EP1437178B1 - Powder pumping installation, Method therefore and powder coating installation - Google Patents

Description

The invention relates to a pump device for powder, in particular for coating powder according to the preamble of claim 1, a method for this and a powder coating device having at least one such pump device.

Accordingly, the invention relates to a pump device for powder, in particular for coating powder, comprising at least one powder pump having a metering chamber which is delimited by a chamber housing and a displacer which is movable relative to the chamber housing during a pressure stroke before and during a suction stroke wherein the pumping chamber comprises a powder inlet channel to which a powder inlet valve is associated, a powder outlet channel associated with a powder outlet valve, and a pressurized gas inlet channel associated with a pressurized gas inlet valve, wherein for aspirating a metered quantity of powder into the dosing chamber the powder inlet valve is openable and the Pulverauslassventil and the compressed gas inlet valve are closable, so that in the suction stroke moving displacement body Powder can suck through the powder inlet channel into the metering chamber, and for conveying the metered amount of powder from the metering chamber, the powder inlet valve is closable and the powder outlet and the pressure gas inlet valve can be opened, so that compressed air flowing from the compressed air inlet channel into the metering chamber, the metered amount of powder from the metering chamber in can push the powder outlet channel.

A pump device of this kind is known from EP-A-0 124 933 known. Pumping devices are also known EP-A-1 106 547 . DE-A-39 00 718 . DE-A-1 087 520 . US 2 667 280 . US 3,391,963 , and US 4,405,289 ,

From practice, a pump device is known, which has two pumps, each having a Pulveransaugkolben and a driving him pneumatic cylinder. The two pumps are driven in opposite directions, so that one performs a suction stroke, while the other performs a pressure stroke. During the suction stroke, the respective powder suction piston draws powder from a powder source into its metering chamber. At the end of the suction stroke, the amount of powder metered out of the metering chamber into a powder discharge line is compressed by means of compressed air introduced into the metering chamber. pushed out. Thereafter, the piston goes back to its original position during a pressure stroke, in order then again to suck in powder from the powder source during a suction stroke. The flow rate per unit of time depends on the frequency with which the pistons are moved back and forth. A pump device of this kind is in the WO 03/024612 A1 only after the priority date of the present new patent application has been described.

Furthermore, so-called injectors are known in which, according to the Venturi principle, a conveying air stream flows from an outlet nozzle into a catching nozzle and generates a negative pressure in the intermediate space therebetween through which coating powder is sucked from a powder source into the conveying air flow. Such injectors have compared to the aforementioned piston pumps the Disadvantages that the powder particles have a abrasive effect on the catching nozzle and thus the efficiency of the powder delivery falls over time: A pneumatic powder delivery of this type requires a large amount of compressed air per unit of time.

The aforementioned piston pumps do not have these disadvantages. However, the piston pumps have the disadvantage that they promote the powder discontinuously stroke and both a more uniform powder delivery and to promote larger amounts of powder per unit time a fast piston movement frequency is required. However, the height of the piston frequency is limited by the driving speed with which the valves in the flow paths of the pump can be controlled. Furthermore, care must be taken that in the pumps and in their flow paths, powder particles are not squeezed, sintered or otherwise adhere and also that there are no gaps, depressions and the like in which powder can accumulate.

By the invention, the object to be achieved, a pump device which has at least one volume displacement body, form such that a defined and, if desired, large flow powder per unit time is conveyed without the aforementioned disadvantages arise. In particular, a high process reliability and high stability of the powder flow rate per unit time (constant powder rate for a defined configuration and defined setting of the pump device) should be achieved over a long service life.

This object is achieved according to the invention by the features of claim 1 and the other independent claims.

Further features of the invention are contained in the subclaims.

Accordingly, the pump device according to the invention is characterized in that a timing device is provided, through which, depending on the past from a predetermined operating situation predetermined delay time period, the conveying of the powder is started from the metering chamber by compressed air in the metering chamber and admitted to the end the amount of powder metered in the delay time period is pressed out of the dosing chamber by means of the compressed air.

Furthermore, according to the invention, a powder spray coating device is provided, which has at least one such pump device.

In addition, the invention discloses methods for conveying powder, in particular coating powder.

Fig. 1

schematisch, teilweise im Querschnitt, eine Doppelpumpeneinrichtung nach der Erfindung,

Fig. 2

schematisch Teile von Fig. 1 zusammen mit einem Funktionsdiagramm zur Erklärung der Erfindung,

Fig. 3

schematisch, teilweise im Querschnitt, eine weitere Ausführungsform einer Doppelpumpeneinrichtung nach der Erfindung,

Fig. 4

schematisch, teilweise im Querschnitt, eine weitere Ausführungsform einer Doppelpumpeneinrichtung nach der Erfindung,

Fig. 5

einen Längsschnitt durch ein Einwegventil nach Art eines Entenschnabels im Schließzustand, welches bei allen Ausführungsformen von Pumpeneinrichtungen nach der Erfindung als Pulvereinlassventil und/oder als Pulverauslassventil verwendbar ist,

Fig. 6

das Einwegventil von Fig. 5 in Vorderansicht entgegen der Durchlassrichtung gesehen,

Fig. 7

das Einwegventil im Längsschnitt gesehen im Offenzustand,

Fig. 8

eine Vorderansicht entgegen der Durchlassrichtung gesehen auf das Einwegventil von Fig. 7 im Offenzustand,

Fig. 9

das Einwegventil der Figuren 5 bis 8 in Seitenansicht gesehen, relativ zu den Figuren 5 und 7 um 90° um die Längsachse gedreht.

The invention will now be described by way of example with reference to the drawings of preferred embodiments. In the drawings show

Fig. 1

schematically, partly in cross section, a double pump device according to the invention,

Fig. 2

1 schematically shows parts of FIG. 1 together with a functional diagram for explaining the invention, FIG.

Fig. 3

schematically, partly in cross-section, another embodiment of a double pump device according to the invention,

Fig. 4

schematically, partly in cross-section, another embodiment of a double pump device according to the invention,

Fig. 5

a longitudinal section through a one-way valve in the manner of a duckbill in the closed state, which is used in all embodiments of pumping devices according to the invention as a powder inlet valve and / or as a powder outlet valve,

Fig. 6

the one-way valve of FIG. 5 seen in front view opposite to the passage direction,

Fig. 7

the one-way valve seen in longitudinal section in the open state,

Fig. 8

3 is a front view opposite to the passage direction on the one-way valve of FIG. 7 in the open state,

Fig. 9

the one-way valve of Figures 5 to 8 seen in side view, rotated relative to the figures 5 and 7 by 90 ° about the longitudinal axis.

