Abstract:
Disclosed is a seal device for painting machine having good sealing performance over a long time and durable, thereby eliminating the need for frequent maintenance operations and minimizing leakage of paint or the like. The seal device  10  is a two-part structure comprising a seal ring  20  of relatively low resiliency and a pre-pressurize member  30  of relatively high resiliency. The seal ring  20  comprises a pair of opposed arms  25 , 26  at both sides of a groove  24  preferably a substantially composite UV-shape in cross section. A base portion  37  of the pre-pressurize member  30  having substantially the same cross sectional shape as the groove  24  is of the groove  24 . By applying a pressure onto the pressure portion  38  of the pre-pressurize member  30  extending from the seal ring  20 , the arms  25 ,  26  of the seal ring  20  are deflected outwardly for better sealing.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a seal device, more specifically to a seal device for a painting machine to be used in a painting machine for spraying paint on an outer surface of an object to be painted such as, for example, automobile bodies for automobiles to be sequentially assembled in a production line.  
         [0002]     It is typical that outer surfaces of various machines and appliances such as, for example, automobiles are covered with aluminum or other metal plates. Such outer surfaces are normally painted with paint for the purpose of securing durability by preventing such materials from staining or improving outer appearances. In particular, painting of automobiles or the like is performed with paint of one color or plural colors selected from a large number of colors depending on users&#39; choice.  
         [0003]     Painting of such automobiles or the like are carried out by melting paint in a liquid form (or in solution) with volatile solvent such as thinner, toluene or the like end sprayed from a nozzle on a surface to be painted by utilizing pressure of gas such as air or the like. Typically, painting is carried out more than one time by repeating a painting step and a drying step from an under painting to an upper (or a finish) painting of a desired thickness using the same or different paints.  
         [0004]     Firstly, a brief description will be made about a typical painting machine with reference to  FIG. 5  and  FIG. 6 .  FIG. 5  shows the entire construction of a painting machine to be used for painting automobiles or the like.  FIG. 6  is a schematic diagram for describing a painting operation of the painting machine as shown in  FIG. 5 .  
         [0005]     In  FIG. 5 , the painting machine  70  comprises a main body (referred to as a painting robot hereunder)  71  having an arm  72  and an ejection control unit  74 , a cartridge bell  73  disposed at the front end of the arm  72  of the painting robot  71 , a cartridge transport unit  75 , a plurality of cartridges  76 , a paint filling unit  77 , a bell cup washing unit  78  and the like.  
         [0006]     The painting robot  71  of the painting. machine  70  freely moves the arm  72  in response to locations and shapes of the object to be painted under control of an internal controller (not shown) and paints the object by ejecting or spraying a predetermined amount of paint accommodated in the cartridge  6  in the cartridge bell  73  that is disposed at the front end of the arm  72  under control of the ejection control unit  74 . The arm  72  of the painting robot  71  can be automatically controlled in the position and time by, for example, a program that is preinstalled in a CPU (Central Processing Unit) in the aforementioned controller.  
         [0007]     The cartridge transport unit  75  is a unit for delivering a plurality of cartridges  76  containing, for example, different paints to the cartridge bell  73  disposed at the front end of the arm  72  of the painting robot  71 . The paint filling unit  77  is a unit for filling a predetermined paint in the respective cartridge  76 . The bell cup washing unit  78  washes the bell cup at the time of changing paints or their colors, thereby preventing plural paints from being mixed.  
         [0008]     By the painting machine as shown in  FIG. 5 , the painting robot  71  is able to move to the optimum position in response to the size and the shape of the object to be painted and for painting a predetermined amount of paint. It is also possible to paint different paints for plural times at the same position of the object to be painted with a certain time interval between paintings. In this manner, desired paint (or paints) can be painted on the object to be painted in a predetermined sequence.  
         [0009]     Now, a painting operation of the painting machine  70  will be described hereunder with reference to  FIG. 6 . A desired cartridge  76  is attached to the cartridge bell  73 . A piston is accommodated in the cartridge together with paint  81 . Also connected from the ejection control unit  74  is a pushing solvent tube  83 . On the other hand, a turbine air tube  86  is connected to the cartridge bell  73  from a rotary controller  84  by way of an electric-air converter  85  and high voltage is also applied to object to be painted by way of a cable  88 .  
