Patent Publication Number: US-9849575-B2

Title: Pneumatic screwer

Description:
This application is a §371 National Stage Entry of PCT International Application No. PCT/IB2012/050217 filed on Jan. 17, 2012. PCT/IB2012/050217 claims priority to IT Applications Nos. MO2011A000006 filed on Jan. 18, 2011 and MO2011A000007 filed on Jan. 18, 2011. The entire contents of these applications are incorporated herein by reference. 
     The invention relates to a pneumatic screwer. 
     The invention further relates to a switch for switching a screwing direction of a pneumatic screwer. 
     Pneumatic screwers are known that comprise a spindle for rotatably supporting a screwing tool. 
     Such screwers are further provided with a rotor that is pneumatically rotatable. 
     The rotor, which is connected mechanically to the spindle, rotates the latter. 
     The rotor includes a cylindrical body having a circular section. 
     The cylindrical body is provided peripherally with seats, arranged radially and angularly spaced apart from one another, inside which respective blades are slidable. 
     Known screwers further comprise a stator, which is internally hollow, for housing the rotor. 
     Between the rotor and the stator a gap is defined that is arranged for receiving pressurised air. 
     The rotor is mounted eccentrically with respect to the stator in such a manner that the blades cooperate with an internal wall of the stator for defining, in the gap, chambers, the volume of which varies during rotation of the rotor. 
     Each chamber is defined between two circumferally consecutive blades, the rotor and the internal wall of the stator. 
     A supply conduit for delivering pressurised air to the gap, a primary discharge conduit and a secondary discharge conduit for discharging the pressurised air from the gap are obtained in the stator. 
     The primary discharge conduit is obtained in an upper zone of the stator corresponding to the maximum distance between the rotor and the stator. 
     More precisely, the primary discharge conduit is in a zone of the screwer opposite a further zone of the screwer from which a handle of the screwer extends. 
     The supply conduit and the secondary discharge conduit are obtained in further zones of the stator arranged symmetrically with respect to a plane passing through a rotation axis of the rotor and comprising the primary discharge conduit. 
     This enables the screwers to be driven in opposite rotation directions by simply exchanging, by a switch, the functions of the supply conduit and of the secondary discharge conduit. More precisely, by means of the switch it is possible to deliver pressurised air into the gap alternatively via the supply conduit or the secondary discharge conduit, and consequently to discharge pressurised air from the gap respectively via the secondary discharge conduit or the supply conduit. 
     The switch comprises a cylindrical element that is slidable in the screwer between an operating position in which the screwer acts with a screwing direction and a further operating position in which the screwer acts with a further screwing direction. 
     On the cylindrical element a first seat and a second seat are obtained that are arranged for engaging respectively with a first locking element and with a second locking element slidably associated with the screwer for positioning the switch respectively in the operating position or in the further operating position. 
     In particular, in the operating position the first locking element engages the first seat whereas the second locking element is disengaged from the second seat, and in the further operating position the second locking element engages the second seat whereas the first locking element is disengaged from the first seat. 
     The first and the second locking element are maintained pressed against the first seat and the second seat by respectively a first spring and a second spring, the stiffness of which is adjustable by respective adjusting screws. 
     Switches are further known in which a single locking element is provided that is alternatively engageable in the first seat or in the second seat. 
     In use, at the start of an operating cycle, the pressurised air is introduced via the supply conduit inside a chamber that is initially of reduced volume, i.e. positioned near a zone in which the rotor is nearer the stator. 
     Forces act on the blades that define the chamber, which forces tend to drive the rotor in opposite directions. 
     The prevailing force is the force that acts on the blade that protrudes the most from the respective seat. 
     The resultant of the aforesaid forces produces a driving torque on the rotor. 
     Subsequently, a portion of air contained in this chamber, which is already partially expanded, is expelled directly into the atmosphere via the primary discharge conduit. 
     This pressurised air can nevertheless, given the position of the primary discharge conduit, hit the operator using the screwer, disturbing the operator during use of the screwer. 
     Still subsequently, following a further rotation of the rotor, a remaining portion of air contained inside this chamber is expelled via the secondary discharge conduit and conveyed towards the outside of the screwer via a conveying conduit, positioned in and extending over the entire length of the handle of the screwer. 
     This pressurised air is thus unable to expand completely as it is “strangled” by the path defined by the conveying conduit, this reducing the performance of the screwer. 
