PUMP ASSEMBLY FOR PUMPING VISCOUS MEDIA, DEVICE COMPRISING SAME, METHOD FOR PRODUCING SURFACE COATING AGENTS, AND USE OF A PUMP ASSEMBLY

Abstract

Described herein is a pump arrangement for conveying viscous media including a membrane pump having a conveying chamber, a working chamber connectable in a fluid-conducting manner to a source of a pressurized working medium, and a membrane that separates the working chamber from the conveying chamber. A controller valve arrangement is mounted between the working media source and the working chamber, and the membrane is movable back and forth between the working chamber and the conveying chamber by means of actuation of the controller valve arrangement. The pump arrangement has an electronic controller element which is connected in a signal-conducting manner to the controller valve arrangement and is set up to control a compressed air volume in the working chamber by means of actuation of the controller valve arrangement as a function of a flow volume of the medium exiting from the conveying chamber.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the national stage entry of PCT/EP2018/061380, filed on May 3, 2018, which claims the benefit of priority to European Patent Application No. 17169310.4, filed May 3, 2017, each of which is incorporated by reference in its entirety herein.

FIELD OF THE INVENTION

The present invention relates to a pump arrangement for conveying viscous media, comprising a membrane pump having a conveying chamber, a working chamber connectable in a fluid-conducting manner to a source of a pressurized working medium, and a membrane that separates the working chamber from the conveying chamber.

BACKGROUND

In the prior art, primarily gear pumps, i.e. internal and external gear pumps, have been used to date in the pump arrangement for production of the above-identified surface coating compositions, especially paints. These pumps are designed to convey constant mass flow rates. Since they cannot convey a gas phase in downstream aggregates for construction-related reasons, they are intended to ensure that, for example, the dispersion unit connected upstream of the pump arrangement can be completely filled permanently in operation and is protected from running dry.

The availability of such pumps on the market and the high maintenance intensity in practice are perceived as disadvantageous for these pumps.

BRIEF DESCRIPTION

In the light of this, it was an object of the present invention to specify a pump arrangement which very substantially overcomes the above-cited disadvantages. More particularly, it was an object of the invention to specify a pump arrangement which is low-maintenance and contamination-proof, and can simultaneously be used in devices and processes of the type identified at the outset. It was thus also a particular object of the invention to specify a means of improving the apparatuses and processes identified at the outset.

The invention achieves its underlying object, in a first aspect, in that a controller valve arrangement is mounted between the working media source and the working chamber, and the membrane is movable back and forth between the working chamber and the conveying chamber by means of actuation of the controller valve arrangement, where the pump arrangement has an electronic controller element which is connected in a signal-conducting manner to the controller valve arrangement and is set up to control the compressed air volume in the working chamber by means of actuation of the controller valve arrangement as a function of the flow volume of the medium exiting from the conveying chamber. Preferably, the electronic controller element has control characteristics having an amplifying component, a time-integrated component, and a differentiated component.

The invention relates, in a further aspect, to an apparatus for production of surface coating compositions, especially of coating compositions for metallic and plastic surfaces, comprising a conveying media source for a viscous medium containing constituents to be dispersed, a dispersing unit, connected in a fluid-conducting manner to the conveying media source, for producing a dispersion from the viscous medium, and a pump arrangement, connected in a fluid-conducting manner to the conveying media source and the dispersing unit, for conveying the viscous medium from the conveying media source to the dispersion unit.

The invention relates, in a further aspect, to a process for producing a surface coating composition, especially a coating composition for metallic and plastic surfaces, comprising the steps of: conveying a viscous medium comprising constituents to be dispersed from a conveying media source to a dispersion unit, and producing a dispersion from the viscous medium by means of the dispersion unit.

In a further aspect, the invention relates to the use of a pump arrangement for supplying a viscous medium comprising constituents to be dispersed to a dispersing unit.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a P&I flow diagram of a pump arrangement and apparatus according to a preferred working example.