         [0010]     Upon sending solvent by way of the pushing solvent tube  83  under control of ejection control unit  74 , the piston in the cartridge  76  is driven and ejects the paint  81  out of a nozzle at the front end of the cartridge bell  73 , thereby uniformly spraying the ejected paint over the surface of the object to be painted  89 . High voltage from the high voltage controller  87  electrically charged the paint and helps to uniformly spraying the paint over the predetermined surface of the object to be painted  89 . In this manner, painting non-uniformity is effectively avoided and ensures the paint to be firmly adhered on the surface of the object to be painted  89 .  
         [0011]     Although not shown in the drawing, the painting machine  70  as described hereinabove uses a large number of seal devices in the cartridge bell  73  and the cartridge  76  for the purpose of preventing paints, air and solvent from leaking or escaping. Particularly, in painting machines for automobiles or the like, painting operations are repeated on different objects to be painted or even on the same object to be painted for under painting or upper painting while frequently replacing paints. Accordingly, it is required for the seal devices to be used therein to ensure a large number of painting operations while maintaining sufficient sealing performance.  
         [0012]     Examples of conventional ring type seal device for allowing a shaft or rod to pass through their center openings are disclosed in some technical publications. For example, Japanese patent publication JP342-721B1 discloses a plate type seal device made from polytetrafluoroethylene and used by fixing at its peripheral part. Also, a seal device to be fixed at its peripheral part in a casing and used with a spring and a cover layer for preventing medium from escaping is disclosed in Japanese patent publication, JP354-14256B1.  
         [0013]     Moreover, the applicant of this patent application has been making and selling ring type seal devices for painting machines under the trade name “V-Seal”. One example of such seal device for painting machine is shown in  FIG. 7 . The seal device for painting machine is a two parts structure comprising a seal ring  50  and an adaptor (pre-pressurize member)  60  made from a relatively hard (i.e., less resilient) material.  FIG. 7  (A) shows a cross section view of the seal ring  50  constituting the V-Seal along the centerline.  FIG. 7  (B) shows a cross section view of the adaptor  60 . And  FIG. 7  (C) shows a partial cross section view in the condition when the seal ring  50  is assembled with the adaptor  60 .  
         [0014]     As shown in  FIG. 7  (A), the seal ring  50  constituting the V-Seal is generally ring shape (or doughnut shape) to be disposed in a casing (not shown) such as a cylinder or the like and has an opening  53  through which a shaft (or a tubular member) reciprocating in response to the painting operation passes. Describing more in details, the seal ring  50  has one surface (or upper surface)  51 , the other surface (or lower surface)  52 , an inner side surface  55  and an outer side surface  56 . And the one surface  51  is slightly larger than the other surface  52 , thus generally inverted frustum of cone as a whole. There is formed a generally V-shaped deep ring groove  54  in cross section is formed in the entire one surface  51 . The angle of the groove  54  is, for example, about 60 degrees.  
         [0015]     On the other hand, the adaptor  60  is generally ring shape having the diameter slightly smaller than that of the seal ring  50  and made from a rigid material. The adaptor  60  has one surface (or an upper surface)  61 , the other surface (or a bottom surface)  62  that is slightly smaller in diameter than that of the one surface  61  and a center opening  63  that is larger in diameter than the opening  53  in the seal ring  50 . The cross section at the lower portion  64  of the adaptor  60  is inverted trapezoidal.  
         [0016]     When the seal device is in use, the seal ring  50  as shown in  FIG. 5  (A) and the adaptor  60  as shown in  FIG. 5  (B) are integrated or combined by inserting the lower portion  64  of the adaptor  60  into the groove  54  in the seal ring  50 . In such using condition, the lower portion  64  of the adaptor  60  is pushed in the groove  54  in the seal ring  50  when pressure is applied onto the one surface  61  of the adaptor  60 , thereby resisting the force applied onto the inner wall  55  and the outer wall  56  of the seal ring  50  and maintaining flexure of these walls  55  and  56 . In this manner, the space between, for example, a movable shaft extending through the center opening in the seal ring  50  and the inner wall of a casing.  
         [0017]     The conventional seal devices as disclosed in the abovementioned patent publications and the conventional V-Seal that the applicant of this patent application has been making and selling may tolerate for, for example, up to about several hundreds thousand to about 1 million painting operations (i.e., numbers of reciprocal movements of the shaft) only if proper materials are used and if they are precisely manufactured. However, if used in excess of such limit of painting operations, sealing performance deteriorates to such level of causing leakage or escape of fluid, i.e., paint, solvent, air or the like, thereby requiring replacement.  
