Patent Publication Number: US-2013248563-A1

Title: Apparatus for Dispensing Powder

Description:
This invention relates to apparatus for dispensing defined amounts of a powder material such as a pharmaceutical powder for use as a dry powder inhaler. 
     Apparatus of this type is used to dispense powder into an inhaler device such as blister packs and many different types of such apparatus exist in the art. The present invention is concerned with a development of this type of apparatus. 
     A number of known systems include drums for delivering powder from a hopper to a receptacle. For example, the documents U.S. Pat. No. 2,913,018 and U.S. Pat. No. 3,656,518 describe arrangements in which powder is drawn into a chamber in a drum using negative gas pressure. In both of these arrangements the powder is expelled using a positive gas pressure. These arrangements are considered disadvantageous because the use of pressurised gas can cause an undesirable dusting of powder on surfaces of the apparatus and the receptacle. 
     Another known arrangement is described in GB 999,030. In this arrangement powder can be transferred from a hopper to receptacles in charge chambers of a drum. No pressurised air is used to retain the powder in the receptacles. The powder is retained by an annular housing as it rotates, but the arrangement may cause powder to be lost from the receptacles as the drum is rotated. In GB 999,030 powder is dispensed from the charge chambers using a spring loaded ejector which is arranged radially within the circular drum. 
     One object of the present invention is to provide an apparatus that can avoid unintentional loss of powder from a drum assembly without causing an undesirable dusting of surfaces. 
     Another object of the invention is to provide an apparatus with a reduced drum diameter that can also be cleaned more easily. 
     According to the present invention there is provided apparatus for dispensing a defined quantity of powder material comprising a drum assembly having a foil mounted for movement relative to a support portion, said foil having at least one through aperture, said support portion having at least one aperture which can be aligned with the through aperture of the foil by said relative movement, the aperture of the support portion being closable to define a compartment into which powder can be delivered at a filling position when said apertures are aligned, and the drum assembly being movable to allow movement of the filled compartment to a dispensing position to allow the contents of the compartment to be dispensed. 
     In this way a predetermined quantity of powder can be accumulated in a compartment and delivered at the dispensing position. By closing the compartment with the foil the present apparatus can deliver powder to the dispensing position without any loss of powder. This can be achieved in the present apparatus without the use of pressurised air in order to prevent powder from coating surfaces of the apparatus. 
     The foil or cover portion is preferably designed to cover the aperture in the support portion and thereby close the compartment. When the compartment is closed it may be safe to move the drum assembly from the filling position to the dispensing position without any loss of powder. 
     The drum assembly includes both the foil and the support portion and preferably both of these components are arranged to rotate together. Thus, the foil can close the compartment and rotate together with the powder until complete alignment is attained with the receiver. Accordingly there is no possibility for any loss of powder due to failure of inter-particle frictional forces to retain the unsupported powder at an end of the compartment during the final alignment. 
     Preferably the drum assembly has a cylindrical portion mounted for movement relative to the support portion, said cylindrical portion having said foil on its outer surface. 
     Preferably the compartment is filled completely with powder so that there is a predetermined dosage of powder. The edge of the foil may doctor off any excess powder when it closes the compartment. 
     Preferably the drum assembly is rotatable between the filling and dispensing positions. Preferably still the drum assembly is rotatable through 180°, with the filling position at ‘ 12  o&#39;clock’ and the dispensing position at ‘6 o&#39;clock’. 
     Preferably the foil has a plurality of spaced through apertures and the support portion has a corresponding number of spaced apertures. In this way a number of compartments can be filled with powder in a single motion. This can provide a convenient mechanism for filling a number of receptacles, such as blister packs, quickly. The apertures may be spaced linearly and regularly. 
     The or each aperture of the support portion may have an associated piston which can be moved into the inner end of the aperture. The piston may be arranged to dispense the contents of the compartment quickly in the dispensing position. In addition the piston may define the base of the compartment so that the initial position of the piston defines the volume of the compartment at the filling position. 
     Each piston may be carried on a carrier, and the carrier may be cam operated to effect movement of said piston or pistons. 
     Preferably said foil and said support portion are moveable axially relative to another to cause opening or closing of said compartment. However, a number of alternative types of relative movement would be possible in order for the foil to close the compartment. For example, the foil may move circumferentially relative to the support portion. 
     A receptacle or receptacles may be located adjacent the dispensing position to receive dispensed powder. Non-limiting examples of the receptacle include a blister strip formed pocket, a bottle, and the bottom portion of a capsule. 