     A drawback of known switches is that they are not much reliable and safe because they have difficulty to maintain a desired operating position. 
     In other words, in use, the switch, owing to the force exerted by the pressurised air circulating in the screwer, moves autonomously from the operating position to the further operating position and vice versa. 
     In order to overcome this drawback, it is common practice to stiffen significantly the springs of the locking elements. 
     Nevertheless, this solution is not satisfactory inasmuch as it greatly compromises the handling of the switch. 
     An object of the invention is to improve pneumatic screwers. 
     A further object is to provide pneumatic screwers that are more efficient than known screwers. 
     A still further object is to improve switches arranged for switching a screwing direction of a pneumatic screwer. 
     Another further object is to provide switches arranged for switching a screwing direction of a pneumatic screwer that are more reliable and easier to handle than known switches. 
     The invention provides a pneumatic screwer, as defined in the independent claim  1 . 
     The screwer according to the invention is more efficient than known screwers. 
     In fact, the discharge conduit is in flowing communication with said expansion chamber, which is positioned on an opposite side of the spindle with respect to the rotor and is in flowing communication with the atmosphere. 
     This enables said pressurised air to reduce the path to be made to expand completely, as it no longer needs to cover the entire handle of the screwer, which enables the performance of the screwer according to the invention to be improved. 
     The invention further provides a switch as defined in independent claim  11 . 
     The switch according to the invention is more reliable and manoeuvrable than known switches. 
     In fact, experimental results have shown that when in the operating position the locking device engages two of the three seats and effectively maintains the switch in the operating position and at the same time ensures easy handling. 
    
    
     
       The invention can be better understood and implemented with reference to the attached Figures, which illustrate some embodiments thereof by way of non-limiting example, in which: 
         FIG. 1  is a perspective view of a pneumatic screwer; 
         FIG. 2  is a partially sectioned side view of the screwer in  FIG. 1 ; 
         FIG. 3  is a perspective view, with some details removed, of the screwer in  FIG. 1 ; 
         FIGS. 4 and 5  are perspective views of some details of the screwer in  FIG. 1 ; 
         FIG. 6  is a side view of part of a pneumatic motor included in the screwer in  FIG. 1 ; 
         FIG. 7  is a section taken along the plane VII-VII in  FIG. 6 ; 
         FIG. 8  is a section taken along the plane VIII-VIII in  FIG. 6  showing a first embodiment of a switch according to the invention; 
         FIG. 9  is a section like that in  FIG. 8  with some details removed; 
         FIG. 10  is a section like that in  FIG. 8  showing a second embodiment of a switch according to the invention; 
         FIG. 11  is a longitudinal section of the second embodiment of the switch according to the invention. 
     
    
    
     With reference to  FIG. 1  there is shown a pneumatic screwer  1 . 
     The pneumatic screwer  1  comprises a main body  2  and a handle  3  projecting from the main body  2 . 
     The pneumatic screwer  1  further includes a spindle element  5  projecting from a first end portion  4  of the main body  2  and arranged for rotatably supporting a screwing tool, which is not shown. 
     The pneumatic screwer  1  further comprises a pneumatic motor  6 , shown in  FIGS. 3 and 6 . 
     The pneumatic motor  6  comprises a stator  7  having a cylindrical shape. 
     The stator  7  which is internally hollow has a variable thickness, which in particular increases from an upper portion  8  to a lower portion  9  thereof. 
     The pneumatic motor  6  further comprises a rotor  10  that is pneumatically rotatable. 
     The rotor  10 , which is connected mechanically to the spindle element  5 , rotates the latter. 
     The rotor  10  is housed inside the stator  7 , between the rotor  10  and the stator  7  a gap  11  being defined that is arranged, as will be disclosed better below, for receiving pressurised air. 
     The rotor  10  has a cylindrical shape with a substantially circular section. 
     The rotor  10  is rotatably coupled with the stator  7  in such a manner as to be rotatable around a rotation axis that is eccentric in relation to a longitudinal axis of the stator  7 . In the rotor  10 , radial seats  13  are obtained externally, in each of which a blade  14  is slidable. 
     The radial seats  13  are mutually angularly equidistant and shaped in such a manner as to each receive a blade  14 . 