         [0018]     Painting process for automobiles or the like is normally automated by the use of aforementioned painting robots. However, periodic maintenance operations by a maintenance personnel are required in order to verify or inspect the sealing performance of the seal devices in the painting process and replacing the deteriorated seal devices. Such maintenance operations not only require considerable manpower but also interrupt painting operations during maintenance or replacement as well as waist of fluid, which results in significant reduction in working efficiency and increase production cost of the products. Particularly, since a large number of seal devices are used in a painting machine, deterioration or defect of even one seal device in such painting machine not only requires replacement and/or maintenance of such defective seal device but also waists leaked paint or the like. This is the reason why high durability and stability of such seal device are extremely important to a painting machine.  
       SUMMARY OF THE INVENTION  
       [0019]     In light of the above problems of the prior art, it is therefore an object of the present invention to provide a seal device for painting machine that maintains sealing performance over a long time and during a large number of painting operations and that can significantly improve efficiency by reducing the frequency of maintenance operations and minimizing leakage of paint or the like.  
         [0020]     The seal device for painting machine according to the present invention is the one comprising a seal ring having an opening through which a shaft moving in response to painting operations for spraying paint from a container and a pre-pressurize member to be inserted into a groove formed in the seal ring, characterized in that: the seal ring is made from a material of relatively low resilient and low friction characteristics and is formed with a pair of arms at both sides of the groove in cross section across the groove; the pre-pressurize member is made from a relatively high resilient material and has a base portion to be inserted into the groove in the seal ring and a pressure portion extending from the seal ring; and the base portion of the pre-pressurize member resiliently maintains deflection of the arm of the seal member.  
         [0021]     In a preferred embodiment of the seal device for painting machine according to the present invention, the seal ring has in cross section across the groove a substantially tuning fork shape with a pair of opposed arms of substantially the same shape at both sides of the groove. The groove in the seal ring is substantially a composite UV-shape in cross section having a substantially U-shape portion followed by a substantially V-shape portion.  
         [0022]     In another embodiment of the seal device for painting machine according to the present invention, the seal ring has in cross section across the groove a first arm substantially parallel with the center axis and a second arm extending from the first arm in a slanted manner toward the center axis. The groove in the seal ring is substantially U-shape slanted toward the center axis.  
         [0023]     The seal ring is made from polytetrafluoroethylene and the pre-pressurize member is made from synthetic rubber. A plurality of seal devices each comprising the seal ring and the pre-pressurize member are disposed in stacking with one another. The seal device for painting machine further comprises a pressure adjusting member for externally adjusting the pressure to be applied to the pre-pressurize member.  
         [0024]     The seal device for painting machine according to the present invention has the following advantage in practical use. That is, unlike the conventional V-seal in which the adaptor made from a relatively hard material inserted into the groove in the seal ring for simply supporting or holding it, the seal device according to the present invention utilizes the pressure member made from a relatively high resilient material such as synthetic rubber or the like and the base portion of the pressure member is filled in the groove of the seal ring for resiliently supporting the arms at both sides of the groove in the seal ring, thereby achieving about 5 millions painting operations as compared to up to about 1 million painting operations of the conventional seal device.  
         [0025]     Moreover, the use of particular constructions in the sealing ring to have a generally composite UV-shaped groove and a pair of opposed arms of substantially the same shape at both sides of the groove in cross section or the first arm substantially parallel to the center axis and the second arm extending from the first arm in a slanted manner toward the center axis with a generally U-shaped groove between the arms helps to outwardly deflect the free ends of the arms with relatively small pressure when pressure is applied to the pre-pressurize member, thereby achieving high sealing performance. Also, the selection of proper characteristics as the materials for the seal ring and the pre-pressurize member and the use of a plurality of seal devices each comprising the seal ring and the pre-pressurize member in tandem manner enhance the sealing performance, especially durability and pressure resistance.  
         [0026]     Additionally, a pressure adjustment member for properly adjusting the pressure to the pre-pressurize member may be used at proper timing in the long time of painting operations for improving sealing performance and durability of the seal device. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]      FIG. 1  is a cross section view of a first embodiment of the seal device for painting machine according to the present invention;  
         [0028]      FIG. 2  is a schematic to describe the actual use of the seal device for painting machine as shown in  FIG. 1 ;  
         [0029]      FIG. 3  is a cross section view of a major part of a painting machine using a second embodiment of the seal device for painting machine according to the present invention;  
         [0030]      FIG. 4  is a magnified cross section view for describing the seal device as shown in  FIG. 3 ;  
         [0031]      FIG. 5  is a schematic to show the entire construction of a typical painting machine;  
         [0032]      FIG. 6  is a diagram for describing the painting operation of the painting machine as shown in  FIG. 5 ; and  
         [0033]      FIG. 7  is a conventional seal device for painting machine; wherein (A) is a cross section view of the seal ring, (B) is a cross section view of the adaptor and (C) is a cross section view of the seal ring and the adaptor in the condition of actual use. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0034]     Now, construction and operation of preferred embodiments of the seal device for painting machine according to the present invention will be described hereunder with reference to the accompanying drawings.  
