Patent Publication Number: US-2021164584-A1

Title: Bistable anti-stall valve system

Description:
FIELD OF THE INVENTION 
     The present invention applies to the technical field of valve systems, and in particular it regards a bistable anti-stall valve system that can be driven mechanically or pneumatically. 
     STATE OF THE ART 
     It is known that controlling devices characterised by alternating linear motions, for example pumps, oscillators, compressed air reciprocating motors, pistons, pneumatic hammers, vibrators, boosters, requires bistable valve systems suitable to alternatingly and selectively convey the working fluid into the two half-chambers of such devices. 
     Two main systems for driving such valve systems, pneumatic or mechanical, both acting directly on the movable parts of the valves are known. 
     A known disadvantage of such types of valve systems lies in the so-called stall or “dead centre” problem, i.e. an operative stall situation in which the valve system blocks, with ensuing stall of the device to which it is connected and thus requires manual intervention. 
     Permanent magnets arranged along the sliding axis of the movable sealing members, as disclosed in the U.S. Pat. No. 5,222,876, were used to overcome such drawback. 
     However, such known problem revealed to be inefficient towards avoiding the aforementioned problem related to stalling or “dead centre”. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to at least partly overcoming the drawbacks illustrated above, by providing a valve system that is highly efficient and functional. 
     A further object of the invention is to provide a particularly effective valve system, that allows overcoming the drawback related to stalling or so-called “dead centre”. 
     A further object of the invention is to provide valve system has a minimum number of components. 
     A further object of the invention is to provide a valve system that is small in size. 
     A further object of the invention is also to provide a valve system that is easy to manufacture and maintain. 
     These and other objects that will be more apparent hereinafter, are attained by a valve system according to what is described, illustrated and/or claimed herein. 
     Advantageous embodiments of the invention are defined in the dependent claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further characteristics and advantages of the invention will be more apparent in light of the detailed description of a preferred but non-exclusive embodiment of valve system  1 , illustrated by way of non-limiting example with reference to the attached drawings, wherein: 
         FIG. 1A  is an axonometric view of a first embodiment of the valve system  1 ; 
         FIGS. 1B, 1C, 1D  are respectively top, lateral and front views of the embodiment of the valve system  1 ; 
         FIG. 2A  is a sectional view along a section plane π 2 -π 2  taken in  FIG. 1B  when the slider  21  is in the first stable working position; 
         FIG. 2B  is a sectional view along a section plane π-π taken in  FIG. 2A  when the slider  21  is in the first or second stable working position; 
         FIG. 2C  is an enlarged detail of  FIG. 2B ; 
         FIG. 2D  is a sectional view along a section plane π 2 -π 2  taken in  FIG. 1B  when the slider  21  is in the second stable working position; 
         FIG. 2E  is an enlarged detail of  FIG. 2D ; 
         FIG. 3A  is a sectional view along a section plane π 2 -π 2   taken in  FIG. 1B  when the slider  21  is in the position defining the stall or the so-called ‘dead centre’; 
         FIG. 3B  is a sectional view along a section plane π-π taken in  FIG. 2A  when the slider  21  is in the position defining the stall or the so-called ‘dead centre’; 
         FIG. 3C  is an enlarged detail of  FIG. 3B ; 
         FIG. 4  is a sectional view along a section plane II-II taken in  FIG. 3B ; 
         FIG. 5  is a sectional view along a section plane III-III taken in  FIG. 1C , in which the pins  37 ,  37 ′ were removed for the sake of simplicity; 
         FIG. 6  is an axial sectional view of a first embodiment of a double membrane pump P 1  which comprises a second embodiment of the valve system  1 ; 
         FIGS. 7A and 7B  are enlarged views of some details of the embodiment of the valve system  1  of  FIG. 6  in which the slider element  21 ′ is respectively in the first and in the second stable working position; 
