Method of controlling a pump apparatus for conveying viscous material, and control system for such a pump apparatus

Description

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the priority of German Patent Application, Serial No. 10 2005 024 174.3-15, filed May 23, 2005, pursuant to 35 U.S.C. 119(a)-(d), the subject matter of which is/are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a method of controlling a pump apparatus for conveying viscous material, and to a control system for such a pump apparatus.

Nothing in the following discussion of the state of the art is to be construed as an admission of prior art.

Pumps of a type involved here are used in the field of concrete conveyance and include at least two main delivery cylinders which convey viscous material to a delivery pipeline. In order to realize a substantially continuous material flow, the main delivery cylinders are operated substantially in opposite mode so that at any given time one of the main delivery cylinders is able to conduct concrete to the delivery pipeline. The delivery pipeline may be the hose, for example which is connected to the lifting boom by which concrete is conducted to the job site.

A problem of such conventional pump apparatuses is the insufficient continuity of the material flow. Attempts were made to address this problem by providing concrete pumps between the main delivery cylinders and the delivery pipeline with a switchable gate mechanism by which a connection between the pumping one of the main delivery cylinders is established with the delivery pipeline, on one hand, while the other intaking one of the main delivery cylinders is able to draw concrete from a reservoir for a next pump stroke. Operation of the gate mechanism leads, however, to interruptions in the material flow in conventional concrete pumps, thereby preventing a continuous conveyance of viscous material.

Control of such concrete pumps is based on the use of position signals produced by position sensors which determine the end position of a piston of a hydraulic cylinder for powering a conveying piston of a main delivery cylinder. In the so-called single-circuit hydraulics, initially it is, for example, determined whether the delivery stroke by the conveying main delivery cylinder has concluded its delivery stroke before the gate mechanism can be switched over. Further, the end position of the piston of the one hydraulic cylinder is ascertained which is used for switching the gate mechanism in order to start the delivery stroke of the next main delivery cylinder after the gate mechanism has been switched.

In two-circuit hydraulics, it is, for example, also known to initiate the switching signal for starting operation of the pump cylinder while the gate mechanism is switched. In other words, the gate mechanism can be operated irrespective as to whether or not the piston of the hydraulic cylinder of the gate mechanism has reached the end position. As a result, the pump stroke of a main delivery cylinder is oftentimes executed simultaneous with a switch-over of the gate mechanism.

The switching signals, triggered by the cylinders in their end positions, are used to predominantly switch the substantially larger main valves which conduct alternatingly the oil flow of the main hydraulic pump to the two main delivery cylinders. As an alternative, this reversal of the cylinder motion is implemented by alternatingly swiveling the controllable hydraulic pump across the zero point to both sides. As a consequence, the need for the arrangement of the large hydraulic valve is eliminated. In the case of the two-circuit hydraulics, the gate mechanism is normally powered by a separate, small-sized hydraulic pump from a hydraulic accumulator. This is possible because the small-sized hydraulic pump charges the accumulator during the long pauses between switching operations of the gate mechanism (about 90% of the clock pulse). This type of system is called two-circuit hydraulics because of the presence of a separate oil circuit for the gate mechanism. The provision of a signal for indicating the end position of the gate mechanism may be omitted here.

In contrast thereto, the single-circuit hydraulics uses the same hydraulic pump alternatingly for driving the pump cylinder or the gate mechanism, whereby a signal is required when the gate reaches the end position to switch to the next pump cylinder.

These control operations for the drive hydraulic of discontinuously operating pumps can be reliably implemented in a simple manner in the absence of electronic control systems.

The position sensors to signal the end position are normally realized as small directional control valves (pilot valves). These valves are actuated by the piston of the hydraulic cylinder after passing a control bore in the cylinder wall. As an alternative, end positions can also be ascertained by mechanically-actuated electric switches or capacitive or inductive sensors and transmitted to magnetic valves.