         [0035]     Firstly, a reference is made to  FIG. 1  that is a cross section view along the centerline of a first embodiment of the seal device for painting machine according to the present invention in an assembled condition. The seal device for painting machine (referred to simply as the seal device below)  10  comprises a seal ring  20  and a pre-pressurize member  30 . Although the seal ring  20  and the pre-pressurize member  30  are separately made from different materials to be described hereinafter, they are assembled together or integrated with each other as shown in  FIG. 1  in a condition of actual use.  
         [0036]     The seal ring  20  has circular upper surface  21  and bottom surface  22  and also an opening  23  aligned with the centerline CL or the centers of the upper surface  21  and the bottom surface  22 . As a result, the seal ring  20  is a generally ring-shape (or doughnut-shape) having the upper surface  21  and the bottom surface  22  and a deep groove  24  is formed in the upper surface at the circumference toward the bottom surface  22 .  
         [0037]     The groove  24  is substantially U-shape at the lower portion and substantially V-shape at the upper portion, thereby a composite UV-shape (or substantially U-shape with tapered at the upper portion) in cross section view as shown in  FIG. 1 . This makes the cross sectional view of the seal device  20  substantially tuning fork shape (or a U-shape) having a pair of right and left arms  25  and  26  of substantially equal size and shape at both sides of the groove. The outer surfaces of these arms  25  and  26  are sloped to expand slightly outwardly toward the upper portion or the upper surface  21  of the seal ring  20 . Additionally, there is formed a tapered portion at the outer circumference near the bottom surface  22 . It is to be noted that the inner side surface of the arm  25  (opposite to the groove  24 ) of the seal ring  20  is designed to slidably contact with a reciprocating shaft (or a tubular member) of a painting machine and constitutes a sealing surface to seal fluid material of a painting machine while the outer side surface of the arm  26  constitutes a sealing surface that abuts against an inner wall of a casing (for example, a cartridge or the like) as will be described hereinafter.  
         [0038]     Preferably, the seal ring  20  is made from a flexible material by molding technology. The seal ring  20  is required to have low friction characteristic as well as excellent chemical stability. Although a preferable material for the seal ring is polytetrafluoroethylene (PTFE), it is more preferable that an appropriate amount of carbon fiber such as carbon black or the like is uniformly filled in such flexible material in order to improve durability.  
         [0039]     On the other hand, the pre-pressurize member  30  is made from a relatively highly resilient material. The pre-pressurize member  30  has an upper surface  31 , a bottom surface  32  and a center opening  33  and is a ring having the diameter smaller than that of the seal ring  20 . And the pre-pressurize member  30  comprises a base portion  37  having an inner side surface  35  and an outer side surface  36  to provide a cross sectional shape substantially corresponding to that of the groove  24  in the seal ring  20  and a pressure portion (or a head portion)  38  above the base portion  37 . It is to be noted herein that the technical terms “relatively low resilient” and “relatively high resilient” are used to compare resiliency of the materials of the seal ring  20  and the pre-pressurize member  30  and the former means relatively rigid while the latter means highly resilient.  
         [0040]     A preferred material for the pre-pressurize member  30  is fluoric synthetic rubber. When used as the seal device for painting machine  10 , the base portion  37  of the pre-pressurize member  30  is pressed into the groove  24  in the seal ring  20  as shown in  FIG. 1 , thereby integrating the seal ring  20  and the pre-pressurize member  30  with each other. Under this condition, the pressure portion (or head portion)  38 , or the upper surface  31  of the pre-pressurize member  30  extend upwardly from the upper surface  21  of the seal ring  20  by the predetermined distance. When used in a painting machine, the pre-pressurize member  30  is pre-pressured by applying appropriate force onto the generally flat upper surface  31  of the pressure portion  38  toward the groove  24  in the seal ring  20  as will be described hereinafter.  