1 shows a pump device according to the invention for powders, in particular for coating powder, which has two powder pumps 2-1 and 2-2, which each contain a metering chamber 4-1 or 4-2, which is separated from a chamber housing 6. 1 and 6-2 and a displacement body in the form of a flexible membrane 8-1 or 8-2 is limited.

The two diaphragms 8-1 and 8-2 have a common drive 10 arranged between them. The drive 10 can be a mechanical, hydraulic, electrical or, according to FIG. 1, a pneumatic drive. The pneumatic drive shown in Fig. 1 includes a transversely to the diaphragms 8-1 and 8-2 sliding drive piston 12, from which extend in the direction of movement piston rods 14-1 and 14-2 away, whose remote from the drive piston 12 ends with the a membrane 8-1 and connected to the other membrane 8-2, so that the two membranes each move together with the drive piston 12. The piston rods 14-1 and 14-2 engage in each case Center of the respective membrane 8-1 or 8-2, which moves in each case together with the drive piston 12 in Kolbenaxialrichtung. The diaphragm peripheral edges 16-1 and 16-2 are respectively fixed to a part of the chamber case 6-1 and 6-2 and can not move with the diaphragm center together with the drive piston 12 across the diaphragm. If in the context of this description of lifting movements of the membrane is mentioned, then in each case the area of the membrane is meant, which is connected to the drive piston 12 for common movement, but not attached to the chamber housing membrane peripheral edges 16-1 and 16-2.

The chamber housings 6-1 and 6-2 of the two powder pumps 2-1 and 2-2 are preferably sections of a common housing part or housing, which is shown in Fig. 1 in section.

The diaphragms 8-1 and 8-2 (with the exception of their diaphragm peripheral edges 16-1 and 16-2) are movable backward during a pressure stroke before and during a suction stroke by means of the common drive 10. FIG. 1 shows the diaphragm 8 shown on the left -1 in an end position "a", which is the end position of the pressure stroke and the initial position of the suction stroke. Here, the associated dosing 4-1 has its smallest volume. In this case, the membrane 8-1 is preferably not completely attached to the chamber housing 6-1, but has a small distance therefrom, so that powder particles can not be squeezed between the membrane 8-1 and the chamber housing 6-1. The same applies to the diaphragm 8-2 shown on the right in FIG. 1, when it is in an end position "d", which is the end position of its pressure stroke and the initial position of its suction stroke. However, Fig. 1 shows the right diaphragm 8-2 in a left end position "c", which is its end position of the suction stroke and its initial position of the pressure stroke. The two diaphragms 8-1 and 8-2 are in each case jointly moved to the left or to the right by the drive piston 12, so that the left diaphragm 8-1 performs its pressure stroke when the right diaphragm 8-2 performs its suction stroke, and vice versa.

The drive piston 12 is located in a cylinder 22 which near cylinder end walls 24 and 25 on both sides of the drive piston 12 each have a compressed air control port 26 and 28 which via a switching valve 30 alternately with a compressed air source 32 or with a vent 34 to the outside atmosphere Ventilation are connectable. In Fig. 1, the compressed air control port 28 shown on the right is connected to the compressed air source 32, which is why their compressed air has forced the drive piston 12 in the left in Fig. 1 position shown, while the left shown compressed air control port 26 to the vent 34 of the changeover valve 30 is connected. The changeover valve 30 is switchable, so that after switching the compressed air control port 28 shown on the right is connected to the vent 34 and the compressed air control port 26 shown on the left is connected to the compressed air source 32. In this reversed position of the switching valve 30, not shown in FIG. 1, the compressed air drives the drive piston 12 together with the two diaphragms 8-1 and 8-2 from left to right. At this time, "b" is moved by the left diaphragm 8-1 from its suction stroke start position (print stroke end position) "a" to its suction stroke end position (print stroke start position) "b". Simultaneously, the right diaphragm 8-2 is moved from its suction stroke end position (print stroke start position) "c" to its suction stroke start position (print stroke end position) "d". The two membranes 8-1 and 8-2 are shown schematically in their left end position by a solid line and in their right end position by a dashed line.

Each metering chamber 4-1 and 4-2 has a powder inlet passage 36-1 and 36-2, one each. Powder inlet valve 38-1 or 38-2 is assigned; a Pulverauslasskanal 40-1 and 40-2, which is associated with a Pulverauslassventil each 42-1 and 42-2; and a compressed gas inlet channel 44-1 and 44-2, which is associated with a respective compressed gas inlet valve 46-1 and 46-2.

For aspirating a metered quantity of powder into the metering chamber 4-1 shown on the left in FIG. 1, the left powder inlet valve 38-1 can be opened, and the left powder outlet valve 42-1 and the left compressed gas inlet valve 46-1 can be closed, so that they are in the suction stroke direction from the suction stroke start position "a" into the suction stroke end position "b" moving left diaphragm 8-1 can suck powder through the left powder inlet passage 36-1 into the left dosing chamber 4-1. For conveying the metered amount of powder from the dosing chamber 4-1 shown on the left into the powder outlet channel 40-1, the left powder inlet valve 38-1 can be closed and the left powder outlet valve 42-1 and the left pressure gas inlet valve 46-1 can be opened, so that pressurized gas, e.g. B. compressed air, from a compressed gas source 45-1, z. B. a compressed air source, through the left Druckgaseinlasskanal 44-1 flow into the left metering chamber 4-1 and can push the metered amount of powder from the metering chamber 4-1 in the left Pulverauslasskanal 40-1. Thereafter, or during this ejection of the powder from the left metering chamber 4-1, depending on the embodiment of the pump device, the left diaphragm 8-1 is moved back from the drive piston 12 back from the right suction stroke stop position "b" to the left suction stroke start position "a". what is referred to here as a pressure stroke, so that they can then perform a suction stroke again.

Corresponding functions also carry the diaphragm 8-2 driven by the drive 10, shown on the right in FIG. 1, and the associated valves 38-2, 42-2, 45-2 and 46-2 with respect to the associated right-hand metering chamber 4-2. the associated right powder inlet channel 36-2 and the associated right powder outlet channel 40-2 and a pressurized gas source 45-2 shown on the right, z. B. a compressed air source. However, the right diaphragm 8-2 makes its pressure stroke when the left diaphragm 8-1 makes its suction stroke, and vice versa.

