Patent Publication Number: US-8123500-B2

Title: Diaphragm pump

Description:
REFERENCE TO PRIOR PENDING PATENT APPLICATION 
     This patent application claims the benefit of pending prior European Patent Application No. 05008040.7, filed Apr. 12, 2005 by Karsten Jüterbock et al. for DIAPHRAGM PUMP, which patent application is hereby incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a diaphragm pump with two diaphragms disposed in a pump housing which act on a fluid medium to be pumped, e.g. a paint, which diaphragms can be actuated by means of an adjusting piston arranged in between the diaphragms upon both sides of which a pressurized medium can act alternately and which diaphragms are supported in the terminal areas of two piston rods that are firmly connected to the adjusting piston. 
     2. Description of the Prior Art: 
     A diaphragm pump of this type is disclosed in DE 195 35 745 C1. In this embodiment, a further pressure space is assigned to each of the two diaphragms and the pressure spaces are separated from the pumping spaces by the diaphragms. In this case, pressurized medium is supplied in a controlled fashion to the pressure spaces synchronously to the adjustment movements of the drive piston of a pneumatic motor that is mechanically connected to the diaphragms, with the effect that although a pressure ratio is achieved, the complexity of the construction and the level of the investment required are both considerable. 
     This is because a separate control device is provided in between the pneumatic motor and one of the diaphragms, and this control device is susceptible to defects and large in size. However, the principal disadvantage is that each of the diaphragms folds over during the transition from a suction stroke to a pressure stroke and their flexing zones are highly stressed by the alternating tensile and compression loads. This leads to damage to the diaphragms after only a relatively short operating time, meaning that the diaphragms have to be renewed and interruptions in operation have to be accepted in such cases. Furthermore, the folding over of the diaphragms has an unfavorable effect on the pumping behavior of the diaphragm pump because changes in volume in the pumping spaces are unavoidable and the pumping flow pulsates as a result. 
     SUMMARY OF THE INVENTION 
     The task of the present invention is therefore to provide a diaphragm pump of the aforementioned type in such a way that the diaphragms are not subjected to alternating loads during operation, but rather retain their specified installation position at all times. Folding over of the diaphragms should therefore be prevented, with the effect that the stresses on them are low in spite of the high pumping pressures and accordingly the possibility of damage is almost excluded. The complexity of the structure required to achieve this should be kept low but nevertheless trouble-free operation should be provided over long periods with a straightforward design. Also, there should not be any changes in the volumes of the pumping spaces. 
     In accordance with the present invention, this is achieved in a diaphragm pump of the aforementioned type in that the two diaphragms are clamped with their curvature facing each other or with their curvature facing away from each other, in opposite directions in each case, with their external edge zones in a fixed location in the pump housing and with their internal edge zones on the adjustable piston rods and in that the two reaction spaces formed between the diaphragms and a cylinder accommodating the adjusting piston are filled with a hydraulic medium and are directly connected together by means of a hydraulic linkage. 
     In this case, the reaction spaces holding the hydraulic linkage assigned to the diaphragms and the connection lines connected to the reaction spaces are completely filled with a hydraulic medium and are configured so they are hermetically sealed, the hydraulic fluid forming the hydraulic linkage acted on by atmospheric pressure or a low pressure of up to 0.09 MPa, and the line connecting the two reaction spaces of the diaphragms is closed or sealed by a plug so it is fluid-tight. In this way, it is assured that the diaphragms are fixed in the specified position. 
     In order to seal the reaction spaces internally, it is advantageous to provide each with a bellows clamped at one end against the cylinder and at the other end against the piston rods. Each of the spaces enclosed by the bellows should always be connected to the immediately adjacent pressure space of the adjusting piston by means of one or more openings worked into the cylinder. 