Compared to discontinuous pumps, the control of a continuously conveying pump is much more complex. When continuous pumps are involved, the start of the concrete pump, for example, from a random (chaotic) starting situation, i.e. the absence of any meaningful association between all main cylinders and control devices, cannot be realized using conventional techniques. These conditions are encountered for example after each major repair or when breaking in a new machine.

It would therefore be desirable and advantageous to provide an improved control system for a pump apparatus for conveying viscous material to obviate prior art shortcomings and to realize a reliable start of the pump even in the presence of an unforeseen starting situation.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a method of controlling a pump apparatus for conveying viscous material from at least two main delivery cylinders to a delivery pipeline includes the step of providing a sequence control having a sequence program for executing operation of at least two control elements of the pump apparatus in a fixed timing sequence.

The term “fixed timing sequence” relates hereby to a fixed ratio of actuation of each control element to the clock signals of a clock pulse. Thus, one control element may, for example, be actuated after execution of 1.25 clock signals following the start of the sequence program, whereas a further control element is actuated after execution of 2.39 clock signals following the start of the sequence program. There is no need to execute operation upon reaching a certain full clock signal. Thus, the term “fixed timing sequence” relates to the implementation of various processes in succession or parallel relationship and to the independence of a process start from the measurement of a state variable. Rather, the execution of the sequence program is predefined. The present invention thus divorces itself from prior art thinking to make the actuation of the control elements solely dependent on the position of individual drive members which are switched by the control elements, such as, for example, the position of a piston of the main delivery cylinders or the position of a piston of the gate mechanism. Rather, the present invention provides for a fixed timing sequence for actuation of the control elements, whereby the implementation depends solely on the start of the sequence program whose ratio in relation to the clock pulse remains constant at all times so that one control element, for example, is actuated always after execution of 2.75 clock signals following the actuation of a first control element. The clock pulse can suitably be adjusted. The sequence of the clock signals may, for example, be realized in a first operating mode in intervals of seconds, whereas in another operating mode the clock signals may occur every 0.5 seconds.

As actuation of the control elements can now depend on the execution of a sequence program and, except for the start signal, can be made independent on a state determination of the system, a reliable control system can be realized which is able to properly position all hydraulic valves of a concrete pump, for example during startup of the concrete pump, so that all drives for an optional gate mechanism, including the shut-off gates and the drives for the pistons of the main delivery cylinders can be moved in appropriate direction or maintained in their position so long as conforming to the executed operations. Moreover, the following pump operation can be carried out reliably, even when the delivery flow changes at short notice and even after standstill.

The present invention provides for a reliable operation of all control tasks for a continuous concrete pump which requires coordination of numerous control and driving operations. Some continuous concrete pumps require, for example, execution of 12 control operations within approximately 0.6 seconds which predominantly overlap in time. Conventional controls cannot reliably realize such operations heretofore.

According to another feature of the present invention, the same sequence program is executed iteratively. As an alternative, several, e.g. two or three different sequence programs may be provided which are executed successively, whereby the start of execution of each sequence program is triggered by a start signal. Suitably, when all provided sequence programs have been executed, execution of the first sequence program is started again.

According to another feature of the present invention, execution of the or one sequence program may begin by triggering a start signal produced by a position sensor which directly or indirectly ascertains a piston position of a main delivery cylinder.

According to another feature of the present invention, the clock pulse for executing the sequence program may be suited to an actual conveying speed of viscous material in the delivery pipeline. The actual conveying speed may hereby be determined by a flow gauge disposed in the delivery pipeline of a main delivery cylinder and controlling on the basis of electric or electronic measuring values the speed of an electric motor or hydraulic motor, executing the sequence program.