The two powder inlet valves 38-1 and 38-2 each have a valve body 38-3 and a valve seat 38-4 with a valve opening, which can be closed by the valve body 38-3. The two powder outlet valves 42-1 and 42-2 each have one Valve body 42-3 and a valve seat 42-4 with a valve opening, which is closed by the valve body 42-3.

The two powder outlet channels 40-1 and 40-2 shown in FIG. 1 have a common powder discharge opening 48, to which a powder receiver 50 is connected via a powder discharge line 50, for example a powder spray device 52 for spraying the powder 54 onto an object to be coated or an intermediate powder container. from which the powder 54 is then fed to a powder spray device 52, or a powder collection container.

The two powder inlet channels 36-1 and 36-2 can be connected separately or together to a common or to different powder sources. In FIG. 2, they are preferably connected to a color changer 60 via a common powder inlet opening 56 and via a powder suction line 58. The color changer 60 is a sewer or powder switch, through which one of several powder containers 62, 63, 64, etc. optionally with the Pulveransaugleitung 58 can be connected depending on the switch position. The switching of the color changer 60 is preferably carried out by means of compressed gas, for. B. compressed air, a compressed gas source, for. B. a compressed air source 66 via a controlled valve assembly 67th

The color changer 60 is also switchable to a switching position in which none of the powder container 62, 63, 64, but instead the compressed gas source 66 is connected via a compressed gas line 69 to the Pulveransaugleitung 58 so that compressed gas, for. B. compressed air via the powder inlet channels 36-1, 36-2 and their powder inlet valves 38-1, 38-2 through the metering chambers 4-1 and 4-2 and then also on their powder outlet valves 42-1 and 42-2 and the Pulverauslasskanäle 40-1, 40-2 can flow to the powder discharge line 50 and from there through the powder injection device 52 into the outside atmosphere to clean the entire system of powder residues. By means of a, preferably electronic or computerized, pump control device 68 may also be provided that at the same time or after this cleaning pressurized gas, for. B. compressed air from a compressed gas source 45-1 and 45-2 via the compressed gas inlet channel 44-1 and 44-2 and their associated controllable compressed gas inlet valve 46-1 and 46-2 in the one end of the metering chamber 4-1 and 4 respectively -2 blown and thus powder from the metering chamber at the other end of the chamber through the local Pulverauslassventil 42-1 or 42-2 and the subsequent Pulverauslasskanal 40-1 or 40-2 is blown out through the powder discharge line 50 and the powder spray device 52. The compressed gas inlet channel 44-1 or 44-2 may have a pressure gas cleaning channel 72-1 or 72-2 arranged parallel to it, which is directed against the downstream parts of the relevant powder inlet valve 38-1 or 38-2, to that of powder particles to clean, if not already the compressed gas inlet channel 44-1 or 44-2 directed against the downstream areas of the powder inlet valves 38-1 and 38-2 and thereby cleans them.

At the same time or after this cleaning can be opened by the pump control device 68 via a control line 70, a valve 71 to compressed gas, for. B. compressed air, from a compressed gas source 75 through an additional gas line 73-1 and 73-2 on the downstream parts of the powder outlet valves 42-1 and 42-2, against which the additional gas line is directed to blow and from there through the Pulverauslasskanäle 40th -1 and 40-2 and the powder discharge line 50 to the powder spray device 52 and from there into the outside atmosphere to conduct.

The pump device 68 controls all controllable valves and the color changer 60.

The pump control device 68 includes a timing device 74, by which, depending on the since a predetermined suction stroke position, z. B. P1 or P2 of the membrane shown on the left 8-1 and a predetermined suction stroke position, z. B. P4 or P3, the membrane shown on the right 8-2, last predetermined delay time period, the feeding of the powder from the respective metering chamber 4-1 and 4-2 is started. At the end of Delay time is the pressurized gas of the compressed gas source 45-1 or 45-2 introduced by the compressed gas inlet valve 46-1 and 46-2 in the metering chamber 4-1 and 4-2, so that the metered until the end of the delay time powder quantity by means of this Compressed gas is pressed out of the metering chamber through the respective powder outlet valve 42-1 or 42-2 in the powder discharge line 50 and from this to the powder injection device 52 or to a powder container.

Said "predetermined suction stroke position" may, according to one embodiment, be the suction stroke start position "a" corresponding to P1 for the left diaphragm 8-1 and "d" corresponding to P4 for the right diaphragm 8-2, which in Fig. 1 for the diaphragm 8 shown on the left -1 is the position "a" shown in solid lines, and which for the diaphragm 8-2 shown on the right in FIG. 1 is the position "d" shown in dashed lines.

The suction stroke start position "a" is detected by a sensor S1 at a position P1 for the membrane 8-1 shown on the left in FIGS. 1 and 2. This is the Druckhubendposition for the left diaphragm 8-1 at the same time. For the right diaphragm 8-2, the position P1 on the sensor S1 is the suction stroke end position and at the same time the pressure stroke start position.

The suction stroke start position "d" is detected by a sensor S4 at a position P4 for the diaphragm 8-2 shown on the right in FIGS. 1 and 2. This is at the same time the Druckhubendposition for the right diaphragm 8-2. For the left diaphragm 8-1, the position P4 at the sensor S4 is the suction stroke end position and at the same time the pressure stroke start position.

When the diaphragms 8-1 and 8-2 have reached an end position "a" corresponding to the sensor S1 at P1 or the sensor S4 at P4 corresponding to "c", or "d" corresponding to "b", the sensor in question indicates a signal the pump control device 68 for reversing the movement of the drive piston 12 and thus also the two membranes in one or the other direction Compressed air supply to the compressed air control port 26 or the compressed air control port 28 and by venting the other compressed air control port.

In the relevant embodiment of the pumping device, if said "predetermined suction stroke position" is the suction stroke start position "a" or "d" of the diaphragm 8-1 and diaphragm 8-2, then the timing controller 74 detects the pump control device 68 based on the signals from the sensors S1 and S4 when the membranes 8-1 and 8-2 have reached the respective end position.

The sensors S1 and S4 can be arranged at any point where positions of the diaphragm 8-1 and 8-2 can be determined, in particular at locations of the cylinder 22 or the drive piston 12 or the piston rods 14-1 and 14-2 or the chamber housing 6-1, 6-2 or membranes 8-1 and 8-2. According to a preferred embodiment, they are arranged on the cylinder 22, preferably on the outside thereof, at positions P1 and P4 which the drive piston 12 has in each case when the diaphragms 8-1 and 8-2 are in one of the two end positions.