         FIGS. 8A and 8B  are axonometric views of some details of the slider element  21 ′—actuator element  36  assembly of the embodiment of the valve system  1  of  FIG. 6  in which the plug  21 ′ is respectively in the first and in the second working position, with in  FIGS. 9A and 9B  respective axial sectional views; 
         FIGS. 10A and 10B  are schematic views of the slider element  21 ′—actuator element  36  assembly of the first embodiment of the valve system  1  of  FIG. 6  respectively in the first and in the second stable working position; 
         FIG. 11  is a schematic view of the slider element  21 ′—actuator element  36  assembly of the embodiment of the valve system  1  of  FIG. 6  in the stall or so-called “dead centre” position; 
         FIG. 12  is an axonometric view of the slider element  21 ′ of the embodiment of the valve system  1  of  FIG. 6 ; 
         FIG. 13  is an axonometric view of the actuator element  36  of the embodiment of the valve system  1  of  FIG. 6 ; 
         FIG. 14  is an axial sectional view of a further embodiment of a double membrane pump P 2  which includes a third embodiment of the valve system  1 ; 
         FIGS. 15A and 15B  are enlarged views of some details of the embodiment of the valve system  1  of  FIG. 14  in which the slider element  21 ′ is respectively in the first and in the second stable working position; 
         FIG. 16  is an axonometric view of some details of the embodiment of the valve system  1  of  FIG. 14 ; 
         FIG. 17  is an axonometric view of some details of the fixed air distributor  2 ′ of the embodiment of the valve system  1  of  FIG. 14 ; 
         FIG. 18  is an axonometric view of the slider element  21 ′ of the embodiment of the valve system  1  of  FIG. 14 ; 
         FIG. 19  is an axonometric view of the actuator element  36  of the embodiment of the valve system  1  of  FIG. 14 ; 
         FIGS. 20A and 20B  are axial sectional views of an embodiment of a double piston pump P 3  which includes a further embodiment of the valve system  1 , in which the slider element  21 ′ is respectively in the first and in the second stable working position. 
     
    
    
     DETAILED DESCRIPTION OF SOME PREFERRED EMBODIMENTS 
     With reference to the aforementioned figures, herein described are some possible embodiments of the valve system  1 . 
     More in particular,  FIGS. 1A to 5  illustrate a first embodiment of the valve system  1 ,  FIGS. 6 to 13  illustrate a second embodiment of the valve system  1  implemented in a double membrane pump P 1 ,  FIGS. 14 to 19  illustrate a third embodiment of the valve system  1  illustrated in a double membrane pump P 2  and  FIGS. 20A and 20B  illustrate a fourth embodiment of the valve system  1  illustrated in a double piston pump P 3 . 
     The present invention has various parts that are equal or however equal to each other. Unless otherwise specified, such parts that are equal or similar will be indicated with a single reference number, it being intended that the indicated characteristics are common to all equal or similar parts. 
     Generally, the valve system  1  may be made using nonmagnetic materials, except for some components indicated hereinafter. 
     The valve system  1  may essentially comprise a valve body  10  with a working chamber  33 , in which a plug  30  and an actuator element  36 , acting on the latter, may be housed. 
     More in particular, the plug  30  and the actuator element  36  may be slidably inserted into the working chamber  33  to slide along respective longitudinal axes X and X′, mutually spaces and substantially parallel with respect to each other. 
     To this end, the working chamber  33  may provide for special first and second guide means for guiding the plug  30  and the actuator element  36  along respective longitudinal axes X and X′. 
     For example, in the embodiment of the valve system  1  of  FIGS. 1A-5 , the same geometry of the working chamber  33  may guide the aforementioned sliding, while in the embodiments of the valve system  1  of  FIGS. 6-20B  suitable guide bars or pins may be provided for. 
     In the embodiments illustrated herein, such valve system  1  may also include pneumatic driving means  50 , which may be connected with a compressor in a per se known manner. It is also clear that in a per se known manner the driving means may be of the mechanical type instead of the pneumatic type. 
