EP1437178A2 - Powder pumping installation, Method therefore and powder coating installation - Google Patents

Abstract

The particulate pump (2.1) has a timer control (74) to allow pressurized gas (36.1) into a metering feed chamber (6.1) at a preset operating point in time for a preset period. At the end of the time period, the powder mix is ejected from the metering chamber. The pump time control can be a cyclic timer to provide control signals at the ends of set time periods.

Description

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

Accordingly, the invention relates to a pump device for powder, in particular for coating powder, containing at least one powder pump, which a Dosing chamber having a chamber housing and a Is displacer limited, which relative to the chamber housing during a Druckhubes before and during a suction stroke can be moved back, the Pump chamber a powder inlet channel, which is a powder inlet valve is assigned a powder outlet channel, which a powder outlet valve is assigned, and a compressed gas inlet channel, which a Compressed gas inlet valve is assigned, one for suction dosed amount of powder into the dosing chamber the powder inlet valve is openable and the powder outlet valve and the compressed gas inlet valve are closable, so that the displacer moving in the suction stroke direction Can suck powder through the powder inlet channel into the dosing chamber, and to Convey the metered amount of powder from the metering chamber Powder inlet valve is closable and the powder outlet valve and that Compressed gas inlet valve are openable, so that from the compressed air inlet duct in the dosing chamber flowing compressed air the dosed amount of powder from the Dosing chamber can press into the powder outlet channel.

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

A pump device is known from practice which has two pumps, each with a powder suction piston and a pneumatic cylinder driving it exhibit. The two pumps are driven in opposite directions, so that one makes one suction stroke while the other makes a pressure stroke. While of the suction stroke, the powder suction piston in question sucks powder from one Powder source in its dosing chamber. At the end of the suction stroke, means Compressed air, which is introduced into the dosing chamber, which dosed there Powder quantity from the dosing chamber into a powder discharge line. pushed out. The piston then returns to its starting position during a pressure stroke back to powder again from the powder source during a suction stroke to suck. The delivery rate per unit of time depends on the frequency with which the pistons are moved back and forth. A pump device of this type is in WO 03/024612 A1 only after the priority date of the present new one Patent application has been described.

So-called injectors are also known, in which according to the Venturi principle a flow of conveying air flows from an outlet nozzle into a collecting nozzle and in Intermediate space creates a negative pressure, through which Coating powder is sucked into the conveying air stream from a powder source. Such injectors have compared to the aforementioned piston pumps Disadvantages that the powder particles have an abrasive effect on the catch nozzle and as a result the efficiency of the powder delivery drops over time: one pneumatic powder conveyance of this type requires a large amount of compressed air per Time unit.

The aforementioned piston pumps do not have these disadvantages. The piston pumps have the disadvantage, however, that they convey the powder discontinuously in batches and both for more even powder delivery and for the promotion of larger powder quantities per unit of time a fast piston movement frequency is required. The level of the piston frequency is however due to the Control speed with which the valves in the flow paths of the Pump can be controlled, limited. It must also be ensured that in Pump particles and in their flow paths do not crush powder particles will, sinter or otherwise stick and that neither Spaces, depressions and the like exist in which powder can accumulate.

The object of the invention is to achieve a pump device, which has at least one volume displacement body, that a defined and, if desired, large flow rate of powder per Unit of time is eligible without the aforementioned disadvantages. In particular, a large one should last over a long service life Process reliability and great stability of the powder delivery rate per unit of time (constant powder rate for a defined configuration and defined setting of the Pump device) can be achieved.

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

Further features of the invention are contained in the subclaims.

Accordingly, the pump device according to the invention is thereby characterized in that a time control device is provided by which in Dependence on the past since a predetermined operating situation predetermined delay period of conveying the powder from the Dosing chamber is started by admitting compressed air into the dosing chamber and the amount of powder dosed by the end of the delay period by means of the Compressed air is pressed out of the dosing chamber.

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

The invention also discloses methods for conveying powder, especially 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 is described below with reference to the drawings using preferred embodiments as examples. Show in the drawings

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 to explain the invention,

Fig. 3

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

Fig. 4

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

Fig. 5

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

Fig. 6

5 seen in a front view against the forward direction,

Fig. 7

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

Fig. 8

7 shows a front view against the forward direction of the one-way valve from FIG. 7 in the open state,

Fig. 9

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

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

The two membranes 8-1 and 8-2 have one arranged between them, common drive 10. The drive 10 can be a mechanical, hydraulic, electrical or a pneumatic drive according to FIG. 1. The one in Fig. 1 Pneumatic drive shown contains a diagonally to the membranes 8-1 and 8-2 displaceable drive piston 12, of which extends in the direction of movement Piston rods 14-1 or 14-2 extend away from the drive piston 12 distal ends with one membrane 8-1 or with the other membrane 8-2 are connected so that the two membranes are each together with the Move the drive piston 12. The piston rods 14-1 and 14-2 each engage in Center of the relevant membrane 8-1 or 8-2, which are each together with the drive piston 12 moved in the piston axial direction. The Diaphragm peripheral edges 16-1 and 16-2 are each on a part of the Chamber housing 6-1 or 6-2 attached and can not with the Membrane center together with the drive piston 12 across the membrane move. If in the context of this description of lifting movements Membrane, then it means the area of the membrane, which is connected to the drive piston 12 for common movement, but not the peripheral membrane edges 16-1 attached to the chamber housing or 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 section in Fig. 1.

