Abstract:
Valve assemblies for the color change valve arrangement of a coating plant, for example for the production coating of vehicle bodies, wherein various measures are proposed to miniaturize the needle valves forming the valve body of the color changer based on the principle of optimizing the drive device acting on the valve needles to open the valve against the force of a pressure spring.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates, in general, to a color change valve arrangement for selectively connecting an applicator of a coating plant to a plurality of supply lines for coating material of different selected colors.  
         [0003]     2. Description of the Related Art  
         [0004]     Valve arrangements for selectively connecting an applicator of a coating plant to a plurality of supply lines for coating material of different selected colors, which are needed in coating plants for the production coating of work pieces such as vehicle bodies, are known from DE 198 36 604 and DE 198 46 073 and others. These color change valve arrangements, or color changers for short, make it possible to switch quickly from one color to another during painting operations in paint plants and consist mainly of a plurality of controllable paint valve assemblies that are distributed along a paint passage common to all of them. To adapt to the particular plant and the number of selectable colors, they are formed in modular fashion from individual modules (connector blocks, manifold blocks, control heads) that can be stacked in rows so that a variable number of connections for paint lines, which can subsequently be enlarged or reduced, can be implemented. In addition to the paint valves there are usually additional, similarly-constructed valves for purging media such as solvent and pulse air. The valve assemblies consist for their part of pin or needle valves, whose valve needles are pressed into the closed position by a pressure spring and are opened against its force by a pneumatically-activated piston drive. The valve needles of the valve assemblies disposed next to each other along the normally straight central passage are moved in parallel planes which lie perpendicular to the axis of the central passage to improve flow characteristics but can also be disposed at an angle (DE 198 46 073, WO 02/09886). To save space, color changers are also known which in place of the customary straight central passage contain a spiral groove at right angles to the longitudinal axis of the color change block (DE 43 39 301). This, however, less conducive to flow than a straight central passage.  
         [0005]     From EP 1 205 256 it is further known to have permanent pilot control of the paint and purging agent valves, using a pressurized air line common to all valve assemblies, and to actuate them by added electronically controlled solenoid valves. This dispenses with the required control air lines found in the normally pneumatically-controlled color changers.  
         [0006]     In principle, color changers of the category under consideration here are distinguished by considerable advantages such as freedom from dead space, good purge capability, little dead volume, small size, low weight, modular construction, small number of different parts, ease of installation, maintenance and repair, etc. They have consequently proved their worth in practice for a long time. The disadvantage with the known color changers is their length in the longitudinal direction of the common central passage to match the number of selectable colors. As a result, the known color changers are relatively poorly suited to installation in confined areas of coating equipment, as for example painting robots, and even less suited to installation in the atomizer itself mounted on these machines, which may be desirable for the reasons explained in the co-pending application filed concurrently herewith in the name of Stefano Giuliano, which is entitled Spraying Device for Serial Spraying of Work Pieces.  
         [0007]     An object of the invention is, therefore, to reduce the length of the color changer in the longitudinal direction of the central passage common to the valve assemblies and in particular to reduce the size of the valve assemblies perpendicular to the needle axes to a minimum without thereby prejudicing the required sealing effect of the valve needle pressed against the valve seat.  
       SUMMARY OF THE INVENTION  
       [0008]     The starting point of the invention is that for safe and reliable operation of the valves, their needles (meaning any type of pins) must be pressed against the valve seat in the closed position with a force that must not fall below a specific minimum because of the required sealing effect. The invention is also based on the understanding that if this necessary minimum closing force is reduced and/or if the force available to overcome the minimum closing force is increased, possibilities open up of miniaturizing the valve assembly, specifically in a dimension perpendicular to the needle axis and thus in the longitudinal direction of the central passage. As a result, the color changer is more suitable than before for installation in small areas with restricted space characteristics, as for example, in relatively slender robot arms or relatively small atomizers. Through the achievable shortening of the central passage for a given number of paint valve assemblies, considerable additional advantages are gained in comparison with known color changers, such as still less dead volume, even lower paint and purging agent losses during a color change (by up to 85%), even faster and more efficient purging of the media carrying spaces and even lower weight.  
