Abstract:
The present invention concerns an air motor comprising a piston and a housing, the piston being received in the housing and dividing the housing into two primary chambers of variable volume. Said motor comprises a first direct supply valve for supplying a first primary chamber of the two primary chambers and a second direct supply valve for supplying the other primary chamber, said two valves each being movable relative to at least one respective seat. The first valve and the second valve are mounted on a same stem movable relative to the housing in a direction parallel to the direction of movement of the piston, and the stem is configured to be moved between a first position and a second position by moving means activated by the piston.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a United States national stage application under 35 U.S.C. §371 of international patent application number PCT/EP2015/081228, filed Dec. 24, 2015, which claims priority to French patent application no. 1463354, filed Dec. 26, 2014, the entireties of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a compressed air motor comprising a piston and a housing, the piston being received in the housing and dividing the housing into two primary chambers of variable volume. 
         [0003]    Compressed air motors are frequently used to drive alternating movement pumps. Such pumps are in particular used to pumps viscous products, such as putty, or liquid products, such as paint. Document FR 2,695,965 A1 describes one such pump comprising a compressed air motor. 
         [0004]    Compressed air motors generally comprise a housing containing a piston. The piston divides the housing into two chambers, commonly called “upper chamber” and “lower chamber”, which are alternately supplied with compressed air. The alternating injection of compressed air into each of the chambers generates the alternating movement of the piston. 
         [0005]    Compressed air motors are frequently equipped with a distributor, which alternately supplies the upper chamber and the lower chamber. The distributor is generally controlled by external control members, of the switch type. Such motors are very reliable, but expensive. Furthermore, the use of distribution and external control members makes the assembly and maintenance of an installation comprising such a motor more complex. 
         [0006]    Other types of motors are equipped with an integrated inverter block including a rotary spring. These motors have a simple design, but have reliability problems. 
         [0007]    Other types of compressed air motors do not require an inverter or distributors. A compressed air motor is for example known from document FR 484,199 A comprising two distributors supplying the upper and lower chambers supported by a same stem. The stem is moved by the piston between two positions to control the supply of the chambers. 
         [0008]    Document DE 19 92 789 U describes a compressed air motor in which two seals supported by a stem control the supply of the upper and lower chambers. 
         [0009]    Several examples of compressed air motors in which the supply of the upper and lower chambers is controlled by two valves mounted on a same stem are known from document EP 0,414,268 A1, DE 28 16 617 A1, DE 28 23 667 A1 and EP 0,319,341 A2. 
         [0010]    Another type of compressed air motor in which the alternating supply of the chambers is obtained by the movement of a stem is described in document WO 2003/058072 A2. 
         [0011]    However, these known compressed air motors often have reliability problems, since in a case where the control stem is stopped in an intermediate position, the two chambers could be supplied at the same time and the motor would then remain blocked. Mechanisms making it possible to keep the stem in its extreme positions exist, but make the structure of the motor more complex. 
         [0012]    Other mechanisms for controlling the supply of the upper and lower chambers of a motor cylinder are known. For example, a valve actuator in which a moving sleeve commands the supply of the upper and lower chambers of a cylinder is known from document U.S. Pat. No. 4,974,495 A. 
       SUMMARY OF THE INVENTION 
       [0013]    The aim of the invention is to propose a reliable compressed air motor having a simple structure, and not requiring an external control member for the supply of its chambers with compressed air. 
         [0014]    To that end, the invention relates to a compressed air motor of the aforementioned type, which comprises a first direct supply valve for supplying a first primary chamber of the two primary chambers and a second direct supply valve for supplying the other primary chamber, these two valves each being movable relative to at least one respective seat. The first valve and the second valve are mounted on a same stem movable relative to the housing in a direction parallel to the direction of movement of the piston. The stem is configured to be moved between a first position and a second position by moving means activated by the piston. 