The membranes 8-1 and 8-2 (with the exception of their membrane peripheral edges 16-1 and 16-2) are during a pressure stroke before and during a suction stroke movable back by means of the common drive 10. In Fig. 1 is the membrane 8-1 shown on the left in an end position "a", which represents the end position of the Pressure stroke and the initial position of the suction stroke. Here, the associated Dosing chamber 4-1 its smallest volume. Here, the membrane is 8-1 preferably not completely on the chamber housing 6-1, but has one small distance from it so that between the membrane 8-1 and the Chamber housing 6-1 powder particles can not be squeezed. The same thing applies to the membrane 8-2 shown on the right in FIG. 1 if it is in a End position "d", which is the end position of its pressure stroke and the Starting position of their suction stroke is. However, Fig. 1 shows the right membrane 8-2 in a left end position "c", which is their end position of the suction stroke and their Initial position of the pressure stroke is. The two membranes 8-1 and 8-2 are 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 is close to Cylinder end walls 24 and 25 have a compressed air control opening on both sides of the drive piston 12 26 or 28, which alternately with a changeover valve 30 a compressed air source 32 or with a vent opening 34 to the outside atmosphere are connectable for ventilation. In Fig. 1 is the compressed air control opening shown on the right 28 connected to the compressed air source 32, which is why its compressed air has pressed the drive piston 12 into the position shown on the left in FIG. 1 while the compressed air control opening 26 shown on the left with the vent opening 34 of the Switch valve 30 is connected. The switching valve 30 is switchable, so that after switching the compressed air control opening 28 shown on the right with the Vent opening 34 is connected and the compressed air control opening shown on the left 26 is connected to the compressed air source 32. In this, not shown in Fig. 1, Reverse position of the switching valve 30 drives the compressed air Drive piston 12 together with the two membranes 8-1 and 8-2 from the left to the right. This is through the left membrane 8-1 of their Suction stroke start position (pressure stroke end position) "a" to its suction stroke end position (Print stroke start position) "b" moved. Simultaneously, the right membrane 8-2 from their suction stroke end position (pressure stroke start position) "c" to their Suction stroke start position (pressure stroke end position) "d" moved. The two Membranes 8-1 and 8-2 are in their left end position by a solid line Line and in its right end position schematically by a dashed line shown.

Each dosing chamber 4-1 and 4-2 has a powder inlet channel 36-1 and 36-2, which one each. Powder inlet valve 38-1 or 38-2 is assigned; one Powder outlet channel 40-1 or 40-2, which each have a powder outlet valve 42-1 or 42-2 is assigned; and a compressed gas inlet channel 44-1 or 44-2, which each a compressed gas inlet valve 46-1 or 46-2 is assigned.

For sucking in a metered amount of powder into the one shown in Fig. 1 on the left Dosing chamber 4-1, 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, see above that the suction stroke direction from the suction stroke start position "a" in the Suction stroke end position "b" moving left membrane 8-1 powder through the left Powder inlet channel 36-1 can suck into the left-hand metering chamber 4-1. To promote the dosed amount of powder from the dosing chamber 4-1 shown on the left into the left Powder outlet channel 40-1, the left powder inlet valve 38-1 is closable and that left powder outlet valve 42-1 and the left compressed gas inlet valve 46-1 openable 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 compressed gas inlet channel 44-1 into the left Dosing chamber 4-1 and the metered amount of powder flow from the dosing chamber 4-1 into the left powder outlet channel 40-1. After or during this expulsion of the powder from the left dosing chamber 4-1, depending on Embodiment of the pump device, the left membrane 8-1 of the Drive piston 12 again from the right suction stroke end "b" into the left Suction stroke start position "a" moved back, which is referred to here as a pressure stroke, so that she can then perform a suction stroke again.

Corresponding functions also lead the one driven by the drive 10 1 membrane 8-2 shown on the right and the associated valves 38-2, 42-2, 45-2 and 46-2 out with respect to the associated right-hand metering chamber 4-2 associated right powder inlet channel 36-2 and the associated right Powder outlet channel 40-2 and a compressed gas source 45-2 shown on the right, e.g. B. a compressed air source. The right diaphragm 8-2, however, makes its pressure stroke when the left membrane 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 extending from the valve body 38-3 is lockable. 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 by the Valve body 42-3 is closable.

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

The two powder inlet channels 36-1 and 36-2 can be connected separately or together a common or connected to different powder sources. In Fig. 2 they are preferably via a common powder inlet opening 56 and a powder suction line 58 connected to a color changer 60. The Color changer 60 is a channel switch or powder switch, through which depending Setting the course of one of several powder containers 62, 63, 64 etc. with the Powder suction line 58 is optionally connectable. Switching the Color changer 60 is preferably carried out using compressed gas, e.g. B. compressed air, one Pressurized gas source, e.g. B. a compressed air source 66 via a controlled Valve arrangement 67.