FIG. 2 shows a schematic diagram of a membrane pump for the pump arrangement according to FIG. 1.

DETAILED DESCRIPTION

Pump arrangements of the type identified at the outset are used to convey a wide variety of different media, and according to the invention especially for conveying viscous media with constituents to be dispersed. According to the invention, viscous media are especially understood to mean liquids, free-flowing suspensions and dispersions. The principle of function of these pump arrangements is based on recurrent buildup and dissipation, in the working chamber, of a pressure that causes movement of the membrane. In one section of the cycle of movement of this membrane viscous medium is sucked into the conveying chamber, and in a further section the viscous medium is driven out of the conveying chamber with an opposing movement of the membrane.

Pump arrangements of the type identified at the outset are particularly suitable for conveying media that are at high risk of contamination or are a high contamination risk, the exit of which from the pump arrangement is thus to be avoided, or where the entry of foreign material into the medium is to be avoided. However, it is a characteristic trait of the principle of conveying that the mass flow conveyed by the pump arrangements, which builds up on displacement by means of the membrane, is dependent on the backpressure exerted by the viscous medium itself to the movement of the membrane in the conveying chamber. The higher the backpressure or viscosity of the viscous medium in the conveying chamber and downstream thereof, the lower the throughput through the membrane pump will normally be.

The avoidance of contamination is a particular aim for apparatuses and processes for production of surface coating compositions of the type identified at the outset. Surface coating compositions are especially understood to mean paints, for example vehicle and automotive repair paints, architectural paints and the like, called coating products. These are based on material dispersions, are usually solvent- or water-based, and sometimes include dispersed additives.

Dispersed constituents of this kind are especially understood to mean binders, pigments and other additives, for example thickeners and fillers.

Apparatuses and processes of the type identified at the outset are especially operated for production of paints in batchwise operation and are thus frequently subject to startup and shutdown operations. This type of plant load leads to an at least abstract risk that fuels or gases, for example oxygen, can penetrate into the conveying stream of the viscous medium. Particular challenges accordingly also arise in regions where the apparatuses and processes have to meet the demands of explosion protection.

The invention is based on the approach that, by means of specific control of the compressed air volume of the working medium to drive the membrane, the construction-related disadvantages of membrane pumps can be compensated for, and so the controlled membrane pump is capable of conveying an essentially constant mass flow rate, and especially of compensating for variations in mass flow as a result of altered viscosities or an altered backpressure of the conveyed medium. The higher the viscosity or backpressure of the conveying medium in the conveying chamber and downstream thereof, the higher the level to which the compressed air volume in the working chamber can be controlled by means of the controller valve arrangement in order to prevent any drop in the mass flow rate. As a result of counteraction of the drop in the mass flow rate, the pump arrangements of the invention can also be used in apparatuses for production of surface coating compositions that have dispersing units and require tightly defined dwell times in the dispersing units. In this way, it is also possible to avoid product damage since the dwell times can be constantly observed owing to the control interventions. At the same time, the pump arrangement of the invention is also usable for environments that are at risk of contamination or are a contamination risk.

The invention is advantageously developed in that a sensor for detecting the flow rate exiting from the conveying chamber is disposed downstream of the conveying chamber, where the electronic controller element is connected to the sensor in a signal-conducting manner and is set up to recognize a deviation in the flow volume detected from a predetermined target value, and if it goes below the target value to actuate the controller valve arrangement in order to increase the compressed air volume in the working chamber, and if it goes above the target value to actuate the controller valve arrangement in order to reduce the compressed air volume in the working chamber.

The electronic controller element preferably has one or more processors, data memories and data interfaces, and programming means configured to execute the stipulated compressed air volume control. The electronic control element may be executed as a separate construction unit or be disposed in or integrated into the compressed air volume controller or the sensor.

Preferably, the controller valve arrangement has a pneumatically, hydraulically or electromagnetically actuated adjustment valve.