A pump apparatus controlled by a control method according to the present invention for conveying viscous material includes in addition to the main delivery cylinders, a switchable gate mechanism which establishes in a first switching mode a connection between an outlet port of a first one of the delivery cylinders and the delivery pipeline, and in a second switching mode a connection between an outlet port of a second one of the delivery cylinders and the delivery pipeline through which the viscous material is then able to flow in flow direction. The pump apparatus may further include a compensating cylinder which is constructed to be able to receive viscous material conveyed in the delivery pipeline and to maintain the delivery flow during switch-over of the gate mechanism by discharging viscous material back into the delivery pipeline. The compensating cylinder is suitably disposed downstream of the gate mechanism. In addition, a shut-off valve can suitably be disposed in the delivery pipeline in flow direction upstream of the compensating cylinder for closing the delivery pipeline during switching of the gate mechanism so as to prevent a return flow of viscous material in the direction towards the gate mechanism, when viscous material is discharged into the delivery pipeline from the compensating cylinder during switching of the gate mechanism. The incorporation of the shut-off valve in the delivery pipeline upstream of the compensating cylinder also enables operation of the shut-off valve at pressure equilibrium. Of course, the present invention is not limited to such a pump apparatus but is applicable also in other configurations of conventional pump apparatuses for viscous material, such as, e.g., pump apparatuses described in German Offenlegungsschrift DE 42 08 754 A1 or European Pat. No. EP 1 003 969 B1.

According to another feature of the present invention, at least one of the control elements may be provided for operating a drive member selected from the group consisting of drive of the main delivery cylinders, drive of a switchable gate mechanism of the pump apparatus, shut-off valve of the pump apparatus, and drive of a compensating cylinder of the pump apparatus.

The control method according to the present invention enables to carry out the start of the pump stroke of the compensating cylinder and the simultaneous closing of the shut-off valve at a fixed timing sequence. In addition, the change in pump function of both main delivery cylinders is carried out at a fixed timing sequence. Also, reduction of a safety pressure of a main hydraulic pump for pre-compressing, switch-over of the gate mechanism, highly compressing to attain an actual conveying pressure and opening of a shut-off gate may be realized at a fixed timing sequence.

According to another feature of the present invention, the control may be implemented electronically in the form of a stored-program controller (SPC) or other electric or electronic controllers to effect the actuation of the control elements in the fixed timing sequence according to the present invention.

According to another feature of the present invention, the rotation of a camshaft with cams for switching the control elements of the pump apparatus may be triggered by a start signal. The use of a camshaft with cams for switching at least two control elements of the pump apparatus provides for a fixed association between the actuation of the control elements relative to one another because the cams of the camshaft are positioned at a fixed relationship to one another while allowing at the same time to freely select the clock frequency so that the timing sequence of the sequence program can be accelerated or retarded, without changing the sequence in actuation of the control elements in relation to the clock pulse.

According to another feature of the present invention, the camshaft is halted after moving about a rotation angle defined by the sequence program to effect the operation of the control elements or after execution of the sequence program in a SPC. This is based on the recognition that there exists a time period absent any switching operations during pumping and intake operations by the main delivery cylinders of a concrete pump. In this phase, it is only necessary to maintain the actual positions of all hydraulic valves. In accordance with the present invention, execution of the sequence program during part of this phase is terminated while maintaining the actual signals. Standstill is realized suitably by the sequence program itself, i.e. the sequence program stops itself.

In the event, a sequence program or sequence programs are executed repeatedly, the system can be stabilized by having all control elements assume an idle position assigned in the sequence program as the sequence program is executed, and by initiating actuation of the control elements only when execution of the next sequence program has been initiated by a start signal. The control elements thus have a fixed position after the sequence program has been fully executed so that the start of a subsequent sequence program does not encounter a chaotic starting situation but a fixed predefined starting situation. Regardless of the starting situation from which the control system according to the present invention begins to control a pump apparatus, an unambiguous and definite configuration of the pump apparatus is realized latest after the initial execution of a sequence program.