The color changer 60 can also be switched into a switch position in which none the powder container 62, 63, 64, but instead the compressed gas source 66 a compressed gas line 69 is connected to the powder suction line 58, so that Compressed gas, e.g. 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 via their powder outlet valves 42-1 or 42-2 and the powder outlet channels 40-1, 40-2 to the powder delivery line 50 and from this through the Powder sprayer 52 can flow to the outside atmosphere around the whole Clean the system of powder residues. By means of a, preferably electronic or computerized pump control device 68 can also be provided that at the same time or after this cleaning pressurized gas, e.g. B. compressed air from a Pressurized gas source 45-1 or 45-2 via the pressurized gas inlet channel 44-1 or 44-2 and the associated controllable compressed gas inlet valve 46-1 or 46-2 in one Blown in end of the dosing chamber 4-1 or 4-2 and thus powder from the Dosing chamber at the other end of the chamber through the local powder outlet valve 42-1 or 42-2 and the adjoining powder outlet channel 40-1 or 40-2 blown out through the powder discharge line 50 and the powder spraying device 52 becomes. The compressed gas inlet channel 44-1 or 44-2 can be parallel to it arranged compressed gas cleaning channel 72-1 or 72-2, which against the downstream parts of the relevant powder inlet valve 38-1 or 38-2 is directed to clean them of powder particles, if not already Compressed gas inlet channel 44-1 and 44-2 against the downstream areas of the Powder inlet valves 38-1 or 38-2 is directed and thereby cleans them.

Simultaneously or after this cleaning, the pump control device 68 Via a control line 70, a valve 71 can be opened to pressurized gas, for. B. Compressed air, from a compressed gas source 75 through an additional gas line 73-1 or 73-2 against the downstream parts of the powder outlet valves 42-1 and 42-2 which the auxiliary gas line is directed to blow and from there through the Powder outlet channels 40-1 and 40-2 and the powder discharge line 50 for Powder spray device 52 and from there to lead into the outside atmosphere.

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

The pump control device 68 contains a time control device 74, through which depending on the predetermined suction stroke position, e.g. B. P1 or P2 of the membrane 8-1 shown on the left and a predetermined one Suction stroke position, e.g. B. P4 or P3, the membrane 8-2 shown on the right, past predetermined delay period of conveying the powder the relevant dosing chamber 4-1 or 4-2 is started. At the end of Delay time is the compressed gas from the compressed gas source 45-1 or 45-2 Compressed gas inlet valve 46-1 or 46-2 into the metering chamber 4-1 or 4-2 so that the amount of powder dosed until the end of the delay time is pressed out of the dosing chamber by means of this compressed gas relevant powder outlet valve 42-1 or 42-2 in the powder discharge line 50 and from this to the powder spraying device 52 or to a powder container.

According to one embodiment, said "predetermined suction stroke position" the suction stroke start position "a" corresponding to P1 for the left diaphragm 8-1 and "d" corresponding to P4 for the right membrane 8-2, which in Fig. 1 for the left membrane 8-1 shown is the position "a" shown in solid lines, and which for the membrane 8-2 shown on the right in FIG. 1 is shown in broken lines position shown is "d".

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

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

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

If in the embodiment of the pump device in question the said "predetermined suction stroke position" means the suction stroke start position "a" or "d" Is membrane 8-1 or membrane 8-2, then the timer 74 the pump control device 68 on the basis of the signals from the sensors S1 and S4, when the membranes 8-1 and 8-2 have reached the relevant end position.

The sensors S1 and S4 can be arranged anywhere, where Positions of the membrane 8-1 and 8-2 can be determined, especially at points 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 the membranes 8-1 and 8-2. According to In a preferred embodiment, they are on the cylinder 22, preferably on the cylinder Outside, arranged at positions P1 and P4, which the drive piston 12th each when the membranes 8-1 and 8-2 are in one of the two End positions.

According to the invention, the compressed gas source 45-1 can be metered by means of compressed gas Powder from the left dosing chamber 4-1, and by means of compressed gas from the compressed gas source 45-2 dosed powder from the right dosing chamber 4-2 not only when the Suction stroke end position "b" of the left membrane 8-1 and "c" of the right membrane 8-2 are expelled through the relevant powder outlet valve 42-1 or 42-2, but also earlier, if only a small amount of powder in the relevant dosing chamber. This is due to a delay period achieved, which is preferably variably adjustable on the time control device 74 is. This makes it possible to dispense smaller amounts of powder from the relevant one Eject dosing chamber 4-1 or 4-2 before the associated membrane 8-1 or 8-2 has completed its full suction stroke. This is the associated one Powder inlet valve 38-1 or 38-2 closed immediately when compressed gas Pressurized gas source 45-1 or 45-2 via the pressurized gas inlet channel 44-1 or 44-2 in the relevant dosing chamber 4-1 or 4-2 is blown. Depending on the size of the predetermined delay time is one at the time of powder discharge larger or smaller amounts of powder are sucked into the relevant dosing chamber Service. This is done by setting different ones Delay times the possibility of the metered powder flow rate of the Dosing chambers 4-1 or 4-2 to vary, regardless of the frequency which the membranes 8-1 and 8-2 from the common drive 10 back and forth be moved. The movement frequency of the membranes can be kept constant will be or also be variable.

