Abstract:
A piston pump for a high-pressure cleaning appliance is provided, including a plurality of pump chambers, into each of which one piston which is movable back and forth plunges, and which are each in flow connection via a suction valve with a suction inlet and via a pressure valve with a pressure outlet, the suction valve including a suction valve closing member which is sealingly positionable on a suction valve seat, and the pressure valve including a pressure valve closing member which is sealingly positionable on a pressure valve seat, the pressure valve seat and the suction valve seat being at different radial distances from a longitudinal pump axis. To increase piston pump mechanical stability without increasing material thickness, the pressure valve seat can be arranged, in relation to the longitudinal pump axis, offset from the suction valve seat in the circumferential direction of the piston pump.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of international application number PCT/EP2012/050869, filed on Jan. 20, 2012, which is incorporated herein by reference in its entirety and for all purposes. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to a piston pump for a high-pressure cleaning appliance, comprising a plurality of pump chambers, into each of which one piston which is movable back and forth plunges, and which are each in flow connection via a suction valve with a suction inlet and via a pressure valve with a pressure outlet, the suction valve comprising a suction valve closing member which is sealingly positionable on a suction valve seat, and the pressure valve comprising a pressure valve closing member which is sealingly positionable on a pressure valve seat, the pressure valve seat being arranged, in relation to a longitudinal pump axis, radially offset from the suction valve seat. 
         [0003]    Such a piston pump is known from WO 2008/086950 A1. By means of it, a liquid, in particular, water, can be pressurized and, for example, directed at a surface or an article in order to clean the surface or the article. The piston pump comprises a plurality of piston chambers into each of which one piston plunges. The piston is reciprocatingly driven. This has the consequence that the volume of the pump chamber changes periodically and, as a result, liquid can be drawn from a suction inlet via a suction valve into the pump chamber, pressurized in the pump chamber and then discharged via a pressure valve and a pressure outlet. A supply line, for example, can be connected to the suction inlet, and a pressure hose, for example, carrying at its free end a discharge member, for example, a spray nozzle or a spray lance, can be connected to the pressure outlet. 
         [0004]    While in operation, the piston pump is subjected to considerable mechanical stress as it must withstand liquid pressures of more than 100 bar. Therefore, the housing of the piston pump usually has a substantial material thickness. This applies, in particular, to the area between the suction valve seats and the pressure valve seats as the pump housing is particularly highly stressed in these areas. 
         [0005]    The object of the present invention is to develop a piston pump of the kind mentioned at the outset in such a way that it has an increased mechanical stability without increasing its material thickness. 
       SUMMARY OF THE INVENTION 
       [0006]    This object is accomplished, in accordance with the invention, in a piston pump of the generic kind in that the pressure valve seat is arranged, in relation to the longitudinal pump axis, offset from the suction valve seat in the circumferential direction of the piston pump. 
         [0007]    Associated with each pump chamber of the piston pump are a suction valve seat and a pressure valve seat. The center points of the suction valve seat and the pressure valve seat are usually positioned in a common section plane of the piston pump, with the section plane containing the longitudinal pump axis. In renunciation of such an arrangement, the pressure valve seat in the piston pump in accordance with the invention is arranged, in relation to the longitudinal pump axis, offset from the suction valve seat in the circumferential direction of the piston pump. It has been found that an increased mechanical stability is imparted to the piston pump by the offset arrangement of the pressure valve seat without the material thickness of the piston pump having to be increased for this purpose. Therefore, the liquid to be pumped can be put under a higher pressure with the material thickness remaining the same. 
         [0008]    It is expedient for the pressure valve seat to be arranged, in relation to the longitudinal pump axis, offset at an angle of 10° to 40° from the suction valve seat. In particular, an angle in the range of between 20° and 30°, for example, 25°, has proven advantageous for increasing the mechanical stability of the piston pump without increasing its material thickness. 
         [0009]    In relation to the longitudinal pump axis, the pressure valve seat is expediently arranged at the same level as the suction valve seat in the axial direction. 
         [0010]    The suction valve seat and the pressure valve seat are advantageously made of a plastic material. 