         [0015]    According to other advantageous aspects of the invention, the motor comprises one or more of the following features, considered alone or according to all technically possible combinations:
       the moving means are activated by the piston when it reaches the upper neutral position or the lower neutral position of its trajectory;   the moving means are elastic means;   the elastic means comprise at least one spring.   the stem bears at least one pin, the spring being wound around the stem and able to exert a force on the pin moving the stem from its second position toward its first position, or vice versa.   the moving means comprise at least a first moving magnet and a second moving magnet exerting a magnetic repulsion force on one another.   the piston is movable relative to the housing along a primary direction and the stem extends in the primary direction through a first primary chamber, the piston and a second primary chamber.   the motor further comprises means for keeping the stem in at least one of its first and second positions.   the first and second valves are made at least partially from a ferromagnetic material, and in that the maintaining means comprise at least a first maintaining magnet able to exert a first retaining force on the first valve, a second maintaining magnet able to exert a second retaining force on the first valve, a third maintaining magnet able to exert a third retaining force on the second valve and a fourth maintaining magnet able to exert a fourth retaining force on the second valve.   the housing comprises a first secondary chamber having a first intake seat and a first discharge seat and a second secondary chamber having a second intake seat and a second discharge seat, the first valve being received in the first secondary chamber and the second valve being received in the second secondary chamber, the first valve bears on the first discharge seat and the second valve bears on the second intake seat, when the stem is in its first position and the first valve is bearing on the first intake seat and the second valve is bearing on the second discharge seat, when the stem is in its second position.   the housing includes at least one cylinder head, and the stem includes at least one bearing sliding sealably in the cylinder head.       
 
         [0026]    The invention also relates to a pump with alternating movement comprising a motor as previously described. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    The features and advantages of the invention will appear upon reading the following description, provided solely as a non-limiting example, and done in reference to the appended drawings, in which: 
           [0028]      FIG. 1  is a longitudinal sectional view of a compressed air motor according to the invention; 
           [0029]      FIG. 2  is an enlarged view of detail II in  FIG. 1 ; 
           [0030]      FIG. 3  is an exploded perspective view of a stem of the motor of  FIGS. 1 and 2  and members that equip it; 
           [0031]      FIG. 4  is an enlarged view of detail IV in  FIG. 1 ; 
           [0032]      FIG. 5  is an enlarged view of detail V in  FIG. 1 ; 
           [0033]      FIG. 6  is an enlarged view of detail VI in  FIG. 1 , in a first operating configuration of the compressed air motor of  FIGS. 1 to 5 ; and 
           [0034]      FIG. 7  is a view similar to  FIG. 6  when the compressed air motor is in a second operating configuration. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0035]    A pump  6  with alternating movement includes a pumping stage  8  and a compressed air motor  10 . 
         [0036]    The pumping stage  8  is able to drive a fluid, such as a coating product, a putty or a glue. The pumping stage  8  is actuated by the motor  10 . 
         [0037]    A first example pump  6  is shown in  FIGS. 1 to 7 . 
         [0038]    The compressed air motor  10  includes a housing  15 , a piston  20  secured to a force transmitting shaft  25 , a reversing stem  30 , a supply tube  35  and two silencers  40 . 
         [0039]    The housing  15  comprises a side wall  45 , a first cylinder head  50  and a second cylinder head  55 . 
         [0040]    The side wall  45  is cylindrical and centered on a first axis A 1 , for example with a circular base. 
         [0041]    The first axis A 1  is oriented along a primary direction Z of the motor  10 . 
         [0042]    The side wall  45  is made from a metal material. For example, the side wall  45  is made from aluminum. Alternatively, the side wall  45  is made from a composite or synthetic material. 
         [0043]    The first cylinder head  50  and the second cylinder head  55  are provided to be fastened to the side wall  55  to form the housing  15 . 
         [0044]    The first cylinder head  50  comprises a first supply duct  70 , a first internal opening for the putty, a first cavity  80 , a first external opening  85 , a first connecting duct  90  and a first tapping  95  for screwing a threaded stop  100 . The first cylinder head  50  also bears a first end block  102  defining a first secondary chamber  103 . 
         [0045]    The first cylinder head  50  is cylindrical with a circular base and centered around a second axis A 2 . The second axis A 2  is combined with the first axis A 1 . 
         [0046]    Along the primary direction Z, the first cylinder head  50  is defined by a first outer face  60  and a first inner face  65 . The first inner face  65  is oriented toward the second cylinder head  55 . The first cylinder head  50  further has a first side face  67 . 
         [0047]    The second cylinder head  55  is cylindrical with a circular base and centered around a third axis A 3 . Preferably, the third axis A 3  is combined with the first axis A 1 . 