In a particularly preferred embodiment, the electronic controller element has a PID controller, or a controller that permits comparable control characteristics, for example a state controller, especially with an observer, or a fuzzy controller, especially one having input channels extended by an integral component and a differentiating component.

The controller especially has three controller components connected in parallel: a P component K_P; an I component K_I/s, and a D component K_D*s. These three controller components are preferably configured such that they have rapid and simultaneously stable control characteristics. The control characteristics are the result of the following transfer function:

K_PID(s)=K_P+K_I/s+K_Ds=K_P(1+1/T_Ns+T_Vs),

with

K_I=K_P/T_N, and

K_D=K_P* T_V.

In this context, T_N represents the integral time and defines the I component of the controller. T_V is the differential time and defines the influence of the D component of the controller. K_P is a constant value as offset of the input signal and defines the P component of the controller.

Preferably, K_P is selected within the range from 1 to 10, more preferably in the range from 2 to 5.

Further preferably, T_N is selected within the range from 1 s to 10 s, more preferably within the range from 2 s to 6 s.

Further preferably, T_V is selected within the range from 0.1 s to 2 s, more preferably within the range from 0.2 s to 1 s.

It has been found that the above preferred combinations of parameters for T_N, T_V and K_P together have a surprisingly good compromise with regard to the control characteristics for a very wide range of application of different fluids to be conveyed and operating parameters.

In a preferred embodiment, the sensor for detection of the flow rate takes the form of a mass flow sensor.

More preferably, the mass flow sensor takes the form of a Coriolis meter, also referred to as Coriolis mass flow meter (CMDM).

In an advantageous development of the pump arrangement, the membrane pump takes the form of a double membrane pump, and has a second conveying chamber, a second working chamber connectable in a fluid-conducting manner to the source of the pressurized working medium, and a membrane that separates the second working chamber from the second conveying chamber. Preferably, the first and second membranes are actuated in an opposing manner, such that, at the juncture when conveying medium is sucked into the first working chamber, conveying medium is expelled from the second working chamber, and vice versa.

Preferably disposed downstream of the membrane pump is a pulsation damper for smoothing the mass flow rate of the viscous medium. The pulsation damper is preferably disposed upstream of the sensor for detecting the mass flow rate. In a preferred development, the pulsation damper has large dimensions in relation to the conveying volume of the membrane pump. More preferably, the pulsation damper has a maximum fluid volume corresponding to twice to four times, especially three times, the discharge volume of the membrane pump over half a conveying cycle. By virtue of such an oversized pulsation damper, the fundamental mass flow variations of the membrane pump are almost completely balanced out. Together with the positioning of the pulsation damper upstream of the sensor for detection of the flow rate, this leads to very stable and well-controlled control characteristics of the pump arrangement.

The invention has been described above with reference to the pump arrangement itself. In a further aspect, the invention additionally achieves the object stated above in an apparatus of the type specified at the outset, in that the apparatus includes a pump arrangement according to one of the above-described preferred embodiments. The invention thus proposes an apparatus for production of surface coating compositions, especially of coating compositions for metallic surfaces, having a conveying media source for a viscous medium containing constituents to be dispersed, a dispersing unit, connected in a fluid-conducting manner to the conveying media source, for producing a dispersion from the viscous medium, preferably a stirred mill, and a pump arrangement, connected in a fluid-conducting manner to the conveying media source and the dispersing unit, for conveying the viscous medium from the conveying media source to the dispersion unit, wherein the pump arrangement has a membrane pump having a conveying chamber, a working chamber connectable in a fluid-conducting manner to a source of a pressurized working medium, and a membrane that separates the working chamber from the conveying chamber, where a controller valve arrangement is mounted between the working media source and the working chamber, and the membrane is movable back and forth between the working chamber and the conveying chamber by means of actuation of the controller valve arrangement, where the pump arrangement has an electronic controller element which is connected in a signal-conducting manner to the controller valve arrangement and is set up to control the compressed air volume in the working chamber by means of actuation of the controller valve arrangement as a function of the flow volume of the medium exiting from the conveying chamber, where the electronic controller element preferably has control characteristics having an amplifying component, an integrating component, and a differentiating component.