         [0011]    In an advantageous embodiment, the piston pump comprises three suction valve seats arranged so as to be uniformly distributed about the longitudinal pump axis and three pressure valve seats arranged so as to be uniformly distributed about the longitudinal pump axis. In such a configuration, the suction valve seats are arranged at an angular distance of 120° from one another, and the pressure valve seats are also at an angular distance of 120° from one another. Both the suction valve seats and the pressure valve seats, therefore, form the corner points of an imaginary equilateral triangle. Here the center point of the imaginary triangle of the suction valve seats coincides with the center point of the imaginary triangle of the pressure valve seats. However, the imaginary triangle of the pressure valve seats is arranged so as to be rotated about the longitudinal piston axis in relation to the imaginary triangle of the suction valve seats. The angle of rotation is expediently 10° to 40°, in particular, 20° to 30°, preferably 25°. 
         [0012]    In a particularly preferred configuration, the piston pump in accordance with the invention comprises a pump block and a pump head, the pump head comprising the suction inlet and the pressure outlet, and the pump block comprising the pump chambers and accommodating the suction valves and the pressure valves, and the pump head being fitted on a triangular rim of the pump block, the suction valves, in a plan view of the pump block, being arranged in the corner areas of the rim, and the pressure valves, in a plan view of the pump block, being surrounded by a cylindrical inside wall within the rim. Such a configuration imparts a particularly high mechanical stability to the piston pump without the material thickness of the piston pump having to be substantially increased for this purpose. 
         [0013]    The suction valves each comprise a suction valve passage which is closable by the suction valve closing member, and a suction valve closing spring which acts upon the suction valve closing member with a spring force in the direction of the suction valve passage. Here it is advantageous for the suction valve closing spring to be positioned at an axial distance from the suction valve passage. In such a configuration, the liquid flowing into the pump chamber can flow past the sides of the suction valve closing spring without it necessarily having the liquid flow through it. This reduces flow losses in the area of the suction valve closing spring as the flow loss exerted by the suction valve closing spring can be kept low. 
         [0014]    The suction valve closing spring is preferably arranged in a suction valve chamber which is in flow connection with a pump chamber via the suction valve passage, a retaining arm, on which the suction valve closing spring is supported, projecting into the suction valve chamber at a distance from the suction valve passage. In known piston pumps, the suction valve closing spring is directly supported on the suction valve passage, and the liquid has to flow through the suction valve closing spring in order to get to the suction valve passage. In a further development of the invention this is not necessary as the suction valve closing spring is supported with its end that faces the suction valve passage on a retaining arm which projects into the suction valve chamber at a distance from the suction valve passage. 
         [0015]    Expediently, the retaining arm is radially aligned in relation to the longitudinal piston axis. 
         [0016]    In an advantageous embodiment of the invention, the retaining arm only penetrates the suction valve chamber partially, i.e., the retaining arm stands away from the wall of the suction valve chamber without reaching the diametrically opposed wall area of the suction valve chamber with its free end. 
         [0017]    It may, for example, be provided that the retaining arm only projects to about the middle of the suction valve chamber. 
         [0018]    It is expedient for the retaining arm to form a guide for the suction valve closing member. It is thereby possible in a constructionally simple way to prevent the suction valve closing member from tilting during a lifting movement. 
         [0019]    The retaining arm expediently comprises a through-opening through which the suction valve closing member passes. 
         [0020]    The suction valve closing member may, for example, be of mushroom-shaped configuration and comprise a valve disk having a valve shaft connected thereto, the valve shaft passing through the through-opening of the retaining arm and being guided by the retaining arm. 
         [0021]    It is particularly expedient for the suction valve closing spring to be clamped on the side of the retaining arm that faces away from the suction valve passage between the retaining arm and the suction valve closing member. In such a construction, the suction valve closing spring is supported, on the one hand, on the side of the retaining arm that faces away from the suction valve passage and, on the other hand, on the suction valve closing member. The suction valve closing member may have a spring holder for this purpose. The spring holder is expediently press-fitted to a shaft of the suction valve closing member. 