         [0048]    Along the primary direction Z, the second cylinder head  55  is defined by a second inner face  105  and a second outer face  110 . The second inner face  105  is oriented toward the first cylinder head  50 . The second cylinder head  55  further has a second side face  115 . 
         [0049]    The first and second cylinder heads  50  and  55  are made from a metal material, for example aluminum. 
         [0050]    The second cylinder head  55  comprises a second supply duct  120 , a second internal opening  125 , a second cavity  130 , a second external opening  135 , a second connecting duct  140  and a second threaded receiving hole  145 , for receiving a second screwed stop  150 . The second cylinder head  55  also bears a second end block  152  defining a second secondary chamber  153 . 
         [0051]    The second cylinder head  55  further comprises a first through hole  155  for receiving the shaft  25  and a first primary bearing  160  positioned around the shaft  25  and in which this shaft  25  slides when the motor  10  is operating. 
         [0052]    The piston  20  is cylindrical and centered on a fourth axis A 4 . The fourth axis A 4  is preferably combined with the first axis A 1 . 
         [0053]    Preferably, the piston  20  is cylindrical with a circular base. 
         [0054]    The piston  20  is able to separate the housing  15  into an upper primary chamber  165 , or first primary chamber, and a lower primary chamber  170 , or second primary chamber. 
         [0055]    The piston  20  is translatable relative to the housing  15 , along the direction Z, between an upper neutral position and a lower neutral position. The piston  20  is translatable along the primary direction Z. 
         [0056]    The piston  20  is made from a metal material, preferably aluminum. 
         [0057]    The piston  20  includes a peripheral receiving groove  180  for receiving a piston seal  175 , a passage opening  185  for the stem  30  and sealing means  190  for the opening  185 . 
         [0058]    The piston  20  is fastened to the shaft  25  using a screw  252  engaged in an axial tapping  254  of the shaft  25 . The screw  252  traverses a screw orifice  202  arranged at the center of the piston and centered on the axis A 4 . Two washers  256  and  258 , respectively positioned in the first primary chamber  165  and in the second primary chamber  170 , are axially tightened around the orifice  202  by the screw  252  and the shaft  25 . 
         [0059]    One end of the shaft  25 , opposite the piston  20 , is coupled to the pumping stage  8 . 
         [0060]    The shaft  25  is cylindrical and centered on a fifth axis A 5 , combined with the first axis A 1 . The shaft  25  is received in the primary bearing  160 . The shaft  25  is translatable, with the piston  20 , along the primary direction Z. The reversing stem  30  has a first end part  192 , a central part  193  and a second end part  194  opposite the first end part  192 . 
         [0061]    The reversing stem  30  bears a first valve  195 , a second valve  200 , first movement means  205 , second movement means  210 , a first bearing  212  (sometimes called “coil”) and a second bearing  213 . 
         [0062]    The reversing stem  30  has a cylindrical symmetry around a sixth axis A 6 , parallel to the first axis A 1  and radially offset relative thereto. The reversing stem  30  is made from a metal material, preferably steel. 
         [0063]    The reversing stem  30  extends, along the primary direction Z, through the first secondary chamber  103 , the first external opening  85 , the first internal opening  75 , the upper primary chamber  165 , the piston  20 , the lower primary chamber  170 , the second internal opening  125 , the second outer opening  135  and the second secondary chamber  153 . 
         [0064]    The reversing stem  30  is translatable, along a secondary direction Z′, relative to the housing  15 . The secondary direction Z′ is parallel to the primary direction Z. 
         [0065]    The reversing stem  30  is movable between a first position, in which the first valve  195  closes off the first external opening  85 , and a second position, in which the second valve  200  closes off the second external opening  135 . 
         [0066]    The supply tube  35  is able to guide a stream of compressed air F 1  arriving from a compressor, not shown, and to deliver this pressurized stream of air F 1  simultaneously to the first supply duct  70  and the second supply duct  120 . 
         [0067]    The supply tube  35  is for example made from a composite material. Alternatively, the supply tube  35  is made from a metal, for example aluminum. 
         [0068]    The first supply duct  70  is able to receive the compressed air stream F 1  from the supply tube  35 , and to deliver the compressed air stream to the first internal opening  75 . 
