DUAL-CYLINDER PISTON PUMP

Abstract

The invention relates to a hydraulically actuated dual-cylinder piston pump (1), with a first differential cylinder (22), with a head-end chamber (51) and a rod-end chamber (53), which actuates a first delivery piston (4) via a first piston rod (6), and also with a second differential cylinder (23), with a head-end chamber (52) and a rod-end chamber (54), which actuates a second delivery piston (5) via a second piston rod (7), and with a switching device (14) which by switching the hydraulic oil flow to the chambers (51, 52, 53, 54) of the differential cylinders (22, 23) establishes a head-end or rod-end operating mode of the dual-cylinder piston pump (1), wherein the switching device (14) is arranged on the bottoms (48, 49) of the head-end chambers (51, 52) of the differential cylinders (22, 23) as a bridge-forming connection between the differential cylinders (22, 23). The invention is distinguished by the fact that the switching device (14) comprises through-passages (28, 29) for the hydraulic oil for actuating the differential cylinders (22, 23), via which the head-end chambers (51, 52) of the differential cylinders (22, 23) are connected to the switching device (14) without hydraulic oil lines. The object of the invention is also a method for operating a hydraulically actuated dual-cylinder piston pump according to the invention.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to International Patent Application No. PCT/EP2016/054779, filed Mar. 7, 2016, which claims the benefit of DE Application No. 10 2015 103 180.9, filed Mar. 5, 2015, both of which are herein incorporated by reference in their entireties.

TECHNICAL FIELD

The invention relates to a dual-cylinder piston pump, for example for pumping thick substances, such as sludge or concrete, as are used for example in automatic concrete pumps, stationary concrete pumps or trailer concrete pumps.

BACKGROUND

A dual-cylinder piston pump, which is operated by hydraulic actuating cylinders which as a rule are designed as differential cylinders, can be operated in a head-end or in a rod-end operating mode. Whereas in the case of the head-end operation the complete surfaces of the hydraulic pistons in the hydraulic cylinder are acted upon by hydraulic oil in each case, in the case of the rod-end operation only a partial surface of the pistons is acted upon because in the case of the rod-end actuation the surface on which the piston rod is attached to the hydraulic piston is not effective for the hydraulic pressure. This leads to the pump being operated with greater delivery volume but low delivery pressure in the case of the rod-end operation and being operated with higher delivery pressure but smaller delivery volume in the case of the head-end operation.

A changeover of the operating mode is advisable for example in the case of stationary concrete pumps during construction of a building in which at the beginning of the concrete delivery concrete is delivered with a higher delivery quantity but low delivery pressure in stories located at low level. With increasing construction progress, after reaching a specified building height, a higher delivery pressure is necessary in certain circumstances in order to pump the concrete through the delivery line to a corresponding building height, for which, however, a lower concrete output is accepted.

As a rule, the hydraulic actuation of dual-cylinder piston pumps according to the prior art, as shown in FIG. 1, in which the head-end actuation is displayed, is constructed so that the hydraulic oil for actuating the differential cylinder 22, 23 of the dual-cylinder piston pump 1 is directed via a control circuit (not shown) to the actuating piston 8 of a differential cylinder 22. Via a bridging oil line 13, which interconnects the two rod-end chambers 53, 54 of the differential cylinders 22, 23, in the case of the head-end actuation of the dual-cylinder piston pump for example shown in FIG. 1, the hydraulic oil is forced from the rod-end chamber 53 of the first differential cylinder 22 into the rod-end chamber 53 of the second differential cylinder 23 and therefore the second hydraulic cylinder 23 is actuated. As soon as the first delivery piston 4 reaches its end point, the hydraulic oil is directed into the chamber 54 instead of into the chamber 53, as a result of which the piston 9 of the second differential cylinder 23 is first of all actuated and the hydraulic oil is directed via the bridging oil line 13 from the rod-end chamber 54 of the second hydraulic cylinder 23 into the rod-end chamber 53 of the first hydraulic cylinder 22.

It is basically possible, by modifying the hydraulic lines, to undertake the changeover of head-end to rod-end operation of a dual-cylinder piston pump, but this is very costly and in practice is hardly possible at a building site since for example draining and replenishing of the hydraulic oil is required in order to alter the hydraulic hose arrangement.