     Generally, the driving means  50  may act on the actuator element  36 , which may in turn act on the plug  30  to cause the displacement of the latter between a first stable working position, illustrated for example in  FIGS. 2A or 7A , and a second stable working position, illustrated for example in  FIGS. 2D or 7B . 
     As better outlined hereinafter, the mode of interaction between the driving means  50 , the actuator element  36  and the plug  30  differs depending on the embodiments of the valve system  1 . 
     More in particular, in the illustrated embodiment of the valve system  1  in  FIGS. 1A-5  the driving means  50  act directly on the actuator element  36 , which is in turn coupled with the plug  30  so that the movements of the latter along the axes X′ and X occur with the same directions. 
     On the other hand, in the illustrated embodiments of the valve system  1  in  FIGS. 6-20B  the driving means  50  act indirectly on the actuator element  36  by means pf suitable pins and the actuator element  36  in turn interacts with the plug  30  by means of permanent magnets M 1 , M 1 ′; M 2 , M 2 ′ so that the movements of the actuator element  36  and of the plug  30  along the axes X′ and X occur with different directions. 
     Suitably, the valve body  10  may comprise an inlet I for the working fluid and a first and a second outlet  51 ,  52  for the working fluid. The plug  30  will alternatingly and selectively place the inlet I in fluid communication with the first outlet  51  or with the second outlet  52 . 
     More in particular, the plug  30  may selectively and alternatingly shut the first outlet  51  or the second outlet  52  to allow the through-flow of the working fluid respectively through the second outlet  52  or the first outlet  51 . 
     Advantageously, in the embodiment of the valve system  1  illustrated in  FIGS. 1A-5  the working fluid may be compressed air which is diverted towards the first or the second outlet  51 ,  52 , while the pneumatic driving fluid coming from a different supply line. 
     On the other hand, in the embodiments of the valve system  1  illustrated in  FIGS. 6-20B  the working fluid may still be compressed air and it may coincide with the driving fluid, while the pumped fluid may be a liquid. 
     In order to overcome the stall or “dead centre” situation, there may be provided for suitable anti-stall means M 1 , M 1 ′; M 2 , M 2 ′ acting on the plug  30  so as to avoid the operative block of the latter in the intermediate position between the first and the second stable working position, said intermediate position being for example illustrated in  FIGS. 3A or 11 . 
     To this end, the anti-stall means may comprise a pair of first permanent magnets M 1 , M 1 ′ and a pair of second permanent magnets M 2 , M 2 ′, interacting with each other. 
     It is clear that even though hereinafter reference will be made to pairs of permanent magnets the present invention may include at least one first permanent magnet and at least one second permanent magnet without departing from the scope of protection of the attached claims. 
     Generally, the first permanent magnets M 1 , M 1 ′ may be operatively connected with the plug  30  to slide integrally therewith along the axis X between the first and the second stable working position, while the second permanent magnets M 2 , M 2 ′ may be arranged in the working chamber  33  and mutually face the first permanent magnets M 1 , M 1 ′. 
     More in particular, as better outlined hereinafter, in the embodiment of the valve system  1  illustrated in  FIGS. 1A-5  the second permanent magnets M 2 , M 2 ′ may be fixed in the working chamber  33 , while in the embodiments of the valve system  1  illustrated in  FIGS. 6-20B  the permanent magnets M 2 , M 2 ′ may be coupled to the slider element  36  to slide integrally therewith along the axis X′. 
     The first and second permanent magnets M 1 , M 1 ′; M 2 , M 2 ′ may have opposite polarities. In other words, the mutually faced poles may have the same polarity. 
     Thus, the first and second permanent magnets M 1 , M 1 ′; M 2 , M 2 ′ may generate forces F 1 , F 2  that are mutually repulsive with respect to each other, so that should the plug  30  stall, it is pushed towards one or the other of the stable working positions. 