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

In the preferred embodiment, this predetermined suction stroke position is for the membrane 8-1 shown on the left in FIGS. 1 and 2 by a sensor S2 on a Position P2 and for the membrane 8-2 shown in FIGS. 1 and 2 on the right by a Sensor S3 defined at a position P3. The two sensors S2 and S3 can like sensors S1 and S2 can be placed anywhere where they defined positions of the membrane 8-1 and 8-2 between their end positions a, b, c and d can be detected, for example on the cylinder 22, on the drive piston 12, on its 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. It becomes a sensor signal triggered when the drive piston 12 or a certain part of the Drive piston 12 is adjacent to the respective sensor. The sensor S2 sends each then a signal to the timing device 74 of the Pump controller 68 when the left diaphragm 8-1 is a sensor S2 Appropriate position reached, which is chosen so that it is the suction stroke of the predetermined suction stroke position of the left diaphragm 8-1. Corresponding The sensor S3 then sends a signal to the time control device 74 in each case Pump controller 68 when the right diaphragm 8-2 is a sensor S3 Appropriate position reached, which is chosen so that it is the suction stroke of the predetermined suction stroke position of the right diaphragm 8-2 corresponds. Through the the signal sequence of the attached sensors recognizes the Time control device, whether on receipt of a signal from sensor S2 or Sensor S3 the left membrane 8-1 or the right membrane 8-2 to this Executes a suction stroke at the time. In the event of a suction stroke, the Time delay device 74 the predetermined time delay period, at the other End of pressurized gas left in the metering chamber 4-1 or in the metering chamber 4-2 is used to squeeze out the metered amount of powder.

According to the preferred embodiment, the movement distance is Membranes 8-1 and 8-2 consistently the same size for all stroke movements and they extends from sensor S1 to sensor S4 or vice versa. By Appropriate control of the drive compressed air by means of the changeover 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 movement distance of the diaphragms 8-1 and 8-2, with the end position P1 in the sensor S1, the end position P4 in the sensor S4, the predetermined partial suction stroke position P2 for the sensor S2 and the predetermined partial suction stroke position P3 for the sensor S3. The suction stroke times It ₀ to It ₁₀ for the membrane 8-1 shown on the left are plotted on the vertical axis of the diagram. In the opposite direction from the end position P4 to the end position P1, this corresponds to the pressure stroke of the membrane 8-1 shown on the left. When the diaphragm 8-1 shown on the left moves from the suction stroke start position P1 to the right, it reaches the predetermined suction partial stroke position P2 at the sensor S2. When this predetermined partial suction stroke position P2 is reached, the timer 74 starts a predetermined, preferably variably adjustable, delay period, during which the compressed gas from the compressed gas source 45-1 is admitted into the metering chamber 4-1 via the compressed gas inlet channel 44-1, so that Pressurized gas presses the amount of powder previously sucked into this metering chamber 4-1 through the powder outlet valve 42-1 into the powder delivery line 50 and through it out of the powder spray device 52. The end of the delay period can be any time during which the drive piston 12 and the like are the membrane 8-1 shown on the left is located between the predetermined partial suction stroke position P2 in the sensor S2 and the suction stroke end position P4 in the sensor S4.

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

When the drive piston 12 moves from the end position P4 shown on the right for sensor S4 to the end position P1 shown on the left for sensor S1 membrane 8-1 shown on the left of its dashed line Pressure stroke start position "b", which corresponds to the suction stroke end position, in the Druckhubendposition "a" moves, which is shown with a solid line 8-1.

During this pressure stroke of the left diaphragm 8-1, the diaphragm 8-2 shown on the right is moved by the drive piston 12 from its suction stroke start position "d" (dash stroke end position) shown in broken lines to the suction stroke end position "c" shown in solid lines, whereby it moves over the Powder inlet valve 38-2 sucks powder from color changer 60 into its dosing chamber 4-2. If the drive piston 12 reaches the predetermined suction stroke position P3 in the sensor S3 during this suction stroke from position P4 at S4, a predetermined, preferably variably adjustable, delay time period is started by a signal from this sensor S3 from the timing control device 74. When this delay period has elapsed, the pump control device 68, triggered by the time control device 74, admitted pressurized gas from the pressurized gas source 45-2 shown on the right in FIG. 1 via its pressurized gas inlet valve 46-2 and the pressurized air inlet channel 44-2 into the metering chamber 4-2 shown on the right. in order to press the quantity of powder sucked in up to this point in time and thus correspondingly from this metering chamber 4-2 through its powder outlet valve 42-2 to the powder discharge line 50 and from there through the powder spraying device 52. This point in time at which the powder is expelled from the metering chamber 4-2 by means of the compressed gas can be at any point in the movement of the drive piston 12 between the predetermined suction stroke position P3 for the sensor S3 and the suction stroke end position P1 for the sensor S1. This corresponds to a time period between the time scale rt ₀ to rt ₁₀ shown in the upper half of the diagram in FIG. 2. When the right membrane 8-2 has reached its suction stroke end position "c", the membrane 8-1 shown on the left has simultaneously reached its pressure stroke end position "a", which simultaneously becomes its suction stroke start position.

Then the cycle starts again.

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

If the from the pump controller 68 in response to signals from the End position sensors S1 and S4 controlled compressed gas supply valves 46-1 and 46-2 cannot be positioned very close to the relevant dosing chamber 4-1 or 4-2 are, it may be appropriate in the compressed 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 into the metering chamber 4-1 or 4-2 to arrange, which opens automatically in the compressed gas supply direction and in opposite flow direction closes automatically. This avoids that powder particles from the dosing chamber 4-1 or 4-2 into the Compressed gas inlet valves 46-1 and 46-2 can migrate back.