     If a diaphragm pump is configured in accordance with the present invention, this guarantees that both diaphragms will always remain in approximately the specified installation position and will not fold over at the transition from a suction stroke to a pressure stroke. The sides of the diaphragms facing towards the cylinder are always in contact with the hydraulic linkage and this linkage does not allow the diaphragms to lift off, so therefore they are only exposed to tensile stress during adjustment movements and are therefore not subjected to alternating loads. The service life of the diaphragms can therefore be increased significantly without the need to design or configure them in any special way. 
     The structural complexity needed to reduce the susceptibility to malfunctions of diaphragm pumps of this kind due to diaphragm damage is small because it is merely necessary to select a certain convex or concave installation position for the diaphragms in relation to the cylinder and, in addition, they are rigidly connected together to a certain extent via the hydraulic linkage. The provided hydraulic linkage against which the diaphragms make contact over a wide area is particularly well suited to this purpose without the need for a mechanical linkage. The hydraulic linkage follows the corresponding adjustment movements of the diaphragms because the reaction spaces are connected together, meaning that the diaphragms cannot fold over and are only subjected to minor flexing movements. Diaphragms that are only subjected to tensile forces can therefore be designed to allow greater elastic deformation. 
     A further advantage is that no spatial expansions occur in the pumping spaces of the diaphragm pump following a change in direction, i.e. after changing over from a suction stroke to a pressure stroke or vice versa, which would, amongst other effects, briefly interrupt the pumping flow. As a result, no pulsation effects can be detected in the pumping line, which means that the operating behavior of the diaphragm pump configured in accordance with the present invention is improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings show a preferred embodiment of a diaphragm pump configured in accordance with the present invention, the details of which are explained below. In the drawings, 
         FIG. 1  shows an axial section of the diaphragm pump with associated peripheral devices represented in a schematic view, 
         FIG. 2  shows a section of the diaphragm pump in accordance with  FIG. 1  in a magnified view, 
         FIG. 3  shows a section from  FIG. 2  with back-to-back curvature. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The diaphragm pump shown in  FIG. 1  and identified with  1  is used for pumping a liquid, for example a paint to be processed, out of a reservoir container  2  to a spray gun  5  and consists in principle of two diaphragms  19  and  20  arranged in a housing  11  being in a driven connection with an adjusting piston  22  upon which a pressurized medium can act alternately. A suction line  3  connects the diaphragm pump  1  to the reservoir container  2 , while a pressure line  4  connects the diaphragm pump  1  to the spray gun  5 . 
     In the embodiment illustrated, the adjusting piston  22  is arranged in a cylinder  21  installed between the two diaphragms  19  and  20  in a housing  11 . Pressurized medium is supplied alternately to the pressure spaces  25  and  26  of the adjusting piston  22  in order to actuate the diaphragms, the pressurized medium being taken from a pressure line  6 , and with a 4/2-way valve for inputting the pressurized medium into downstream pressure lines  8  or  9  that are connected to the pressure spaces  25  or  26 . 
     Each of the diaphragms  19  and  20  is clamped with their external edge zones between disks  37  and the cylinder  21 , with their inner edge zones, in contrast, held between disks  38  and  39  ( FIG. 2 ) that are connected to piston rods  23  or  24  projecting from the adjusting piston  22 . Clamping is performed in this case by a nut  40  screwed onto a threaded projection  24 ′ of the piston rods  23 ,  24  with the effect that the disks  38  and  39  are supported against the piston rods  23 ,  24  that are offset in the edge zone, as can be seen in particular in  FIG. 2 . 
     Each of the diaphragms  19  and  20  has a pressure space  13  or  14  assigned to it, into which the medium to be pumped flows through a duct  12  connected to the suction line  3  and formed into the housing  11 , with the flow also being via inlet valves  15  or  16 . The medium to be pumped passes through outlet valves  17  or  18  connected downstream of the pressure spaces  13  and  14  into a duct  12 ′ running as a mirror image to the duct  12  with duct  12 ′ connected to the pressure line  4 . 