     With specific reference to the embodiment of the valve system  1  illustrated in  FIGS. 1A-5 , the valve body  10  may consist of a cover  11  and a base  12 , couplable to each other for example by means of screws V ( FIG. 1A ). 
     The cover  11  may comprise the inlet I for the working fluid F and at least one first and one second inlet  50 ′,  50 ″ for the pneumatic driving pulses. 
     The base  12  may include openings  54 ,  55  for alternatingly and selectively placing inlet I and the outlets  51 ,  52  positioned in the base  12  in fluid communication. 
     The outlet  53  connected with an external environment and the relative opening  56  (discharge) may be provided. 
     In a per se known manner, the outlets  51 ,  52  may be operatively connected with a device acting by means of alternating linear motions, for example pumps, oscillators, compressed air reciprocating motors, pistons, pneumatic hammers, vibrators, boosters. 
     Suitably, the outlets  51 ,  52  may alternatingly and selectively be delivery and discharge channels in cooperation with the outlet  53 , as will be described in detail hereinafter. 
     More, when the working fluid flows out from the outlet  51  the plug places the outlets  53  and  52  in fluid communication to allow the discharge of the used working fluid flowing in through the outlet  52 , and vice versa when the working fluid flows out from the outlet  52  the plug places the outlets  53  and  51  in fluid communication to allow the discharge of the used working fluid flowing in through the outlet  51 . 
     Preferably, the working chamber  33  may define the axis X′ and a shuttle, which may define the actuator element  36 , may be sealingly slidably inserted thereinto. More in particular, the latter may slide along the axis X′ guided by the internal surface  330  of the working chamber  33 , which will define guide means for the actuator element  36 . 
     The latter may divide the working chamber  33  into three working half-chambers  33 ′″,  33 ′,  33 ″ fluidically independent from each other. 
     The working chambers  33 ′,  33 ″ may be closed at the ends by sealing caps  18 ,  18 ′, which may include abutment surfaces  14 ,  14 ′ defining the end-stop of the actuator element  36 . 
     Suitably, the shuttle defining the actuator element  36  may include—at the ends thereof—two pins  37 ,  37 ′, which are not represented in  FIG. 5  for the sake of simplicity. 
     The shuttle defining the actuator element  36  may have end surfaces  31 ,  31 ′ suitable to come to mutual contact respectively with the abutment surfaces  14 ,  14 ′ during the alternating motion thereof. 
     The shuttle defining the actuator element  36  may also have a through hole  34  in a substantially central position into which a pin  40  arranged along an axis Z perpendicular to the axis X′ may be slidably inserted in a removable fashion. This will simplify the assembly and maintenance of the valve system  1 . 
     Furthermore, the axis Z may be susceptible to pass through the centre C of the shuttle defining the actuator element  36 . The same axis Z and the axis X may define a plane π. 
     Advantageously, the pin  40  may slide integrally with the shuttle defining the actuator element  36  along the same axis X′. 
     Suitably, the pin  40  may include the first permanent magnets M 1 , M 1 ′ at the ends  41 ,  41 ′ thereof. 
     Advantageously, the pin  40  may be made of metal, so that the magnets M 1 , M 1 ′ are naturally coupled therewith without glue or other coupling means. 
     As mentioned above, the second permanent magnets M 2 , M 2 ′, mutually arranged adjacent to the first permanent magnets M 1 , M 1 ′, may be arranged in the working chamber  33 . Preferably, such second permanent magnets M 2 , M 2 ′ may be arranged along an axis Z′ lying on the plane π, parallel to the axis Z and passing through the centre of the working chamber  33 . 
     Advantageously, the magnets M 1 , M 1 ′, M 2 , M 2 ′ may be natural or artificial magnets, and not electromagnetic. 
     Preferably, the cover  11  may have a peripheral wall  15  with a pair of through holes  15 ′,  15 ″. 