The apparatus of the invention appropriates the advantages and preferred embodiments of the above-described pump arrangement. In this regard, reference is made to the remarks above. The apparatus of the invention can economically and at the same time reliably produce coating compositions for metallic and plastic surfaces, such as, in particular, vehicle paints and automotive repair paints, architectural paints and other paints. More particularly, the prejudice that a membrane pump is unsuitable for supplying viscous media to a dispersing unit, for example a stirred mill, is overcome.

The invention further relates to a process for producing a surface coating composition, especially a coating composition for metallic surfaces as described above. The process achieves the object defined at the outset with the steps of: conveying a viscous medium comprising constituents to be dispersed from a conveying media source to a dispersion unit, preferably of a stirred mill, and producing a dispersion from the viscous medium by means of the dispersing unit, wherein the step of conveying the viscous medium comprises: conveying the viscous medium by means of a membrane pump having a conveying chamber for the viscous medium and a working chamber for moving a membrane, by means of which the viscous medium is conveyed through the conveying chamber, detecting a mass flow rate of the viscous medium leaving the conveying chamber, and controlling the compressed air volume in the working chamber as a function of the mass flow rate detected. The process is especially performed by means of a pump arrangement or an apparatus according to one of the above-described preferred embodiments. The process also appropriates the advantages and preferred embodiments of the above-described aspects, and so reference is made to the above remarks in this regard.

The process is also advantageously developed by the steps of: recognizing a deviation in the flow rate detected from a predetermined target value, increasing the compressed air volume in the working chamber when the value goes below the target value, and reducing the compressed air volume in the working chamber when the value goes above the target value.

Further preferably, the process comprises the step of: smoothing the mass flow rate of the viscous medium downstream of the membrane pump, and preferably upstream of a sensor used to detect the mass flow rate.

In a further aspect, the invention relates to a use of a pump arrangement. According to the invention, a pump arrangement is used to feed a viscous medium comprising constituents to be dispersed to a dispersing unit, preferably a stirred mill, wherein the pump arrangement is designed according to any of the preferred embodiments described above.

More particularly, the invention relates to the use of a membrane pump, especially in a pump arrangement for feeding a viscous medium comprising constituents to be dispersed to a dispersing unit, preferably a stirred mill, for the purpose of producing a surface coating composition as described further up.

The invention is described in detail hereinafter with reference to the appended figures, using a preferred working example. FIG. 1 shows the schematic setup of a pump arrangement 1. The pump arrangement 1 has a first connection 2 via which the pump arrangement 1 is supplied with a viscous medium to be conveyed, especially with constituents to be dispersed. The pump arrangement 1 also has a membrane pump 7 by means of which the viscous medium is sucked in by the first connection 2 and conveyed further. For this purpose, the membrane pump 7, in a commonly known manner, has a conveying chamber (shown in detail in FIG. 2) and a working chamber, with the conveying chamber and the working chamber separated from one another by means of a membrane. Membrane pumps of this kind are described, for example, in “Leckfreie Pumpen, Verdichtung and Vakuumpumpen” [Leak-Free Pumps, Sealing and Vacuum Pumps], Gerhard Vetter (ed.)—Essen, Vulkanverlag, 1998 (ISBN: 3-827-2185-3). Preferably, the membrane pump takes the form of a double membrane pump.

The working chamber of the membrane pump 7 is connected in a fluid-conducting manner to a second connection 4 of the pump arrangement 1 and is supplied by the second connection 4 with a pressurized working medium, for example compressed air. Preferably, the working media supply already introduces an oscillating pressure into the second connection 4 in a pilot-controlled manner. Alternatively, the pressure oscillation is controlled directly at the membrane pump. The membrane in the membrane pump 7 is moved back and forth between the conveying chamber and the working chamber in order to achieve suction into the conveying chamber and onward conveyance of the viscous medium from the conveying chamber.