     The apparatus may include a hopper containing powder for delivering to the or each compartment. In addition the hopper may include means for compressing the powder towards the or each compartment, such as a roller. An agitator may be provided for aerating the powder in the hopper before it is compressed towards a compartment. 
     The apparatus may include a cleaning station positioned between the dispensing position and the filling position. The cleaning station may use pressurised air to remove small amounts of powder from an empty compartment in the support portion, including the faces of the pistons. 
     The or each piston may be arranged to compact the powder in a closed compartment. Thus, the powder may be compacted between the piston and the foil that closes the end of the compartment. This may be desirable so that the piston can lightly compress the dose to conform to the required properties of the powder to be dispensed. 
     The apparatus may be mounted on a carriage that permits translational movement relative to a receptacle. In this way the drum may be translated in synchronisation with a moving receptacle in order to optimise the filling of the receptacle. 
     The powder may be pharmaceutical powder for use as a dry powder inhaler. However, the apparatus may be used for dispensing predetermined quantities of a number of different types of powder. 
     According to another aspect of the present invention there is provided a method of dispensing defined quantity of powder material, the method comprising the steps of: positioning a foil relative to a support portion of a drum assembly so that at least one through aperture in the foil can be aligned with an aperture in the support portion; filling a compartment in the support portion by delivering powder through the aperture of the foil and the aperture of the support portion; moving the foil relative to the support portion in order to close the compartment; moving the drum assembly so that the filled compartment can be moved to a dispensing position; and dispensing the contents of the compartment when it is in the dispensing position. 
     According to another aspect of the invention there is provided an apparatus for dispensing a predetermined dose of powder, the apparatus comprising: a drum assembly having a main axis and at least one aperture into which powder can be delivered at a receiving position; a piston associated with the or each aperture for dispensing powder out of the aperture at a dispensing position; a driving assembly that is connectable to the piston, wherein the driving assembly is arranged to drive the piston radially with respect to the main axis of the drum assembly; wherein the drum assembly is rotatable from the filling position to the dispensing position, and wherein the driving assembly is located axially of the piston with respect to the main axis of the drum assembly. 
     In this way a powder dispenser can be provided with a reduced diameter in comparison to a drum assembly having a radial piston cylinder or a radial piston spring. A reduced diameter is advantageous because it decreases the overall cost of the apparatus. 
     By providing the piston in a position that is axially displaced from the driving assembly it is also possible to isolate the driving assembly from the powder filling region. This is advantageous because it means that powder is less likely to interfere with moving parts in the driving assembly. Also, the drum assembly, including the piston, can be easily disconnected from the driving assembly for cleaning. This means that powder coated surfaces can be cleaned easily without stripping the entire machine apart. In addition, the driving assembly can be isolated from any cleaning products which could interfere with its normal operation. 
     Preferably the apparatus includes a plurality of pistons, each associated with a separate aperture. In this way the drum may be able to fill a plurality of powder receptacles simultaneously. 
     The apparatus may include an alignment adjuster for adjusting the inclination of the or each piston relative to its associated aperture. It is important that each piston can slide easily into an aperture with minimal clearance around the periphery of the piston. This minimises any loss of powder during operation of the apparatus. The alignment adjuster is preferably arranged to provide microscopic adjustments in the inclination of the piston in order to optimise alignment. 
     A plurality of pistons may be provided on a flexible piston plate in the drum assembly. The piston plate may be flexed by the alignment adjuster so that all of the pistons on the piston plate can have their alignment adjusted at the same time. 
     The radial movement of the or each piston may be provided by the geared-down motion of a component in the drive assembly. Thus, a large motion in the drive assembly can be converted into a smaller movement in the piston. For example, a stroke reducer may be provided in the drive assembly for converting an axial motion into a radial motion with a ratio of approximately 10:1. The stroke reducer can increase the accuracy with which the piston is positioned, thereby improving accuracy in the control of the powder dosage. 
     The piston may define the base of a compartment into which powder can be delivered, and the position of the piston can be controlled in order to adjust the volume of the compartment. By adjusting the position of the piston it is possible to adjust the position of the base of the compartment and thereby alter the volume of the compartment. In this way it is possible to adjust the dose that is delivered by the apparatus. 
     The piston may be arranged to compress the powder in the compartment. In this way, powder can be received in the compartment in the receiving position, and the powder can be subsequently compressed by the piston. The motion of the piston can be carefully controlled to maintain the integrity of the dose and to allow any air to escape. 