         [0009]     The invention is suitable for color changers with or without paint recirculation (through the intrinsically known return lines) as a single color changer or also to create double color changers which, as is known, have common paint supply lines and are connected to the atomizer over separate paint runs. For example, especially compact color changer valve arrangements in accordance with the invention are well suited to creating double color changers. On the other hand, and in many cases particularly for shortening the central passage length, the advantageous possibility exists of arranging the valve assemblies in a star formation in which at least two, preferably at least three or four or more, valve assemblies whose outlet ports lie in a common plane perpendicular to the longitudinal axis of the central passage are disposed distributed around the longitudinal axis of the central passage. Preferably at least two or more additional valve assemblies whose outlet ports lie in a second plane parallel to the first are disposed around the longitudinal axis of the central passage distributed in such a way that the valve assemblies of the second plane lie in the circumferential direction of the central passage between the valve assemblies of the first plane. The result is a particularly compact arrangement in the longitudinal direction of the central passage, since the distance between the valves assemblies of the two planes can be smaller than the diameter of the valve assemblies measured in the longitudinal direction of the passage.  
         [0010]     The reduction in accordance with the invention of the aforementioned minimum closing force necessary for the valves to be able to operate can be achieved in different ways. One expedient possibility consists in particular by forming the sealing surface of the valve needle opposite the surface of the valve seat, preferably including its face and/or the surface of the valve seat, from an elastomer material, so that due to the softer sealing materials a substantially better sealing effect can be achieved than before with relatively low force. The elastomer surface is suitably shaped so that no undercuts or dead spaces are created in which paint can be deposited such that it cannot be flushed free of all residue. Furthermore, the elastomer surface, similar to the previously customary valve needles and valve seats, is suitably formed so that the sealing edge lies as close as possible to the central passage and preferably at least approximately aligns with its inner wall (c.f DE 198 36 604). The surfaces in question of the valve needle and of the valve seat can run in linear fashion parallel to each other in the normal way or, for example, can run curved in the way described in DE 102 28 277, where the valve needle has an essentially spherical outer contour. A variation of the possibility described here is to use a spring element consisting of, for example, an elastomer O-ring in the interior of a needle tip produced from a plastic such as UHMPE or UHMWPE (polyethylenes with an ultra-high molar mass) such that the result is a flexibly yielding (“soft”) needle tip.  
         [0011]     It is already known to furnish the valve needles of the paint valves of a color changer adjoining the conical tip with an annular groove and an O-shaped seal ring located therein in order to achieve additional sealing (DE 198 46 073). By comparison, the invention has the advantage that undercuts and dead spaces created by the O-shaped seal ring are avoided. In such undercuts and dead spaces non-purgeable paint remnants can be deposited, become detached later and cause paint defects in the coating. The invention also has the advantage that the sealing edge of the needle can lie immediately against the central passage.  
         [0012]     In the case of the color change valve arrangement described here, the closing force is preferably generated by a spring whose force must be overcome by the pressure medium of the piston drive device to open the valve. In this case, a further effective possibility exists for reducing the necessary minimum closing force by using a spring with a degressive characteristic. In this regard, the invention is based on the understanding that the greatest closing force is necessary only in the normal position of the closed valve, while when the valve is actuated, a magnitude of the application force to be overcome which decreases with piston stroke is desirable. Preferably, therefore, a pressure spring is used whose characteristic when compressed runs more or less (hard or soft) in a degressive curve. The same applies in the equally possible use of a tension spring in place of a compression spring.  
         [0013]     Several different possibilities in accordance with the invention also exist for similarly effectively increasing the energy available to overcome the minimum closing force. The increase in energy should be achieved without making the valve assemblies larger in at least one dimension, specifically in the dimension corresponding to the diameter of the valve assembly perpendicular to the needle axis, that is to say in the dimension measured along the central passage. With the same energy exerted on the valve needle to overcome a given closing force, the increase in energy should rather be associated with a reduction of the dimension of the valve assembly in the said dimension. In other instances, however, an increase in the force exerted on the valve needle through the energy amplifying device without enlarging the stated dimension of the valve assembly can make sense.  
         [0014]     A particularly simple constructional possibility of energy amplification consists in the use of a piston which has a non-circular, for example, a flat, rectangular or oval, cross-section on the surface pressurized by the pressure medium. The short axis of this cross-section should lie parallel to the direction in which the valve assembly is to be miniaturized, for example, in the longitudinal direction of the central passage. If this piston drive is compared with the previously customary valve drive using a cylindrical piston, the result with the same piston dimension in the direction of the short cross-sectional axis is substantially greater force (pressure x piston area) and, for the same force, a substantially narrower piston.  