         [0041]     Now, reference is made to  FIG. 2  that is a diagram for describing the seal device for painting machine as shown in  FIG. 1  used in a painting machine. The seal device  10  is disposed in a space between left and right sidewalls  41  of a casing  40  of the painting machine, a first member (for example, a bottom surface of the casing  40 )  42  and a second member (for example, a push-down lid)  43 . That is, the bottom surface  22  of the seal ring  20  of the seal device  10  contacts with the upper surface of the first member  42  of the casing  40  and the upper surface  31  of the pre-pressurize member  30  contacts with the bottom surface of the second member  43  of the casing  40 . The outer side surface (or the outer sidewall) of the arm  26  of the seal ring  20  constituting the seal device  10  makes contact with the inner surface of the sidewall  41  of the casing  40 . Furthermore, the shaft  44  that reciprocates in response to the painting operation of the painting machine extends through the opening  23  of the seal ring  20  and the opening  33  of the pre-pressurize member  30  of the seal device  10  and the outer side surface of the arm  25  of the seal ring  20  constituting the seal device  10  makes contact with the outer surface of the shaft  44  of the painting machine. The shaft  44  is,for example, a metal tubular member that reciprocates with respect to the casing  40 .  
         [0042]     By the construction as shown in  FIG. 2 , upon application pressure P on the upper surface  31  of the pre-pressurize member  30  of the seal device  10  (by way of, for example, push-down lid  43 ), a force is applied onto the both sides of the groove  24  of the seal ring  20 , that is the left and right arm portions of the tuning fork in cross section are forced to bend outwardly. And the base portion  37  of the pre-pressurize member  30  develops counter force of the above force onto the arm portions by its resiliency. As a result, the seal device  10  provides smooth and firm closure (or sealing) between the reciprocating shaft  44  and the inner wall of the casing  40 . That is, the seal device  10  is able to surely seal the paint that is oily or aqueous fluid containing slurry of acidic or alkaline solvent, pigment, mica particles, aluminum foils and the like, thereby preventing it from leaking. Since the seal ring  20  is made from a material having low friction characteristic as described hereinabove, a stable sealing is ensured even if the shaft  44  may reciprocate inside the casing  40  (i.e., mutual movement between the shaft  44  and the casing  40 ).  
         [0043]     It is to be noted that the cross sectional shape of the groove  24  in the seal ring  20  is generally composite UV-shape as described hereinabove, the pressure applied to the pressure portion  38  of the pre-pressurize member  30  is largely applied to the end portions (i.e., free ends) of the arms  25  and  26 . This ensures to form seal lips (or sealing surfaces) for making contact with the shaft  44  and the inner surface of the casing  41 .  
         [0044]     By taking the construction and choosing appropriate materials as described hereinabove, experiments demonstrate that the seal device of the particular embodiment according to the present invention can maintain excellent sealing performance before and after about 5 million painting operations (i.e., reciprocal movements of the shaft  44 ). Because of such excellent sealing performance, the seal device is able to significantly reduce maintenance operations of the painting machine using such seal device, effectively prevent paint or the like from leaking and significantly improve painting efficiency, thereby leading to significant reduction of the painting cost.  
         [0045]     Now, a second embodiment of the seal device for painting machine according to the present invention will be made with reference to  FIG. 3  and  FIG. 4 .  FIG. 3  is a cross section view of a major portion of a painting machine to show how the seal device for painting machine is incorporated.  FIG. 4  is a magnified cross section view of the seal device. It is to be noted, however, that the center portion may not be equally sized with respect to the circumferential sealing portion for convenience of illustration.  
         [0046]     Firstly, as shown in  FIG. 3 , an opening  12  is formed in a portion of a pump main body  110  of a painting machine from a fluid (for example, paint) side at the left side toward an atmospheric side at the right side in  FIG. 3 . A rotary shaft (or cylinder)  120  for a painting machine extends through the opening  112 . Moreover,the pump main body  110  is formed with a cylindrical portion  114  around the opening  112  to extend toward the atmospheric side. The cylindrical portion  114  has a larger inner diameter than the diameter of the opening  112  so as to form a seal accommodation portion  116  and is formed with a screw (not shown) on the outer surface.  
         [0047]     The seal accommodation portion  116  is designed to dispose he seal device  150 . In the particular embodiment as shown in  Fig. 3 , a pair of seal devices  150  are disposed in stacking with each other. A seal pushing cap  130  is screwed onto the cylindrical portion  114  by way of, for example, a washer  140 . As a result, an appropriate pressure is applied to the seal device  150  as disposed between the outer surface of the pump main body  110  and the inner surface of the seal pushing cap  130  in the seal accommodation portion  116  inside the cylindrical portion  114 .  