     The apparatus may comprise a compaction band against which the piston can compress the powder. Preferably the compaction band is arranged to follow the motion of the compartment, at least in part, while it moves from the receiving position to the dispensing position. The compaction band can, therefore, lie against the top of the compartment while the piston compresses the powder. Preferably there is no relative circumferential movement between the compaction band and the compartment when the piston compresses the powder; this minimises any loss of powder between the compartment and the compaction band. 
     The drum assembly, the piston and the driving assembly may be mounted on a carriage that permits translation of the components. By mounting the apparatus on a translatable carriage powder can be delivered into receptacles on a moving conveyor belt with a minimal relative movement between the drum compartment and the receptacles. This arrangement allows powder to be dispensed more slowly which can reduce powder loss and improve dose integrity. 
     According to another aspect of the invention there is provided a method of cleaning the apparatus as defined above, the method comprising the steps of: disconnecting the piston from the drive assembly; removing the drum assembly from the drive assembly; cleaning the drum assembly; and re-attaching the drum assembly by connecting the piston and the drive assembly. 
     In this way the drum assembly can be removed quickly and easily so that it can be cleaned. The drum assembly can be removed without a complicated sequence of steps for stripping the machine down because the drum assembly is cantilevered relative to the drive assembly, which means the drum assembly is connected to the drive assembly from one side only. 
     Any apparatus features may be provided as method features and vice-versa. Preferred features of the invention are set out in the dependent claims. 
    
    
     
       The invention will be described now by way of example only with particular reference to the accompanying drawings. In the drawings: 
         FIG. 1  is schematic illustration of a device in accordance with the present invention; 
         FIG. 2  is an exploded view of the device of  FIG. 1 ; 
         FIG. 3  is a view showing part of the device of  FIG. 1 ; 
         FIG. 4  is a sectional view showing another part of the device of  FIG. 1 ; 
         FIGS. 5 ,  6  and  7  illustrate the operation of the device of  FIG. 1 ; 
         FIG. 8  is a perspective view of a detailed embodiment of a device in accordance with the present invention; 
         FIG. 9  is a plan view of the device of  FIG. 8 ; 
         FIG. 10  is a sectional view along the line  9 - 9  of  FIG. 9 ; 
         FIG. 11  shows the clamping of the foil to the drum; 
         FIG. 12  shows an alternative form of the foil structure; 
         FIG. 13  shows a schematic illustration of a device in another embodiment of the present invention; 
         FIG. 14  is a cross-sectional view of a powder dispensing apparatus in an embodiment of the invention; 
         FIG. 15  is a more detailed view of one of the features in  FIG. 14 . 
     
    
    
     Referring to  FIGS. 1 to 7  a device for dispensing defined amounts of a powder comprises a drum  2  which is supported on a structure  10  extending outwardly from a wall  11  of a housing. A hopper  12  is mounted above the drum  2 . A thin stainless steel foil  14  is wrapped around the circumference of the drum  2 . Referring to  FIG. 2  of the drawings the drum  2  has a longitudinal slot  15  that is arranged to coincide with the location of the hopper  12 . The support structure  10  extending out from the housing  11  has upper and lower limbs  16  and  17  which project outwardly from the wall  11 . The free ends of the limbs  16  and  17  are connected by a member  18 . Each limb has formed therein a series of longitudinally spaced through apertures or bores  20 . Mounted between the limbs  16  and  17  are longitudinal members  22  and  23  each of which carries a series of outwardly extending pins  24 , the number and spacing of the pins corresponding to the number and spacing of the apertures  20 . The longitudinal members  22  and  23  are moveable radially by a mechanism not shown in  FIG. 2  so that the pins act as pistons and can move into the apertures  20  to thereby close the lower end of the apertures. This enables the apertures to define a variable size cavity or compartment depending upon the extent to which the pistons move into the apertures. The capacity of each cavity is set by an adjustment screw stop which limits the extent of the inward radial pin travel to control the fillable volume of the cavity. The upper limb  16  is received within the slot  15  formed in the drum when the drum is mounted upon the structure  10  and the limb  17  is received in a similar longitudinal slot not shown in the drawings. 
     The foil  14  wrapped around the circumference of the drum has formed therein a series of apertures  25  whose number and spacing corresponds to the number and spacing of the apertures  20 . By appropriate placement of the drum longitudinally on the support structure  10  the apertures  25  formed in the foil  14  can be aligned or misaligned with the apertures  20  to thereby open or close the cavities or compartments. 