     The blades  14  are, for example, made of carbon fibre and are arranged for being struck by an operating fluid, in particular pressurised air, arranged for rotating the rotor  10 . 
     Each blade  14  is radially slidable inside the respective seat  13 , in such a manner as to be movable between a compact configuration, in which the blade  14  is contained completely inside the seat  13 , and an extended configuration, in which the blade  14  projects outside the seat  13 . 
     The blade  14  is positioned in the compact configuration when the respective seat  13  is in the point of minimum distance from an internal wall of the stator  7  facing the seat. 
     On the other hand, the blade  14  is positioned in the extended configuration when the respective seat  13  is at the point of maximum distance from the aforesaid internal wall. 
     During rotation of the rotor  10 , an end  15  of each blade  14  is maintained in contact with the internal wall of the stator  7 , in such a manner that two circumferally consecutive blades  14  define, in the gap  11 , together with the stator  7 , with the rotor  10 , with a first closing flange  16  and with a second closing flange, which is not shown, the first closing flange  16  and the second closing flange being provided at opposite ends of the stator  7 , a plurality of chambers having a volume that varies over the course of rotation of the rotor  10 . 
     In the stator  7 , a supply conduit  17  for delivering pressurised air to the gap  11 , primary discharge conduits  18  and secondary discharge conduit  19  for discharging the pressurised air from the gap  11  are obtained. 
     The primary discharge conduits  18  are obtained in the upper portion  8  of the stator  7 , corresponding to the maximum distance between the rotor  10  and the stator  7 . 
     In particular, the primary discharge conduits  18  are in a zone of the pneumatic screwer  1  opposite a further zone of the screwer from which the handle  3  extends. 
     The supply conduit  17  and the secondary discharge conduit  19  are obtained in further zones of greater thickness of the stator  7  that are arranged symmetrically in relation to a plane passing through a rotation axis of the rotor  10 . 
     This enables the pneumatic screwer  1  to be driven in opposite rotation directions by simply exchanging, by means of a switch  20 ,  120 , disclosed below, the functions of the supply conduit  17  and of the secondary discharge conduit  19 . 
     More precisely, by means of the switch  20 ,  120  it is possible to deliver into the gap  11  pressurised air alternatively via the supply conduit  17  or the secondary discharge conduit  19 , and consequently discharge pressurised air from the gap  11  respectively via the secondary discharge conduit  19  or the supply conduit  17 . 
     The supply conduit  17  and the secondary discharge conduit  19  extend longitudinally in the stator  7  and each comprise a plurality of slits, which are not shown, in flowing communication with the gap  11 . 
     The pneumatic screwer  1  further comprises a cover  33  positioned in a second end portion  34  ( FIG. 1 ) of the pneumatic screwer  1  opposite the first end portion  4 . 
     The cover  33  comprises a seat  35  ( FIGS. 8, 9 and 10 ) for slidably housing the switch  20 ,  120 . 
     Also, in the cover  33  an expansion chamber  39  ( FIG. 7 ) is obtained that is in flowing communication, not only with the atmosphere, but also with the supply conduit  17 , the primary discharge conduits  18  and the secondary discharge conduit  19  for expanding the pressurised air. 
     In particular, the expansion chamber  39  is positioned on an opposite side of the spindle element  5  with respect to the rotor  10 , i.e. in a rear portion of the pneumatic screwer  1 . 
     The expansion chamber  39  comprises a first grid  50  and a second grid  51  provided respectively with first openings  44  and with second openings  45  in flowing communication with the atmosphere. 
     The first openings  44  and the second openings  45  enable the pressurised air coming from the gap  11  to be discharged into the atmosphere. 
     The first openings  44  and the second openings  45  are positioned laterally with respect to the handle  3  of the pneumatic screwer  1  and are mutually opposite. 
     In an embodiment of the invention that is not shown, only the first grid  50  is provided, whereas the second grid  51  is replaced by a closing element. In this manner, the pressurised air, by exiting only from the first openings  44 , favours use by a left-handed operator. 
     In another embodiment of the invention that is not shown, only the second grid  51  is provided, whereas the first grid  50  is replaced by a closing element. In this manner, the pressurised air, by exiting only from the second openings  45 , favours use by a right-handed operator. 
     In another further embodiment of the invention that is not shown, with the first grid  50  and with the second grid  51  respective door elements are associated that are drivable independently between a first position in which they close the first openings  44  and/or the second openings  45  and a second position in which they leave the first openings  44  and/or the second openings  45  open. 
