive pistons in the hydraulic cylinders is antiparallel. This means that the hydraulic cylinders are preferably arranged relative to each other such that the strokes of the drive pistons in the cylinders are parallel to each other.

[0029] The first and second hydraulic cylinders are directly adjacent to each other. Therefore, the two hydraulic cylinders share a cylinder wall, either completely or partially.

[0030] In the preferred embodiment, in which the hydraulic cylinders are arranged relative to each other such that the stroke paths of the drive pistons in the cylinders are parallel to each other, the hydraulic cylinders preferably border directly on each other in the direction along the lines or surfaces defined by the stroke paths of the drive pistons, and thereby share, for example, the cylinder wall completely or partially in this direction.

[0031] The two working pistons, which are mechanically coupled to each other, are preferably rigidly connected to each other.

[0032] Preferably, the two front faces of the working pistons are rigidly connected to each other, usually by a rigid rod. In this embodiment, an opening is provided in the cylinder walls of the hydraulic cylinders through which the rigid connecting elements are guided from the front face of the first working piston to the front face of the second working piston.

[0033] These openings are designed in such a way that they are sealed against the connecting elements, so that, for example, no hydraulic fluid can escape from the hydraulic cylinders through these openings.

[0034] Advantageously, the rigid connecting element can also be guided through an opening in a cylinder wall shared by both hydraulic cylinders. This has the advantage that there is only one opening, and that hydraulic fluid can only pass from one hydraulic cylinder to the other when it penetrates this opening.

[0035] Preferably, the two working pistons move linearly, and preferably along the same imaginary line.

[0036] This is particularly preferred in the embodiment described in more detail above, in which the hydraulic cylinders have a rectangular shape when viewed in cross-section and the stroke movements of the two drive pistons are antiparallel.

[0037] In this embodiment, the preferred rigid connection between the front faces of the working pistons can be made by a rigid, linear rod.

[0038] Furthermore, in the preferred embodiment, where the hydraulic cylinders are directly adjacent to each other and at least partially share a cylinder wall, the rigid linear rod can be guided through an opening in this cylinder wall from one hydraulic cylinder directly into the other hydraulic cylinder.

[0039] Preferably, a portion of the internal volume of one or both hydraulic cylinders is not encompassed by the stroke of the respective drive and working pistons associated with the hydraulic cylinder. This means that no piston enters this part of the hydraulic cylinder(s) on its way from top dead center to bottom dead center.

[0040] Furthermore, the displacement volume per stroke is preferably the same for the drive and working pistons assigned to a hydraulic cylinder, preferably for both drive and working pistons assigned to the respective hydraulic cylinders.

[0041] The drive and working pistons of a hydraulic cylinder can also have the same displacement area and / or the piston stroke of the drive and working pistons assigned to a hydraulic cylinder can be the same.

[0042] The stroke distances, i.e. the distances from one dead center of the piston movement to the other and back, of the drive and working pistons assigned to each hydraulic cylinder preferably do not overlap.

[0043] The pump units can be designed in various ways, e.g. as a pump cylinder / pump piston combination or as a diaphragm pump unit, whereby the pumping of the fluid to be pumped is effected by the force transmitted from the back of the working pistons, for example by the movement of the pump piston in the pump cylinder or by the movement of the diaphragm.

[0044] Preferably, one or both pump units each comprise a pump cylinder and a pump piston movable therein.

[0045] In this embodiment, the pump piston(s) are preferably mechanically coupled to the respective working piston in such a way that the pump piston and working piston move in opposite directions in the respective cylinder.

[0046] Preferably, the pump piston(s) and the respective working piston(s) are rigidly connected to each other. This is usually achieved by connecting the rear side of the working piston(s) to the rear side of the pump piston(s), for example, by a rigid rod. The piston stroke of the rigidly connected pump and working piston(s) is the same.

[0047] Preferably, the working pistons and pump pistons move in parallel directions, and preferably linearly along the same imaginary line.