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 no controlled valves, but automatically opening and closing valves like a check valve. Here, the powder inlet valves 38-1 and 38-2 arranged so that they are suction or vacuum in their metering chamber 4-1 or 4-2 during the suction stroke of the associated membrane 8-1 or 8-2 opened to remove powder from the relevant powder container 62, 63 or 64 through the powder inlet channel 36-1 or 36-2 into the metering chambers 4-1 or 4-2 suck. The one for ejecting the dosed amount of powder from the concerned Dosing chamber 4-1 or 4-2 used gas pressure of the compressed gas source 45-1 or 45-2 is greater than the negative pressure and causes the powder inlet valve 38-1 or 38-2 is closed automatically. According to another embodiment are the powder inlet valves 38-1 and 38-2 and / or the powder outlet valves 42-1 and 42-1 valves controlled by the pump controller 68.

The powder outlet valves 42-1 and 42-2 are reversed from the powder inlet valves arranged. As a result, the relevant powder outlet valve 42-1 or 42-2 is Negative pressure during the suction stroke of the associated membrane 8-1 or 8-2 closed and from the compressed gas in the metering chambers to expel the dosed amount of powder opened to the dosed amount of powder by means of Compressed gas through the opened powder outlet valve 42-1 or 42-2 and the subsequent powder outlet channel 40-1 or 40-2 into the powder discharge line 50 and to press it into the powder spraying device 52. The compressed gas overcomes the negative pressure.

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

The powder spray device 52, usually also as a powder spray device referred to, a nozzle or a for spraying or spraying the powder Have a rotating body or a rotating nozzle, as is known from the prior art Technology is known.

Thus, according to the invention, a method for conveying powder, especially coating powder, in which by enlarging the Volume of a dosing chamber 4-1 and / or 4-2 powder from a powder source in the dosing chamber 4-1 or 4-2 can be sucked in and then the compressed gas metered amount of powder can be pressed out of the metering chamber. 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 the dosing chamber 4-1 or 4-2 determined and after a predetermined Time delay after reaching the predetermined phase is determined by the Compressed air the previously metered amount of powder from the dosing chamber 4-1 or 4-2 pushed out.

It is obvious that the invention also with only one dosing chamber 4-1 or 4-2 is executable without a second dosing chamber 4-2 or 4-1. Furthermore is 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 can have its own drive 10.

The use of a membrane 8-1 or 8-2 as a displacer enables one compact small design. However, the invention is not based on the use of a Limited membrane, but instead of a membrane can also be a piston in a cylinder can be used.

Fig. 3 shows an embodiment of the invention in which instead of one Membrane a piston is used as a displacer. 3 shows the Possibility of replacing a single drive for two or more displacers (Membrane or piston) one for each displacement body (membrane or piston) to use your own drive.

In Fig. 3 parts corresponding to Figs. 1 and 2 are given the same reference numerals Mistake. The above description of FIGS. 1 and 2 thus also applies to FIG. 3 to. 3 also shows the possibility of not using the sensors S1, S2, S3 and S4 Arrange detection of the drive piston 12, but for the detection of the respective Position of the displacer piston 8-1 or 8-2. 3, however also the possibility of these sensors not the displacer piston 8-1 and 8-2 assign, but the drive piston 12 or another element.

In Fig. 3 there is a separate one for each powder inlet channel 36-1 and 36-2 Powder suction line 58 is provided, which leads to different powder sources (Powder container or color changer) or according to Fig. 3 to a common Powder source, e.g. B. can lead a powder container 62. Instead of this Embodiment could also be similar to a common powder suction line 58 Fig. 1 can be provided for both powder inlet channels 36-1 and 36-2. This can go directly to a powder container, e.g. B. 62, lead to or Color changer 60 corresponding to FIG. 1.

Features of FIGS. 1 and 2 on the one hand and FIG. 3 on the other hand are mutual interchangeable to form new combinations.

The invention is also for combinations of three or more powder pumps usable, the powder inlet channels to a common or to different Powder sources are connected or connectable and their Powder outlet channels are all connected to a common powder discharge opening are, wherein a pump control device is designed such that it Pumps are controlled to offset their suction strokes relative to one another and to do so to execute their pressure strokes at a corresponding time, so that the Pumps suck in powder at different times and at different times dispense dosed amounts of powder, but with at least one pump Displacer (membrane or powder displacer) in one Intermediate position between end positions when the displacer from at least one of the other pumps is in an end position.

All of the pressurized gases and pressurized gas sources mentioned can use compressed air or Be compressed air sources. However, other compressed gases, e.g. B. noble gases, and corresponding other pressurized gas sources, e.g. B. noble gas sources can be used. Two or more or all of the pressurized gas sources mentioned can be a single one Be a pressurized gas source from which the various pressurized gases can be removed.

In the preferred embodiments of the invention, which are shown in FIGS 3 and 3, the pump controller 68 is configured to control the Switching the movements of the displacement bodies 8-1 and 8-2 of suction stroke on pressure stroke, and vice versa, depending on signals from sensors S1 and S4, each of which generates a signal when the Displacer 8-1 or 8-2 along the stroke on one or the other from two predetermined motion reversal positions.

This is only one way in which the pump control device 68 can recognize when the displacer 8-1 or 8-2 in question predetermined suction stroke position.