     In the operating position of the diaphragm pump  1  that is illustrated, the medium to be processed is sucked into the into the pressure space  13  with the help of the diaphragm  19  driven by adjusting piston  22 , whereas the medium in pressure space  14  is forced out by the diaphragm  20 . The inlet valve  15  and the outlet valve  18  are open in this operating position but the inlet valve  16  and the outlet valve  17  are closed, with the effect that the medium can be sucked out of the reservoir container  2  via the suction line  3  and the duct  12  into the pressure space  13  and from the pressure space  14  via the duct  12 ′ and the pressure line  4  to the spray gun  5 . 
     A controlled changeover of a directional control valve  7  reverses the adjusting movement of the adjusting piston  22  and the diaphragms  19  and  20  that are firmly connected to it as soon as the pressurized medium from the pressure line  6  enters the pressure space  26  of the adjusting piston  22  via the pressure line  9 . This means the inlet valve  15  is opened and the outlet valve  17  is closed. At the same time, the inlet valve  17  is closed and the outlet valve  15  is opened with the effect that the medium in the pressure space  13  is forced out and additional medium is sucked into the pressure space  14 . As a result, pulsation-free pumping in the pressure line  4  is assured. 
     In the diaphragm pump, diaphragms  19  and  20  are clamped in such a way that their curvatures  41  or  41 ′ are facing one another ( FIG. 2 ) or facing away from one another ( FIG. 3 ). In addition, reaction spaces  27  and  28  formed between the diaphragms  19  and  20 , as well as the cylinder  21 , are connected together by a line  29  that is sealed by a plug  30  so it is fluid-tight and are completely filled with a fluid that forms a hydraulic linkage H. The surfaces of the diaphragms  19  and  20  that face one another are therefore in contact with the hydraulic linkage H and are fixed in place by this linkage, because atmospheric pressure or a slight low pressure of up to 0.09 MPa acts on the hydraulic linkage H. 
     This means the diaphragms  19  and  20  cannot fold over when the adjusting movements are reversed, rather the diaphragms  19  and  20  remain in the illustrated position shown by dashed lines in  FIGS. 2 and 3 . During the adjusting movements, diaphragms  19  and  20  are only subjected to tensile stress, meaning that they can be configured in an elastically deformable manner in their flexing area and nevertheless achieve a long service life. 
     To preclude the fluid in the reaction spaces  27  and  28  passing through the piston rods  23  and  24  through penetrations in the cylinder  21  over the operating time and entering the pressure chambers  25  and/or  26  and therefore allowing a void to form in the reaction spaces  27  and  28 , each of the reaction spaces  27  and  28  is firmly sealed by a bellows  31  or  32  in the area of the piston rods  23  and  24 . The bellows  31  and  32  are clamped against the piston rods  23  and  24  at one end, while their other ends are attached to the cylinder  21 . In addition, the spaces  33  or  34  enclosed by the bellows  31  and  32  are connected to the pressure spaces  25  and  26  via holes  35  or  36  worked into the cylinder  21 , with the effect that the pressure is equalized automatically. 
     In the embodiment shown in  FIG. 3 , the two diaphragms  19 ,  20  of the diaphragm pump  1  have their curvatures  41 ′ facing away from one another and are clamped in the external edge zone between the disks  37  and the cylinder  21  and in the internal edge zone between the disks  38  and  39 . The reaction spaces  27  and  28  are also completely filled with a hydraulic fluid and have a communicating connection between them, therefore folding over of the diaphragms  19  and  20  is also excluded. Instead, they are supported on the hydraulic linkage H. 
     There is no need to account for changes in volume of the pressure spaces  13  and  14  caused by folding over of the diaphragms  19  and/or  20  because the hydraulic linkage H fixes the diaphragms  19  and  20  in position, which means that the diaphragm pump  1  can be used for supplying the medium to be processed to the spray gun  5  without pulsations. Also, the diaphragms  19  and  20  are only subjected to tensile stress and therefore it is possible to guarantee that the diaphragm pump  1  will operate without malfunctions over a long period.