[0048] In this embodiment, the preferred rigid connection between the rear of the working pistons and the rear of the pump pistons can be made by a rigid, linear rod.

[0049] Preferably, the pump cylinder(s) are directly adjacent to the respective hydraulic cylinder, usually in the direction of movement of the working or pump piston(s).

[0050] Preferably, in the embodiment in which the front sides of the working pistons are connected to each other by a rigid, linear rod and the rear sides of the working pistons are each connected to the rear side of the pump piston by a rigid, linear rod, these connecting rods are all on the same line.

[0051] The displacement volume per stroke of a working piston, preferably of both working pistons, is different, preferably larger, than the displacement volume per stroke of the respective associated pump piston.

[0052] This means that the pressure exerted on the fluid to be conveyed in the associated pump units is greater than the pressure exerted on the hydraulic fluid by the drive pistons in the respective associated hydraulic cylinder.

[0053] Preferably, the pumping device is symmetrically constructed, except for the connection of the crankshaft to the engine, which normally only takes place at one end of the crankshaft, and is mirror-symmetrical to the plane running through the center of the pumping device, which separates the two units of the pumping device.

[0054] Even where not explicitly mentioned, the described embodiments apply to one or both units (hydraulic cylinder and pump unit) of the pumping device according to the invention. Typically, the pistons used in the device according to the invention have piston rings for sealing.

[0055] The cross-section of hydraulic cylinders in the direction perpendicular to the direction of piston movement is, in principle, arbitrary, preferably circular or rectangular, e.g., square. The same applies to the cross-section of pump cylinders.

[0056] Typically, the cylinders and their associated components of the two pump units are identical in construction.

[0057] Preferably, the pistons and connecting rods belonging to the first and second cylinders, respectively, are also identical in construction.

[0058] Typically, the pump units of the pumping device according to the invention each have at least one inlet and one outlet valve for the fluid to be pumped.

[0059] Typically, bearings of the device according to the invention are supplied with lubricant in a conventional manner, e.g. bearings of the crankshaft.

[0060] Suitable fluids for pumping include liquids such as water, but also gases that are pumped and compressed, for example.

[0061] The pumped fluids can, for example, power hydraulic machines.

[0062] The fluid to be pumped is preferably split into two equal streams before the pumping device, which are then pumped accordingly in the two pumping units and afterwards recombined; thus, the pumping device preferably includes corresponding elements that effect this.

[0063] The device according to the invention can be used as a pump, but also as a compressor, e.g. for generating compressed air for high-pressure cleaners or pneumatic tools.

[0064] The present invention also relates to a device comprising a double piston pump device in one of the embodiments described herein.

[0065] Furthermore, the present invention also relates to a method for conveying a fluid, wherein a double piston pump device is used in one of the embodiments described herein. Example

[0066] One embodiment of the double piston pump according to the invention is described in more detail below with reference to the figure.

[0067] Fig. 1 shows a cross-section of an embodiment of the double piston pump according to the invention.

[0068] In a crankshaft housing, which is part of the overall housing of the pump device, there is a crankshaft 1 with two crank throws spaced 180° apart, to whose crankpins 4 and 5 respectively a connecting rod 2 and 3 is rotatably attached, which in turn is connected to the drive piston (A) 9 in the hydraulic cylinder (A) 11 and to the drive piston (B) 10 in the hydraulic cylinder (B) 12, so that when the crankshaft 1 is rotated, a counter-directional, linear (anti-parallel) movement of the two drive pistons (A) 9 and (B) 10 takes place.

[0069] The crankshaft 1 is rotatably mounted in the crankcase 6, 7, which is part of the pump housing 15. One crankshaft end 8 is connected to a power unit (not shown) which transmits a torque to the crankshaft 1, thus setting it into a rotational motion.

[0070] The connecting rods are guided through openings 13, 14 in the lower end of the crankcase into the hydraulic cylinder housing 15.

[0071] The drive pistons (A) 9 and (B) 10 are shown at one of their dead centers in the respective hydraulic cylinders (A) 11 and (B) 12; the dashed lines indicate the positions of the drive pistons (A) 9 and (B) 10 at the respective other dead center.