A hydraulic circuit, which enables the switching between a rod-end and head-side operating mode without modifying the hydraulic lines, is known from document DE 292 56 74. Such a circuit, shown in principle in FIG. 2, includes a switching block 14 which is connected via hydraulic lines 15, 16, 17, 18 to the chambers of the differential cylinders 22, 23. The arrows in FIG. 2 show the hydraulic oil flow in the head-end operating mode of the dual-cylinder piston pump 1. Via a suitable switching device in the switching block 14, the hydraulic oil flow is switched over so that the dual-cylinder piston pump 1 is operated in rod-end mode.

In the case of such a switching device according to the prior art, a disadvantage is that leak tightness problems frequently occur on account of the numerous connecting points for the hydraulic lines and high pressure losses occur on account of the numerous system components, which makes economical use of such hydraulic circuits difficult. Moreover, numerous hydraulic lines are required, which create a high installation and financial outlay and the complexity of the hose arrangement increases the risk of leaks.

In order to position the switching device 14 as close as possible to the hydraulic cylinders, this is attached to the hydraulic cylinders in the middle, for example, as shown in FIG. 2. Since, however, the hydraulic cylinders can move relative to each other as a result of the high and varying hydraulic pressures in the chambers, there is the danger that cracks or other damage occur in the connecting point between the hydraulic cylinders and the switching device.

SUMMARY

The switching of the operating mode of a dual-cylinder piston pump, which could also be carried out automatically, is, however, safety-critical and should only be carried out if the operator is clear about the altered operating conditions regarding the altered delivery pressure and the pumped delivery volume during the switching of the operating mode.

It is therefore the object of the present invention to provide a simple device for switching between head-end and rod-end operating mode of a dual-cylinder piston pump, and also to provide a method for the switching of the operating mode, which resolve the aforesaid disadvantages of the prior art.

These objects are achieved by means of a dual-cylinder piston pump, a switching device, and methods according to the claims. Reference is to be made to the fact that the features which are individually quoted in the claims can also be combined with each other in an optional and technologically sensible manner and therefore demonstrate further embodiments of the invention.

A hydraulically actuated dual-cylinder piston pump according to the invention comprises a first hydraulically operated differential cylinder, with a head-end chamber and a rod-end chamber, which actuates a first delivery piston via a first piston rod, a second differential cylinder, with a head-end chamber and a rod-end chamber, which actuates a second delivery piston via a second piston rod, and a switching device, which by switching the hydraulic oil flow to the chambers establishes a head-end or rod-end operating mode of the dual-cylinder piston pump, wherein the switching device is arranged on the bottoms of the head-end chambers of the differential cylinders as a bridge-forming connection between the differential cylinders. The invention is distinguished by the fact that the switching device comprises through-passages for the hydraulic oil for actuating the differential cylinders, via which the head-end chambers of the differential cylinders are connected to the switching device without hydraulic oil lines.

Compared with the prior art, the dual-cylinder piston pump according to the invention has the advantage that on the one hand a particularly force-locked connection of the components to each other is created so that damage (e.g., crack developments, fractures) at or in the region of the connecting points between the differential cylinders and the switching device is not to be taken into account. On the other hand, the dual-cylinder piston pump according to the invention, compared with the prior art, has the advantage that the risk of rupturing of hydraulic hoses is greatly reduced since hydraulic hoses are required only between the rod-end chambers of the differential cylinders and the switching block. Moreover, the cost for the installation and screw-connecting of the hydraulic hoses is greatly reduced.

In a preferred embodiment of the invention, the switching device is fastened on the bottoms of the differential cylinders with the aid of adapter flanges. The particular advantage of this embodiment of the invention exists in the fact that a modification of the switching device is dispensed with if the switching device is to be attached to differential cylinders with different diameters because via the adapter flanges with different diameters, which are adapted in each case to the inside diameter of the head-end chamber of the differential cylinder, the switching device of the same type of construction can be adapted to differential cylinders with different diameters. The adapter flanges can be arranged in corresponding recesses in the switching block. The recesses in the switching block increase the stability of the arrangement and at the same time unload the fastening/screwing of the adapter flanges.

The hydraulically actuated dual-cylinder piston pump can furthermore comprise flanges arranged on the differential cylinders, by means of which the differential cylinders are fastened, preferably screwed, to the switching device. Such flanges enable a simple fastening/screwing of the differential cylinders to the switching device. The flanges are for example attached to the tubular differential cylinders by means of a welded or screwed connection or already form a unit with the cylinder tubes during production.