According to the invention, by means of compressed gas of the compressed gas source 45-1 metered powder from the left metering chamber 4-1, and by means of compressed gas of the compressed gas source 45-2 metered powder from the right metering chamber 4-2 not only when reaching the suction stroke end position "b" of the left membrane 8-1 and "c" of the right diaphragm 8-2 are ejected by the respective powder outlet valve 42-1 and 42-2, respectively, but earlier even when a smaller amount of powder is in the respective metering chamber. This is achieved by a delay time duration which is preferably variably adjustable at the time control device 74. This makes it possible to eject smaller amounts of powder from the respective metering chamber 4-1 or 4-2 before the associated membrane 8-1 or 8-2 has completed its full intake stroke. In this case, the respectively associated powder inlet valve 38-1 or 38-2 is closed immediately in each case if compressed gas of the compressed gas source 45-1 or 45-2 via the compressed gas inlet channel 44-1 or 44-2 in FIG the respective dosing chamber 4-1 or 4-2 is blown. Depending on the size of the predetermined delay time, a larger or smaller amount of powder has been sucked in the respective metering chamber at the time of powder ejection. As a result, by setting different delay time periods, it is possible to vary the metered powder delivery rate of the metering chambers 4-1 and 4-2, irrespective of the frequency with which the membranes 8-1 and 8-2 reciprocate from the common drive 10 become. The movement frequency of the membranes can be kept constant or also variable.

According to the preferred embodiment of the invention, the "predetermined suction stroke position" is at a position between the suction stroke start position "a" and "d" and the suction stroke end position "b" and "a", respectively, preferably closer to the suction stroke start position than to the suction stroke end position.

In the preferred embodiment, this predetermined suction stroke position for the diaphragm 8-1 shown on the left in FIGS. 1 and 2 is indicated by a sensor S2 at a position P2 and by a sensor S3 for the diaphragm 8-2 shown on the right in FIGS defined a position P3. The two sensors S2 and S3, like the sensors S1 and S2, can be arranged at any point where they can detect defined positions of the diaphragm 8-1 and 8-2 between their end positions a, b, c and d, for example on the cylinder 22 , on the drive piston 12, on the piston rods 14-1 and 14-2 or on the membranes themselves or on the chamber housing 6-1, 6-2. According to a preferred embodiment of the invention, they are arranged on the cylinder 22. A sensor signal is triggered when the drive piston 12 or a specific part of the drive piston 12 is adjacent to the respective sensor. The sensor S2 then sends a signal to the timing device 74 of the pump control device 68, when the left diaphragm 8-1 reaches a position corresponding to the sensor S2, which is selected so that it during the suction stroke of predetermined suction stroke position of the left diaphragm 8-1 corresponds. Accordingly, the sensor S3 sends a signal to the timing controller 74 of the pump controller 68 each time the right diaphragm 8-2 reaches a position corresponding to the sensor S3, which is selected to be at the suction stroke of the predetermined suction stroke position of the right diaphragm 8-2 equivalent. Due to the chronological sequence of the signals of the attached sensors, the timing controller detects whether, upon receipt of a signal from the sensor S2 or the sensor S3, the left diaphragm 8-1 or the right diaphragm 8-2 performs a suction stroke at this time. In the case of a suction stroke, the time delay device 74 starts the predetermined time delay period, at the end of which compressed gas is left in the metering chamber 4-1 or in the metering chamber 4-2 for pushing out the metered amount of powder.

According to the preferred embodiment, the movement distance of the membranes 8-1 and 8-2 is constantly the same for all strokes and extends from the sensor S1 to the sensor S4 or vice versa. By appropriate control of the drive pressure air by means of the switching valve 30, the movement distance could also be shortened.

FIG. 2 shows a diagram above the pump device in which, on the horizontal axis S, the stroke distance of the drive piston 12, which corresponds to the travel distance of the diaphragms 8-1 and 8-2, coincides with the end position P1 at the sensor S1, the end position P4 the sensor S4, the predetermined partial suction stroke position P2 at the sensor S2 and the predetermined partial suction stroke position P3 at the sensor S3. Plotted on the vertical axis of the diagram are the suction stroke times It ₀ to It ₁₀ for the membrane 8-1 shown on the left. In the reverse direction from the end position P4 to the end position P1, this corresponds to the pressure stroke of the diaphragm 8-1 shown on the left. When the diaphragm 8-1 shown on the left moves from the suction stroke initial position P1 to the right, it reaches the predetermined partial suction stroke position P2 at the sensor S2. Upon reaching this predetermined suction Teilhubposition P2 is of the Time control means 74 a predetermined, preferably variably adjustable, delay period started at the end of the pressurized gas of the pressurized gas source 45-1 is introduced via the Druckgaseinlasskanal 44-1 in the metering chamber 4-1, so that the pressurized gas sucked into this metering chamber 4-1 until then The end of the delay period may be any time during which the drive piston 12 and, correspondingly, the membrane 8-1 shown on the left between the predetermined suction and the powder discharge valve 42-1 presses into and out of the powder injection device 50 Partial stroke position P2 at the sensor S2 and the suction stroke end position P4 at the sensor S4.

When the drive piston 12 has reached the sensor S4 in the end position P4, this is detected by the pump control device 68 by a signal of the sensor S4. The pump control device 68 then switches the changeover valve 30 to the position shown in FIG. 1, in which compressed air of the compressed air source 32 drives the drive piston 12 back to the other end position P1 in the sensor S1. A signal from the sensor S1 then starts the cycle again. The switching of the movement of the two membranes 8-1 and 8-2, and thus also of the drive piston 12, from one direction of movement in the other direction of movement at the movement points can be carried out without or with a time delay. The time delay may be fixed or variably adjustable, for example programmable in a program.

During the movement of the drive piston 12 from the end position P4 shown at the right end position P4 at the sensor S4 to the left end position P1 shown in the sensor S1, the diaphragm shown on the left 8-1 from its dashed line Druckhubanfangsposition "b", which corresponds to the Suction stroke, in the Druckhubendposition Moves "a", which is shown in solid line 8-1.