Downstream of the membrane pump 7 is disposed a pulsation damper 9 set up to smooth the mass flow of the viscous medium that exits from the conveying chamber of the membrane pump 7. The maximum fluid volume of this pulsation damper 9 is preferably greater than the conveying volume of the membrane pump 7 over half a conveying cycle, preferably two to 4 times as high, more preferably three times as high.

The pulsation damper 9 is likewise connected in a fluid-conducting manner to the second connection 4 by means of a distributor 19.

Downstream of the pulsation damper is disposed a sensor to detect the flow rate of the viscous medium exiting from the membrane pump 7. The sensor 11 preferably takes the form of a mass flow meter, more preferably of a Coriolis mass flow sensor.

Downstream of the sensor 11 is preferably disposed a pressure transducer 13 in order to enable manual inspection of the conveying pressure. Downstream of that is provided a third connection 6 via which the viscous medium is released from the pump arrangement 1.

Between the second connection 4 and the membrane pump 7 or the distributor 19, there is an intermediately connected controller valve arrangement 21, preferably with a KV value=1. The pump arrangement 1 also has an electronic controller element 23 having a controller, preferably a PID controller or another controller type with similar control characteristics, by means of which the maximum pressure of the working medium in the membrane pump 7 is controlled as a function of the flow rate of the viscous medium exiting from the membrane pump 7. The control characteristics of the electronic controller element more preferably comprise an amplifying component, an integrating component and a differentiating component. For this purpose, the electronic controller element 23 is connected in a signal-conducting manner both to the controller valve arrangement 21 and to the sensor 11 for detecting the flow rate. In addition, the electronic controller element 23 has a data interface by means of which a predetermined target value w_s can be set, which is to form the basis for the control as reference parameter. The sensor 11 supplies the electronic controller element 23 with actual parameter w_i. The controller provided in the electronic controller element 23 detects a deviation in wi relative to the target value ws. If w_i<w_s, the electronic controller element 23 controls the controller valve arrangement 21 in such a way that the compressed air volume in the working chamber of the membrane pump 7 is increased. If w_i>w_s, the electronic controller element 23 controls the valve arrangement 21 in such a way that the compressed air volume in the working chamber of the membrane pump 7 is reduced. In a preferred working example, the controller used is a PID controller with a value constant K_P=3 for the P component of the controller, an integral time T_N=4 s for the I component of the controller and a differential time T_V=0.5 s for the D component of the controller. As an alternative to a conventional PID controller, it is also possible in accordance with the invention to use other controller types that replicate the control characteristics described above. For example, rather than a PID controller, it would be possible to use a state controller that produces corresponding control characteristics on the basis of mathematical models.

The basic mode of function of the membrane pump 7 is shown in FIG. 2. In this working example, the membrane pump 7 takes the form of a double membrane pump and has a first conveying chamber 8a and a second conveying chamber 8b. In addition, the membrane pump 7 has a first working chamber 10a separated from the first conveying chamber 8a by means of a first membrane 20a. The membrane pump 7 also has a second working chamber 10b separated from the second conveying chamber 8b by means of a second membrane 20b. The first and second membranes 20a,b are mechanically connected by means of a connecting rod 12 and are thus moved in such a way that movement of the first membrane 20a into the conveying chamber 8a is associated with a movement of the second membrane 20b out of the conveying chamber 8b. This produces an expansion in volume and contraction in volume of the respective chambers. An expansion in volume of the conveying chamber is associated with a simultaneous contraction in volume of the adjacent working chamber, and vice versa.