     In use the drum  2  is located longitudinally relative to the limbs  16  and  17  so that the apertures  25  of the foil  14  are aligned with the apertures  20 . The elements  22  and  23  are moved radially outwardly so that the pistons extend into the apertures  20  to form a cavity or compartment of a predefined size. Powder is located in the hopper  12  and enters the cavities by way of the apertures  25  in the foil  14 . The powder can be forced into the cavities by an arrangement of rollers and blades not shown in the drawings. Such arrangements will be known to those skilled in the art.  FIG. 5  of the drawings illustrates a configuration in which the bases of the apertures  20  formed in the limbs  16  are closed by the pistons  24 . The apertures  25  formed in the foil layer are shown to be in alignment with the upper side of apertures  20  formed in the element  16 . In this configuration powder can enter the cavity defined by the aligned apertures. 
     Once the cavities have been filled the drum and hence the foil  14  are displaced longitudinally relative to the limb  16  so that the apertures  25  in the foil become displaced from the apertures  20  in the limbs  16 . This situation is illustrated in  FIG. 6  of the drawings. In this configuration the cavities or compartments containing the powder are closed. 
     When the compartments containing powder have been closed the elements  22  and  23  can be moved radially outwardly so that the pistons  24  can compact the powder against the foil  14 . This optional compaction or densification may be arranged to lightly compress the powder so that the powder particles can be held together by cohesion and dispensed into a receptacle with predetermined compaction properties. 
     The drum with the structure  10  is then rotated so that the cavities move from the upper, filling position illustrated in  FIG. 2  of the drawings through 180° to a lower position from which the powder in the cavities can be dispensed to a receptacle which is not shown in  FIGS. 1 to 7 . When the drum is rotated the foil  14  is rotated as well. This means that there is no relative movement between the powder and the foil  14  during rotation. The optional compaction or densification can take place before, during or after rotation of the drum, but optimal efficiency may be achieved if compaction is performed during rotation. 
     Once the drum and associated structure have been rotated through 180° the foil  14  is then adjusted longitudinally so that the apertures  25  become aligned with the apertures  20 . In order to eject the powder from its respective cavity the elements  22  and  23  are moved radially outwardly so that the pistons  24  move radially outwardly and force the powder from the cavity into the receptacle. This is shown in  FIG. 7 . The receptacles used may be any type of receptacle for receiving dosed quantities of powder, such as, for example, a blister-type pack. 
     The apparatus may further include a cleaning station (not shown) for cleaning at least the compartments, the support portion  10  and the pistons  24  when they move from the dispensing position towards the filling position. Preferably the drum is arranged to dwell adjacent the cleaning station so that pressurised air can be used to expel any remnants of powder from the apparatus. 
     Referring to  FIGS. 8 ,  9  and  10 , a more detailed embodiment of a dosing device in accordance with the present invention will be described. Elements corresponding to those shown in  FIGS. 1 to 7  are shown by like reference numerals. With reference to  FIG. 8  the drum with its encircling foil is shown mounted between an upstanding plate  30  and housing structure  31 , each of which is mounted upon a supporting base  32 . A receptacle  34  for receiving dispensed powder is mounted on the supporting base  32  beneath the drum. Referring now to  FIGS. 8 to 10  the end wall  30  supports a shaft  35  which extends through an aperture in the wall  30 . The shaft  35  is supported in the aperture on a bearing  36  so that the shaft can rotate relative to the wall. The outer end of the shaft carries a manually operable wheel  37 . The internal end of the shaft  35  is connected to the member  18 . 
     The array of pistons  24  are shown mounted upon an element  38 , which is guided for radial movement by way of slides  40 , 41  extending between the limbs  16  and  17 . The supporting element  38  is provided with cams  42  which locate in inclined slots  43 . A shaft  58  extends through the housing  31  towards the mounting element  38 . At the outer end of the shaft  58  a micrometer adjusting mechanism  59  is provided external to the housing  31 . The micrometer  59  provides a means to set the filling volume of the cavity or cavities and thereby controls the dose weight. The shaft  58  can be moved longitudinally by means of an arrangement comprising a handle  60  which has a downwardly extending shaft  61  connected to an eccentric arrangement  64 . Rotation of the handle  60  about its shaft  61  causes through the eccentric lateral movement of a disc  66  through which the shaft  68  extends. This movement occurs against the bias of a return spring  69 . Movement of the disc  66  causes a corresponding longitudinal movement of the shaft  58 . At its lower extremity the disc  66  is guided by a detent arrangement  70  which locates the fill and discharge rotational positions. 