         [0015]     To increase the force generated by a piston of given area, the pressure of the medium pressurizing the piston can be increased in accordance with a further possibility. Since it would normally be impractical because of the associated expense to increase the pressure of 6 or at best 8 bar (dynamic minimum pressure) in the pressurized air systems of normal coating plants today, the pressurized air needed for the piston drive of the color change valve arrangement is to be preferably generated in a small, independent separate supply unit, which in many plants may already be available, for example for the cleaning slug equipment. This separate pressure elevating station can supply the valves of the color changer with a pressure of more than 10 bar, preferably at least 20 bar, in typical cases for example with about 25 bar. Instead of air, the pressure medium can also be a fluid for a hydraulic drive device to pressurize the piston.  
         [0016]     In accordance with a further possibility, the drive device can further contain at least two piston surfaces, disposed for example one behind the other along the axis of piston motion, to each of which pressure is applied by the drive medium, which can be located in two piston cavities sealed off from each other or suitably coupled together in another way. For a given diameter of the valve assembly, a substantial increase in force is enabled thereby or, for the same force, a substantial reduction in size of the valve assembly perpendicular to the needle axis. More than two piston surfaces each pressurized by the drive medium can also be coupled to each other.  
         [0017]     As a further possibility, the drive device to pressurize the piston can contain an energy converter to amplify the force of the pressure medium. A wide variety of energy converters can be employed, which normally are intended to convert a relatively low linear force into a higher linear force or, more generally, a given force or pressure component into a different linear force while amplifying the force. Some of the known principles which can be used for amplifying force are law of leverage, pulley, bell crank, shears, inclined plane, etc. Since the valve assemblies are designed in the usual way with a positive valve seat and the pressure medium is introduced on the side of the piston facing away from the central passage, force amplification can usefully be linked to a reversal of motion and/or to the conversion of linear into rotational motion and conversely. Embodiments will be explained in more detail hereinafter.  
         [0018]     Especially small needle or pin-valve assemblies can be realized if, in accordance with a further possibility, the drive unit to which the pressure medium is supplied to actuate the valve is situated at a remote location outside the actual valve assembly of the color changer and is connected to said assembly by a preferably flexible mechanical drive element. With an arrangement of this type, a piston of large dimensions can be used to generate a correspondingly high force for the valve needle without taking up space in the valve assembly, which in consequence can be of extremely small dimensions. The connection can be created, for example, by means of a flexible control shaft (such as a Bowden cable or the like).  
         [0019]     Suitable actuation of the valves can make a further contribution to miniaturization of the color changer, particularly insofar as their control lines are concerned. In themselves, the valve assemblies can be the same as known designs, for example FIG. 2 of DE 198 36 604, according to which the valve needle furnished with the piston is pressed by pressurized air against the force of a pressure spring into the open position in which it opens the way into the central passage for the paint or purging medium. In contrast to DE 198 36 604, in which the needle tip is pushed into the central passage to open the valve, in many cases the opposite opening direction can be more suitable (positive valve seat as in the aforementioned DE 198 46 073). Accordingly, the previously customary control technology using pneumatic hoses leading to the valves and solenoid valves installed in an external pneumatic cabinet can be used for the color changer described here. But in many cases, such as locating the color changer in an atomizer, in accordance with the similarly aforementioned EP 1 205 256, it can be more appropriate instead to incorporate a miniature pilot valve in the form of an electromagnetically-piloted pneumatic valve. The pneumatic valves for the paint or purging medium opening into the central passage of the color changer are actuated by pressurized air or another pressurized gas from a common pressurized gas line leading through the valve arrangement to all valves, and within the valve arrangement a solenoid valve replacing the conventional pressure connection can be inserted into the pressurized gas path of the pneumatic valves. The actuation of the solenoid valves is preferably managed using a data bus leading through the valve arrangement for digital control data, which is linked to the solenoid valves by way of an electronic circuit. The pilot valves can also be actuated piezo-electrically, instead of electromagnetically, allowing further miniaturization to be achieved.  