[0072] The hydraulic cylinders are directly adjacent to each other along their entire length in the direction of movement of the drive pistons and share the cylinder wall where they directly adjoin each other.

[0073] Hydraulic cylinder (A) 11 and hydraulic cylinder (B) 12 each contain a working piston (A) 26 and (B) 27, respectively, which also move linearly. The directions of the strokes of the respective drive pistons 9 and 10 and working pistons 26 and 27 in hydraulic cylinders (A) 11 and (B) 12 are perpendicular to each other.

[0074] Furthermore, the strokes of the drive and working pistons in the respective cylinder do not overlap, but are directly adjacent to each other. The part of the hydraulic cylinders (A) and (B) in which the strokes of the working pistons are located is in Fig. 1 marked with 16 (stroke of working piston (A)) or 17 (stroke of working piston (B)) and furthermore the part of the hydraulic cylinder internal volume in which the strokes of the working pistons are located is in Fig. 1 marked with 24 (stroke of working piston (A)) or 25 (stroke of working piston (B)).

[0075] A portion of the hydraulic cylinder's internal volume 31, 41 is located outside the stroke paths of the respective drive and working pistons assigned to the cylinder.

[0076] The facing front surfaces of the working pistons 26, 27 are rigidly connected to each other by a linear rigid connecting rod 32. This connecting rod 32 is guided from hydraulic cylinder (A) 11 through an opening 29 in the common cylinder wall into hydraulic cylinder (B) 12. The opening 29 is sealed against the reciprocating connecting rod 32, for example with a sealing ring.

[0077] Directly adjacent to the lateral ends of the hydraulic cylinders (A) 10 and (B) 11 perpendicular to the direction of movement of the working pistons is a pump cylinder (A) 20 and (B) 21, in which a pump piston (A) 22 and (B) 23 can move linearly back and forth.

[0078] The rear sides of the working pistons 26, 27 are rigidly connected to the opposite rear sides of the pump pistons 18, 19 by means of rigid, linear connecting rods 22, 23. These connecting rods 22, 23 are aligned with the connecting rod 32 that connects the front sides of the working pistons.

[0079] On the sides of the pump cylinders 20, 21 opposite the front faces of the pump pistons, the internal volume of the pump cylinder (in Fig. 1 Shown: empty internal volume of pump cylinder (B) 25) each connected to a line for the fluid to be pumped. This line includes an inlet 39, 40 for the fluid to be pumped, an inlet valve 33, 34, an outlet 37, 38, and an outlet valve 35, 36. The flow direction of the pumped fluid is indicated by arrows, e.g., outlet direction 42 of the fluid pumped by pump unit (B).

[0080] The pump pistons 18, 19 in the pump cylinders 20, 21 have the same stroke length as the working pistons 26, 27, wherein the pump cylinders 20, 21 are designed such that their internal volume corresponds substantially or completely to the volume swept by the pump pistons 18, 19 in one stroke.

[0081] The internal cross-sectional area of ​​the pump cylinders 20, 21, and thus also the piston area of ​​the pump pistons 18, 19, is smaller than the internal cross-sectional area of ​​the hydraulic cylinders 11, 12 in the region of the stroke of the working pistons 26, 27, and thus also the surface area of ​​the working pistons 26, 27. Therefore, with the same transmitted force, a higher pressure acts on the fluid to be pumped in the pump cylinders 20, 21 than on the hydraulic fluid displaced by the drive pistons 9, 10 with the same stroke length; thus, a pressure increase is achieved.

[0082] The two openings 30 serve to fill and empty the internal volume 31, 41 of the hydraulic cylinder with hydraulic fluid, for example hydraulic oil. All pistons of the pump device have piston rings 28 for sealing.