         [0069]    The first supply duct  70  has a cylindrical symmetry around a seventh axis A 7 , perpendicular to the first axis A 1 . Along the seventh axis A 7 , the first supply duct  70  is defined by the first side face  67  and by the first internal opening  75 . 
         [0070]    The first internal opening  75  is cylindrical with a circular base. The central axis of the first internal opening  75  is the sixth axis A 6 . 
         [0071]    Along the primary direction Z, the first internal opening  75  is defined by the first inner face  65  and by a first frustoconical wall  215 . 
         [0072]    The first cavity  80  is arranged in the first outer face  60 . The first cavity  80  is cylindrical with a circular base. The central axis of the first cavity  80  is the sixth axis A 6 . A first intake seat  220 , traversed by the first external opening  85 , and first maintaining means  225  are positioned in the first cavity  80 . 
         [0073]    The first cavity  80  is closed off by the first end block  102 , which is fastened on the first external face  60 , for example by screws. The first end block  102  is preferably made from metal, for example aluminum. The first end block  102  further bears a silencer  40 . The first cavity  80  and the first end block  102  together define the first secondary chamber  103 . 
         [0074]    The first external opening  85  extends between the first frustoconical wall  215  and the first cavity  80 . 
         [0075]    The first external opening  85  has a cylindrical symmetry around the sixth axis A 6 . For example, the first external opening  85  is cylindrical with a circular base. 
         [0076]    The first connecting duct  90  extends between the first cavity  80  and the first inner face  65 . 
         [0077]    The first connecting duct  90  is cylindrical with a circular base and centered around an eighth axis A 8 , parallel to the first axis A 1  and radially offset relative thereto. The first connecting duct  90  is able to allow the passage of compressed air between the first secondary chamber  103  and the upper primary chamber  165 , and vice versa. 
         [0078]    The first stop  100  is configured so that the piston  20  bears on this stop, when the piston  20  is in the upper neutral position of its trajectory. The stop  100  is for example made from a synthetic material. 
         [0079]    The first end block  102  comprises a first discharge opening  235  and a first discharge seat  240  surrounding the first discharge opening  235 . The first end block  102  further comprises second maintaining means  242 . 
         [0080]    The second supply duct  120  is able to receive the compressed air stream F 1  from the supply tube  35 , and to deliver the compressed air stream to the second internal opening  125 . 
         [0081]    The second supply duct  120  has a cylindrical symmetry around a ninth axis A 9 . The ninth axis A 9  is perpendicular to the first axis A 1 . Along the ninth axis A 9 , the second supply duct  120  is defined by the second side face  115  and by the second internal opening  125 . 
         [0082]    The second internal opening  125  is cylindrical with a circular base. The central axis of the second internal opening  125  is the sixth axis A 6 . 
         [0083]    Along the primary direction Z, the second internal opening  125  is defined by the second inner face  105  and by a second frustoconical wall  245 . 
         [0084]    The second cavity  130  is arranged in the second outer face  110 . 
         [0085]    The second cavity  130  is cylindrical with a circular base. The central axis of the second cavity  130  is the sixth axis A 6 . 
         [0086]    A second intake seat  250 , traversed by the second external opening  135 , and third maintaining means  255  are positioned in the second cavity  130 . 
         [0087]    The second cavity  130  is closed off by the second end block  152 , which is fastened on the second external face  110 , for example by screws. The second end block  152  is preferably made from metal, for example aluminum. The second end block  152  further bears a silencer  40 . The second cavity  130  and the second end block  152  together define a second secondary chamber  153 . 
         [0088]    The second external opening  135  extends between the second frustoconical wall  245  and the second cavity  130 . 
         [0089]    The second cavity  130  has a cylindrical symmetry around the sixth axis A 6 . For example, the second cavity  130  is cylindrical with a circular base. 
         [0090]    The second connecting duct  140  extends between the second cavity  130  and the second inner face  105 . 
         [0091]    For example, the second connecting duct  140  is cylindrical with a circular base and centered around a tenth axis A 10 , parallel to the first axis A 1 . The tenth axis A 10  is combined with the eighth axis A 8 . The second connecting duct  140  is able to allow the passage of compressed air between the first secondary chamber  153  and the lower primary chamber  170 , and vice versa. 