         [0020]     A further possibility for miniaturizing the color changer consists in the attachment of a central control module of the type described in DE 101 42 355 (see FIGS. 7 to 9 there) located upstream from the valve assemblies. These control modules contain a valve common to the paint valves, whose pneumatic output signal can be taken to the particular paint valve to be actuated by way of a directional control unit. The unit contains a specific number of directional valves connected to each other in a common housing block through openings inside the housing block.  
         [0021]     To reduce the length of the valve assemblies in the longitudinal direction of the needle and under certain conditions also to improve the electrical and/or hose-line arrangement it can be advantageous to house pilot valves for controlling the valves in a separate, for example, cylindrical or annular add-on control unit, which can be located in the space intended for the hose lines. The control unit can be connected to a common supply line and if necessary an electrical power cable for controlling the color changer, preferably with field bus control.  
         [0022]     In many cases and particularly with the installation of the color changer in an atomizer, it may be appropriate to provide a quick-change coupling for all the connections of the color changer, which enables the rapid installation and removal of the color changer, and in addition good hose routing. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0023]     The invention is explained in more detail with reference to the embodiments shown in the drawing wherein like reference numerals refer to like parts throughout the several views, and wherein:  
         [0024]      FIG. 1  shows a schematic representation of a valve assembly of the color changer;  
         [0025]      FIG. 2  shows the schematic representation of a valve assembly having two piston surfaces coupled to each other;  
         [0026]      FIG. 3  shows another embodiment of a valve assembly having two piston surfaces coupled to each other;  
         [0027]      FIG. 4  is the schematic representation of a linear drive serving as an energy converter;  
         [0028]      FIG. 5  is another embodiment of a linear drive serving as an energy converter;  
         [0029]      FIG. 6  is the schematic representation of a linear drive energy converter having fluid force amplification;  
         [0030]      FIG. 7  is the schematic representation of a drive device with indirect force generation;  
         [0031]      FIG. 8  is a useful embodiment of the sealing surface of a valve needle of the color changer;  
         [0032]      FIG. 9  is another embodiment of a valve needle of the color changer;  
         [0033]      FIG. 10  is the schematic representation of a modular color changer with the valves in a star arrangement; and  
         [0034]      FIG. 11  is the schematic representation of a color changer having a quick-change coupling array. 
     
    
     DETAILED DESCRIPTION  
       [0035]     With the exception of the cross-sectional shape of the piston, the valve assembly  1  of the color changer described shown in  FIG. 1  corresponds to the prior art and contains accordingly a movably mounted valve needle  10 , to which the peripherally sealed piston  11  is attached, the piston  11  movable in the cylinder cavity  12 . A coil spring  13 , which is seated against the valve housing  14 , presses against the piston  11  on the side facing away from the cylinder cavity  12 . The free end of the valve needle  10  is pressed by the spring  13  against the valve seat  15  of the housing  14  into its closed position, representing the normal position. To open the valve shown, pressurized air indicated by the arrow DL is led into the sealed cylinder cavity  12  by way of a control valve  16  (which can be located, for example, in a remote control cabinet when conventional control technology is used). The piston  11  is thereby pressed against the force of the spring  13  into the actuating position, in which the valve needle  10  is lifted from the valve seat  15  and opens the way for the controlled medium, for example, paint F which is led into the chamber  18  of the valve assembly  1  and exits through the open valve seat  15  into the central passage  19  of the color changer, here indicated only as an opening in the housing. The arrow  17  identifies the necessary venting.  
         [0036]      FIG. 1A  is a section through the wall of the housing  14  surrounding the periphery of the piston  11  and the cylinder area  12 , perpendicular to the direction of displacement and shows in this embodiment the oval cross-sectional shape of the piston  11  and of the housing  14  wherein they have in one transverse direction a shorter diameter and in the other transverse direction perpendicular thereto a longer diameter.  
         [0037]     The modified valve assembly  2  shown in  FIG. 2  differs from the embodiment in accordance with  FIG. 1  in that, in accordance with the drawing, two pistons  11 ′ and  21  spaced apart in the longitudinal direction of the needle are attached coaxially to the valve needle  20  and are carried movably in their own sealed off cylinder cavities  12 ′ or  22 . When the control valve  16  is open, pressure is applied therein to each by the pressurized air DL against the force of the spring  13 ′. For a given small diameter of the valve assembly  2 , the force generated by the pressurized air can thereby be doubled.  
