Patent Publication Number: US-2006002799-A1

Title: Peristaltic pump comprising a bearing member and a counter-member adapted to cooperate with a tube

Description:
The invention relates to the general field of peristaltic pumps.  
      It relates more particularly to a peristaltic pump comprising a bearing member and a counter-member between which a tube on which said pump must act is gripped.  
      A peristaltic pump, as used in the medical field in particular, is a pump whose rotor is provided incorporating rollers that progressively compress the cross section of an elastic tube to move a liquid along the tube.  
      This kind of pump is therefore used to circulate a fluid inside a tube by operating only on the tube, without coming into contact with the liquid. This type of pump is therefore suitable for any application requiring the fluid to remain in a confined atmosphere, for example to avoid contamination of the fluid when working in a sterile environment. A peristaltic pump is generally adapted to operate in an environment where the concept of sterility is of primordial importance. The pump must therefore not only fulfill its function of circulating a fluid and preventing its contamination by the environment, but also avoid contamination of the environment by the pump itself. The various components of the pump must therefore be easy to clean, where appropriate by being demountable, at the same time as ensuring a perfect seal.  
      A peristaltic pump typically comprises a rotor comprising rollers at its periphery and a mobile jaw adapted to assume an open position, in which it is moved away from the rotor so that an elastically deformable tube on which the pump has to act may be placed between the jaw and the rotor, and a closed position, in which the mobile jaw is moved toward the rotor so that the tube is gripped between a curved bearing surface on the mobile jaw and at least one roller of the rotor.  
      Peristaltic pumps of the above kind are known in the art in which the mobile jaw comprises an excrescence formed by a bearing member and in which the pump body is provided with a counter-member disposed so that, when the jaw is in its open position, the member is moved away from the counter-member and, when the mobile jaw is in its closed position, the bearing member is moved toward the counter-member so that, when a tube is fitted into the pump, the tube is gripped between the bearing member and the counter-member. This gripping action generally has the function of holding the tube in place while the pump is operating.  
      The peristaltic pumps available at present generally allow visual inspection of the correct position of the tube between the rotor and the mobile jaw when the latter is in the closed position. Similarly, correct circulation of the fluid inside the tube may be monitored visually or automatically on the upstream and/or downstream side of the pump.  
      The object of the invention is to improve the above type of pump.  
      To this end, the invention provides a peristaltic pump comprising a rotor incorporating rollers and a mobile jaw that is provided with a bearing member and assumes: 
          an open position in which it is moved away from the rotor, the bearing member then being moved away from a fixed counter-member on the pump, with the result that a tube on which said pump must act may be fitted between the jaw and the rotor, on the one hand, and between the bearing member and the counter-member, on the other hand, and     a closed position in which the mobile jaw is moved close to the rotor, which moves the bearing member toward said counter-member, with the result that said tube is gripped between a curved bearing surface of the mobile jaw and at least one roller of the rotor, on the one hand, and between the bearing member and the counter-member, on the other hand,     this pump being characterized in that it further comprises:     a sensor of the force exerted between the bearing member and the counter-member; and     a processing unit comprising means for determining, from the signal supplied by the sensor, if predetermined conditions indicative of correct positioning of the tube between the bearing member and the counter-member have been satisfied.        

      The above kind of pump therefore has access at all times to information relating to the force that is exerted by the tube when it is fitted into the pump. This force being representative of the elastic behavior of the combination of the tube and the liquid that it conveys, various measurement or monitoring parameters can be monitored in this way.  
      Firstly, the sensor may provide information relating to the presence or the absence of a force exerted between the bearing member and the counter-member.  
      The processing unit therefore has access to information indicating that the tube is in place or, to the contrary, that a misoperation has occurred since the tube is not in position between the bearing member and the counter-member.  
      To obtain the best results, the force sensor may be integrated into the counter-member.  
      In this case, the counter-member may comprise a first assembly that comprises: 
          a base provided with means for fixing it to the pump;     a test body comprising a curved portion and rigidly connected by one of its ends to the base and comprising a contact member at its other end;     a strain gauge applied to the curved portion of the test body.        