When a continuous concrete pump is involved having at least two main delivery cylinders in the absence of a compensating cylinder, the start signal may be triggered briefly before a piston of the main delivery cylinders has reached the rearward position, for example at the end of a rapid intake operation, in particular 50 mm before the end position. In a continuous pump with compensating cylinder, both main delivery cylinders normally run synchronously in opposite mode. In other words, one main delivery cylinder has reached the forward end position and the other main delivery cylinder has reached the rearward position at the same time. Thence, the start signal for initiating operation of the signal generator can be triggered by the main delivery cylinder in the forward or rearward position. The synchronization of the pump with the sequence program may be implemented in particular at each pump stroke immediately before the switching operations begin, especially the e.g. 12 switching operations. For the same reason, the running speed by which the sequence program is executed can be suited to the actual pump speed at fairly slight accuracy and thus can be implemented in a cost-effective manner.

The camshaft may be halted, for example, after rotating about a rotation angle of 180°. The cams are disposed at an angular relationship of 0 to 180° and actuate the control elements. The arrangement of the individual cams in this angular range and their concrete construction are predefined by the sequence program. In the angle range from 180° to 360°, a different cam disposition may be provided in the event a second sequence program should be executed after running the first sequence program.

According to another feature of the present invention, the camshaft may be halted by a signal. Suitably, the camshaft has one cam that actuates a clutch for separating the camshaft from its drive. Suitably, the drive has a reduction gear unit.

When using a camshaft, stopping and restarting of the sequence program may involve the use of a clutch arranged in a very slowly rotating region, i.e. in proximity of the camshaft. Through use of the clutch and its arrangement in proximity of the camshaft, the drive motor and an optional reducing gear for the camshaft can continue to run in the pause phase of the sequence program and thus there is no need to slow them down. In view of the very slight kinetic energy, the camshaft comes to a stop at a precise point when stopping by itself. The same is true for restart.

According to another feature of the present invention, the start signal may be generated, when a position sensor determines that a piston of a main delivery cylinder has reached its end position.

According to another feature of the present invention, the camshaft may be driven by means of a drive motor which operates at a speed which can be suited to the volumetric flow-rate of a hydraulic pump of the pump apparatus, whereby the volumetric flow-rate is ascertained by a measuring sensor. As a result, the clock frequency can be matched to the actual conveying speed.

According to another feature of the present invention, the respectively intaking one of the main delivery cylinders runs at a higher piston speed than the pumping main delivery cylinder so that an intake port is closed after conclusion of the intake stroke, whereupon a compression stroke can be executed and a connection to the delivery pipeline can be cleared before the pumping main delivery cylinder reaches its end position. The sequence program is started by a the position signal shortly before the intake stroke ends and triggers one of the control elements for at least one process selected from the group consisting of closing the intake port, pre-compressing of drawn viscous material, highly compressing to attain an actual conveying pressure, opening the connection to the delivery pipeline, switching a main hydraulic pump to a new pump stroke, closing the connection of the other one of the main delivery cylinders to the delivery pipeline, and starting its intake stroke and opening its intake port.

According to another aspect of the present invention, a control system for a pump apparatus for conveying viscous material includes a camshaft having at least one cam for actuating a contact member for operating a control element of a pump apparatus having at least two main delivery cylinders for conveying viscous material. The use of a camshaft for switching the control elements of the pump apparatus permits execution of a sequence program by which a fixed timing sequence is established for actuating the control elements of the pump apparatus. As a result, the control elements can be actuated in fixed relationship to one another after starting the sequence program.

According to another feature of the present invention, the at least one cam is provided for a control element to switch a drive member selected from the group consisting of drive of the main delivery cylinders, drive of a switchable gate mechanism of the pump apparatus, shut-off valve of the pump apparatus, and/or drive of a compensating cylinder of the pump apparatus.

According to another feature of the present invention, a position sensor may be provided for direct or indirect determination of at least a piston position of a main delivery cylinder. The position sensor may be used for example for producing a start signal for execution of the sequence program.

According to another feature of the present invention, the camshaft may be connected via a clutch to a drive. Disengagement of the clutch quickly terminates the rotation of the camshaft in a simple manner so that once the sequence program has been executed, a restart of a sequence program cannot take place until the clutch connects the camshaft again with the drive.