Another possibility is in another preferred embodiment of the Invention embodies, which is shown schematically in Fig. 4. In the 4, the pump controller 68 includes one Clock timer 80, by which the time-delayed injection of compressed gas in the dosing chamber 4-1 or 4-2 is subject to a fixed cycle time. After this Cycle time, the pump controller 68 sends control signals to the Changeover valve 30, which in and out by compressed gas supply and discharge the cylinder 22 of the drive 10, the movements of the displacer 8-1 and 8-2 and thus the opposite volume changes of the two Dosing chambers 4-1 and 4-2 effect.

These control signals, preferably the control signal for starting the suction stroke, at the same time also cause the time delay of the timing control device 74 is started. As soon as the predetermined delay period has expired is compressed gas through the one compressed gas inlet valve 46-1 into one Dosing chamber 8-1 or through the other compressed gas inlet valve 46-2 into the other Dosing chamber 4-2 initiated for powder conveyance in the with reference to the figures 1 to 3 described way. The difference to Figures 1 to 3 is that the pump controller 68 is the predetermined one Suction stroke position of the displacer 8-1 and 8-2 not based on Recognizes sensor signals (sensors S1, S2, S3, S4), but through control signals, which are each generated when the cycle time of the clock timer 80 expires.

It is assumed that the drive piston 12 and thus also the Displacer 8-1 and 8-2 their predetermined at the end of the cycle time Have reached end positions. Deviations between the predetermined End positions and the actually reached end positions can then arise when the resistance to movement of the elements to be moved change, for example through material wear, material fatigue or through Dirt. To detect such deviations between Setpoint positions and actual value positions can be moved along the movement path Displacer 8-1 or 8-2 or along one with them fixed in motion connected element, preferably the drive piston 12, at a distance of whose end positions, a sensor S5 can 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 in position P5 of the control sensor S5. By comparing the time of the Control signal of the control sensor S5 with the time of the control signal at Switching the direction of movement of the drive piston 12 can Pump drive control device 68 calculate whether the drive piston 12 the Control sensor S5 has reached in a predetermined period of time (or with a predetermined speed), which is required so that it is timely reached its end position. In the event of deviations by a predetermined value the pump controller 68 generate a fault signal (or warning signal).

4 shows a further control sensor S6 in addition to the control sensor S5 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 each time the drive piston 12 opposite one of these two control sensors S5 or S6. At this Embodiment of the invention may control the pump controller 68 Compare the time difference between the generation of the two control signals of the two control sensors S5 and S6 determine with a set time whether the Displacer 8-1, 8-2 each within the cycle time their predetermined Reach the end position. Also in this embodiment, the Time difference the speed of the drive piston 12 or Displacer 4-1, 4-2 calculated by the pump control device and with a target speed can be compared. If there are deviations between the target time and actual time or between target speed and 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 Reversal of movement, by a certain deviation value, can Pump control device 68 generate a defect signal.

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

According to another embodiment of the invention, the defect signal can be used for this be used depending on the difference between target time (or -speed) and actual time (or -speed) of the drive piston 12 das Control switch 30 to be controlled accordingly so that the changed Speed of the drive piston 12 by changing 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, with the Exception that the pump control device 68 contains the clock timer 80 and the sensors S1, S2, S3 and S4 by the control sensor S5 or by the two Control sensors S5 and S6 are replaced. The same parts have the same parts Reference numerals.

The embodiments of the invention described with reference to FIG. 4 are also applicable to embodiments which are not like FIGS. 1, 2 and 4 Membranes, but pistons according to FIG. 3 as displacer 8-1 or 8-2 to have.

According to preferred embodiments of the invention, the cycle time and / or the delay time can be variably adjustable. According to particularly preferred Embodiment of the invention is made to a desired change of Set powder feed rate per unit of time, keep the cycle time constant and the delay time is variably adjustable to the desired one Set powder feed rate per unit of time. The delay period is here the length of time by which the powder is conveyed out of the concerned Dosing chamber 4-1 or 4-2 is started after the relevant delayed Cycle time has expired at which the displacer 8-1 or 8-2 of Pressure stroke was switched to suction stroke.

Figures 5 to 8 show a further embodiment of the invention, according to which are the powder inlet valves 38-1 and 38-2 and / or the powder outlet valves 42-1 and 42-2 self-acting one-way valves Duck bill valve (duck bill valve), which are in the forward direction of the pressure of the compressed gas automatically opened and in the blocking direction from the pressure of the Compressed gas and / or automatically closed by its own material spring elasticity become. Such a one-way valve is in Figures 5 to 8 with the reference number Designated 38/42. It consists of a one-piece body made of resilient Material such as rubber. It contains a cylindrical part 82 with a radially outwardly projecting flange 84 at one end and with a duckbill tapered tube portion 86 at the other end.

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

When the one-way valve 38/42 is pressurized with compressed gas 90 , this compressed gas 90 presses the two duckbill parts 86-1 and 86-2 apart so that the valve opens. This open position of the one-way valve is in Fig. 7 in longitudinal section and in Fig. 8 in front view against Forward direction shown.

9 shows the one-way valve 38/42 in a side view relative to FIGS. 5 and 7 turned by 90 degrees.

In all embodiments of the invention, the movement reversal points can (Dead points) of the displacer 8-1, 8-2 a waiting time can be provided, during which the pump device can calm down before the next one The lifting movement begins.

The description, claims and drawings describe and show preferred embodiments of the invention without the invention thereon is limited. However, the invention also includes any combination of at least two features from the description, the claims and / or the Drawings.