[0083] During operation of the device, the crankshaft 1 is set into rotation by the connected engine, and the resulting torque is transmitted by the connecting rods 3, 4 to the drive pistons 9, 10, which accordingly perform a counter-movement. Thus, for example, hydraulic fluid is forced by the drive piston (A) 9 into the internal volume 41 of the hydraulic cylinder (A) 11 (propulsion), which in turn moves the working piston (A) 26 in the return direction. The pump piston (A) 18, which is rigidly connected to the working piston (A) 26, moves in the same direction and thus pushes the fluid to be pumped out of the pump cylinder (A) 20.

[0084] Simultaneously, drive piston (B) 10 is set in a return motion opposite to drive piston (A) 9, which in turn causes a forward motion of working piston (B) 27. Pump piston (B) 19, which is rigidly connected to working piston (B) 27, moves in the same direction, which, however, is the return direction with respect to the pump cylinder (B) 21, and thus draws the fluid to be pumped into the pump cylinder (B) 21.

[0085] This thrust movement of working piston (B) is supported by the rigid connection with working piston (A) 26, which is pushed in the return direction by the hydraulic fluid pressed into the internal volume of hydraulic cylinder (A) 11 by drive piston (A) 9.

[0086] These processes alternate in the two pump units.

[0087] The fluid to be pumped is split into two equal streams before entering the pumping device. These streams are then pumped separately in the two pump units and subsequently recombined. This ensures a uniform flow. Reference symbol list:

[0088] 1 Crankshaft 2 Connecting rod Drive piston (A) 3 Connecting rod Drive piston (B) 4 Crankpin to connecting rod Drive piston (A) 5 Crankpin to connecting rod Drive piston (B) 6, 7 Crankshaft bearing 8 Crankshaft end for connection to engine 9 Drive piston (A) 10 Drive piston (B) 11 Hydraulic cylinder (A) 12 Hydraulic cylinder (B) 13, 14 Openings in pump housing for connecting rod passage 15 Pump housing 16 Part of hydraulic cylinder (A), piston stroke area Working piston (A) 17 Part of hydraulic cylinder (B), piston stroke area Working piston (B) 18 Pump piston (A) 19 Pump piston (B) 20 Pump cylinder (A) 21 Pump cylinder (B) 22 Connecting rod working piston (A) with pump piston (A) 23 Connecting rod working piston (B) with pump piston (B) 24 Internal volume hydraulic cylinder (A) Working piston stroke range (A) 25 Internal volume hydraulic cylinder (B) Working piston stroke range (B) 26 Working piston (A) 27 Working piston (A) 28 Piston rings drive piston (B) 29 Connecting rod bushing 30 Hydraulic fluid inlet / outlet31 Internal volume of the hydraulic cylinder (B) 32 Linear connecting rod between working piston (A) and (B) 33 Inlet valve of the conveying fluid, pump unit (A) 34 Inlet valve of the conveying fluid, pump unit (B) 35 Outlet valve of the conveying fluid, pump unit (A) 36 Outlet valve of the conveying fluid, pump unit (B) 37 Outlet of the conveying fluid, pump unit (A) 38 Outlet of the conveying fluid, pump unit (B) 39 Inlet of the conveying fluid, pump unit (A) 40 Inlet of the conveying fluid, pump unit (B) 41 Internal volume of the hydraulic cylinder (A) 42 Flow direction of the conveyed fluid (B)

Claims

1. A double piston pump device comprising a first hydraulic cylinder (11) and a second hydraulic cylinder (12), each of which is entirely filled with a fluid and in each of which a driving piston (9, 10) and a working piston (26, 27) are arranged so as to be movable back and forth, the device being designed so that an outer driving force can act on the driving pistons (9, 10), causing the driving pistons (9, 10) to move in opposite directions, whereby the working pistons (26, 27) likewise move in opposite directions, and this movement in opposite directions is supported by a mechanical coupling of the working pistons, and the device furthermore comprising a first and a second pump unit for pumping a fluid, preferably a liquid, which are assigned to the first hydraulic cylinder (11) and the second hydraulic cylinder (12), respectively, rear sides of the working pistons (26, 27) of the first hydraulic cylinder (11) and second hydraulic cylinder (12) in each case being connected to the assigned pump unit so that the back and forth movement of the working pistons (26, 27) causes fluid to be alternately suctioned and ejected in the pump unit connected thereto, and the suction and ejection of the fluid to be pumped taking place temporally offset in the two pump units, characterized in that the first and second hydraulic cylinders (11, 12) directly adjoin one another and share a cylinder wall, either entirely or partially.