According to another feature of the present invention, the drive may include a reduction gear unit. In this way, the drive can be coupled to the hydraulic system of the pump apparatus. The selection of the respective reduction enables a fixed relation of the rotation of the camshaft to the oil flow in the hydraulic line. Suitably, a fluid-operated motor, such as a hydraulic motor, may be used for driving the camshaft and disposed in a fluid flow of a main hydraulic pump for driving the main delivery cylinders or in its return flow.

BRIEF DESCRIPTION OF THE DRAWING

Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which:

FIG. 1 is a partly sectional schematic illustration of a pump apparatus according to the present invention;

FIG. 2 is a schematic sectional view of a shut-off valve of the pump apparatus;

FIG. 3 is a schematic sectional view of the shut-off valve, taken along the line III-III in FIG. 2;

FIG. 4 is a schematic sectional view of the shut-off valve in closed position; and

FIG. 5 a schematic illustration of a sequence program of a control system according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Throughout all the Figures, same or corresponding elements are generally indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the drawings are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted.

This is one of two applications both filed on the same day. Both applications deal with related inventions. They are commonly owned and have the same inventive entity. Both applications are unique, but incorporate the other by reference. Accordingly, the following U.S. patent application is hereby expressly incorporated by reference: “PUMP APPARATUS AND METHOD FOR CONTINUOUSLY CONVEYING A VISCOUS MATERIAL”.

The following description of a control system according to the present invention is described with reference to a concrete pump, although the control system may be applicable for any pump apparatus intended for conveying any type of viscous material, including those used in the food industry.

Turning now to the drawing, and in particular to FIG. 1, there is shown a partly sectional schematic illustration of a pump apparatus according to the present invention, including two main delivery cylinders 1, 2. Each main delivery cylinder 1, 2 accommodates a piston 14 which can move into the main delivery cylinder 1, 2, as indicated by arrow A, to realize a pump stroke, or in a direction out of the main delivery cylinder 1, 2, as indicated by arrow C, to realize an intake stroke. Connected to the main delivery cylinders 1, 2 is a gate mechanism, generally designated by reference numeral 3 and having a swingable transfer tube 12 with an inlet port 15 for selective fluid communication with either one of the main delivery cylinders 1, 2. In an area of the inlet port 15, the transfer tube 12 has a self-adjusting ring 17 for connection to the outlet ports of the delivery cylinders 1, 2. The transfer tube 12 is fluidly connected to a first section 4 of a delivery pipeline, generally designated by reference numeral 5, with a shut-off valve, generally designated by reference numeral 6 being disposed in the pipeline section 4. A compensating cylinder, generally designated by reference numeral 7, connects the pipeline section 4 with a second pipeline section 8 of the delivery pipeline 5.

The gate mechanism 3 includes a housing 10 having an interior space 11 for accommodating the transfer tube 12 which is operated by a hydraulic cylinder 13 via a connecting rod 16. The transfer tube 12 can be shifted between a first switching mode for establishing a connection between the outlet of the main delivery cylinder 1 and the pipeline section 4, and a second switching mode for establishing a connection between the outlet of the main delivery cylinder 2 and the pipeline section 4. Although not shown in detail, a reservoir or priming tank is fluidly connected to the interior space 11 of the gate mechanism 3.

The shut-off valve 6 is configured in the form of a two-port rotary gate valve and includes a casing 20 and a valve body 21 received in the casing 20 and formed with a through channel 23. The valve body 21 can be moved by a hydraulic cylinder 22 between an open position in which the through channel 23 is aligned with two opposing ports 24, 25 of the shut-off valve 6, as shown in FIG. 2, and a closed position in which the connection between the through channel 23 and the ports 24, 25 is cut, as shown in FIG. 4.