     Furthermore, a pair of closing caps  13  each having a respective end  13 ′,  13 ″ having one of the second permanent magnets M 2 , M 2 ′ may be provided for. 
     Advantageously, the closing caps  13  may be suitable for the removable screwing into the through holes  15 ′,  15 ″ along the axis Z′ so that the second permanent magnets M 2 , M 2 ′ face the shuttle  36 . 
     This simplifies the assembly of the valve system  1 . 
     Advantageously, the caps  13  may be made of metal, so that the second magnets M 2 , M 2 ′ are naturally coupled therewith without glue or other coupling means. 
     Suitably, the magnets of each pair of permanent magnets M 1 , M 1 ′, M 2 , M 2 ′ may be mutually symmetrical with respect to a plane π 2  substantially perpendicular to the plane π 1 . The plane π 2  may be a symmetry plane for the cover  11  so that the axis X′ lies thereon. 
     Furthermore, the plug  30  may advantageously be defined by a slider  21  slidable along a sliding plane π 1 , on which the axis X may lie. 
     The sliding plane π 1  may comprise openings  54 ′,  55 ′ placed in fluid communication with the openings  54 ,  55  and with the outlets  51 ,  52 . 
     It is clear that even though hereinafter reference will exclusively be made to the slider  21 , the plug  30  may also comprise or consist of the latter without departing from the scope of protection of the attached claims. 
     The slider  21  may have a circular or rectangular shape defined by an upper surface  23  with a central portion comprising a male connection element  23 ′ and a lower surface  25  with a portion  25 ′ at mutual contact with the plane π 1  so as to define a circular or rectangular working chamber  38 . 
     The sliding plane π 1  and the portion  25 ′ of the slider  21  will define guide means for the sliding of the latter. 
     Advantageously, the lower surface  25  of the slider  21  and the chamber  38  may face the openings  54 ,  55 ,  56 . 
     Preferably, the shuttle defining the actuator element  36  may have a seat or a female connection element  35 , for example circular or slot-shaped, into which the male connection element  23 ′ may be inserted. 
     As particularly illustrated in  FIGS. 2A and 5 , the connection element  23 ′ of the slider  21  will take a determined position from the position of the slot  35  obtained in the shuttle defining the actuator element  36 . 
     Suitably, the slider  21  may be susceptible to move in the working chamber  33  along the plane π 1  on which the axis X lies substantially parallel to the plane π on which the axis X′ lies and spaced by the anti-stall means M 1 , M 1 ′, M 2 , M 2 ′. 
     Suitably, the cover  11  may comprise a lower wall  11 ′ susceptible to face the base  12 . p In addition, the lower wall  11 ′ may comprise a through hole  16 , into which a closing element  17  may be inserted to remain interposed between the base  12  and the cover  11 . 
     The closing element  17  may comprise a lapping surface defining the sliding plane π 1  and the openings  54 ,  55 ,  56  for placing the three outlets  51 ,  52 ,  53  and the working chamber  33  in fluid communication. 
     Operatively, as illustrated in  FIGS. 2A-2E , when the shuttle defining the actuator element  36  for example receives a driving pulse from the inlet  50 ″, the end surface  31  thereof will be mutually at contact with the abutment surface  14  of the sealing cap  18 . The working fluid F, which flows in through the inlet I, will fill the working chamber  33  and it will be ejected through the opening  55  and the outlet  52 . Thus, the inlet I of the valve body  10  will be in fluid communication with the second outlet  52  so as to allow the outflow of the working fluid F. 
     Simultaneously, the discharge of the used working fluid F coming from the user device sequentially through the outlet  51 , the opening  54 , the chamber  38 , the opening  56  and the outlet  53  will be allowed. 
     Vice versa, the operation will be mirror-like when the shuttle defining the actuator element  36  will receive a driving pulse from the inlet  50 ′ so that the end surface  31 ′ of the shuttle defining the actuator element  36  is at mutual contact with the abutment surface  14 ′ of the sealing cap  18 ′. 