In a further preferred embodiment, the bottoms of the head-end chambers of the differential cylinders comprise close-fitting seats into which the adapter flanges are fitted. As a result of this measure, the adapter flanges absorb in an optimally form-locking manner the radial forces which originate from the differential cylinders and therefore avoid the transverse force loading of the flange screws between the differential cylinders and the control block. Moreover, the adapter flanges increase the mechanical loadability/durability of the connection between the differential cylinders and the switching device.

In a further preferred embodiment of the invention, expansion sleeves are arranged on the flanges for accommodating screws. As a result of this, a secure screw fastening can be ensured between the flanges and the switching device. As a result of the expansion sleeves, longer screws can be used and the expansion sleeve absorbs some of the expansion, e.g., as a result of thermal loads and pressure loads, in the material and therefore acts like a buffer, as a result of which the leak tightness of the cylinder chambers under high pressure is always ensured and high safety standards are met.

A further preferred embodiment of the invention is distinguished by the fact that the switching device comprises an inlet for a control line for the switching of the operating mode of the dual-cylinder piston pump. This control line can be for example hydraulically or electrically designed.

In a further preferred embodiment, the operating mode of the dual-cylinder piston pump is switched over via a pilot valve which is actuated via the control line. By means of a latching device, this pilot valve is preferably also held in its last switched position in the event of the control line being shut off or in the event of a signal to the control line not being present, for example with the pump switched off. As a result of this, the effect of the pump being inadvertently started in an operating mode with differs from the last used operating mode, e.g., during restarting, is prevented.

The invention is furthermore distinguished by a method which controls the changeover of the operating mode of the dual-cylinder piston pump during startup of the pump. A further method relates to the changeover of the operating mode while the pumping process is running.

The invention and also the technical field are explained in more detail below with reference to the figures. Reference is to be made to the fact that the figures show a particularly preferred embodiment variant of the invention. The invention, however, is not limited to the depicted embodiment variant. In particular, the invention, providing it is technically sensible, covers any combinations of the technical features which are quoted in the claims or are described in the description as being relevant to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawing:

FIG. 1 shows a dual-cylinder piston pump according to the prior art without a switching device for the operating mode,

FIG. 2 shows a dual-cylinder piston pump with a switching device for the operating mode according to the prior art,

FIG. 3 shows a dual-cylinder piston pump according to the invention in a head-end operating mode,

FIG. 4 shows a dual-cylinder piston pump according to the invention in a rod-end operating mode,

FIG. 5 shows a perspective view of a switching device according to the invention,

FIG. 6 shows a perspective view of a switching device with connected differential cylinders according to the invention,

FIG. 7 shows a sectional view of the connection between the switching block and a differential cylinder according to the invention,

FIG. 8 shows a hydraulic circuit according to the invention,

FIG. 9 shows a flow diagram for a method according to the invention, and

FIG. 10 shows a flow diagram for a further method according to the invention.

DETAILED DESCRIPTION

Shown in FIG. 1 and FIG. 2 are dual-cylinder piston pumps 1 according to the prior art, as have already been explained further above. The dual-cylinder piston pump 1 according to FIG. 1 comprises two delivery cylinders 2, 3 with delivery pistons 4, 5 which in each case are actuated via piston rods 6, 7 of differential cylinders 22, 23 with hydraulic pistons 8, 9. Arranged between the delivery cylinders 2, 3 and the differential cylinders 22, 23 is a water tank 10 in which there is water which flushes the delivery pistons 8, 9 on their rear side in order to cool and to lubricate the pistons. Connected to the head-end chambers 51, 52 of the differential cylinders 22, 23 are hydraulic feed/drain hoses 11, 12 via which the hydraulic oil for actuating the differential cylinders 22, 23 is fed from a hydraulic pump, which is not shown. The rod-end chambers 53, 54 are interconnected via a bridging oil line 13. A cylinder bottom 49, 50 is located in each case at the end of the head-end chambers 51, 52. The arrows in FIG. 1 show the flow direction of the hydraulic oil for the head-end actuation of the dual-cylinder piston pump 1.