         [0022]    The following description of a preferred embodiment of the invention serves for further explanation in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  shows a schematic longitudinal sectional view of an advantageous embodiment of a piston pump in accordance with the invention; 
           [0024]      FIG. 2  shows a plan view of a pump block of the piston pump from  FIG. 1 ; 
           [0025]      FIG. 3  shows a sectional view of the pump block along line  3 - 3  in  FIG. 2 ; 
           [0026]      FIG. 4  shows a sectional view of a suction valve along line  4 - 4  in  FIG. 3 ; and 
           [0027]      FIG. 5  shows a sectional view of the pump block along line  5 - 5  in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]    An advantageous embodiment of a piston pump in accordance with the invention, generally denoted by reference numeral  10 , is shown schematically in the drawings. It comprises a pump head  12  with a suction inlet  14  and a pressure outlet  16 . A supply line, via which liquid to be pressurized can be supplied to the piston pump  10 , can be connected to the suction inlet  14 . A discharge line, via which the liquid pressurized by the piston pump  10  can be directed at an article or a surface in order to clean the article or the surface, can be connected to the pressure outlet  16 . The discharge line can carry at its free end a discharge member, for example, a spray lance or a spray nozzle. 
         [0029]    The pump head is fitted on a pump block which comprises a total of three identically constructed pump chambers, into each of which one piston plunges.  FIGS. 1 ,  3 ,  4 , and  5  show one of the piston chambers  20  into which a piston  22  extends. A suction valve  24  and a pressure valve  26  are associated with each pump chamber  20 . Via the suction valve  24  liquid can be drawn from the suction inlet  14  into the pump chamber  20 , and via the pressure valve  26  the liquid pressurized in the pump chamber  20  can escape from the pump chamber  20 . 
         [0030]    The suction valves  24  each comprise a suction valve closing member  28  which is sealingly positionable on a suction valve seat  30 . The suction valve seat  30  surrounds a suction valve passage  32 . Via the suction valve passage  32 , the pump chamber  20  is in flow connection with a suction valve chamber  34  formed in the pump block  18  on the side of the pump block  18  that faces the pump head  12 . Projecting into the suction valve chamber  34  at an axial distance from the suction valve passage  32  is a retaining arm  36 , which extends to about the middle of the suction valve chamber  34  and has a through-opening  38  in alignment with the suction valve passage  32 . 
         [0031]    The suction valve closing member  28  is of mushroom-shaped configuration. It comprises a valve disc  40  which projects into the pump chamber  20  and is integrally adjoined by a valve shaft  42  which passes through the suction valve passage  32  and extends into the suction valve chamber  34 . The valve shaft  42  passes through the through-opening  38  of the retaining arm  36  and carries at its free end a spring holder  44  which is pressed onto the valve shaft  42 . A suction valve closing spring  46  is clamped between the spring holder  44  and the retaining arm  36 . The suction valve closing spring  46  is configured as a helical spring and surrounds the valve shaft  42  in the area between the retaining arm  36  and the spring holder  44 . The valve disc  40  of the suction valve closing member  28  is pressed against the suction valve seat  30  under the action of the suction valve closing spring  46 . 
         [0032]    The pressure valve  26  has a pressure valve closing member  48  which is pressed by a pressure valve closing spring  50  against a pressure valve seat  52 . The pressure valve  26  is arranged in a pressure valve chamber  54 . 
         [0033]    A suction valve chamber  34  and a pressure valve chamber  54  are associated with each pump chamber  20  of the piston pump  10 , and all of the pressure valve chambers  54  of the piston pump  10  merge into a common central chamber  56  which is formed by the pump block  18  and the pump head  12 . Inserted in the central chamber  56  is a central insert part  58  which is surrounded by sealing rings and has a central passage  60  which is closable by a central closing member  62 . The closing member  62  forms in combination with the central insert part a central check valve to which a pressure line  66 , aligned coaxially with a longitudinal pump axis  64 , is connected, via which the central chamber  56  is in flow connection with the pressure outlet  16 . 
         [0034]    The pump head  12  is fitted in the axial direction on the pump block  18  with the interposition of an elastically deformable element. In the illustrated embodiment, the elastically deformable element is configured as a sealing ring  68 . The sealing ring  68  surrounds a collar-shaped rim  70  of the pump block  18 . This is evident, in particular, from  FIG. 2 . The rim  70  has the shape of an equilateral triangle with rounded corner areas. With reference to a plan view of the pump block  18 , the suction valves  24  are each arranged in a corner area of the rim  70 . This is evident, in particular, from  FIG. 2 . The rim  70  surrounds a cylindrical inside wall  72  which in the area of the pump block  18  defines the central chamber  56 . In a plan view of the pump block  18 , the pressure valves  26  are arranged within the inside wall  72 . This is also evident from  FIG. 2 . 