     The working fluid F will fill the working chamber  33  and it will be ejected through the opening  54  and the outlet  51 . Thus, the inlet I of the valve body  10  will be in fluid communication with the first outlet  51  thereof to allow the outflow of the working fluid F. 
     Simultaneously, the discharge of the working fluid F coming from the user device sequentially through the outlet  52 , the opening  55 , the chamber  38 , the opening  56  and the outlet  53  will be allowed. 
     Suitably, the first pair of magnets M 1 , M 1 ′ will generate a pair of forces F 1  of equal module and direction opposite to the pair F 2  generated by the second pair of magnets M 2 , M 2 ′. 
     Advantageously, the forces F 1  and F 2  will be generated on the plane π parallel to the sliding plane π 1  of the slider  21  or other known valve systems. 
     This will allow providing different known types of valve systems, for example of the slider type, as described herein, of the sleeve type or of the plug type, in which the plane π and π 1  can be kept distinct. Thus, there will be obtained a magnetic unbalancing system suitable to overcome the so-called ‘dead centre’ situation defined by an operative block position. 
     Given that the forces F 1  and F 2  are mutually repulsive with respect to each other, the latter will keep the translation of the shuttle defining the actuator element  36  quick and controlled. 
     The valve system  1  illustrated in  FIGS. 1A to 5  will have the same operation choosing an actuation of the mechanical type operated by external forces alternatingly acting along the axis X, for example on the pins  37 ,  37 ′. 
     In such case, the driving inlets  50 ′,  50 ″ will serve as discharge for the air volume respectively and alternatingly accumulated in the chambers  33 ″,  33 ′ by the alternating motion of the shuttle defining the actuator element  36 . 
     With reference to the embodiments illustrated in  FIGS. 6-20B , illustrated are pumps P 1 , P 2  of the double membrane type, in particular in  FIGS. 6 to 19 , or a pump P 3  of the double piston type, in particular in  FIGS. 20A and 20B . 
     It is clear that the operation of the pumps P 1 , P 2  and P 3  is substantially identical, both as concerns the double membrane pump and the double piston pump. Thus, in the description hereinafter, reference will be made to the membrane pump P 1  illustrated in  FIGS. 6 to 13 , it being deemed that the description also applies to the membrane pump P 2  illustrated in  FIGS. 15-19  and the double piston pump P 3  illustrated in  FIGS. 20A-20B . 
     The pump P 1  may include a support structure  2  with a first half-chamber  200  which includes a first membrane  210 , and a second half-chamber  300  which includes a second membrane  310 . 
     In a per se known manner, the support structure  2  of the pump P 1  may also comprise a third and a fourth half-chamber  400 ,  500  suitable to house the pumped fluid, in a per se known manner. Furthermore, such third and fourth half-chamber  400 ,  500  will be connected to an intake circuit S and a delivery circuit D. 
     The first and the second membrane  210 ,  310  may be mechanically connected to each other. For example, in the embodiment shown in  FIG. 1 a   , the two membranes  210 ,  310  may be connected through an extended rod  600 . 
     In the embodiments of the valve system  1  illustrated in  FIGS. 6 to 20B , the valve body  10  may be interposed between the half-chambers  200 ,  300  to alternatingly and selectively convey to the latter the working fluid coming from a compressor for example. 
     To this end, a fixed air distributor  2 ′ which will fluidically connect the valve body  10  and the half-chambers  200 ,  300  through selective interaction with the plug  30  may be provided for. 
     The valve body  10  may include the working chamber  33 , which may in turn include the plug  30  and the actuator element  36 . 
     More in particular, the plug  30  may comprise a first slider element  21 ′ with sleeve slidable along the fixed air distributor  2 ′, which will define the axis X between the first and the second stable working position, illustrated for example in  FIGS. 7A and 7B . 