         [0038]     In the case of the valve assembly  3  shown in  FIG. 3 , in principle similarly to  FIG. 2 , two piston surfaces  31  and  32  to which pressure is also applied simultaneously by the pressurized air are rigidly attached to the valve needle  30  and disposed one behind the other coaxially therewith in the longitudinal direction, so that the result is a similar increase in force. The two pistons here form a hollow cylinder body  33  with, for example, cylindrical or, as in  FIG. 1A , oval cross-section which is carried movably in the housing  34  of the valve assembly  3 . At its one outer side facing the valve seat the cylinder body  33  forms the first piston surface  31 , and at the inner wall of its interior facing away from the first piston surface  31  the cylinder body  33  forms the second piston surface  32 . The pressure spring  13 ″ applies pressure at the outer side of the cylinder body  33  opposite to the first piston surface  31 . With its cylindrical or oval inner wall, the cylinder body  33  slides on the correspondingly-shaped periphery of a guide body  35  rigidly connected to the housing  34 . This body  35  seals the cylinder cavity  37  adjacent the second piston surface  32  from the other part of the interior of the cylinder body  33  on its other side. The said other interior section is vented through an opening  39  in the cylinder body  33 . The pressurized air DL, as shown in the drawing, passes out of the cylinder cavity  12 ′ of the housing  14  adjacent the piston surface  31  through a bore  38  leading through the valve needle  30  and the guide body  35  into the second cylinder cavity  37 . Since the interior space of the cylinder body  33  is closed except for the vent opening  39 , the two cylinder cavities  12 ′ and  37  are also sealed off from each other.  
         [0039]      FIG. 4  shows a first embodiment of a suitable energy converter  40 , suitable in at least one dimension to miniaturize the valve assembly, which is essentially formed by two racks  41  and  42  linearly parallel to each other, carried to be movable in opposite directions. The racks  41  and  42  are coupled to each other by means of a stationary, rotatably-mounted arrangement of two coaxial pinions  43  and  44  of different sizes fixedly connected on the same axis. When, for example, the input rack  41  is moved in the direction of the arrow K 1  by the pressure available to actuate the valve, it transmits this motion to the small pinion  43  which meshes with it, while the larger pinion  44  being turned at the same time transmits the motion to the output rack  42 . The rack  42  is thereby moved in the direction of the arrow K 2  opposite to K 1  and applies a force to the valve needle in this example that is greater than the force with which the rack  41  is being driven in proportion to the ratio between the pinions  43  and  44 . The pinions and/or racks are preferably arranged at least in pairs in order to achieve a favorable balance of forces. In a further development of this embodiment, the one rack can be implemented as a hollow shaft with internal splining and the other rack as a shaft located in the hollow shaft with external splining, whereby a particularly space-saving construction results in the transverse direction. The intermediate pinions which are fixed relative to an outer housing can be carried internally as though in a cage in any number.  
         [0040]     Coaxially coupled linear gears with two ball screws with different thread pitches are also feasible as energy converters for the purpose under consideration here. Ball screws are known intrinsically for converting rotary motion into linear motion and conversely, wherein the pitch of the spindle thread determines the transmission ratio. In accordance with a derivation of the linear gear described having a double ball screw, the drive unit for the valve needle can also be formed by a linear gear having a swivel drive and a spindle. In the manner known from swivel drives, a rotating piston can convert the rotary motion generated into a linear motion by means of the spindle and spindle nut.  
         [0041]     As shown in  FIG. 5 , the energy converter  50  can contain a first spindle  51  driven in the direction of the arrow K 1  (similar to  FIG. 4 ), which turns the stationary nut element  52  having axially-spaced threaded sections of different pitch. The second spindle  53  sits in the other threaded section and is moved linearly in the same direction as the first spindle  51  by the rotary motion of the nut element  52  and exerts a force in the direction of the arrow K 2  that is greater than the drive force of the first spindle  51  by an amount equal to the ratio between the different thread pitches.  
         [0042]     The working principle described for the energy converters  40 ,  50  can also be reversed as needed, including the possibility of achieving opposing direction of motion of the spindles by using right-hand or left-hand threads.  
