Patent Publication Number: US-2018045186-A1

Title: Dual-cylinder piston pump

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 d 2  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 d 2 , but identical diameters d 1 , 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