The working chambers are connected in a fluid-conducting manner to a control chamber 14 which, in turn (in a manner not shown), is connected in a fluid-conducting manner to the second connection 4 of the pump arrangement and is supplied with pressurized air thereby. A control element 16 alternately establishes a fluid-conducting connection between the first working chamber 10a and the control chamber 14, or between the second working chamber 10b and the control chamber 14, while the respective other working chamber is separated from the control chamber 14. In the state in which the working chamber is separated from the control chamber, air present in the respective working chamber is removed via an outlet (not shown). According to the position of the control element 16, the pressure of the working medium thus bears on the first or second membrane 20a,b and ensures displacement of the viscous medium from the respective conveying chamber 8a,b.

In the position shown in FIG. 2, the working medium is introduced into the first working chamber 10a. The first membrane 20a reduces the volume in the first conveying chamber 8a, which moves a first sealing element 18a into a closed position, and a second sealing element 18b into an open position, such that viscous medium can be removed from the first conveying chamber 8a in the direction of the outlet. At the same time, a reduced pressure that arises in the second conveying chamber 8b moves a third sealing element 18c into an open position, and a fourth sealing element 18d into a closed position, such that viscous medium which is supplied from the first connection 2 can flow into the second conveying chamber 8b.

The pump arrangement 1 is part of an apparatus 100 for production of surface coating compositions, for example paints for metallic and plastic surfaces. The apparatus 100 has a source 103 for a viscous medium comprising constituents to be dispersed that is to be conveyed, which is connected in a fluid-conducting manner by means of a hose conduit 105 to the first connection 2 of the pump arrangement 1. In addition, the apparatus 100 has a source 115 for a pressurized working medium, for example compressed air, for the membrane pump 7, which is connected in a fluid-conducting manner by means of a hose conduit 117 to the second connection 4 of the pump arrangement.

The apparatus 100 also has a dispersing unit 125, for example a stirred mill, which is connected in a fluid-conducting manner to the third connection 6 of the pump conduit 1, and into which the pump arrangement 1 transfers the viscous medium.

In the operation of the apparatus 100, the viscous medium is provided in the source 103 and is admixed either therein or already in a preceding step with constituents to be dispersed. The membrane pump 7 of the pump arrangement is pneumatically driven by means of the working medium from the source 115 and sucks in the viscous medium from the source 103. The pulsation evaporator 9 smooths the mass flow of the viscous medium exiting from the membrane pump 7.

The sensor 11, which preferably runs permanently in the operation of the pump arrangement 1, detects the flow rate of the viscous medium exiting from the membrane pump 7 and sends it as the actual value w_i to the electronic controller element 23. The electronic controller element 23 calculates the deviation of w_i from a previously input target value w_s and, as a function of any deviation detected, controls the open position of the controller valve arrangement 21, in order to either increase or reduce the compressed air volume in the working chamber of the membrane pump 7.

If, for example, there is a rise in the back pressure in the conveying chamber of the membrane pump, the control mechanism responds with a corresponding increase in the compressed air volume in the working chamber in order to assure a constant mass flow rate at the third connection 6, whence the viscous medium is transferred into the dispersing unit 125 in order to produce the dispersion of the viscous medium and its constituents therein.

Plants such as that shown in FIG. 1 are frequently run in circulation operation, indicated in the figure by the dotted line which connects the dispersing unit 125 to the source 103 of the viscous medium. In these plants, owing to the constantly changing viscosity of the medium conveyed in the course of the circulation conveying, the advantages of the invention are particularly manifested.

The membrane pump used is, for example, a 1.5″ or 2″ compressed air membrane pump from the manufacturer WP-ARO, model: PD15A-BSS-STT (or PD20A-BSS-STT). The pulsation damper used is, for example, a 3″ pulsation damper from the manufacturer WP-ARO, model: SP30A-BSS-T. The controller valve arrangement 21 preferably has a control valve, preferably with a KV value=1, from manufacturer Samson, model: 3241. The sensor 11 is preferably a mass flow meter from the manufacturer Micro Motion, model: CMFS075.