         [0092]    The second stop  150  is configured so that the piston  20  bears on this stop, when the piston  20  is in the lower neutral position of its trajectory. The second stop screw  150  is for example made from a synthetic material. 
         [0093]    The second end block  152  comprises a second discharge opening  265  and a second discharge seat  270  surrounding the second discharge opening  265 . The second end block  152  further comprises fourth maintaining means  272 . 
         [0094]    The first through hole  155  extends between the second inner face  105  and the second outer face  110 . 
         [0095]    The first through hole  155  is cylindrical with a circular base. The central axis of the first through hole  155  is the first axis A 1 . 
         [0096]    The first through hole  155  receives the first primary bearing  160  able to allow the shaft  25  to translate along the primary direction Z. The first primary bearing  160  is further capable of preventing the passage of compressed air between the second primary chamber  170  and the outside of the housing  15 . 
         [0097]    The piston seal  175  is capable of preventing the passage of compressed air between the upper primary chamber  165  and the lower primary chamber  170  at the side wall  45 . The piston seal  175  is for example an O-ring made from a synthetic material. 
         [0098]    The passage opening  185  receives the central part  193  of the reversing stem  30 . The passage opening  185  of the reversing stem  30  is cylindrical with a circular base. The central axis of the passage opening  185  is the sixth axis A 6 . The sealing means  190  are able to prevent the passage of pressurized air through the passage opening  185  when the central part  193  is received in the passage opening  185 . 
         [0099]    The sealing means  190  are able to allow the central part  193  to translate along the primary direction Z relative to the piston  20 . 
         [0100]    The sealing means  190  comprise a ring  230 , two stem seals  232  and two covers  233 . The ring  230  is able to guide the reversing stem  30  in translation along the secondary direction Z′. The ring  230  is made from a synthetic material, such as a polyacetal. The stem seals  232  are able to prevent the passage of compressed air between the upper primary chamber  165  and the lower primary chamber  170  when the central part  193  is received in the passage opening  185 . 
         [0101]    The stem seals  232  are O-rings, for example made from plastic. The two covers  233  are configured to keep the stem seals  232  and the ring  230  in position. The two covers  233  are fastened to the piston  20 . For example, the two covers  233  are screwed to the piston. The two covers  233  are for example made from metal, such as aluminum. 
         [0102]    The central part  193  is cylindrical, preferably with a circular base, and its central axis is the sixth axis A 6 . The central part  193  traverses the piston  20 . 
         [0103]    The first valve  195  is able to prevent the passage of compressed air from the first secondary chamber  103  toward the first external opening  85 , when the first valve  195  is bearing on the first intake seat  220 . 
         [0104]    The first valve  195  is able to prevent the passage of compressed air between the upper primary chamber  165  and the first discharge opening  235 , when the first valve  195  is bearing on the first discharge seat  240 . 
         [0105]    The first valve  195  is housed in the first secondary chamber  103 . The first valve  195  is fastened, for example by screwing, to the first end part  192 . The first valve  195  is at least partially made from a ferromagnetic material. For example, the first valve  195  comprises a core made from steel. Preferably, the first valve  195  is at least partially covered with a thermoplastic material. For example, the thermoplastic material is polyurethane. 
         [0106]    The second valve  200  is able to prevent the passage of compressed air from the second secondary chamber  153  toward the second external opening  135 , when the second valve  200  is bearing on the second intake seat  250 . 
         [0107]    The second valve  200  is able to prevent the passage of compressed air between the lower primary chamber  170  and the second discharge opening  265 , when the second valve  200  is bearing on the second discharge seat  270 . 
         [0108]    The second valve  200  is housed in the second secondary chamber  153 . The second valve  200  is fastened, for example by screwing, to the second end part  194 . The second valve  200  is at least partially made from a ferromagnetic material. For example, the second valve  200  comprises a core made from steel. Preferably, the second valve  200  is at least partially covered with a thermoplastic material. For example, the thermoplastic material is polyurethane. 
         [0109]    The first moving means  205  are able to cooperate with the piston  20  to move the reversing stem  30  between its second position shown in  FIG. 7  and its first position shown in  FIGS. 4 to 6 . 
         [0110]    The first moving means  205  are for example elastic means. The first elastic moving means  205  include a spring  275 , a nut  280 , a pin  285  and a molders&#39; pin  290 . 