     Thus, the slider element  21 ′ with sleeve will alternatingly and selectively place the inlet I of the working chamber  33  in communication with the first or the second half-chamber  200 ,  300  through the outlets  51 ,  52 . 
     Thus, when the half-chamber will increase the volume due to the working fluid flowing thereinto, the volume of the other half-chamber will reduce, emptying. The fluid discharged by the emptying half-chamber will end up in a fifth half-chamber  5  connected with the external environment and interposed between the first and the second half-chamber  200 ,  300 . 
     In order to allow such operation, the fixed air distributor  2 ′ may include a first duct  3  for placing the working chamber  10  and the first half-chamber  200  in fluid communication and a second duct  4  for placing the working chamber  10  and the second half-chamber  300  in fluid communication. 
     The actuator element  36  may comprise a second slider element  83  with respective guide bars or pins  81 ,  81 ′, which may define the axis X′. Simultaneously, the guide bars or pins  81 ,  81 ′ may selectively come into contact with the respective first or second membrane  210 ,  310  to define pushing means, as illustrated hereinafter. 
     Given that the two membranes  210 ,  310  are connected, as shown in  FIG. 6 , the displacement of the first membrane  210 , due to the increase of the volume thereof, corresponds to the displacement of a second membrane  310  in the same direction. 
     The second membrane  310  may come into contact with the guide pin or bar  81  for actuating the displacement of the slider element  21 ′, which will slide along the axis X guided not only by the fixed air distributor  2 ′ but also by the guide bars  72 ,  72 ′ inserted into respective through seats  77 ,  77 ′. 
     The second slider element  83  of the actuator element  36  may be slidably guided along the axis X′ not only by the pins  81 ,  81 ′ but also by the guide bars  84 ,  84 ′ inserted into respective through seats  88 ,  88 ′. 
     The second slider element  83  may be arranged substantially facing the first slider element  21 ′. 
     Suitably, the first and the second slider element  21 ′,  83  may respectively include the first natural permanent magnets M 1 , M 1 ′ and the second natural permanent magnets M 2 , M 2 ′, of the same polarity and facing each other. 
     In a preferred but non-exclusive embodiment, the magnets M 1 , M 1 ′; M 2 , M 2 ′ may be arranged on the first and second slider element  21 ′,  83  at respective end portions designated to be arranged facing each other when the magnets M 1 , M 1 ′; M 2 , M 2 ′ are in mutual correspondence during their mutual sliding along the axes X, X′, for example as illustrated in  FIG. 11 . 
     Thus, the magnets M 1 , M 1 ′; M 2 , M 2 ′ will advantageously generate the repulsive forces F 1 , F 2 , as outlined above. 
     The sliding constraint of the first slider element  21 ′ and of the second slider element  83  on the respective guide bars  72 ,  72 ′;  84 ,  84 ′ will allow to eliminate the normal component of the repulsive magnetic force, which will develop solely along the axes X, X′ with high intensity, increasing as the magnets M 1 , M 1 ′; M 2 , M 2 ′ approach. 
     This fully solves the problem relating to the so-called “dead centre”, in particular at low speeds or low working pressure. 
     From a construction point of view, the pump  1  consists of a minimum number of pieces. As a matter of fact, the support structure of the pump  1  may consist of two end covers  90 ,  91  and a central element which includes the valve system  1 . 
     The end cover  90  may include the first half-chamber  200 , the third half-chamber  400  and the first membrane  210 , while the end cover  910  may respectively include the second half-chamber  300 , the fourth half-chamber  500  and the second membrane  310 . 
     In light of the above, it is clear that the invention attains the pre-set objectives. 
     The invention is susceptible to numerous modifications and variants all falling within the inventive concept outlined in the attached claims. Furthermore, all details can be replaced by other technically equivalent elements, and the materials can be different depending on the needs, without departing from the scope of protection defined by the attached claims.