      The counter-member may also comprise a second assembly identical to and independent of the first assembly in order to be able to carry out independent measurements relating to the two passages of a dual passage tube.  
      According to one preferred feature of the invention, the processing unit comprises a memory in which a signal-pressure coefficient is stored, the processing unit being adapted to process the value of the signal supplied by the force sensor according to said signal-pressure coefficient to obtain the pressure of the fluid circulating in the tube.  
      Thus the sensor may provide information relating to the pressure of the fluid circulating in the tube. The processing unit then has access to a conversion coefficient for the force measured by the fluid pressure sensor. The above kind of pump may therefore provide a display of the instantaneous pressure of the fluid circulating in the tube.  
      For enhanced measurements, the following features may be implemented independently of each other: 
          the processing unit may comprise a module for compensating creep of the tube adapted to measure periodically the value of the signal supplied by the force sensor and to recalibrate the sensor dynamically as a function of the lowest measured value of said signal;     the processing unit may comprise a module for filtering pulsation of the pump;     the pump may comprise a motorized device for closing the mobile jaw at a variable speed;     the closure device may provide a first or approach speed and a second or closure speed lower than the approach speed;     the contact member may have a plane bearing surface adapted to come into contact with the tube;     the contact member may be a rigid member attached to the test body.        

      Also, the pump may have additional functions by virtue of the following features, which may be implemented independently of each other: 
          the processing unit may be adapted to slave the rotation speed of the rotor to indications supplied by the force sensor;     the processing unit may be adapted to stop the pump if the force exerted between the bearing member and the counter-member exceeds a predetermined threshold.       

    
    
      Other features and advantages of the invention will become apparent in the light of the following description of a preferred embodiment of the invention, which is given by way of nonlimiting example and with reference to the appended drawings, in which:  
       FIG. 1  is a perspective view of a peristaltic pump and its accessories ready for operation;  
       FIG. 2  is a bottom perspective view of a protective cap placed on the top of the pump shown in  FIG. 1 ;  
       FIG. 3  is a plan view of the pump shown in  FIG. 1  when the protective cap shown in  FIG. 2  has been removed;  
       FIG. 4  shows a rotor incorporating rollers that is visible on top of the pump in  FIG. 3 ;  
       FIG. 5  is a view similar to  FIG. 3  when the rotor shown in  FIG. 4  has been removed;  
       FIG. 6  is a different perspective view of the pump shown in  FIG. 1 ;  
       FIG. 7  is a view to a larger scale of the framed portion VII of  FIG. 6 ;  
       FIG. 8  is a view in longitudinal section of the top of the pump shown in  FIGS. 1 and 6 , showing the placing of the tube into the protective cap;  
       FIG. 9  is a perspective view showing manual fitting of the tube into the pump shown in  FIGS. 1 and 6 ;  
       FIG. 10  is a diagrammatic view similar to  FIG. 9  showing lateral adjustment of the tube shown in  FIG. 9 ;  
       FIG. 11  is a perspective view of the head of the pump shown in  FIG. 3 ;  
       FIG. 12  is a perspective view similar to  FIG. 11  also showing the mobile jaw shown in  FIG. 2 ;  
       FIG. 13  is a side view of the assembly shown in  FIG. 12  in section on a plane passing through the rotor incorporating rollers and a cam actuating the mobile jaw;  
      FIGS.  14  to  16  are plan views of the pump head shown in  FIG. 12 , showing the mobile jaw in different positions;  
      FIGS.  17  to  19  are views from below, from the side, and from in front, respectively, of the counter-member shown in  FIG. 12 , facing a bearing member of the mobile jaw;  
      FIGS.  20  to  22  show the counter-member, in a similar manner to FIGS.  17  to  19 , but after receiving a treatment intended to seal it;  
       FIG. 23  is a view in longitudinal section of the counter-member shown in  FIG. 18 , showing the cooperation between the counter-member, the bearing member and the pipe, which in this figure is seen in section; and  
       FIG. 24  is a diagram representing the disposition of the force sensor and the processing unit and their connection to certain elements of the pump. 
    