During this stroke of the left diaphragm 8-1, the diaphragm 8-2 shown on the right is moved by the driving piston 12 from its suction stroke starting position "d" shown in dotted lines to the suction stroke end position "c" shown in solid lines Powder inlet valve 38-2 sucks powder from color changer 60 into its metering chamber 4-2. When the drive piston 12 reaches the predetermined intake stroke position P3 in the sensor S3 during this intake stroke from position P4 at S4, a predetermined, preferably variably adjustable, delay time duration is started by the timer 74 by a signal from this sensor S3. At the end of this delay period of the pump control device 68, triggered by the timing means 74, pressurized gas of the pressure gas source 45-2 shown on the right in Fig. 1 45-2 on the Druckgaseinlaßventil 46-2 and the compressed air inlet channel 44-2 in the dosing chamber 4-2 shown on the right, to press the amount of powder sucked up to this point in time and thus correspondingly metered from this metering chamber 4-2 through its powder outlet valve 42-2 to the powder delivery line 50 and from there through the powder injection device 52. This timing at which the powder is ejected from the metering chamber 4-2 by means of the pressurized gas may be anywhere in the movement of the driving piston 12 between the predetermined suction stroke position P3 at the sensor S3 and the suction stroke end position P1 at the sensor S1. This corresponds to a period between the time scale rt ₀ to rt ₁₀ shown in FIG. 2 in the upper half of the diagram. When the right diaphragm 8-2 has reached its suction stroke end position "c", at the same time, the left-hand diaphragm 8-1 has reached its compression stroke end position "a" which simultaneously becomes its suction stroke start position.

Then the cycle starts from the beginning.

The numbers of the time axes It ₀ to It ₁₀ and rt ₀ to rt ₁₀ are arbitrarily selected.

When the pressurized gas supply valves 46-1 and 46-2 controlled by the pump controller 68 in response to signals from the end position sensors S1 and S4 are not positionable very close to the respective metering chamber 4-1 and 4-2, respectively, it may be desirable to position the pressure gas inlet channel 44-1 or 44-2, or its supply line to the controlled valve, a check valve 76-1 or 76-2 near the inlet of the compressed gas inlet channel 44-1 or 44-2 in the metering chamber 4-1 and 4 respectively -2 to arrange, which opens automatically in the compressed gas supply direction and closes automatically in the opposite flow direction. This prevents powder particles from the metering chamber 4-1 or 4-2 from being able to migrate back into the compressed gas inlet valves 46-1 and 46-2.

According to the preferred embodiment of the invention, the powder inlet valves 38-1 and 38-2 and / or the powder outlet valves 42-1 and 42-2 are not controlled valves, but are self-opening and closing valves in the manner of a check valve. Here, the powder inlet valves 38-1 and 38-2 are arranged such that they are opened by suction or negative pressure in their metering chamber 4-1 and 4-2 during the suction stroke of the associated membrane 8-1 and 8-2, respectively To suck powder from the respective powder container 62, 63 or 64 through the powder inlet channel 36-1 or 36-2 into the metering chambers 4-1 and 4-2, respectively. The gas pressure of the compressed gas source 45-1 and 45-2 used for discharging the metered powder amount from the respective metering chamber 4-1 and 4-2, respectively, is greater than the negative pressure, and causes the powder inlet valve 38-1 and 38-2 to be automatic is closed. According to another embodiment, the powder inlet valves 38-1 and 38-2 and / or the powder outlet valves 42-1 and 42-1 are valves controlled by the pump controller 68.

The powder outlet valves 42-1 and 42-2 are disposed in reverse to the powder inlet valves. As a result, the respective powder outlet valve 42-1 or 42-2 is closed by the negative pressure during the suction stroke of the associated membrane 8-1 or 8-2 and opened by the compressed gas in the metering chambers for ejecting the metered amount of powder to the metered amount of powder by means of Press compressed gas through the open Pulverauslassventil 42-1 or 42-2 and the subsequent Pulverauslasskanal 40-1 or 40-2 in the powder discharge line 50 and from there into the powder injection device 52. The compressed gas overcomes the negative pressure.

The powder suction line 58 could go directly to one of the powder containers 62, 63 or 64 instead of a color changer 60.

The powder spray device 52, also commonly referred to as a powder spray device, may comprise a nozzle or a rotary body or a rotating nozzle for spraying or spraying the powder, as known from the prior art.

Thus, according to the invention, there is provided a method for conveying powder, in particular coating powder, in which, by increasing the volume of a metering chamber 4-1 and / or 4-2, powder can be sucked from a powder source into the metering chamber 4-1 or 4-2 and then the metered amount of powder from the metering chamber can be pressed out by means of compressed gas. The cycle is periodically repeatable. By means of the sensors S1, S4, S2 and S3, a predetermined phase or position of the periodic volume changes of the metering chamber 4-1 or 4-2 is determined and after a predetermined time delay after reaching the predetermined phase by means of the compressed air metered until then Quantity of powder is pushed out of the dosing chamber 4-1 or 4-2.

It is obvious that the invention can also be implemented with only one metering chamber 4-1 or 4-2, without a second metering chamber 4-2 or 4-1. Furthermore, it can be seen that instead of a single drive 10 for both membranes 8-1 and 8-2, each membrane 8-1 and 8-2 may have its own drive 10.

The use of a membrane 8-1 or 8-2 as a displacer allows a compact, compact design. However, the invention is not limited to the use of a membrane, but instead of a membrane, a piston can also be used in a cylinder.

Fig. 3 shows an embodiment of the invention, in which instead of a membrane, a piston is used as a displacement body. Furthermore, FIG. 3 shows the possibility of using a separate drive instead of a single drive for two or more displacement bodies (diaphragm or piston) for each displacement body (diaphragm or piston).

In Fig. 3, Figs. 1 and 2 corresponding parts with the same reference numerals. Thus, the above description of Figs. 1 and 2 applies to Fig. 3. FIG. 3 also shows the possibility of not arranging the sensors S1, S2, S3 and S4 for the detection of the drive piston 12, but for detecting the respective position of the displacement body piston 8-1 or 8-2. In Fig. 3, however, there is also the possibility of not assigning these sensors to the displacement piston 8-1 and 8-2, but the drive piston 12 or another element.

In Fig. 3, a separate Pulveransaugleitung 58 is provided for each powder inlet channel 36-1 and 36-2, which to various powder sources (powder container or color changer) or according to in Fig. 3 to a common powder source, for. B. can lead a powder container 62. Instead of this embodiment, a common Pulveransaugleitung 58 similar to FIG. 1 could be provided for both powder inlet channels 36-1 and 36-2. These can go directly to a powder container, eg. B. 62, lead or to a color changer 60 according to FIG. 1.

Features of Figs. 1 and 2 on the one hand and Fig. 3 on the other hand are mutually interchangeable to form new combinations.