     In this manner, the pneumatic screwer  1  becomes particularly flexible, inasmuch as, by acting on the door elements opportunely, it can easily be used by both a right-handed and by a left-handed operator. 
     Also, the expansion chamber  39  is shaped such as to be above to house a silencer, which is not shown, which is arranged for reducing the noise of the pneumatic screwer. 
     In the cover  33  a delivery conduit  36  for delivering pressurised air to the gap  11 , a first distributing channel  37  and a second distributing channel  38  are further obtained. The first distributing channel  37  and the second distributing channel  38  are connectable in flowing communication with the expansion chamber  39  by respectively a hole  42  and a further hole  43 . 
     The aforesaid first closing flange  16  ( FIG. 4 ) comprises a first passage  40  to put the first distributing channel  37  in flowing communication with the supply conduit  17  and a second passage  41  to put the second distributing channel  38  in flowing communication with the secondary discharge conduit  19 . 
     Also, in the first closing flange  16  a first groove  46  is obtained that is connected to the supply conduit  17  and arranged for making a certain quantity of pressurised air penetrate inside the seats  13 , inducing the blades  14  to exit from the seats  13 , in such a manner that the ends  15  of the blades  14  are maintained in contact with the internal wall of the stator  7  for preventing leaks of air between the chambers In the first closing flange  16  a second groove  47  is further obtained that is connected to the secondary discharge conduit  19  and is arranged for enabling the pressurised air to exit from the seats  13 , such as to enable the blades  14  to move from the extended to the compact position. 
     The functions of the first groove  46  and of the second groove alternate according to the screwing direction of the pneumatic screwer  1 . 
     The pneumatic screwer  1  further comprises a manifold  48  ( FIGS. 1 and 2 ) facing the primary discharge conduits  18  and arranged for expanding, partially, the pressurised air coming from the primary discharge conduits  18  and conveying the pressurised air towards the expansion chamber  39 . 
     The manifold  48  comprises a first protrusion  55  and a second protrusion  56 , internally provided respectively with a first cavity and with a second cavity, which are not shown, arranged for expanding, partially, the pressurised air and for conveying the pressurised air in a more effective manner towards the expansion chamber  39 . 
     The aforesaid primary discharge conduits  18  face the first cavity if the pneumatic screwer  1  unscrews anticlockwise, this provides the pneumatic screwer  1  with greater power for this anticlockwise unscrewing. 
     In this configuration, the primary discharge conduits  18  are tilted by an angle of about 20° with respect to a vertical plane passing through the handle  3 . 
     In use, by rotating the stator  7  opportunely, it is possible to position the primary discharge conduits  18  in such a manner that they face the second cavity in such a manner as to provide the pneumatic screwer  1  with greater power in the event of clockwise unscrewing. 
     Also in this configuration, which is symmetric with respect to the preceding configuration, the primary discharge conduits  18  are tilted by an angle of about 20° with respect to a vertical plane passing through the handle  3 . 
     In order to move from one configuration to the next, it is sufficient to rotate the stator  7  by about 180° around a vertical axis. 
     With reference to  FIGS. 8 and 9  there is shown a first version of the aforesaid switch, indicated with the numeric reference  20 . 
     The switch  20  comprises a cylindrical slider  21  that is slidable in the pneumatic screwer  1  between an operating position in which the pneumatic screwer  1  acts with a screwing direction, and a further operating position in which the pneumatic screwer  1  acts with a further screwing direction. 
     On the cylindrical slider  21  a first seat  22 , a second seat  23  and a third seat  24  are obtained. 
     The first seat  22 , the second seat  23  and the third seat  24  are arranged in sequence, the second seat  23  being interposed between the first seat  22  and the third seat  24 . 
     The first seat  22  and the third seat  24 , i.e. the end seats, have the same depth, which is greater than the depth of the second seat  23 . 
     In a version of the invention that is not shown the first seat  22 , the second seat  23  and the third seat  24  have different depths. 
     In a further embodiment of the invention that is not shown, the first seat  22 , the second seat  23  and the third seat  24  have the same depths. 
     Further, the first seat  22 , the second seat  23  and the fourth seat  24  have respective concave abutting surfaces, for example curved abutting surfaces. 