         [0035]    As mentioned above, a suction valve  24  with a suction valve seat  30  and a pressure valve  26  with a pressure valve seat  52  are associated with each pump chamber  20 . As is evident, in particular, from  FIG. 2 , the respective pressure valve seat  52  is arranged, in relation to the longitudinal pump axis  64 , offset from the suction valve seat  30  in both the radial direction and the circumferential direction of the piston pump  10 . The radial distance of the pressure valve seat  52  from the longitudinal pump axis  64  is less than the radial distance which the suction valve seat  30  assumes from the longitudinal pump axis  64 , and in the circumferential direction of the piston pump  10 , the pressure valve seat in the illustrated embodiment is offset through an angle α of about 25° from the suction valve seat  30 . 
         [0036]    The piston pump  10  has a total of three suction valve seats  30  and three pressure valve seats  52 , with the suction valve seats  30  as well as the pressure valve seats  52  defining an imaginary equilateral triangle. The center points of the imaginary triangles are arranged on the longitudinal pump axis  64 , but the imaginary triangle of the pressure valve seats  52  is rotated about the longitudinal pump axis  64  through the angle α of 25° to the imaginary triangle of the suction valve seats  30 . 
         [0037]    Adjoining the pump block  18  in the axial direction, in relation to the longitudinal pump axis  64 , is a support shield  74  made of a plastic material with three cylindrical support sleeves  78 , each in alignment with a longitudinal piston axis  76 . The support sleeves  78  are each welded to an annular wall  80  of the pump block  18 , which extends into the respective support sleeve  78  and surrounds a sealing ring  82  which lies by way of a sealing lip sealingly against the piston  22 . 
         [0038]    The support shield  74  is supported in the axial direction on a guide shield  84 . The guide shield  84  has three cylindrical guide sleeves. One guide sleeve  86  is recognizable in  FIG. 1 . The guide sleeves  86  form guide elements for the pistons  22  and are aligned coaxially with the respective longitudinal piston axis  76 . The guide shield  84  forms a cover of convex construction, which is seated on a swash plate housing  88  in which a swash plate  90  is mounted for rotation about the longitudinal pump axis  64 . Each piston  22  is pressed by a resetting spring  92  against the swash plate  90 . This makes it possible by way of a rotational movement of the swash plate  90  to move the pistons  22  back and forth in the axial direction in relation to the longitudinal pump axis  64 , so that the volumes of the pump chambers  20  are periodically changed. The swash plate  90  is driven in the usual way by means of a drive motor, known per se and, therefore, not shown in the drawings, for example, an electric motor, which is coupled by way of a gearing  94 , shown only schematically in  FIG. 1 , with the swash plate  90 . 
         [0039]    When the piston  22  moves backwards in the direction facing away from the pump head  12 , liquid is drawn in from the suction inlet  14  via the suction valve chamber  34  and the suction valve passage  32  into the pump chamber  20 , and the suction valve closing member  28  lifts off from the suction valve seat  30  counter to the action of the suction valve closing spring  46  and opens the suction valve passage  32 . The liquid can thereby flow within the suction valve chamber  34  past the sides of the suction valve closing spring  46  and, therefore, is only subject to low flow losses in the suction valve chamber  34 . 
         [0040]    When the piston  22  then moves forwards in the direction facing the pump head  12 , the suction valve closing member  28  transfers to the its closed position in which it lies sealingly against the suction valve seat  30 , as shown in  FIGS. 3 ,  4  and  5 . The liquid is thereupon pressurized in the pump chamber  20  until the pressure valve closing member  48  lifts off from the pressure valve seat  52  counter to the closing force of the pressure valve closing spring  50  and thus opens the flow connection between the pump chamber  20  and the central chamber  56 . The pressure valve closing spring  50  is supported on the central insert part  58 , the passage  60  of which is opened by the central closing member  62  so that the pressurized liquid can flow via the pressure line  66  to the pressure outlet  16 . 
         [0041]    The liquid can be pressurized in the pump chamber  20  to a pressure of more than  100  bar. In spite of a relatively low material thickness, the pump block  18  made of a plastic material can withstand the high pressures of the liquid. To this end, the pressure valve seats  52  are arranged, as already explained above, offset from the suction valve seats  30  in the radial direction and in the circumferential direction in relation to the longitudinal pump axis  64 . The piston pump  10  is, therefore, distinguished by high mechanical stability and relatively low material thickness.