     A second handle  80  is supported relative to the housing  31  and is connected to a second eccentric arrangement  82 . Operation of the handle  80  to rotate the handle results in the eccentric causing longitudinal movement of the drum and hence its foil sleeve  14  to effect the relative longitudinal motion described with reference to  FIGS. 1 to 7 . This movement occurs against the bias of a return spring  84   
     The internal ends of the limbs  16  and  17  are connected to a sleeve  85 , which is supported within a bearing arrangement  86  to thereby allow rotary motion of the drum with the structure of limbs the  16  and  17 . 
     Thus it can be seen in the detailed arrangement of  FIGS. 8 to 10  that radial movement of the pistons  24  is effected by rotation of the handle  60 . Rotation of the handle  60  results in longitudinal movement of the shaft  58  and this causes the element  38  to move upwardly by virtue of sliding motion of the cams  42  within their slots  43 . The amount by which the pistons are moved radially can be controlled by appropriate rotation of the handle  60  and fine adjustment can be achieved by operation of micrometer adjustment. Thus this operation sets the size of the cavity to be used in any dosing operation. 
     In this arrangement the radial movement of the pistons  24  is caused by rotation of the handle  60 , which is located axially of the pistons, with respect to the main axis of the drum  2 . This is preferable to providing radial driving means for the pistons  24 , such as radial springs, because it allows the diameter of the drum  2  to be minimised. 
     Sliding movement of the drum  2  and its foil  14  relative to the ports  20  is achieved by operating the handle  80  to thereby open or close those ports. It will be appreciated that the cavities are filled by powder from the hopper  12  in the manner already described, with reference to  FIGS. 1 to 7 . 
     The foil  14  is secured to the drum by bolts  90  which sandwiches adjacent ends of the foil between the face of the drum and a clamp bar  92  (see  FIG. 11 ). The foil or cover  14  which is made from stainless steel and should be as thin as practicable whilst maintaining its necessary strength. Typically the foil will have a thickness of the order of 75 μm. Once the cavities have been filled and the foil has been moved to a position in which those cavities are closed, the drum together with the limbs  16  and  17  of the support system can be rotated through 180° by operation of the handle  37 . This brings the cavities to a position immediately above the receiving receptacle  34  for the dosed quantities of powder. Once in this position the drum and its foil are adjusted longitudinally by operation of the handle  80  in order to open the cavities. The shaft  58  is then actuated by operation of the handle  60  in order to force the pistons further outwardly radially to thereby cause the powder to be ejected from the cavities into the appropriate receptacles. 
     It will be appreciated that whilst manually operable elements  37 ,  60  and  80  are shown in the embodiment described, these will normally be replaced by automatically operable devices such as motors to enable the device to operate automatically. 
     As an alternative to a foil having its ends clamped to the drum by the bolts  90  and clamp bar  92 , the foil may be a welded ring of material. 
     The described embodiments use a single sheet of foil  14 . In an alternative arrangement the foil  14  could include a number of segments  14   a,b,c,d  as shown in  FIG. 12 . In radial cross-section the segments  14   a,b,c,d  may form arcs of a circle. 
     A fixed cam  29  is provided at one end of the drum  2 . Each foil segment  14   a,b,c,d  is connected to a corresponding cam follower  27   a,b,c,d  that is rotatable relative to the cam  29 . The cam  29  and cam followers  27   a,b,c,d  are arranged so that the powder compartments are open when the foil segments  14   b,d  are at the top and bottom positions (the 12 o&#39;clock and the 6 o&#39;clock positions). The powder compartments are arranged to be closed when they are away from these positions. 
     In one configuration the entire apparatus may be mounted on a carriage that can oscillate with a translational movement above a moving conveyor belt including powder receptacles. In this way the movement of the carriage can match movement of the receptacles so that the receptacles can be filled without any relative movement between them and the dispensing powder compartments in the drum. This arrangement may be desirable in order to optimise powder transfer into the receptacles. 
       FIG. 13  is a schematic view of another embodiment of a powder dispensing apparatus. The apparatus includes a drum  102  including a plurality of compartments  107  for accepting powder. A piston  124  defines the base of each compartment  107 , as will be explained in more detail later. A hopper  112  is mounted above the drum assembly  102 , and powder recirculating elements  109  are provided to aerate the powder  113  in the hopper  112 . 