The invention is also applicable to combinations of three or more powder pumps whose powder inlet passages are connected or connectable to a common or different powder source and whose powder outlet passages are all connected to a common powder discharge port, a pump control device being arranged to drive the pumps, offset relative to each other their suction strokes and correspondingly offset in time also their pressure strokes, so that the pumps suck in time offset powders and temporally staggered metered quantities of powder deliver, but at least one pump their displacer (diaphragm or Pulververdrängerkolben) in an intermediate position between end positions, when the displacer of at least one of the other of the pumps is in an end position.

All mentioned compressed gases and compressed gas sources can be compressed air or compressed air sources. However, other compressed gases, eg. B. noble gases, and corresponding other sources of compressed gas, eg. B. noble gas sources, usable. Two or more or all of the compressed gas sources mentioned can together be a single compressed gas source, from which the various compressed gases can be taken.

In the preferred embodiments of the invention shown in Figs. 1, 2 and 3, the pump control means 68 is adapted to switch the movements of the displacers 8-1 and 8-2 from suction stroke to compression stroke, and vice versa, depending on To cause signals from the sensors S1 and S4, which each generate a signal when the displacement body 8-1 or 8-2 is along the stroke at one or the other of two predetermined movement reversal positions.

This is just one way in which the pump control device 68 can detect when the respective displacement body 8-1 or 8-2 is in a predetermined suction stroke position.

Another possibility is embodied in another preferred embodiment of the invention, which is shown schematically in Fig. 4. In the embodiment of Fig. 4, the pump controller 68 includes a clock timer 80 through which the time-delayed injection of pressurized gas into the metering chamber 4-1 and 4-2, respectively, is subject to a fixed cycle time. After this cycle time sends the pump control device 68 control signals to the switching valve 30, which by pressurized gas supply and gas discharge in or out of the cylinder 22 of the drive 10, the movements of the displacement 8-1 and 8-2 and thus the opposing volume changes of the two metering chambers 4-1 and 4-2 causes.

These control signals, preferably the control signal for starting the suction stroke, at the same time also cause the time delay of the timer 74 to be started. Then, as soon as the predetermined delay period has elapsed, pressurized gas is introduced through the one pressure gas inlet valve 46-1 into one dosing chamber 8-1 or through the other pressure gas inlet valve 46-2 into the other dosing chamber 4-2 for powder feeding in relation to FIGS to 3 described way. The difference from FIGS. 1 to 3 is that the pump control device 68 does not detect the predetermined suction stroke position of the displacers 8-1 and 8-2 on the basis of sensor signals (sensors S1, S2, S3, S4), but rather by control signals, which respectively occur Expiration of the cycle time of the clock timer 80 are generated.

It is assumed that the drive piston 12 and thus also the displacement body 8-1 and 8-2 have reached their predetermined end positions at the end of the cycle time. Deviations between the predetermined end positions and the end positions actually achieved can arise when the movement resistance of the elements to be moved change, for example as a result of material wear, material fatigue or due to soiling. To detect such deviations between setpoint positions and actual value positions along the movement path of the Displacer 8-1 or 8-2 or along an immovably connected element, preferably the drive piston 12, with distance from its end positions, a sensor S5 may be arranged at a position P5, which the pump control device 68 provides a signal when the relevant Element, in the preferred embodiment, the drive piston 12 is located in the position P5 of the control sensor S5. By comparing the timing of the control signal of the control sensor S5 with the timing of the control signal for switching the moving direction of the driving piston 12, the pump driving controller 68 can calculate whether the driving piston 12 has reached the control sensor S5 (or at a predetermined speed) in a predetermined time required is, so that he reaches his final position in time. In case of deviations by a predetermined value, the pump controller 68 may generate a defect signal (or warning signal).

4 shows in addition to the control sensor S5 a further control sensor S6 at a position P6 at a distance in the direction of movement of the drive piston 12 from the one control sensor S5 and also at a distance from the two end positions of the drive piston 12, for generating a control signal in the pump control device 68 then when the drive piston 12 is opposite one of these two control sensors S5 or S6. In this embodiment of the invention, by comparing the time difference between the generation of the two control signals of the two control sensors S5 and S6 with a target period of time, the pump controller 68 can determine whether the displacers 8-1, 8-2 each reach their predetermined end position within the cycle time. Also in this embodiment, based on the time difference, the speed of the drive piston 12 or the displacement body 4-1, 4-2 can be calculated by the pump control device and compared with a desired speed. In case of deviations between the set time and the actual time or between the set speed and the actual speed, and thus also between deviations from the predetermined end position and the actually reached end position of the drive piston 12 at its In order to reverse the movement, by a certain amount of deviation, the pump controller 68 may generate a defect signal.

The defect signal can be used for various purposes, for example for optical and / or acoustic display of the defect or for storing the defect value in the memory of a computer for diagnostic purposes.

According to another embodiment of the invention, the defect signal can be used, depending on the difference between the set time (or speed) and actual time (or speed) of the drive piston 12, the switching valve 30 accordingly to control so that the changed speed of the drive piston 12 through a change in its stroke frequency is compensated, so that the powder volume delivery of the pump device remains constant within a predetermined tolerance range.

The embodiment of FIG. 4 is identical to that of FIGS. 1 and 2, except that the pump controller 68 includes the clock timer 80 and the sensors S1, S2, S3 and S4 are controlled by the control sensor S5 or by the two control sensors S5 and S5 S6 are replaced. The same parts have the same reference numbers.

The embodiments of the invention described with reference to FIG. 4 are also applicable to embodiments which, unlike FIGS. 1, 2 and 4, have diaphragms but pistons according to FIG. 3 as displacers 8-1 and 8-2, respectively.

According to preferred embodiments of the invention, the cycle time and / or the delay time may be variably adjustable. According to a particularly preferred embodiment of the invention, to set a desired change in the powder delivery rate per unit time, the cycle time is kept constant and the delay time period is variably adjustable to the desired To set the powder delivery rate per unit of time. The delay time period is here the time duration by which the delivery of the powder from the respective metering chamber 4-1 or 4-2 is started after the relevant cycle time has expired, at which the displacer 8-1 or 8-2 of the pressure stroke has started Suction stroke has been switched.

Figures 5 to 8 show a further embodiment of the invention, according to which the powder inlet valves 38-1 and 38-2 and / or the powder outlet valves 42-1 and 42-2 are self-acting one-way valves in the manner of a duck bill (duck bill valve) be opened automatically in the forward direction of the pressure of the compressed gas and closed automatically in the reverse direction of the pressure of the compressed gas and / or by its own material spring elasticity. Such a one-way valve is designated in Figures 5 to 8 by the reference numeral 38/42. It consists of a one-piece body made of elastic material, such as rubber. It includes a cylindrical portion 82 with a radially outwardly annular flange 84 protruding at one end and with a duckbill tapered tube portion 86 at the other end.