         [0048]     Now, the seal device  150  will be described in greater detail with reference to  FIG. 4  together with  FIG. 3 . As shown in  FIG. 4 , each seal device  150  comprises a seal ring (or a main body)  160  that is made from relatively low resilient material, preferably, for example, polytetrafluoroethylene or the like and a pre-pressurize member  170  to be used in combination with the seal ring  160 . The pre-pressurize member  170  is an elastic member that is made from a relatively high resilient material, preferably, for example, fluoric synthetic rubber. The seal ring  160  and the pre-pressurize member  170  are formed with center openings so that the rotary shaft  120  as shown in  FIG. 3  can extend therethrough.  
         [0049]     The seal ring  160  has a ring shape as its name implies and has a cross sectional shape comprising a first arm  162  locating at the outer periphery and substantially parallel with the axis and a second arm  164  that extends inwardly (i.e., toward the center axis) from the first arm  162  thereby leaving a substantially U-shaped groove  166  slanted toward the center axis between the first arm  162  and the second arm  164 . As a result, the outer circumference of the seal ring  160  has a substantially “         ”-shape in cross section. And the free end portion of the second arm  164  constitutes a seal lip (or a sealing surface)  165  that makes contact with the outer surface of the rotary shaft  120 .  
         [0050]     On the other hand, the pre-pressurize member  170  comprises a main portion (or a base portion)  172  having a shape to fit the substantially U-shaped groove  166  in the seal ring  160  and a pressure portion  174  extending outwardly from the main portion  172 . When the seal ring  160  and the pre-pressurize member  170  are compressed in their axial direction between the outer surface of the pump main body  10  and the inner surface of the seal pushing cap  130  in the condition where the main portion  172  of the pre-pressurize portion of the pre-pressurize member  170  is inserted into the substantially U-shaped groove  166 , the compressing force applied to the pre-pressurize member  170  pushes the second arm  164  inwardly (or to the direction toward the rotary shaft  120 ), thereby deflecting the seal lip portion  165  at the end the second arm  164  to be pressed onto the outer surface of the rotary shaft  120 . In this manner, the highly pressurized fluid (or paint) is effectively prevented from leaking from the fluid side to the outside or the atmospheric side through the opening  112  in the pump main body  110  (i.e., providing complete sealing).  
         [0051]     Now, a special attention should be paid to the fact that the second arm  164  of the seal ring  160  is slanted toward the center axis or the rotary shaft  120  and the main portion (or the base portion)  172  of the pre-pressurize member  170  is inserted into the substantially U-shaped groove  166 . When a pressure is applied to the pressure portion  174  of the resilient pre-pressurize member  170 , the pressure primarily deflect the second arm  164  of the seal ring  160  toward the rotary shaft  120  in a resilient manner. And the deflection of the second arm  164  is resiliently maintained so that the seal lip  165  at the end provides a resilient contact pressure onto the rotary shaft  120 . As a result, the seal lip  165  is able to provide an excellent sealing between the inside (i.e., the fluid side) and the outside (i.e., the atmospheric side) of the pump main body  110  over a long time and even after a large number of painting operations.  
         [0052]     It is to be noted that the use of a plurality of seal devices  150  (for example,  2  seal devices in the particular embodiment) in stacking manner as shown in  FIG. 3  is able to provide more reliable sealing. It is possible here that an appropriate pressure is applied to the pre-pressurize member  170  by adjusting the screw rotation of the seal pushing cap  130 . Also, it is possible to further screwing the seal pushing cap  130  for readjusting the pressure of the pre-pressurize member  170  whenever the sealing performance is deteriorated as a result of a large number of painting operations. As a result, the seal pushing cap  130  has the function as a pressure adjusting member.  
         [0053]     Although construction and operation of preferred embodiments of the seal device for painting machine according to the present invention have been described in detail hereinabove, it is to be noted that such embodiments are nothing but examples of the present invention and are not demonstrated for restricting the present invention. It is a matter of course that a person having an ordinary skill in the art is able to make various modifications depending on particular applications without departing from the scope and spirit of the present invention. For example, the circumferential shape of the seal ring and the pre-pressurize member is not necessarily circular. It is also possible to use more than two seal devices each comprising the seal ring and the pre-pressurize member in a stacking manner (or in tandem) for particular applications. Moreover, the seal device for painting machine can be applied not only to the cartridge type painting machines but also to various other types of painting machines.