The compensating cylinder 7 includes a pipe bend 30 having an upstream end 31 of greater cross section than a downstream end 32 of the pipeline section 4 so that the upstream end 31 of the pipe bend 30 can be pushed over the downstream end 32 of the pipeline section 4. The downstream end 33 of the pipe bend 30 has a cross section which is smaller than an upstream end 34 of the pipeline section 8 so that the downstream end 33 of the pipe bend 30 can be inserted into the upstream end 34 of the pipeline section 8. Seals 35, 36 are provided between the pipe bend 30 and the pipeline sections 4, 8. A movement of the pipe bend 30 in and out in relation to the delivery pipeline 5 is realized by a hydraulic cylinder 37 via a connecting rod 38 secured to the pipe bend 30.

FIGS. 2 and 3 show the shut-off valve 6 in open position. The shut-off valve 6 has a self-adjusting ring in the form of a cutting ring 26 which is supported by a flexible rubber ring 27 upon a pipe flange 28. The casing 20 of the shut-off valve 6 has a zone of spherical shape in an area surrounding the port 24, whereas the pivotable valve body 21 has a complementary zone 29 of spherical shape. The valve body confronting surface of the cutting ring 26 of the self-adjusting ring is also configured to have a zone of spherical shape. As shown in FIG. 3, the casing 20 may otherwise have flattened areas to save installation space.

FIG. 4 shows the shut-off valve 6 in closed position. The spherical-shaped zone 29 of the valve body 21 is moved to a position in front of the port 24. Thus, the valve body 21 seals off the port 24 in cooperation with the cutting ring 26, urged by the flexible rubber ring 27 against the valve body 21.

The mode of operation of the pump apparatus according to the present invention is as follows: FIG. 1 shows the main delivery cylinder 1 of the pump apparatus in a starting phase of the pump stroke. The transfer tube 12 is moved by the hydraulic cylinder 13 in the direction of the outlet port of the main delivery cylinder 1. As indicated by arrow A, the main delivery cylinder 1 has already started its pump stroke. As a consequence of the partial overlap between the inlet port 15 of the transfer tube 12 and the outlet port of the main delivery cylinder 1, concrete from the main delivery cylinder 1 is slightly pre-compressed against a cutting ring of the transfer tube 12. The shut-off valve 6 is closed so that concrete being pumped into the pipeline section 4 build up pressure in the pipeline section 4. Compression to the actual pressure level is realized after the transfer tube 12 reaches the end position. When the pressure on both sides of the shut-off valve 6 is the same, the hydraulic cylinder 22 is activated to pivot the valve body 21 so as to open the shut-off valve 6. The operation is executed without a need to overcome great friction forces as the concrete on both sides of the shut-off valve 6 is under the same pressure.

As the transfer tube 12 has reached the switching position in which a connection is established between the outlet of the main delivery cylinder 1 and the pipeline section 4 across the entire cross section of the outlet, the main delivery cylinder 1 is now able to pump concrete through the pipeline section 4 and the compensating cylinder 7 into the pipeline section 8. During the pumping operation, the hydraulic cylinder 37 moves the pipe bend 30 to the outside by the concrete pressure acting thereon (to the left in FIG. 1) to thereby increase the volume of the delivery pipeline 5. The thus extended pipe bend 30 is now able to store concrete.

Once the main delivery cylinder 1 has reached the end of its pump stroke, the shut-off valve 6 is closed. As the pipe bend 30 retracts in a direction indicated by arrow B, the concrete stored in the pipe bend 30 is pumped into the pipeline section 8 so that pressure in the delivery pipeline 5 is maintained. Return flow of concrete into the pipeline section 4 is prevented by the closed shut-off valve 6.

The main delivery cylinder 1 commences the intake stroke immediately following the closing of the shut-off valve 6. As a consequence, concrete in the transfer tube 12 and the pipeline section 4 up to the shut-off valve 6 relaxes. The transfer tube 12 is then moved in the direction of the other switching position by the hydraulic cylinder 13. In view of the pressure relief, the pressure difference between concrete in the transfer tube 12 and in the interior space 11 of the gate mechanism 3 is substantially negated so that the transfer tube 12 can easily be moved.

As further shown in FIG. 1, the main delivery cylinder 2 executes the intake stroke, as indicated by arrow C, to draw concrete from the interior space 11, whereby additional concrete is able to flow from the unillustrated reservoir to the interior space 11.