Claims (26)

Pump device 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 separated from a chamber housing (6-1, 6-2) and a displacer (8-1, 8-2) is limited; which can be moved back and forth relative to the chamber housing during a pressure stroke before and during a suction stroke, the pump chamber having a powder inlet channel (36-1, 36-2), to which a powder inlet valve (38-1, 38-2) is assigned, a powder outlet channel (40 -1.40-2), to which a powder outlet valve (42-1.42-2) is assigned, and a compressed gas inlet channel (44-1.44-2), to which a compressed gas inlet valve (46-1, 46-2) is assigned , wherein the powder inlet valve (38-1, 38-2) and the powder outlet valve (42-1,42-2.) can be opened to draw a metered amount of powder (54) into the metering chamber (4-1,4-2) ) and the compressed gas inlet valve (46-1, 46-2) can be closed, so that the displacer body powder (54) moving in the suction stroke direction through the powder inlet channel (36-1, 36-2) into the metering chamber (4-1.4- 2) can suck, and to convey the metered amount of powder from the metering chamber (4-1, 4-2) the powder inlet valve (38-1, 38-2) can be closed and the powder can be removed inlet valve (42-1,42-2) and the compressed gas inlet valve (46-1,46-2) can be opened, so that from the compressed gas inlet channel (44-1,44-2) into the dosing chamber (4-1,4-2 ) flowing compressed gas can push the metered amount of powder from the metering chamber (4-1,4-2) into the powder outlet channel (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 pump control device (68) has a time control device (74), by means of which the conveying of the powder from the metering chamber (4-1, 4-2) is started as a function of the predetermined delay time that has elapsed since a predetermined operating time, At the end of the delay period, the compressed gas is admitted into the metering chamber (4-1, 4-2) and the amount of powder dosed until the end of the delay period is pressed out of the metering chamber (4-1, 4-2) by means of the compressed gas. Pump device according to claim 1,
characterized in that the pump control device (68) has a cycle timer and, after a predetermined cycle time, control signals to a switching device (34) for switching over the movement of the displacement body (8-1, 8-2) from suction stroke to pressure stroke and vice versa from pressure stroke on the suction stroke, sends in the rhythm of the predetermined cycle time, and that the pump control device (68) is designed to start the predetermined delay time period on the time control device (74) in each case as a function of the time of the occurrence of the control signal which causes the start of the suction stroke, at the end of the delay period the compressed gas is admitted into the metering chamber (4-1, 4-2) and the amount of powder metered until the end of the delay period is pressed out of the metering chamber (4-1, 4-2) by means of the compressed gas. Pump device according to claim 1 or 2,
characterized in that at least one control sensor (S5, S6) is provided for detecting when the displacement body (8-1, 8-2) is in a predetermined position and for generating a sensor signal upon detection when the displacement body is in the predetermined position, that the pump control device (68) is functionally connected to the at least one control sensor, and 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 to check whether the time period between deviates from a predetermined value at the two points in time, and for generating a defect signal if a predetermined deviation from the predetermined value arises. Pump device according to claim 1 or 2,
characterized in that at least two control sensors (S5, S6) are provided and connected to the pump control device (68) for detecting when the displacer (8-1, 8-2) is in one of two different predetermined positions and for generating sensor signals upon detection of the displacer in the predetermined positions, and that the pump control device (168) is designed to compare the time difference between the signals of one control sensor and the signals of the other control sensor with a predetermined time period, and to generate a defect signal when the Time difference from the predetermined time period deviates by more than a predetermined value. Pump device according to claim 1,
characterized in that the pump control device (68) has a time control device (74) in order to start conveying the powder from the metering chamber as a function of the predetermined delay time period which has elapsed since a predetermined suction stroke position of the displacer body (8-1, 8-2), wherein at the end of the delay period the compressed gas is admitted into the dosing chamber (4-1,4-2) and the amount of powder dosed up to the end of the delay period is pressed out of the dosing chamber (4-1,4-2) by means of the compressed gas. Pump device according to claim 5,
characterized in that the predetermined suction stroke position is a suction stroke start position. Pump device according to claim 5,
characterized in that the predetermined suction stroke position is between a suction stroke start position and a suction stroke end position. Pump device according to claim 5,
characterized in that the predetermined suction stroke position between a suction stroke start position and a suction stroke end position is closer to the suction stroke start position than to the suction stroke end position. Pump device according to at least one of the preceding claims 5 to 8,
characterized in that the time control device (74) has at least one sensor (S1, S4; S2, S3) for generating a signal when the displacer (8-1, 8-2) is in the predetermined suction stroke position. Pump device 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 displacer (8-1, 8-2) are switched from suction stroke to pressure stroke and vice versa, depending on signals from sensors (S1, S4), which each generate a signal when the displacer (8-1,8-2) is located at one or the other of two predetermined movement reversal positions along the stroke. Pump device according to at least one of the preceding claims,
characterized in that the distance of movement of the displacer (8-1, 8-2) is constantly the same for all stroke movements. Pump device according to at least one of the preceding claims,
characterized in that a second time delay period is provided at at least one of the movement reversal death points of the displacer body (8-1, 8-2) before the displacer body (8-1, 8-2) moves in the other movement direction in question after one movement direction becomes. Pump device according to at least one of the preceding claims,