A typical field of use of a pump arrangement of the invention is the production of surface coating compositions, for example paints. Paint formulations comprise not only color pigments and binders but also a multitude of other constituents to be dispersed, such as fillers, additives, auxiliaries and admixtures.

Fillers frequently used in paint formulations are calcium carbonate (chalk), barium sulfate (heavy spar) and kaolin. As well as the reduction in the amount of pigment required, fillers serve to adjust the level of gloss, a defined surface structure and the improvement in the mechanical properties.

Paint formulations typically comprise additives and/or auxiliaries, the addition of which affects properties of the paint formulation or of a paint film formed therefrom. Addition of wetting and dispersing auxiliaries, siccatives, antioxidants and the like affects the processibility of paint formulations. Hardening accelerators lead to quicker hardening of the paint film. Plasticizers lower the softening range of the binder and ensure better elasticity of the paint films. Antimicrobial additives or biocidal substances improve the storability of paint formulations by preventing paints from becoming unusable as a result of microorganisms. Additives increase service life and facilitate processing. They preserve, ensure film prevent “skinning” in the container (can, pot) and bring about a particular viscosity that makes the paint drip-free, or accelerate drying (siccatives). Preservatives (pot preservers), required in the case of water-thinnable paints and varnishes, are biocidal substances that are intended to prevent the paint in the container from becoming unusable as a result of microorganisms.

For a test of function of the pump arrangement of the invention, one option is to use, rather than a paint formulation or other surface coating formulation, an aqueous test conveying medium into which a thickener is metered to establish a viscosity typical of the formulation to be conveyed. Conventional thickeners can be used for this purpose, for example thickeners available under the “Acrysol” trade name. It is possible here, by continuously metered addition of the thickener, to reproduce the change in viscosity of a paint formulation to be dispersed in a stirred mill in an illustrative manner.

Claims

1. A pump arrangement for conveying viscous media, the pump arrangement comprising:

a membrane pump having a conveying chamber, a working chamber connectable in a fluid-conducting manner to a source of a pressurized working medium, and a membrane that separates the working chamber from the conveying chamber,

wherein a controller valve arrangement is mounted between the source of the pressurized working medium and the working chamber, and the membrane is movable back and forth between the working chamber (and the conveying chamber by means of actuation of the controller valve arrangement, and

wherein the pump arrangement has an electronic controller element which is connected in a signal-conducting manner to the controller valve arrangement and is set up to control a compressed air volume in the working chamber by means of actuation of the controller valve arrangement as a function of a flow volume of a medium exiting from the conveying chamber, wherein the electronic controller element has control characteristics having an amplifying component, an integrating component, and a differentiating component.

2. The pump arrangement according to claim 1, further comprising a sensor, arranged downstream from the conveying chamber, for detecting the flow volume exiting from the conveying chamber, wherein the electronic controller element is connected to the sensor in a signal-conducting manner and is set up to recognize a deviation in the flow volume detected from a predetermined target value (ws), wherein:

when the flow volume is below the target value (ws), the electronic controller element is configured to actuate the controller valve arrangement in order to increase the compressed air volume in the working chamber, and

when the flow volume is above the target value (ws), the electronic controller element is configured to actuate the controller valve arrangement in order to reduce the compressed air volume in the working chamber.

3. The pump arrangement according to claim 1, wherein the controller valve arrangement has a pneumatically, hydraulically, or electromagnetically actuated adjustment valve.

4. The pump arrangement according to claim 1,

wherein the electronic controller element is selected from: a PID controller; a state controller, especially with observer; and a fuzzy controller.

5. The pump arrangement according to claim 2,

wherein the sensor for detection of the flow volume is a mass flow sensor.

6. The pump arrangement according to claim 1,

wherein the membrane pump is a double membrane pump, and has a second conveying chamber, a second working chamber connectable in a fluid-conducting manner to the source of the pressurized working medium, and a membrane that separates the second working chamber from the second conveying chamber.