         [0043]      FIG. 6  shows a linear gear with fluidic power amplification used as a energy converter  60 . In this example, it is a hydraulic piston gear. The energy converter  60  is located in a valve assembly, which can be identical to  FIG. 1  with respect to the paint path (arrows F) controlled by the valve needle  61 . The generally cylindrical housing  62  of the valve assembly contains two cylinder chambers  622  and  623  lying axially one behind the other, sealed off from one another by a radial dividing wall  621 . As shown in the illustration, a hollow cylinder  624  of relatively small diameter, coaxial to the housing  62  and fixedly connected to it and open to the cylinder chamber  622 , extends from the dividing wall  621  into the cylinder chamber  622  and ends there in a radially-projecting fixed guide plate  625 . The guide plate  625  is sealed at its periphery and sits inside a hollow cylindrical piston body  68  attached coaxially to the valve needle  61  and movable with it in the housing  62 . The pressure spring  63  provided to close the valve and seated on its other side against the dividing wall of the housing  621  bears against the outer wall of said piston body  68  facing away from the valve needle  61 . The movable piston  64  in the other cylinder chamber  623 , which is driven in the manner described by control air DL, acts to open the valve. The piston  64  in this case is not attached to the valve needle  61 , but extends axially movably into the stationary hollow cylinder  624  with a coaxially-projecting, cylindrical shaft  641 . The interior of the hollow cylinder  624  has at  626  an opening into the intermediate space  627  formed between the fixed sealing guide plate  625  and the inner wall of the movable piston body  68  lying axially opposite thereto. This intermediate space  627  and the interior of the hollow cylinder  624  communicating with it are filled up to the end face of the piston shaft  641  with a hydraulic (or other suitable, possibly even “plastic”) medium.  
         [0044]     When the shaft  641  of the piston  64  is pushed into the hollow cylinder  624  by control air DL, the medium contained therein transmits this force to the piston body  68  by reversing its direction, which consequently opens the valve against the force of the spring  63 . This brings about a gain in force equal to the ratio between the piston surfaces of the shaft  641  and the pressurized inner wall of the piston body  68 .  
         [0045]      FIG. 7  represents a valve assembly  7  with indirect control drive. Its pneumatic drive device  70 , to which control air DL is brought as the pressure medium, contains a cylinder space  72  similar to  FIG. 1  in that the piston  71 , which is pressurized by the pressure medium, can be moved. The pneumatic drive device  70  is located in this example outside the valve assembly  7  and is connected thereto by a preferably flexible mechanical connecting element, for example the Bowden cable shown with the customary wire pull  73 . The wire pull  73  is attached at its one end to the piston  71  and at the other end to a connecting piston  74  located on the valve needle that is impinged upon by the pressure spring  75 . For the rest, the valve assembly  7  is identical to the one in accordance with  FIG. 1  and to this extent requires no explanation. The connecting piston  74  located in the valve assembly, which is pulled only by the wire  73  into the open position, can have a considerably smaller diameter than the external piston  71 . The external piston  71  can generate a correspondingly high force for the miniaturized valve assembly  7  because, to a large extent, the piston surface can be of any size.  
         [0046]     As was already explained, miniaturization of the valve assembly can also be achieved by means to reduce the opposingly directed force which the drive device has to overcome, usually the valve closing force required for adequate sealing. One possibility for this is the valve needle  80  shown in  FIG. 8  with a conical tip  81  on the radial outer side, whose linear cross-sectional sealing surface  82  abuts the matching conically-shaped surface of the valve seat  83  when the valve is closed. Under the invention, at least the sealing surface  82  of the valve needle  80  and/or that of the valve seat  83  is to consist of an elastomer material. In the example shown, an elastomer sheath  84  is applied, for example, by spray coating or vulcanization on an inner section of the needle tip  81 , completely enclosing it. The face  85  of the needle tip in the closed position should at least approximately align with the wall of the central passage  86  common to all valve assemblies, so that no possible dead space is formed in the paint passage  87  of the valve assembly discharging there. The elastomer material of the sheath  84  is selected in consideration of the high requirements for durability of the valve and resistance to the paints and other media employed; plastics such as perfluoroelastomers are suitable.  