FIG. 2 shows a dual-cylinder piston pump 1 corresponding to FIG. 1, which is equipped with a switching device 14 for switching between rod-end and head-side operating mode. The switching device 14 as a rule consists of a solid metal block in which are introduced control valves and through-passages for the hydraulic valves which are arranged in the switching device 14 and is therefore also referred to as a control block or switching block. The references switching block and switching device 14 are used synonymously in the following text. The switching block 14 includes a hydraulic circuit which is suitable for controlling the hydraulic oil flow to the cylinder chambers 51, 52, 53, 54 so that a corresponding operating mode can be established. The hydraulic oil feed/drain lines 11, 12 are connected to the switching block 14. The arrows show in FIG. 2 the flow direction of the hydraulic oil and the movement direction of the delivery pistons for a head-end operation of the dual-cylinder piston pump 1.

FIG. 3 shows an embodiment according to the invention of a dual-cylinder piston pump 1 which comprises a first differential cylinder 22 with a head-end chamber 51 and a rod-end chamber 53, wherein the differential cylinder 22 actuates a first delivery piston 4 via a first piston rod 6. The dual-cylinder piston pump 1 also comprises a second differential cylinder 23 with a head-end chamber 52 and a rod-end chamber 54, which actuates a second delivery piston 5 via a second piston rod 7. The dual-cylinder piston pump 1 also comprises a switching device 14 which by switching the hydraulic oil flow to the chambers 51, 52, 53, 54 of the differential cylinders 22, 23 establishes a head-end or rod-end operation of the dual-cylinder piston pump 1.

The switching device 14 is arranged on the bottoms 48, 49 of the head-end chambers 51, 52 of the differential cylinders 22, 23 as a bridge-forming between the differential cylinders 22, 23.

The switching block 14 comprises two through-passages 28, 29 (see also FIG. 6) via which the head-end chambers 51, 52 of the differential cylinders 22, 23 are connected directly to the switching device 14. Via the through-passages 28, 29, the hydraulic oil is directed directly from the switching device 14 to the head-end chambers 51, 52 of the differential cylinders 22, 23, as a result of which a failure-prone hydraulic hose arrangement according to the prior art between the switching block 14 and the head-end chambers 51, 52 can be avoided.

Arranged between the switching device 14 and the bottoms 49, 50 of the differential cylinders 22, 23 are adapter flanges 20, 21 which enable an individual adaptation of the switching block 14 to the differential cylinders 22, 23 with different diameters.

The hydraulic oil flow represented by arrows in FIG. 3 shows the head-end operating mode of the dual-cylinder piston pump 1. That is to say, the hydraulic oil, which is conducted from a hydraulic pump, not shown, at high pressure via the hydraulic oil line 11 into the switching block 14, is directed from the switching block 14 into the head-end chamber 51 of the differential cylinder 22. In the chamber 51, the greater volume in conjunction with the larger piston surface than in the case of the rod-end actuation (see FIG. 4) creates the effect of the delivery piston 4 being pushed to the left in the first delivery cylinder 2 with high force but comparatively slowly. The hydraulic oil in the rod-end chamber 53 is transported in the course of the movement via the hydraulic line 16, the switching block 14 and the hydraulic line 18 into the rod-end chamber 54 of the differential cylinder 23 and creates the effect of the hydraulic piston 9 being pushed to the right. In the process, the hydraulic oil is drained from the head-end chamber 52 of the differential cylinder 23 via the switching block 14 and the hydraulic line 12. The delivery cylinder 2 in FIG. 3 is in pump mode, whereas the delivery cylinder 3 is in suction mode.

As soon as the delivery pistons 4, 5 or the hydraulic pistons 8, 9 have reached their end position, which for example is detected by means of suitable limit switches or detectors, the hydraulic oil flow is switched over and the hydraulic oil flows from the hydraulic pump through the line 12 into the switching block 14 and first all actuates the hydraulic piston 9 via the head-end chamber. This mode, which is not shown, now creates the effect of the delivery cylinder 3 working in pumping mode, whereas the delivery cylinder 2 works in suction mode.