Referring now to FIG. 5, there is shown a schematic illustration of a sequence program of a control system according to the present invention for controlling the pump apparatus. As shown in FIG. 5, the pump apparatus includes a camshaft 100 with cam disks 112, 113, 114, 115, 116. The camshaft 100 is connected to a motor 1 11 via a clutch 108.

FIG. 5 shows the pump apparatus in a position in which the main delivery cylinder 1 still pumps. The cylinder 101 of the main delivery cylinder 1 is situated shy of its one end position whereas the cylinder 102 of the intaking main delivery cylinder 2 is situated shy of its other end position. Both cylinders 101, 102 are synchronized via an interconnecting line 103.

As the piston 14 in cylinder 101 of the main delivery cylinder 1 sweeps over the control bore 104 in the cylinder wall, the control valve 105 to the left of main delivery cylinder 1 can change in opposition to the spring from the right switching mode to the left switching mode. As a result, line 201 is acted upon by the accumulator pressure, as indicated by reference numeral 106. In general, reference numeral 106 designates in FIG. 5 the connection of the respective valve to a hydraulic accumulator which is able to power the various switching operations in the absence of any appreciable pressure drop. The energy storage means in the hydraulic accumulator may, for example, be compressed nitrogen.

On the suction side of the clutch cylinder 107, the accumulator pressure generates a high spring force in opening direction of the clutch 108. The greater piston area is pressureless to the tank 203, i.e. relieved. Oil flows hereby from the piston side of the clutch cylinder 107 to the tank 203 via shut-off valve 109 through the right switching mode of the control valve 105, via the left switching mode of the control valve 110, disposed to the right of main delivery cylinder 2, and via valve 112a for start and stop of the camshaft 100.

Although FIG. 5 shows the camshaft 100 provided with cam disks 112 to 116, further cams may be arranged to control other operations such as pre-compression of the conveyed material during switching of the gate mechanism 3 and immediately thereafter (high compression).

As valve 112a is positioned upon the cam of cam disk 112, the piston side of the clutch cylinder 107 is connected to the tank 203. Control valve 105 assumes the left switching mode as a result of the end position of cylinder 101, the accumulator pressure 106 acts upon the piston area of the clutch cylinder 107, causing the clutch 108 to close since the piston area is greater as the annular area on the opposite side which is acted upon by the same pressure. As a result, the camshaft 100 rotates in the direction indicated by arrow 117.

The cam disk 112 includes two very short cams at an angular distance of 1800. Thus, the camshaft 100 comes to a halt by a self-generated stop signal after each rotation of 180°. At high flow rates the fast rotation through 180° can approximately take 0.7 seconds. The time period from a start to a next start of the camshaft 100 takes, however, 1.8 seconds at the so-selected maximum flow rate. As a consequence, the camshaft 100 thus has a downtime of 1.1 seconds. Since the camshaft 100 stands still in this time interval, all control valves actuated by the camshaft 100 retain their position, which means that all control elements, such as e.g. larger directional control valves for controlling drive members like hydraulic cylinders and hydraulic motors, which are operated by the control valves retain their position. Of course, the afore-stated times are indicated by way of example only and other running speeds may be selected.

During stoppage of the camshaft 100, one of the main delivery cylinders 1, 2 pumps while the other one draws viscous material. Moreover, the compensating cylinder 7 moves outwards to receive material from the delivery pipeline 5, with the material being returned again into the delivery pipeline 5 during standstill of the one main delivery cylinder 1, 2 when the gate mechanism 3 is switch over.

The motor 11 runs continuously and powers one side of the clutch 108 at a speed which is constantly suited to the effective flow rate of primary hydraulic pump 119.