         [0047]      FIG. 9  shows another embodiment having a needle tip  91  for the valve needle  90  whose exterior is elastically yielding. The elastomer material  94  on the tip  91  is formed on here in one piece onto flexible bellows  95  that encloses the periphery of the needle  90  over a considerable part of its length to permit the necessary motion of the stroke and that can be attached to or formed onto a fixed seal  96  in which the needle  90  is guided. Such valves with good sealing properties can be particularly advantageous in color changers for 2K paints for example.  
         [0048]     As a further possibility for better utilization of the available drive force, the use of a spring was mentioned initially whose force is greatest when the valve is closed and decreases with the opening stroke of the valve needle.  
         [0049]      FIG. 10  shows a miniaturized color changer in the longitudinal direction of the central passage  101  common to all valve assemblies, for 24 colors in this example. It is composed of a plurality of segments  102  stacked in modular fashion along the central passage  101 , each of which contains four star-shaped valve assemblies  103  or  103 ′ distributed at equal angular intervals around the central passage  101 . The needle axes of the assemblies in the example shown lie in a common plane perpendicular to the central passage  101 . If the valve assemblies are intended to open in a known way into the central passage  101  with their needle axes at an angle different from 90°, at least the center points of the valve seats of the four valves lie in a common plane perpendicular to the central passage. To save even more space, the valve assemblies of adjacent segments  102  of the color changer, as shown in the drawing, are offset to each other in such a way that the valve assemblies  103  of one plane lie in each case in the middle between the adjacent valve assemblies  103 ′ of the other plane in the circumferential direction of the central passage  101 .  
         [0050]     The arrangement shown in  FIG. 10  of four pin valves disposed in a star in each plane of the modular manifold block of the color changer represents in many cases an optimum particularly with respect to paint change losses, which among other things depend on the required diameter of the central passage  101 . If an even flatter shape is preferred, a greater number of valves can be distributed in one plane around the central passage  101 , for example, six or eight valve assemblies. Undesirable paint change losses can be prevented here and in other embodiments by other measures, such as for example, by reducing the cross-section of the central passage  101  by means of a central internal body (c.f DE 102 12 601).  
         [0051]     The possibility explained with reference to  FIG. 10  of shortening the required length of the common central passage through the offset-angle arrangement of the valve assemblies  103  and  103 ′ is not restricted to the example described with several valve assemblies distributed in each plane around the central passage, but can be applied in general to reduce the space required perpendicular to the central passage, going so far as the placement of only two valve assemblies or even only one valve assembly in each plane. For example, in the last-named case, a single row of valve assemblies can be disposed along the central passage, in which adjacent valve assemblies along the central passage are offset to each other by a suitably selected angle, for example approximately 45°, so that two nested groups of valve assemblies is created, each aligned with the other in the longitudinal direction of the central passage. The offset angle should be as small as possible on the one hand to save space in the direction perpendicular to the central passage and perpendicular to the two valve groups; but on the other hand it must be selected such that the distance between the needle axes measured in the longitudinal direction of the central passage is smaller than the maximum diameter of the valve assemblies similarly measured in this longitudinal direction if there is to be any space saving in the longitudinal direction of the central passage. The mutual distance between the longitudinal needle axes of the adjacent valve assemblies should thus be smaller than the minimum distance which they would have to have for the same outside dimensions of the valve assemblies, if the neighboring valve assemblies were to be aligned with each other without angular offset, as with known color changers.  
         [0052]     A color changer  110  is shown schematically in  FIG. 11  that is connected by way of a quick-change coupling arrangement to its supply lines. In particular, the necessarily numerous paint lines like  112  can be connected by quickly detachable and closeable couplings  113  to short hose sections  114  inside the color changer  110 . If the color changer  110  contains electrically-controlled pilot valves and an electronic control unit for them  115 , an electrical plug  116  for the preferred field bus control of the control unit  115  can be furnished. Suitable quick-change couplings are know in the art, including those which permit quick separation of hoses under pressure and/or filled with paint. The color changer shown in  FIG. 11  can otherwise be identical, for example, to the valve arrangement in accordance with  FIG. 10 . Accordingly, the outlet for the common central passage is identified as  118 , two valve assemblies of adjoining planes offset to each other in the circumferential direction as  119  and  119 ′ and the line connected to a valve assembly for control air (DL in  FIG. 1 , etc.) as  120 .