2. The double piston pump device according to claim 1, wherein the movement of the driving pistons (9, 10) in opposite directions is effectuated by means of a crankshaft (1).

3. The double piston pump device according to claim 2, wherein the crankshaft (1) is connected to a prime mover which transmits torque to the crankshaft (1).

4. The double piston pump device according to any one of the preceding claims, wherein the movements of the driving pistons (9, 10) and / or of the working pistons (26, 27) in the respective hydraulic cylinder (11, 12) are linear.

5. The double piston pump device according to any one of the preceding claims, wherein the hydraulic cylinders (11, 12) are designed so that the movements of the driving pistons (9, 10) and of the working pistons (26, 27) in the respective hydraulic cylinder (11, 12) are perpendicular to one another.

6. The double piston pump device according to any one of the preceding claims, wherein the movement of the two driving pistons (9, 10) in opposite directions in the two hydraulic cylinders (11, 12) is anti-parallel.

7. The double piston pump device according to any one of the preceding claims, wherein the first and second hydraulic cylinders (11, 12) directly adjoin one another.

8. The double piston pump device according to any one of the preceding claims, wherein the two working pistons (26, 27), preferably the front sides thereof, are rigidly connected, preferably linearly rigidly connected, to one another.

9. The double piston pump device according to any one of the preceding claims, wherein the two working pistons (26, 27) move linearly, on the same imaginary line.

10. The double piston pump device according to any one of the preceding claims, wherein part of the internal volume of one hydraulic cylinder or both hydraulic cylinders (11, 12) is not covered by the stroke of the driving pistons (9, 10) and working pistons (26, 27) that are each assigned to the hydraulic cylinder (11, 12).

11. The double piston pump device according to any one of the preceding claims, wherein the displacement volume per stroke is the same for the driving pistons (9, 10) and working pistons (26, 27) assigned to a hydraulic cylinder (11, 12), and preferably for both driving pistons (9, 10) and working pistons (26, 27) assigned to the hydraulic cylinders (11, 12).

12. The double piston pump device according to any one of the preceding claims, wherein the stroke travels of the driving pistons (9, 10) and working pistons (26, 27) that are each assigned to a hydraulic cylinder (11, 12) do not overlap.

13. The double piston pump device according to any one of the preceding claims, wherein one pump unit comprises, or both pump units comprise, respective pump cylinders (20, 21) and pump pistons (18, 19).

14. The double piston pump device according to claim 13, wherein the pump piston is, or pump pistons (18, 19) are, mechanically coupled to the respective associated working piston (26, 27) in such a way that the pump piston (18, 19) and the associated working piston (26, 27) move in opposite directions in the respective cylinder.

15. The double piston pump device according to claim 14, wherein the pump piston or pistons (18, 19) and the respective associated working piston (26, 27) are rigidly, preferably linearly rigidly, connected to one another.

16. The double piston pump device according to claim 15, wherein the working pistons (26, 27) and the pump pistons (18, 19) move in parallel directions, more preferably linearly on the same imaginary line.

17. The double piston pump device according to any one of claims 13 to 16, wherein the pump cylinder or the pump cylinders (20, 21) directly adjoins or adjoin the respective hydraulic cylinder (11, 12).

18. The double piston pump device according to any one of claims 13 to 17, wherein the displacement volume per stroke of one working piston (26, 27), and preferably of both working pistons (26, 27), is different, preferably greater, than the displacement volume per stroke of the respective assigned pump piston (18, 19).

19. A device comprising a double piston pump device according to any one of the preceding claims.

20. A method for pumping a fluid, wherein a double piston pump device according to any one of claims 1 to 18 is used.