At least the following operations are executed after start of the camshaft 100:

The cam disk 112 moves the control valve 112a to the right switching mode. This ensures a running of the camshaft 100 for as long as about 0.7 seconds. The start signal for the camshaft 100 has been given beforehand by valve 105 and expires when the piston 14 of cylinder 101 leaves its forward position during the subsequent stroke. Then, the signal to cause running of the camshaft 100 is still operative by means of the valve 112a.

When the camshaft 100 starts to rotate, the cam disk 113 controls via valve 113a the change-over of main directional control valve 120 for a new pump stroke which, however, should be slightly retarded as relief and pre-compression operations (not shown here for sake of clarity) should take place together with the switching of the gate mechanism 3 with the transfer tube 12.

The transfer tube 12 starts to move only after the shut-off valve 6 has closed, whereby the start of the transfer tube 12 is also controlled by the cam disk 113 which reverses the directional control valve 122 in conjunction with the control valve 113b.

Following the start of the camshaft 100, the cam disk 114 closes a shut-off gate 124 of shut-off valve 6 via control valve 114a and control element (directional control valve 123). In addition, as the camshaft 100 rotates, the cam disk 115 causes the start of pump stroke of the compensating cylinder 7 via control valve 115a and the directional control valve 125.

The cam disk 116 closes via its control valve 116a a two-port seat valve 127. As a result, compressed oil is prevented from flowing from the primary hydraulic pump 119 to the large directional control valve 120. Instead, the primary hydraulic pump 119 powers the drive cylinder 118a of the compensating cylinder 7. As described above, the pump stroke of cylinder 118a is started as the direction control valve 125 is switched over to the left switching mode.

Small hydraulic pump 128 is a so-called zero-stroke pump. This type of pump is constructed to have almost zero flow rate when reaching a maximum pressure. In the present case, this condition exists, for example, in the short holding times between the intake stroke and discharge stroke of the compensating cylinder 7. Thus, the presence of a maximum force of the hydraulic cylinder, directed to the left, remains. Jointly with the force of the compensating cylinder 7, also directed to the left and applied by the existing concrete pressure, an overall force is exerted which exceeds the force applied by the cylinder 118a in the opposite right direction. The same is true also for the preceding intake stroke which is implemented in opposition to the drive force on the piston side of the cylinder 118a. After changing over the directional control valve 125 to the left switching mode immediately after start of the camshaft 100, the force of the cylinder 118a, directed to the left, is removed. Thus, the cylinder 118a executes the pump stroke (to the right). At the end of the compensating stroke, cylinder 118a switches the valve 126 point-accurately (position-dependent control) to the left switching mode. As a result, seat valve 127 clears the path from the primary hydraulic pump 119 to the directional control valve 120 to thereby restart a new pump stroke.

Shortly before, shut-off gate 124 opens, with valve 114a assuming the right switching mode again (and roller tappet has moved out). At the time of starting a new pump stroke, about 0.5 seconds have passed. The camshaft 100 rotates about 0.7 seconds at maximum flow rate of the pump about a rotation angle of 180°. The camshaft 100 comes then automatically to a halt so that the other cam of the cam disk 112 urges the control valve 112a again against the spring to assume the left switching mode.

After starting the new pump stroke 0.5 seconds following the start of the camshaft 100 up to its halt after about 0.7 seconds, the following further control operations are executed by the camshaft 100:

• • The control valve 116a is switched back into the position shown in FIG. 5.

This is necessary before the directional control valve 126 assumes the right switching mode (spring force at pressure equilibrium) as a result of the intake operation by the compensating cylinder 7.

• • The directional control valve 125 is moved into the position shown in FIG. 5. As a result, the intake stroke by the compensating cylinder 7 to the left begins via the cam disk 115. In addition, functions of the unillustrated compression processes are switched back and forth during the running time of 0.7 second by the camshaft 100.

While the camshaft 100 is at a standstill, the main delivery cylinder 2 pumps and the main delivery cylinder 1 draws in viscous material. During a major part of the standstill period of about 1.1 seconds, the compensating cylinder 7 executes its intake stroke to draw material from the delivery pipeline 5.

While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. The embodiments were chosen and described in order to best explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.