If no differential pressure acts on the one-way valve in both directions of flow, it is closed according to the longitudinal section of Fig. 5 and the front view of the valve tip of Fig. 6 by its own material spring elasticity. The valve closing force is increased when pressurized gas 88 acts in the valve blocking direction on the one-way valve according to FIG. 5.

When the one-way valve 38/42 is applied in the forward direction of compressed gas 90, this compressed gas 90 pushes the two duckbill parts 86-1 and 86-2 apart, so that the valve opens. This open position of the one-way valve is shown in Fig. 7 in longitudinal section and in Fig. 8 in front view opposite to the passage direction.

Fig. 9 shows the one-way valve 38/42 in side view relative to Figures 5 and 7 rotated by 90 °.

In all embodiments of the invention can be provided at the movement reversal points (dead points) of the displacement body 8-1, 8-2 a waiting time during which the pumping device can calm down before the next stroke movement begins.

Claims (26)

1. Pumping installation for powder (54), in particular for coating powder, containing at least one powder pump (2-1, 2-2) which has a metering chamber (4-1, 4-2) which is bounded by a chamber housing (6-1, 6-2) and a displacement body (8-1, 8-2) which can be moved forwards, relative to the chamber housing, during a delivery stroke and back during a suction stroke, the pump chamber having a powder inlet duct (36-1, 36-2) to which a powder inlet valve (38-1, 38-2) is assigned, a powder outlet duct (40-1, 40-2) to which a powder outlet valve (42-1, 42-2) is assigned, and a compressed-gas inlet duct (44-1, 44-2) to which a compressed-gas inlet valve (46-1, 46-2) is assigned, it being possible, in order to suck up a metered quantity of powder (54) into the metering chamber (4-1, 4-2), for the powder inlet valve (38-1, 38-2) to be opened and for the powder outlet valve (42-1, 42-2) and the compressed-gas inlet valve (46-1, 46-2) to be closed, with the result that the displacement body moving in the suction-stroke direction can suck powder (54) through the powder inlet duct (36-1, 36-2) into the metering chamber (4-1, 4-2), and being possible, in order to convey the metered quantity of powder out of the metering chamber (4-1, 4-2), for the powder inlet valve (38-1, 38-2) to be closed and for the powder outlet valve (42-1, 42-2) and the compressed-gas inlet valve (46-1, 46-2) to be opened, with the result that compressed gas flowing from the compressed-gas inlet duct (44-1, 44-2) into the metering chamber (4-1, 4-2) can press the metered quantity of powder from the metering chamber (4-1, 4-2) into the powder outlet duct (40-1, 40-2), and a pump control device (68) for controlling the compressed-gas inlet valve (46-1, 46-2), characterized in that the electronic or computerized pump control device (68) has a timing device (74) by means of which the conveying of the powder out of the metering chamber (4-1, 4-2) is started as a function of the predetermined delay period which has passed since a predetermined operating time, the compressed gas being admitted into the metering chamber (4-1, 4-2) at the end of the delay period, and the quantity of powder metered up to the end of the delay period being pressed out of the metering chamber (4-1, 4-2) by means of the compressed gas.
2. Pumping installation according to Claim 1, characterized in that the pump control device (68) has a cycle time transmitter and each time a predetermined cycle time has expired transmits control signals to a switching-over device (34) for switching over the movement of the displacement body (8-1, 8-2) from suction stroke to delivery stroke, and vice versa from delivery stroke to suction stroke, at the rhythm of the predetermined cycle time, and in that the pump control device (68) is designed in order, at the timing device (74), to start the predetermined delay period in each case as a function of the time of production of that control signal which brings about the starting of the suction stroke, the compressed gas being admitted into the metering chamber (4-1, 4-2) at the end of the delay period, and the quantity of powder metered up to the end of the delay period being pressed out of the metering chamber (4-1, 4-2) by means of the compressed gas.
3. Pumping installation according to Claim 1 or 2, characterized in that at least one monitoring sensor (S5, S6) is provided in order to detect when the displacement body (8-1, 8-2) is in a predetermined position, and in order to generate a sensor signal upon detection of when the displacement body is in the predetermined position, in that the pump control device (68) is functionally connected to the at least one monitoring sensor, and in that the pump control device (68) is designed to automatically compare the time of the sensor signal with the time of at least one of the control signals in order to monitor whether the period between the two times deviates from a predetermined value, and in order to generate a defect signal when there is a predetermined deviation from the predetermined value.
4. Pumping installation according to Claim 1 or 2, characterized in that at least two monitoring sensors (S5, S6) are provided and are connected to the pump control device (68) in order to detect when the displacement body (8-1, 8-2) is in each case in one of two different, predetermined positions and in order to generate sensor signals upon detection of the displacement body in the predetermined positions, and in that the pump control device (68) is designed to compare the difference in time between the signals of the one monitoring sensor and the signals of the other monitoring sensor with a predetermined period, and to generate a defect signal if the difference in time deviates from the predetermined period by more than a predetermined value.
5. Pumping installation according to Claim 1, characterized in that the pump control device (68) has a timing device (74) in order to start the conveying of the powder out of the metering chamber as a function of the predetermined delay period which has passed since a predetermined suction-stroke position of the displacement body (8-1, 8-2), the compressed gas being admitted into the metering chamber (4-1, 4-2) at the end of the delay period, and the quantity of powder metered up to the end of the delay period being pressed out of the metering chamber (4-1, 4-2) by means of the compressed gas.
6. Pumping installation according to Claim 5, characterized in that the predetermined suction-stroke position is a suction-stroke starting position.
7. Pumping installation according to Claim 5, characterized in that the predetermined suction-stroke position lies between a suction-stroke starting position and a suction-stroke end position.
8. Pumping installation according to Claim 5, characterized in that the predetermined suction-stroke position between a suction-stroke starting position and a suction-stroke end position is closer to the suction-stroke starting position than to the suction-stroke end position.
9. Pumping installation according to at least one of the preceding Claims 5 to 8, characterized in that the timing device (74) has at least one sensor (S1, S4; S2, S3) for generating a signal when the displacement body (8-1, 8-2) is in the predetermined suction-stroke position.
10. Pumping installation according to one of Claims 5 to 9, characterized in that a pump control device (68) is provided by means of which the movements of the displacement body (8-1, 8-2) are switched over from suction stroke to delivery stroke, and vice versa, as a function of signals of sensors (S1, S4) which each generate a signal when the displacement body (8-1, 8-2) is situated at the one or other of two predetermined movement-reversing positions along the stroke section.
11. Pumping installation according to at least one of the preceding claims, characterized in that the distance over which the displacement body (8-1, 8-2) moves is always the same in all of the stroke movements.