         [0111]    In an alternative that is not shown, the first elastic moving means  205  comprise a deformable block, in particular made from elastomer. 
         [0112]    The second moving means  210  are able to cooperate with the piston  20  to move the reversing stem  30  between its first position and its second position. 
         [0113]    The second moving means  210  are for example elastic means. The second elastic moving means  210  are identical to the first elastic moving means  205 . 
         [0114]    In an alternative that is not shown, the second elastic moving means  205  comprise an elastic block made from elastomer. 
         [0115]    The first bearing  212  guides the reversing stem  30  in translation in the internal opening  75 , along the sixth axis A 6 . The first bearing  212  is received in the first internal opening  75 . The first bearing  212  is further able to prevent the passage of compressed air between the upper primary chamber  165  and the first supply duct  70 . This means that the first bearing  212  slides sealably in the first internal opening  75 . 
         [0116]    The second bearing  213  guides the reversing stem  30  in translation in the internal opening  125 , along the sixth axis A 6 . The second bearing  213  is received in the second internal opening  125 . The second bearing  213  is further able to prevent the passage of compressed air between the lower primary chamber  170  and the second supply duct  120 . This means that the second bearing  213  slides sealably in the second internal opening  125 . 
         [0117]    The first and second bearings  212  and  213  each bear a bearing seal  295 . 
         [0118]    The first intake seat  220  is arranged in the first cavity  80 . 
         [0119]    The first intake seat  220  is in the form of a cylindrical crown with a circular base. The axis of the first intake seat  220  is the sixth axis A 6 . 
         [0120]    The first maintaining means  225  are able to exert a first retaining force E 1  on the first valve  195 . The first maintaining means  225  are able to keep the reversing stem  30  in its second position. 
         [0121]    The first retaining force E 1  is an attraction force. The first retaining force E 1  for example has a value comprised between 2 and 4 decaNewtons (dN). 
         [0122]    In practice, the first maintaining means  225  are formed by a first maintaining magnet  225 . The first maintaining magnet  225  is made in the form of a cylindrical crown with a circular base. The axis of the first maintaining magnet  225  is the sixth axis A 6 . The first maintaining magnet  225  surrounds the first intake seat  220  around the sixth axis A 6 . 
         [0123]    The first discharge opening  235  has a cylindrical symmetry around the sixth axis A 6 . The first discharge seat  240  is arranged in the first end block  102 . The first discharge seat  240  is made in the form of a cylindrical crown with a circular base. The axis of the first discharge seat  240  is the sixth axis A 6 . 
         [0124]    The second maintaining means  242  are able to exert a second retaining force E 2  on the first valve  195 . The second maintaining means  242  are able to keep the reversing stem  30  in its first position. 
         [0125]    The second retaining force E 2  is an attraction force. The second retaining force E 2  for example has a value comprised between 2 and 4 dN. 
         [0126]    In practice, the second maintaining means  242  are formed by a second maintaining magnet  242 . The second maintaining magnet  242  is made in the form of a cylindrical crown with a circular base. The axis of the second maintaining magnet  242  is the sixth axis A 6 . The second maintaining magnet  242  is preferably identical to the first maintaining magnet  225 . The second maintaining magnet  242  surrounds the first discharge seat  240  around the sixth axis A 6 . 
         [0127]    The second intake seat  250  is arranged in the second cavity  130 . The second intake seat  250  is made in the form of a cylindrical crown with a circular base. 
         [0128]    The third maintaining means  255  are able to exert a third retaining force E 3  on the second valve  200 . The third maintaining means  255  are able to keep the reversing stem  30  in its first position. 
         [0129]    The third retaining force E 3  is an attraction force. The third retaining force E 3  for example has a value comprised between 2 and 4 dN. 
         [0130]    For example, the third maintaining means  255  are formed by a third maintaining magnet  255 . The third maintaining magnet  255  is made in the form of a cylindrical crown with a circular base. The axis of the third maintaining magnet  255  is the sixth axis A 6 . The third maintaining magnet  255  is preferably identical to the first maintaining magnet  225 . The third maintaining magnet  255  surrounds the second intake seat  250  around the sixth axis A 6 . 
         [0131]    The second discharge opening  265  has a cylindrical symmetry around the sixth axis A 6 . 