     A roller (not shown) is provided in the hopper  112  for filling compartments  107  with powder. The drum  102  is rotatable so that the compartments can rotate from the ‘12 o&#39;clock’ position to the ‘6 o&#39;clock’ position where the powder can be dispensed. 
     The apparatus includes a compaction station  121  where powder in the compartments  107  can be compressed. The compaction station  121  includes an endless belt  119  that is arranged to follow the motion of a compartment  107  along an arc of the drum  102 . The powder in each compartment  107  can be compressed against the belt  119  by the piston  124 . In this way the piston  124  can control the density or degree of compaction of powder in each compartment  107 . 
     The apparatus also includes a first cleaning station  127  for the endless belt  119 . The first cleaning station  127  is arranged to remove any excess powder from the endless belt  119 . The first cleaning station  127  is located between the drum  102  and a conveyor belt  126  that carries a plurality of receptacles  134 . Thus, the first cleaning station  127  can provide a cover for the incoming receptacles  134  to prevent any contamination before they are filled with powder. 
     The receptacles  134  are filled with powder when the compartments  107  are at the dispensing position. This is achieved by actuating the pistons  124 , as described previously. 
     The apparatus also includes a second cleaning station  137  that is arranged to clean the compartments  107  and the pistons  124  once the dose has been dispensed. The second cleaning station is located between the drum  102  and the conveyor belt  126  so that it can provide a cover for the filled receptacles  134  and prevent any contamination with foreign objects or excess powder. 
     A cross-sectional view of the powder dispensing apparatus is shown in  FIG. 14 . As is apparent from  FIG. 14 , the drum  102  is connected to the remainder of the apparatus, which includes the driving mechanism, from one side only. In other words, the drum  102  is cantilevered with respect to the remainder of the apparatus. 
     The drum  102  includes a plurality of pins  124  that act as pistons, extending radially from a piston plate  202 , as can be seen in greater detail in  FIG. 15 . The piston plate  202  is flexible relative to a main arm  204  that extends axially towards the drive mechanism. An adjustment screw  206  is provided in order to flex the piston plate  202  about a hinge point  203  relative to the main arm  204 . The purpose of the adjustment screw  206  is to allow fine control of the orientation of the pins or pistons  124  relative to corresponding apertures in the drum  102 . The piston plate  202  is flexed so that all of the pistons  124  can line up accurately with their corresponding aperture. This ensures that the pistons  124  can slide easily into the apertures so that no powder is lost around the edges of the pistons  124 . 
     The pistons, the main arm  204  and the piston plate  202  can be connected to a drive mechanism so that they can be actuated. Bolts  208 ,  210  are provided in order to assemble the main arm  204  to the drive assembly. 
     The drive mechanism includes a main driving mechanism  212  that extends axially relative to the main axis of the drum  102 . The main driving mechanism  212  is connected to a stroke reducer  214  which is a wedge-shaped member for converting axial motion into radial motion. The stroke reducer  214  is connected to two vertically extending members  216 ,  218  that are assembled to the main arm  204  with the bolts  208 ,  210 . The stroke reducer  214  is arranged to convert axial motion into radial motion with a ratio of around 10:1. Thus the stroke reducer  214  provides a mechanism for enabling geared-down radial motion. This is advantageous because it allows very fine control of the position of the pistons  124 . 
     The driving force that allows the pistons  124  to be actuated can be traced back to the main driving mechanism  212 . The main driving mechanism  212  is located axially of the pistons  124  so that it is not a limiting factor when choosing a diameter for the drum  102 . In this way it is possible to design a drum  102  with a reduced diameter because the drum  102  does not need to include a radial piston cylinder or spring. 
     The driving mechanism includes a motor  200  that is arranged to rotate the drum  102 . 
     In order to remove the drum  102  from the drive assembly it is necessary merely to remove the bolts  208 ,  210 . This allows the entire drum assembly, including the pistons  124  and their associated parts to be removed from the drive assembly. The drum assembly can then be cleaned in a remote location without exposing any of the drive assembly to cleaning products. 
     It will be appreciated that the present arrangement allows the drum  102  to be cantilevered relative to the drive assembly. In other words, the drum  102  is supported entirely from one side. This is advantageous because it facilitates easy removal of the drum  102  without completely stripping down the apparatus.