12. Pumping installation according to at least one of the preceding claims, characterized in that, at at least one of the movement-reversing dead-centre positions of the displacement body (8-1, 8-2), a second time delay period is provided before the displacement body (8-1, 8-2) is moved after one direction of movement into the other relevant direction of movement.
13. Pumping installation according to at least one of the preceding claims, characterized in that the delay period can be varied.
14. Pumping installation according to at least one of the preceding claims, characterized in that the displacement body (8-1, 8-2) is a flexible membrane.
15. Pumping installation according to at least one of the preceding claims, characterized in that the pump inlet valve (38-1, 38-2) and the pump outlet valve (42-1, 42-2) are automatic valves which open and close automatically by means of the differential pressure between their two valve sides.
16. Pumping installation according to Claim 15, characterized in that the pump inlet valve (38-1, 38-2) and the pump outlet valve (42-1, 42-2) are automatic valves which can be actuated in the manner of a nonreturn valve by differential gas pressure over their valve body (38-3, 42-3), it being possible for the valve body (38-3, 42-3) to be moved as a function of this differential gas pressure relative to a valve seat (38-4, 42-4) into the open position or into the closed position and to be retained in the relevant position.
17. Pumping installation according to Claim 15, characterized in that the pump inlet valve (38-1, 38-2) and the pump outlet valve (42-1, 42-2) are automatic valves in the manner of a duckbill, the duckbill opening and closing automatically by means of the difference in pressure between the inside of the duckbill and outside of the duckbill.
18. Pumping installation according to at least one of the preceding claims, characterized in that at least two of the abovementioned powder pumps (2-1, 2-2) are provided, the pump inlet ducts (36-1, 36-2) of which can be connected or are connected to a powder source, and the powder outlet ducts (40-1, 40-2) of which can be connected or are connected to a joint powder-dispensing opening (48), and in that the two powder pumps (2-1, 2-2) can be operated in an opposed manner relative to each other, with the result that a metered quantity of powder can be ejected by means of the compressed gas into the powder outlet duct (40-1, 40-2) in an alternating manner from the metering chamber (4-1) of the one powder pump (2-1) or from the metering chamber (4-2) of the other powder pump (2-2), and, in an opposed alternating manner, powder can be sucked in through the powder inlet ducts (36-1, 36-2) into either the metering chamber (4-2) or into the metering chamber (4-1).
19. Pumping installation according to Claim 18, characterized in that the displacement bodies (8-1, 8-2) of the two pumps have a common drive (10).
20. Powder coating installation, characterized by a pumping installation according to at least one of the preceding claims, for conveying coating powder.
21. Method for conveying powder (54), in particular coating powder, in which enlargement of the volume of a metering chamber (4-1, 4-2) enables powder (54) to be sucked from a powder source into the metering chamber (4-1, 4-2), and subsequently compressed gas is used to push the metered quantity of powder out of the metering chamber (4-1, 4-2), after which the volume of the metering chamber (4-1, 4-2) is reduced, and then the cycle is repeated periodically, characterized in that sensors (S1, S4; S2, S3) and an electronic or computerized pump control device are used to determine a predetermined phase of the periodically changing volume of the metering chamber (4-1, 4-2), and in that, with a predetermined time delay after the predetermined phase has been reached, the compressed gas is used to press the quantity of powder which has been metered up until then out of the metering chamber (4-1, 4-2).
22. Method according to Claim 21, characterized in that in a powder inlet duct (36-1, 36-2) into the metering chamber (4-1, 4-2) and in a powder outlet duct (40-1, 40-2) out of the metering chamber (4-1, 4-2) at least one valve is used in each case in the relevant path, the said valve automatically opening and shutting in the manner of a nonreturn valve as a function of the respective difference in gas pressure between its upstream side and its downstream side.
23. Method for conveying powder (54), in particular coating powder, in which enlargement of the volume of at least one metering chamber (4-1, 4-2) enables powder (54) to be sucked from a powder source into the metering chamber (4-1, 4-2), and subsequently compressed gas is used to push the metered quantity of powder out of the metering chamber (4-1, 4-2) after which the volume of the metering chamber (4-1, 4-2) is reduced, and then the cycle is repeated periodically, characterized in that an electronic cycle time transmitter (80) is used to control the changes in volume of the at least one metering chamber (4-1, 4-2) by means of a predetermined cycle time, in that, in each case after the predetermined cycle time has elapsed, at least one control signal is generated, in that this at least one control signal reverses the direction of the change in volume from enlargement to reduction or from reduction to enlargement, and at the same time a predetermined time delay is started, and in that only when the predetermined time delay has elapsed is the compressed gas used to press the metered quantity of powder out of the metering chamber.
24. Method according to Claim 23, characterized in that the changes in volume of the at least one metering chamber (4-1, 4-2) are brought about by means of a displacement body (8-1, 8-2), in that the presence of the displacement body in a predetermined position is determined by means of at least one monitoring sensor (S5, S6) and, in the process, a monitoring signal is generated upon detection of the displacement body in the predetermined position, and in that the difference in time between the time of the control signal and the time of the at least one control signal is compared with a predetermined period which the difference in time would contain if the displacement body were to cover a predetermined distance within each cycle time, and in that a defect signal is generated if the difference between the difference in time and the predetermined period exceeds a predetermined value.
25. Method according to Claim 23, characterized in that the changes in volume of the at least one metering chamber is brought about by means of a displacement body (8-1, 8-2), in that at least two monitoring sensors (S5, S6), which are arranged at a distance from each other along a distance corresponding to the maximum movement distance of the displacement body, are used to generate monitoring signals if the displacement body is in a position corresponding to the sensor position, in that the difference in time between the monitoring signals of the at least one monitoring sensor with respect to the monitoring signals of the other monitoring sensor is compared with a predetermined period which would amount to the difference in time if the displacement body should move over a predetermined desired movement distance within the cycle time, and in that in each case at least one defect signal is generated if the difference in time deviates from the predetermined period by more than a predetermined value.
26. Method according to one of Claims 21 to 25, characterized in that two of the metering chambers (4-1, 4-2) are changed in respect of their volume simultaneously, but in a phase-displaced manner with respect to each other, with the volume of the one metering chamber being enlarged while the volume of the other metering chamber is reduced, and vice versa.

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