characterized in that the delay period is variably adjustable. Pump device according to at least one of the preceding claims,
characterized in that the displacement body (8-1,8-2) is a flexible membrane. Pump device according to at least one of the preceding claims,
characterized in that the powder inlet valve (38-1, 38-2) and the powder outlet valve (42-1, 42-2) are automatic valves which automatically open or close by differential pressure between their two valve sides. Pump device according to claim 15,
characterized in that the powder inlet valve (38-1, 38-2) and the powder outlet valve (42-1, 42-2) are automatic valves which, in the manner of a check valve, by differential gas pressure above their valve body (38-3,42-3) can be actuated, the valve body (38-3,42-3) depending on this differential gas pressure being movable relative to a valve seat (38-4,42-4) in the open position or in the closed position and being stable in the position concerned. Pump device according to claim 15,
characterized in that the powder inlet valve (38-1, 38-2) and the powder outlet valve (42-1, 42-2) are automatic valves in the manner of a duckbill, the duckbeak of which automatically opens or closes due to the pressure difference between the inside of the duckbill and the outside of the duckbill. Pump device according to at least one of the preceding claims,
characterized in that at least two of said powder pumps (2-1,2-2) are provided, the powder inlet channels (36-1,36-2) of which can be connected or are connected to a powder source and the powder outlet channels (40-1,40 -2) can be connected or connected to a common powder discharge opening (48), and that the two powder pumps (2-1,2-2) can be operated in opposite directions relative to one another, so that alternately from the metering chamber (4-1) one Powder pump (2-1) or the metering chamber (4-2) of the other powder pump (2-2) a metered amount of powder can be ejected into the powder outlet channel (40-1.40-2) by means of the compressed gas, and vice versa Powder can be sucked through the powder inlet channels (36-1, 36-2) into the other or into one metering chamber (4-1, 4-2). Pump device according to claim 18,
characterized in that the displacement bodies (8-1, 8-2) of the two pumps have a common drive (10). Powder coating equipment,
marked by
a pump device according to at least one of the preceding claims for conveying coating powder. Method for conveying powder (54), in particular coating powder, in which, by increasing the volume of a metering chamber (4-1,4-2), powder (54) is sucked into the metering chamber (4-1,4-2) from a powder source and then the dosed amount of powder is pressed out of the dosing chamber (4-1,4-2) by means of compressed gas, after which the volume of the dosing chamber (4-1,4-2) is reduced, and then the cycle is repeated periodically,
characterized in that a predetermined phase of the periodically changing volume of the dosing chamber (4-1,4-2) is determined by means of sensors (S1, S4; S2, S3) and
that with a predetermined time delay after reaching the predetermined phase by means of the compressed gas, the amount of powder dosed so far is pressed out of the dosing chamber (4-1,4-2). A method according to claim 21,
characterized in that in a powder inlet channel (36-1,36-2) into the metering chamber (4-1,4-2), and in a powder outlet channel (40-1,40-2) from the metering chamber (4-1, 4-2), at least one valve is used in the respective path, which opens and closes automatically depending on the respective gas pressure difference between its upstream side and its downstream side in the manner of a check valve Method for conveying powder (54), in particular coating powder, in which, by increasing the volume of at least one metering chamber (4-1, 4-2), powder (54) from a powder source into the metering chamber (4-1, 4-2) sucked in and then the dosed amount of powder is pressed out of the dosing chamber (4-1, 4-2) by means of compressed gas, after which the volume of the dosing chamber (4-1, 4-2) is reduced, and then the cycle is repeated periodically,
characterized in that the volume changes of the at least one dosing chamber (4-1, 4-2) are controlled by a predetermined cycle time, that at least one control signal is generated each time after the predetermined cycle time, that this at least one control signal indicates the direction of the volume change of Increasing to reducing, or from reducing to increasing, is reversed, and at the same time a predetermined time delay is started, and that the metered powder quantity is only pressed out of the metering chamber when the predetermined time delay has elapsed by means of the compressed gas. The method of claim 23
characterized in that the volume changes of the at least one dosing chamber (4-1, 4-2) are brought about by a displacement body (8-1, 8-2), that by means of at least one control sensor (S5, S6) the presence of the displacement body in a predetermined position is determined and a control signal is generated upon detection of the displacer in the predetermined position, and that the time difference between the time of the control signal and the time of the at least one control signal is compared with a predetermined time which would have the time difference if the Displacer would cover a predetermined distance within each cycle time, and that a defect signal is generated if the difference between the time difference and the predetermined time period exceeds a predetermined value. The method of claim 23
characterized in that the volume changes of the at least one dosing chamber is effected by a displacer (8-1, 8-2) with at least two control sensors (S5, S6) which are arranged at a distance from one another along a distance corresponding to the maximum movement distance of the displacer body control signals are generated when the displacer is in a position corresponding to the sensor position, that the time difference between the control signals of the one control sensor is compared to the control signals of the other control sensor with a predetermined length of time, which would be the time difference if the displacer is within of the cycle time would move a predetermined target movement distance, and that a defect signal is generated at least when the time difference deviates from the predetermined time period by more than a predetermined value. Method according to one of claims 21 to 25,
characterized in that two of the metering chambers (4-1, 4-2) are changed simultaneously, but out of phase with respect to one another, with respect to their volume, the volume of one metering chamber being increased while the volume of the other metering chamber being reduced, and vice versa.

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