     The pneumatic screwer  1  further comprises a first channel  25  and a second channel  26 , which are substantially rectilinear, into which respectively a first locking element  27  and a second locking element  28  are slidable. 
     The first locking element  27  and the second locking element  28  have a cylindrical shape with one rounded end. 
     In a version of the invention that is not shown, the first locking element  27  and the second locking element  28  have a spherical shape. 
     The first locking element  27  and the second locking element  28  are arranged for engaging, in an operating position of the switch  20  corresponding to a desired screwing direction of the pneumatic screwer  1 , with a pair of the aforesaid seats  22 ,  23 ,  24 . 
     In particular, in a first operating position A of the switch  20 , shown in  FIG. 8 , the first locking element  27  and the second locking element  28  engage respectively with the second seat  23  and with the third seat  24 , whereas in a second operating position of the switch  20  that is not shown the first locking element  27  and the second locking element  28  engage respectively with the first seat  22  and with the second seat  23 . 
     Consequently, both in the first operating position A and in the second operating position, the first locking element  27  and the second locking element  28  engage with two of the seats  22 ,  23 ,  24 , the second seat  23  engaging alternatively with the first locking element  27  or with the second locking element  28 . 
     The first locking element  27  and second locking element  28  are pressed against the seats  22 ,  23 ,  24  by respectively a first spring  29  and a second spring  30 . 
     The first spring  29  and the second spring  30  can be adjusted by respectively a first adjusting screw  31  and a second adjusting screw  32 . 
     Also, the stiffness of the first spring  29  and the second spring  30  can differ. 
     In use, at the start of an operating cycle, the switch  20  is positioned, for example, in the first operating position A. 
     In the first operating position A, the switch  20  places the delivery conduit  36  in flowing communication with the first distributing channel  37 . 
     Also, in the first operating position A, the switch  20  puts the second distributing channel  38  in flowing communication with the expansion chamber  39  via the further hole  43 . 
     Also, in the first operating position A, the switch  20  separates the first distributing channel  37  from the expansion chamber  39 , closing the hole  42 . In other words, when the switch  20  is in the first operating position A, the first distributing channel  37  is not in flowing communication with the expansion chamber  39 . 
     The pressurised air, introduced by the delivery conduit  36 , passes through the first distributing channel  37 , the first passage  40 , the first channel  46  and the supply conduit  17 , which delivers the pressurised air to the gap  11  inside a chamber that is initially of reduced volume, which is namely positioned near a zone in which the rotor  10  is nearer the stator  7 . 
     Forces that tend to drive the rotor  10  in opposite directions act on the blades  10  that define this chamber. 
     The prevailing force is the one that acts on the blade  14  that protrudes most from the respective seat  13 . 
     The resultant of the aforesaid forces produces a driving torque on the rotor  10 . 
     Subsequently, a portion of air contained in this chamber, which is already partially expanded, is expelled via the primary discharge conduits  18  which, via the manifold  48 , are in flowing communication with the expansion chamber  39 , the latter being in flowing communication with the atmosphere. 
     Still subsequently, following a further rotation of the rotor  10 , a remaining portion of air contained inside this chamber is expelled via the secondary discharge conduit  19  and conveyed via the second passage  41 , the second channel  47 , the second distributing channel  38 , and the further hole  43  until it reaches the expansion chamber  39  in flowing communication with the atmosphere. 
     When it is desired to use the pneumatic screwer  1  with another screwing direction, opposite the preceding one, it is sufficient to act on the switch  20  by positioning the switch  20  in the second operating position. 
     In the second operating position, the switch  20  puts the delivery conduit  36  in flowing communication with the second distributing channel  38 . 
     Also, in the second operating position, the switch  20  puts the first distributing channel  37  in flowing communication with the expansion chamber  39  via the hole  42 . 
     Also, in the second operating position, the switch  20  separates the second distributing channel  38  from the expansion chamber  39  by closing the further hole  43 . In other words, when the switch  20  is in the second operating position, the second distributing channel  38  is not in flowing communication with the expansion chamber  39 . 
     The pressurised air, introduced by the delivery conduit  36 , passes through the second distributing channel  38 , the second passage  41 , the second channel  47  and the secondary discharge conduit  19 , which now acts as a supply conduit, that delivers the pressurised air into the gap  11  inside a chamber that is initially of reduced volume, i.e. positioned near a zone in which the rotor  10  is nearer the stator  7 . 