Shown in FIG. 4 is the dual-cylinder piston pump 1 from FIG. 3, in which the switching block 14 is changed over via the control line 19 from the head-end operating mode into the rod-end operating mode of the dual-cylinder piston pump 1. That is to say, the hydraulic oil coming from the hydraulic feed line 11 in FIG. 4 is first of all conducted via the switching block 14 into the rod-end chamber 53 of the differential cylinder 22, as a result of which the delivery cylinder 2 with the delivery piston 4 is in suction mode at comparatively high speed but with lower force. In the process, the hydraulic oil from the head-end chamber 51 of the differential cylinder 22 is conducted via the switching block 14 into the head-end chamber 52 of the differential cylinder 23 and actuates the hydraulic piston 9 or the delivery piston 5 in pumping mode. After switching of the hydraulic oil flow, the pumping direction of the delivery pistons of the dual-cylinder piston pump 1 is reversed, wherein the rod-end actuation is maintained providing the switching block 14 is not switched over via the control line 19 into the head-end operating mode.

FIG. 5 shows a perspective view of the switching block 14 according to the invention with installed adapter flanges 20, 21 with the through-passages 28, 29. The adapter flanges 20, 21 are fitted in corresponding recesses in the switching block 14 and are preferably screwed to the switching block by means of six screws in each case. The adapter flanges 20, 21 could also be screwed onto the switching block 14 without the recesses in the switching block 14. The recesses in the switching block 14 increase the stability of the arrangement and at the same time unload the screw fastening of the adapter flanges 20, 21. Shown on the sides of the switching block 14 are inlet/outlet passages 57 for the hydraulic lines. Arranged on the switching block 14 at the top is the housing of a pilot valve 33 (see also FIG. 8) which by the control line 19 is electronically acted upon by the control signal for the establishing of the operating mode.

FIG. 6 shows the switching block 14 together with the differential cylinders 22, 23 which via flanges 24, which are preferably connected to the differential cylinders 22, 23 by means of welded connections 26, are fastened to, preferably screwed to, the switching block 14. The screw fastening of the flanges 24 to the switching block 14 is not shown in this drawing, only the drilled holes 25 for the screw fastening are visible. The flanges 24 can for example also be screwed to the cylinder tubes or produced in one piece.

FIG. 7 shows in a perspective cross section the connection of the differential cylinder 22 via the adaptor flange 20 to the switching block 14. On the bottom 49 of the differential cylinder 22 provision is made for a close-fitting seat 55 so that the adapter flange 20 is fitted into the differential cylinder 22 in a form-fitting manner. For leakage-free sealing between the adapter flange 20, the switching block 14 and the differential cylinder 22, two sealing rings 30 are inserted in grooves in the adapter flange 20.

The adapter flange 20, on the side facing the switching block 14, has an outside diameter dl which fits into a prepared cutout in the switching block 14. On the side facing the differential cylinder 22, the adapter flange 20 has the diameter d2 which is adapted to the inside diameter of the close-fitting seat 55 of the differential cylinder 22. The switching block 14 is preferably also provided with fits/close-fitting seats with the diameter dl for accommodating the adapter flanges 20, 21 in the recesses provided for it. Arranged in the adapter flange 20, in the middle, is a hole through which the hydraulic oil flows from the passage 28 of the switching block 14 into the head-end chamber 51 of the differential cylinder 22. By using adapter flanges 20, 21 with different diameters d2, but identical diameters d1, the switching block 14 together with the differential cylinders 22, 23 can be operated with different diameters. In the case of concrete pumps, diameters of the differential cylinders of 20-25 cm, for example, are customary, wherein the middle point of the differential cylinders in relation to each other is often the same so that a switching block 14 of the same type of construction can be connected to different differential cylinders 22, 23.

The differential cylinder 22 is screwed via the welded-on flange 24 to the switching block 14 by screws 27. The screwed connections have expansion sleeves 36 which increase the security of the screw fastening even under high pressure and extreme thermal loads because the hydraulic pressure in concrete pumps can be up to over 400 bar.

Shown in FIG. 8 is a possible hydraulic circuit, arranged in the switching block 14, which is suitable for undertaking the switching of the operating mode of the dual-cylinder piston pump 1. The hydraulic circuit mainly comprises six cartridge valves 41-46 which are controlled by an electromagnetically controlled pilot valve 33. Via the control oil inlet 35, which is protected by a check valve 34, hydraulic oil is conducted to the pilot valve 33 for controlling the cartridge valves 41-46. Via the hydraulic oil inlet/outlets 47 and 48, the hydraulic oil which is required for operating the differential cylinders 22, 23 is fed to/drained from the switching block 14.