         [0132]    The second discharge seat  270  is made in the form of a cylindrical crown with a circular base. The axis of the second discharge seat  270  is the sixth axis A 6 . 
         [0133]    The fourth maintaining means  272  are able to exert a fourth retaining force E 4  on the second valve  200 . The fourth maintaining means  272  are able to keep the reversing stem  30  in its second position. 
         [0134]    The fourth retaining force E 4  is an attraction force. The fourth retaining force E 4  for example has a value comprised between 2 and 4 dN. 
         [0135]    In practice, the fourth maintaining means  272  are formed by a fourth maintaining magnet  272 . 
         [0136]    The fourth maintaining magnet  272  is made in the form of a cylindrical crown with a circular base. The axis of the fourth maintaining magnet  272  is the sixth axis A 6 . The fourth maintaining magnet  272  is preferably identical to the first maintaining magnet  225 . The fourth maintaining magnet  272  surrounds the second discharge seat  270  around the sixth axis A 6 . 
         [0137]    The spring  275  is wound around the reversing stem  30 . The spring  275  bears on the nut  280 . The nut  280  bears on the pin  285 . 
         [0138]    The pin  285  is received in a corresponding opening  302  of the reversing stem  30 . The pin  285  is configured to serve as a stop for the nut  280  along the reversing stem  30 . 
         [0139]    The molders&#39; pin  290  traverses the pin  285 . The molders&#39; pin  290  prevents the pin  285  from being removed from the corresponding opening of the reversing stem  30 . 
         [0140]    The operation of the motor  10  will now be described. In  FIG. 6 , the reversing stem  30  is in its first position. 
         [0141]    The first valve  195  is bearing on the first discharge seat  240 . The first valve  195  is therefore not bearing on the first intake seat  220 . 
         [0142]    The second valve  200  is bearing on the second intake seat  250 . The second valve  200  is therefore not bearing on the second discharge seat  270 . 
         [0143]    The compressed air present in the second internal opening  125  exerts a first pressure force Ep 1  on the second bearing. The compressed air present in the second chamber exerts a second pressure force Ep 2  on the second valve  200 . 
         [0144]    The compressed air stream F 1 , coming from the supply tube  35 , traverses the first supply duct  70  and penetrates the first secondary chamber  103  via the first outer opening  85  in the form of a secondary air stream F 1 ′, which is possible because the first valve  195  is separated from the intake seat  220 . The secondary compressed air stream F 1 ′ next traverses the first connecting duct  90  to penetrate the upper primary chamber  165 . 
         [0145]    The compressed air therefore causes the piston  20  to move toward the lower neutral position. The air contained in the lower primary chamber  170  is expelled through the second connecting duct  140 , the second secondary chamber  153 , the second discharge opening  265  and the silencer  40 , in the form of a discharge air stream F 2 ′. 
         [0146]    The piston  20  next bears on the second moving means  210 . In particular, the piston  20  compresses the spring  275 . The spring  275  exerts a first moving force D 1  on the reversing stem  30  tending to move the reversing stem  30  toward its second position. When the piston  20  has not yet reached the lower neutral position, the first moving force D 1  is lower than the sum of the second retaining force E 2 , the third retaining force E 3 , and the first and second pressure forces Ep 1  and Ep 2 . The reversing stem  30  therefore remains in its first position. 
         [0147]    When the piston  20  has reached the lower neutral position, the first moving force D 1  due to the spring  275  is higher than the sum of the second and third retaining forces E 2  and E 3  and first and second pressure forces Ep 1  and Ep 2 . The reversing stem  30  is then moved from its first position toward its second position to reach the configuration of  FIG. 7 . 
         [0148]    In  FIG. 7 , the first valve  195  is bearing on the first intake seat  220 . The second valve  200  is therefore bearing on the second discharge seat  270 . 
         [0149]    The compressed air stream F 1  then no longer penetrates the upper primary chamber  165 , but the lower primary chamber  170  in the form of a secondary air stream F 1 ″. The piston  20  is then set in motion from the low neutral position toward the high neutral position. The air contained in the upper primary chamber  165  escapes through the first connecting duct  90 , the first secondary chamber  103 , and the first discharge opening  235 , in the form of a discharge air stream F 2 ″. 