     Forces that tend to drive the rotor  10  in opposite directions act on the blades  10  that define this chamber. 
     The prevailing force is the one that acts on the blade  14  that protrudes most from the respective seat  13 . 
     The resultant of the aforesaid forces produces a driving torque on the rotor  10  by driving the rotor  10  in an opposite direction than before. 
     Subsequently, a portion of air contained in this chamber, which has already been partially expanded, is expelled via the primary discharge conduits  18  which, via the manifold  48 , are in flowing communication with the expansion chamber  39 , the latter being in flowing communication with the atmosphere. 
     Still subsequently, following a further rotation of the rotor  10 , a remaining portion of air contained inside this chamber is expelled via the supply conduit  17 , which now acts as secondary discharge conduit, and is conveyed via the first passage  40 , the first channel  46 , the first distributing channel  37 , and the hole  42  until it reaches the expansion chamber  39  in flowing communication with the atmosphere. 
     With reference to  FIGS. 10 and 11 , there is shown a second version of the aforesaid switch, indicated by the numeric reference  120 . 
     The switch  120  comprises a cylindrical slider  121  that is slidable in the pneumatic screwer  1  between an operating position in which the pneumatic screwer  1  acts with a screwing direction, and a further operating position in which the pneumatic screwer  1  acts with a further screwing direction. 
     On the cylindrical slider  121  a first seat  122 , a second seat  123  and a third seat  124  are obtained. 
     The first seat  122 , the second seat  123  and the third seat  124  are arranged in sequence, the second seat  123  being interposed between the first seat  122  and the third seat  124 . The first seat  122  and the third seat  124 , i.e. the end seats, have the same depth, which is greater than the depth of the second seat  123 . 
     In a version of the invention that is not shown, the first seat  122 , the second seat  123  and the third seat  124  have different depths. 
     In a further embodiment of the invention that is not shown, the first seat  122 , the second seat  123  and the third seat  124  have the same depth. 
     Also, the first seat  122 , the second seat  123  and the fourth seat  124  have respective concave, for example curved, abutting surfaces. 
     Also the switch  120  is movable between a first operating position A, shown in  FIG. 10 , and a second operating position, which is not shown. 
     In particular, in the first operating position A of the switch  120 , the first locking element  27  and the second locking element  28  engage respectively with the second seat  123  and with the third seat  124 , whereas in the second operating position of the switch  120 , which is not shown, the first locking element  27  and the second locking element  28  engage respectively with the first seat  122  and with the second seat  123 . 
     Consequently, both in the first operating position A and in the second operating position, the first locking element  27  and the second locking element  28  engage with two of the seats  122 ,  123 ,  124 , the second seat  123  engaging alternatively with the first locking element  27  or with the second locking element  28 . 
     The first locking element  27  and the second locking element  28  are pressed against the seats  122 ,  123 ,  124  by respectively the first spring  29  and the second spring  30 . 
     The first spring  29  and the second spring  30  can be adjusted by respectively the first adjusting screw  31  and the second adjusting screw  32 . 
     Also, the stiffness of the first spring  29  and of the second spring  30  can differ. 
     In use, at the start of an operating cycle, the switch  120  is positioned, for example, in the first operating position A. 
     In the first operating position A, the switch  120  puts the delivery conduit  36  in flowing communication with the second distributing channel  38 . 
     Also, in the first operating position A, the switch  120  puts the first distributing channel  37  in flowing communication with the expansion chamber  39  via the hole  42 . 
     Also, in the first operating position A, the switch  120  separates the second distributing channel  38  from the expansion chamber  39  by closing the further hole  43 . In other words, when the switch  120  is in the first operating position A, the second distributing channel  38  is not in flowing communication with the expansion chamber  39 . 
     The pressurised air, introduced by the delivery conduit  36 , passes through the second distributing channel  38 , the second passage  41 , the second channel  47  and the secondary discharge conduit  19 , which now acts as supply conduit, that delivers the pressurised air to the gap  11  inside a chamber of initially reduced volume, i.e. positioned near a zone in which the rotor  10  is nearer the stator  7 . 
     On the blades  14  that define this chamber, forces act that tend to drive the rotor  10  in opposite directions. 
     The prevailing force is the one that acts on the blade  14  that protrudes most from the respective seat  13 . 