7. The pump arrangement according to claim 1,

further comprising a pulsation damper, disposed downstream of the membrane pump, for smoothing the mass flow of the working medium.

8. The pump arrangement according to claim 7, wherein the pulsation damper has a maximum fluid volume corresponding to two to four times, the conveying volume of the membrane pump over half a conveying cycle.

9. An apparatus for production of surface coating compositions, the apparatus comprising:

a conveying media source for a viscous medium containing constituents to be dispersed,

a dispersing unit, connected in a fluid-conducting manner to the conveying media source, for producing a dispersion from the viscous medium, and

a pump arrangement, connected in a fluid-conducting manner to the conveying media source and the dispersing unit, for conveying the viscous medium from the conveying media source to the dispersion unit,

wherein the pump arrangement comprises a membrane pump comprising a conveying chamber, a working chamber connectable in a fluid-conducting manner to a source of a pressurized working medium, and a membrane that separates the working chamber from the conveying chamber, wherein a controller valve arrangement is mounted between the source of the pressurized working medium and the working chamber, and the membrane is movable back and forth between the working chamber and the conveying chamber by means of actuation of the controller valve arrangement, wherein the pump arrangement has an electronic controller element which is connected in a signal-conducting manner to the controller valve arrangement and is set up to control a compressed air volume in the working chamber by means of actuation of the controller valve arrangement as a function of a flow volume of a medium exiting from the conveying chamber.

10. The apparatus according to claim 9, wherein the electronic controller element has control characteristics having an amplifying component, an integrating component, and a differentiating component.

11. The apparatus according to claim 9, wherein the pump arrangement further comprises a sensor, arranged downstream from the conveying chamber, for detecting the flow volume exiting from the conveying chamber, wherein the electronic controller element is connected to the sensor in a signal-conducting manner and is set up to recognize a deviation in the flow volume detected from a predetermined target value (ws), wherein:

when the flow volume is below the target value (ws), the electronic controller element is configured to actuate the controller valve arrangement in order to increase the compressed air volume in the working chamber, and

when the flow volume is above the target value (ws), the electronic controller element is configured to actuate the controller valve arrangement in order to reduce the compressed air volume in the working chamber.

12. A process for producing a surface coating composition, especially a coating composition for metallic and plastic surfaces, the process comprising the steps of:

conveying a viscous medium comprising constituents to be dispersed from a conveying media source to a dispersion unit, and

producing a dispersion from the viscous medium by means of the dispersing unit, wherein the step of conveying the viscous medium comprises:

conveying the viscous medium by means of a membrane pump having a conveying chamber for the viscous medium and a working chamber for moving a membrane, by means of which the viscous medium is conveyed through the conveying chamber,

detecting a mass flow rate of the viscous medium leaving the conveying chamber, and

controlling a compressed air volume in the working chamber as a function of the mass flow rate detected.

13. The process according to claim 12, further comprising the steps of:

recognizing a deviation in the flow rate detected from a predetermined target value (ws),

increasing the compressed air volume in the working chamber when the flow rate goes below the target value (ws), and

reducing the compressed air volume in the working chamber when the value flow rate goes above the target value (ws).

14. The process according to claim 12, further comprising the step of:

smoothing the mass flow rate of the viscous medium downstream of the membrane pump, and preferably upstream of a sensor used to detect the mass flow rate.

15. A method for supplying a viscous medium comprising constituents to be dispersed to a dispersing unit, the method comprising using a pump arrangement according to claim 1.

16. The pump arrangement according to claim 4, wherein the fuzzy controller comprises input channels extended by an integral component and a differentiating component.

17. The pump arrangement according to claim 9, wherein the pulsation damper has a maximum fluid volume corresponding three times the conveying volume of the membrane pump over half a conveying cycle.

18. The apparatus according to claim 9, wherein the dispersing unit is a stirred mill.

19. The process according to claim 12, wherein the dispersing unit is a stirred mill.

20. The method according to claim 15, wherein the dispersing unit is a stirred mill.