The cartridge valves 41-45 control the hydraulic oil flow to the head-end/rod-end chambers of the differential cylinders in the respectively established operating mode. The cartridge valve 46 is of slightly larger dimensions than the other cartridge valves 41-45. The valve 46 opens or closes the connection between the two head-end chambers 51, 52 of the differential cylinders 22, 23 via the through-passages 28, 29 which are shown schematically in FIG. 8.

The pilot valve 33 is set in FIG. 8 so that the cartridge valves 41, 45 and 44 are closed via the control line 32 as a result of the control oil pressure and the cartridge valves 42, 43 and 46 are opened by spring force action. As a result of this valve setting, the rod-end operating mode of the dual-cylinder piston pump 1 is established.

Via the electric control line 19, the pilot valve 33, by means of two solenoids which are located at the side on the valve body, is reversed in a known manner. A mechanical latching device 56 ensures that the pilot valve 33 remains in the last established position even with the control line 19 shut down (e.g. after a shutdown of the entire machine).

In the rod-end operating mode, as explained further above, the pistons 8, 9 move more quickly than in the head-end operating mode, which is why the hydraulic oil quantity to be passed through the cartridge valve 46 between the head-end chambers is particularly large, which requires a larger dimensioning of this valve.

The hydraulic lines 16, 18 and also the hydraulic connections 47, 48 are shown as being doubled here because the quantity of hydraulic oil to be passed through is of such magnitude that a simple hose arrangement with thicker hydraulic lines would not be feasible so that a parallel hose arrangement with thinner hydraulic lines is provided.

FIGS. 9 and 10 show flow diagrams for methods for controlling a dual-cylinder piston pump 1, which relate to the switching process between the rod-end and the head-end operating mode.

In FIG. 9, startup of the pump 1 is requested by an operator in step 100. Before the pump starts, the operating mode established during the last operation of the pump 1, e.g., with reference to a memory input, is first of all determined in step 101. In step 102, the operator, for example via a display on the control unit of the machine or on a remote control unit, asks whether the pump is to be used again in the last established operating mode, which is also displayed, during startup. If the operating mode is to be maintained, via step 103 the pump is started in this operating mode in step 105. If the operating mode is to be altered, because the pump conditions have been altered (e.g., concrete delivery location at a higher or lower level during the restart), in step 104, by switching of the pilot valve 33, the operating mode is switched over and only then is the pump started in step 105.

The sequence could also be configured so that in step 102 the operator of the pump can acknowledge the maintaining of the operating mode in a relatively simple manner, whereas the switching of the operating mode requires a specific acknowledgement which expressly refers the operator to the altered pump behavior. It is also conceivable that the operating mode in step 102 is maintained after a certain waiting period (for example 5 or 10 seconds) and the pump is automatically started in step 105 if the operator makes no input within the waiting period.

FIG. 10 shows a method for switching the operating mode of the pump 1 during continuous operation, in which the pressure of the pumped medium or the hydraulic pressure of the hydraulic oil is measured at a suitable point, e.g., in one or both delivery cylinders 2, 3 in one or both differential cylinders 22, 23 or in the switching block 14, in order to switch the pump over into a suitable operating mode.

In step 110, the pump 1 is in normal pumping operation. At regular intervals, or even continuously, the pump pressure is checked in step 111, and in step 113, based on the established operating mode 112, a check is made as to whether the pump pressure lies within a tolerance range for the operating mode. In the case of the rod-end actuation, which is better suited to speedier pumping at lower pressure, the pump pressure should not exceed for example a certain tolerance limit because beyond this limit the head-end operation is more suitable in certain circumstances so as not to overload the hydraulic system. Since, however, various reasons can exist for the higher pump pressure, e.g., even a blockage of the pipeline, the operator first of all asks in step 114 whether the operating mode is to be maintained. If this is the case, the pump operation continues normally in step 110. If the change of the operating mode is requested by the operator in step 115, the pilot valve 33 is switched over and the pump operation is continued in step 117 with the altered operating mode.

An automatic switching over from the head-end operating mode to the rod-end operating mode (and vice versa) would also be conceivable if the pump pressure falls short of a certain tolerance limit in order to increase the pump output. Since, however, the spontaneous change of the operating mode at the building site can also bring problems along with it, a manual switching over with interrogation is to be preferred. Conversely, for example an automatic changeover to the head-end operating mode could also be undesirable because the piping system connected to the pump is not designed for high pump pressure and pipes or hoses could burst.