     The resultant of the aforesaid forces produces a driving torque on the rotor  10  that rotates the rotor  10 . 
     Subsequently, a portion of air contained in this chamber, which has already been partially expanded, is expelled via the primary discharge conduits  18 , which, via the manifold  48 , are in flowing communication with the expansion chamber  39 , the latter being in flowing communication with the atmosphere. 
     Also subsequently, following a further rotation of the rotor  10 , a remaining portion of air contained inside this chamber is expelled via the supply conduit  17 , which now acts as secondary discharge conduit, and is conveyed via the first passage  40 , the first channel  46 , the first distributing channel  37 , and the hole  42  until it reaches the expansion chamber  39  in flowing communication with the atmosphere. 
     When it is desired to use the pneumatic screwer  1  with another screwing direction, opposite the previous one, it is sufficient to act on the switch  120  by positioning the switch in the second operating position. 
     In the second operating position, the switch  120  puts the delivery conduit  36  in flowing communication with the first distributing channel  37 . 
     Also, in the second operating position, the switch  120  puts the second distributing channel  38  in flowing communication with the expansion chamber  39  via the further hole  43 . 
     Also, in the second operating position, the switch  120  separates the first distributing channel  37  from the expansion chamber  39  by closing the hole  42 . In other words, when the switch  20  is in the second operating position, the first distributing channel  37  is not in flowing communication with the expansion chamber  39 . 
     The pressurised air, introduced by the delivery conduit  36 , passes through the first distributing channel  37 , the first passage  40 , the first channel  46  and the supply conduit  17  which delivers the pressurised air into the gap  11  inside a chamber of initially reduced volume, i.e. positioned near a zone in which the rotor  10  is nearer the stator  7 . 
     Forces that tend to drive the rotor  10  in opposite directions act on the blades  10  that define this chamber. 
     The prevailing force is the one that acts on the blade  14  that protrude most from the respective seat  13 . 
     The resultant of the aforesaid forces produces a driving torque on the rotor  10 . 
     Subsequently, a portion of air contained in this chamber, which has already been partially expanded, is expelled via the primary discharge conduits  18  which, via the manifold  48 , are in flowing communication with the expansion chamber  39 , the latter being in flowing communication with the atmosphere. 
     Also subsequently, following a further rotation of the rotor  10 , a remaining portion of air contained inside this chamber is expelled via the secondary discharge conduit  19  and is conveyed via the second passage  41 , the second channel  47 , the second distributing channel  38 , the further hole  43  until it reaches the expansion chamber  39  in flowing communication with the atmosphere. 
     It should be noted how, for the same operating position, the switch  20  and the switch  120  induce opposite screwing directions to the pneumatic screwer  1 . 
     It should be noted that the pneumatic screwer  1  is more efficient than known screwers. 
     In fact, the primary discharge conduits  18  and the secondary discharge conduit  19  are in flowing communication with the expansion chamber  39 , which is positioned on an opposite side of the spindle element  5  with respect to the rotor  10  and is in flowing communication with the atmosphere. 
     This enables the pressurised air to reduce the path that it needs to travel to expand completely, as it no longer has to travel over the entire handle  3  of the pneumatic screwer  1 , which enables the performance of the pneumatic screwer  1  according to the invention to be increased. 
     Also, it should be noted that the pneumatic screwer  1  according to the invention is more comfortable for the operator to use. 
     In fact, the pressurised air is expelled into the atmosphere via the first grid  50  and/or the second grid  51  positioned laterally with respect to the handle  3 , this enabling it to be prevented that jets of pressurised air hit the operator. 
     It should be further noted how, in use, the primary discharge conduits  18  and the secondary discharge conduit  19 , or the supply conduit  17  when it acts as a discharge conduit, define paths that are different and separate from one another for the air exiting from the gap  11 , these paths both leading into the expansion chamber  39 , in which the air can mix and exit into the atmosphere. 
     Also, it should be noted that the switch  20 ,  120  according to the invention is more reliable and manoeuvrable than known switches. 
     In fact, the results of experiments have shown that the first locking element  27  and the second locking element  28  engaging, in the operating position, with two of the three seats  22 ,  23 ,  24 , or  122 ,  123 ,  124 , enable the switch  20 ,  120  to maintain effectively the operating position, at the same time ensuring the easy manoeuvrability of the operating position.