         [0150]    When the piston  20  reaches the upper neutral position, the reversing stem  30  is moved from its second position toward its first position, according to a sequence opposite that described above. 
         [0151]    The motor  10  is able to command the alternating power supply of the upper primary chamber  165  and the lower primary chamber  170 , without using an external device. Furthermore, the motor  10  is highly reliable. 
         [0152]    According to a second embodiment that is not shown, the pump  6  includes two pumping stages  8 . 
         [0153]    The first cylinder head  50  then includes a second through hole for receiving the shaft  25  and a second primary bearing positioned around the shaft  25  and in which this shaft  25  slides when the motor  10  is operating. 
         [0154]    The second through hole extends between the first inner face  65  and the first outer face  60 . 
         [0155]    The second through hole is cylindrical with a circular base. The central axis of the second through hole is the first axis A 1 . 
         [0156]    The second through hole receives the first primary bearing able to allow the shaft  25  to translate along the primary direction Z. The second primary bearing is further capable of preventing the passage of compressed air between the first primary chamber  165  and the outside of the housing  15 . 
         [0157]    The shaft  25  traverses the first cylinder head  50  and the second cylinder head  55 . 
         [0158]    Each end of the shaft  25  is coupled to a pumping stage  8 . 
         [0159]    The operation of the second example is identical to the operation of the first example. 
         [0160]    The flow rate of the pump  6  is then increased. 
         [0161]    According to a third example embodiment that is not shown, the pump  6  includes a first motor  10  including a first housing  15 , a first piston  20 , a first valve  195  and a second valve  200 , and a second motor  10  including a second housing  15 , a second piston  20 , a third valve and a fourth valve. 
         [0162]    The reversing stem  30  is shared by the first motor  10  and the second motor  10 . 
         [0163]    The first housing  15  includes a first cylinder head  50  and a second cylinder head  55 . The first housing  15  is identical to the housing  15  described in the second example. 
         [0164]    The first piston  20  divides the first housing  15  into a first primary chamber  165  and a second primary chamber  170 . 
         [0165]    The second housing  15  includes a third cylinder head and a fourth cylinder head. 
         [0166]    The second piston  20  divides the second housing  15  into a third primary chamber and a fourth primary chamber. The second piston  20  is identical to the first piston  20 . 
         [0167]    The third cylinder head is identical to the first cylinder head described in the first example. 
         [0168]    The fourth cylinder head is identical to the second cylinder head described in the first example. The fourth cylinder head is across from the first cylinder head  165 . 
         [0169]    The stem  30  extends in the primary direction Z through the second primary chamber  165 , the first piston  20 , the second primary chamber  170 , the first cylinder head  50 , the fourth cylinder head, the fourth primary chamber, the second piston, the third primary chamber and the third cylinder head. 
         [0170]    The stem  30  bears the first valve  195 , the second valve  200 , the third valve and the fourth valve. 
         [0171]    The stem  30  is movable between a first position and a second position. 
         [0172]    The pistons  20  are both mounted on a same shaft  25 . 
         [0173]    The operation of this third example will now be described. 
         [0174]    When the stem  30  is in the first position, the first primary chamber and the third primary chamber are supplied with compressed air. When the stem  30  is in the second position, the second primary chamber and the fourth primary chamber are supplied with compressed air. 
         [0175]    The two pistons  20  are actuated simultaneously, and both drive the shaft  25 . 
         [0176]    The pump  6  is therefore more powerful. 
         [0177]    According to a fourth example embodiment, the first moving means  205  and the second moving means  210  are magnetic means. 
         [0178]    The first moving means include at least a first moving magnet and a second moving magnet. 
         [0179]    The first moving magnet is for example supported by the stem  30 . The second moving magnet is for example supported by the piston  20 . The first and second moving magnet are able to exert a repulsive magnetic force on one another. 
         [0180]    The second moving means include at least a third moving magnet and a fourth moving magnet. 
         [0181]    The third moving magnet is for example supported by the stem  30 . The fourth moving magnet is for example supported by the piston  20 . The third and fourth moving magnet are able to exert a repulsive magnetic force on one another. 
         [0182]    The operation of the fourth example is identical to the operation of the first example. 
         [0183]    The fabrication of the motor  10  is then simpler. 
         [0184]    The features of the embodiments and alternatives described above may be combined to generate new embodiments of the invention.