LIST OF DESIGNATIONS

1 Dual-cylinder piston pump

2 First delivery cylinder

3 Second delivery cylinder

4 First delivery piston

5 Second delivery piston

6 First piston rod

7 Second piston rod

8 First hydraulic piston

9 Second hydraulic piston

10 Water tank

11 Hydraulic feed line

12 Hydraulic drain line

13 Bridging oil line

14 Switching device/switching block

15 First hydraulic line

16 Second hydraulic line

17 Third hydralic line

18 Fourth hydraulic line

19 Control line

20 First adapter flange

21 Second adapter flange

22 First differential cylinder

23 Second differential cylinder

24 Flange

25 Holes

26 Welded seam

27 Screws

28 Through-passage

29 Through-passage

30 Seals

31 First hydraulic control line

32 Second hydraulic control line

33 Pilot valve

34 Check valve

35 Connection for hydraulic control oil

36 Expansion sleeves

41-45 Cartridge valves for switching

46 Cartridge valve for connection of piston chambers

47 Hydraulic oil feed/drain

48 Hydraulic oil feed/drain

49 Bottom of differential cylinder 22

50 Bottom of differential cylinder 23

51 Head-end chamber of differential cylinder 22

52 Head-end chamber of differential cylinder 23

53 Rod-end chamber of differential cylinder 22

54 Rod-end chamber of differential cylinder 23

55 Close-fitting seat

56 Latching device for pilot valve

57 Inlet/outlet passages for the hydraulic lines

Claims

1. Hydraulically actuated dual-cylinder piston pump comprising:

a first differential cylinder, with a head-end chamber and a rod-end chamber, which actuates a first delivery piston via a first piston rod,

a second differential cylinder, with a head-end chamber and a rod-end chamber, which actuates a second delivery piston via a second piston rod,

a switching device which by switching the hydraulic oil flow to the chambers of the differential cylinders establishes a head-end or rod-end operating mode of the dual-cylinder piston pump, wherein the switching device is arranged on the bottoms of the head-end chambers of the differential cylinders as a bridge-forming connection between the differential cylinders,

characterized in that

the switching block comprises through-passages for the hydraulic oil for actuating the differential cylinders, via which the head-end chambers of the differential cylinders are connected to the switching device without hydraulic oil lines.

2. Hydraulically actuated dual-cylinder piston pump according to claim 1, characterized by flanges, arranged on the differential cylinders, by means of which the differential cylinders are fastened, preferably screwed, to the switching device.

3. Hydraulically actuated dual-cylinder piston pump according to claim 1, characterized by-adapter flanges which are arranged between the switching device and the bottoms of the differential cylinders.

4. Hydraulically actuated dual-cylinder piston pump according to claim 3, characterized in that the adapter flanges are inserted into close-fitting seats which are introduced into the bottoms of the differential cylinders.

5. Hydraulically actuated dual-cylinder piston pump according to claim 2, characterized in that the expansion sleeves are arranged on the flanges for accommodating screws.

6. Hydraulically actuated dual-cylinder piston pump according to claim 1, characterized in that-the switching device comprises an inlet for a control line for the switching over of the operating mode.

7. Hydraulically actuated dual-cylinder piston pump according to claim 6, characterized by a pilot valve for switching over the operating mode of the switching device, which can be controlled by the control line.

8. Hydraulically actuated dual-cylinder piston pump according to claim 7, characterized by a latching device which holds the pilot valve in its switched position when the control line is shut down.

9. Switching device for establishing the operating mode of the hydraulically actuated dual-cylinder piston pump according to claim 1.

10. Method for operating the hydraulically actuated dual-cylinder piston pump according to claim 1, characterized in that before startup of the dual-cylinder piston pump the last established operating mode is determined a check is carried out as to whether the last established operating mode is to be used for startup of the pump, and in that in dependence of this the operating mode is maintained or switched over before the pump is started.

11. Method according to claim 10, characterized in that the last established operating mode is specified as the operating mode during startup of the pump.

12. Method for operating a hydraulically actuated dual-cylinder piston pump according to claim 1, characterized in that during the operation of the dual-cylinder piston pump the pump pressure is detected; it is determined whether the detected pump pressure lies within a specified tolerance for the established operating mode, and a check is carried out as to whether the operating mode is to be maintained, and in that in dependence of the result of the check the operating mode is maintained or switched over.