    
       FIG. 1  shows a peristaltic pump  1  in one of the applications of this type of pump.  
      In the present example, the pump  1  comprises accessories such as a bottle rack  2  and a flow drawer  3 . This configuration is used to pump the liquid contained in a bottle  4  toward two containers  5  through a tube connected at one end to the bottle  4  and at the other end to the containers  5 .  
      In this example the tube  6  comprises two separate passages sealed with respect to each other and connected to each other by a longitudinal web  7  that is easy to cut.  
      The peristaltic pump  1  comprises a pump body  8  on which are disposed a display  9  and control keys  10 .  
      The pump  1  also comprises a pump head  11  (shown in  FIG. 3 ) which is covered by a protective cap  12  in  FIG. 1 .  
       FIG. 2  is a bottom perspective view of the protective cap  12  when it has been removed from the pump  1 . The protective cap  12  comprises an envelope  13  in the form of a cover adapted to cover the mobile elements of the pump head  11  to prevent the user coming into contact with them. The envelope  13  comprises a straight groove  14  of sufficient width for the tube  6  to slide therein.  
      A mobile jaw  15  is fixed to the inside wall of the envelope  13  by three screws  16 . The general shape of the mobile jaw  15  is that of a crescent moon, the inside wall of its curved portion comprising a curved bearing surface  17  of circular arc shape. On respective opposite sides of this bearing surface  17  the mobile jaw  15  comprises a tooth  18  and a bearing member  19 , both adapted to cooperate with the tube  6 , like the bearing surface  17 .  
      The mobile jaw  15  further comprises a hole  20  through the wall of the envelope  13  (see  FIG. 1 ).  
      A round hole  21  communicating with an oblong hole  22  is also formed in the thickness of the mobile jaw  15 . In  FIG. 13 , which shows the profile of the oblong hole  22 , it is apparent that the latter comprises a shoulder  22 ′ substantially halfway through the thickness of the mobile jaw  15 . The round hole  21  does not include this shoulder.  
       FIG. 3  shows the pump head  11  when the protective cap  12  has been removed. The pump head  11  takes the form of a plate on which are fixedly mounted a counter-member  24 , a stop pin  25 , and a shaft  23  adapted to be inserted into the hole  20  in the mobile jaw  15  to enable the jaw to rotate.  
      The pump head  11  also receives a rotatably mounted rotor  26  incorporating rollers and a plate  27  from which projects an eccentric finger  28 .  
       FIG. 4  represents the rotor  26  incorporating rollers when removed from the pump  1 . The rotor  26  comprises two flanges  29  between which are rotatably mounted three cylindrical rollers  30  and two centering rollers  31 , the cylindrical rollers  30  being regularly spaced at 120° to each other around the contour of the flanges  29 .  
      The flange  29  that is the upper flange in  FIG. 4  comprises a flat  32 .  
      The disposition of the cylindrical rollers  30 , the centering rollers  31  and the flat  32  may be seen in  FIG. 14 .  
       FIG. 5  shows the pump head shown in  FIG. 3  when the rotor  26  has been removed. This figure shows a drive shaft  33  which drives rotation of the rotor  26  to fulfill the main function of the pump  1 .  
       FIG. 6  is a perspective side view of the pump  1 , a framed portion VII of this figure showing the cooperation of the tube  6  and the cap  12 .  
       FIG. 7 , which is a view to a larger scale of the framed portion VII of  FIG. 6 , shows the portion of the groove  14  in which the tube  6  is engaged. This portion of the groove  14  is delimited by a bottom  35  in the shape of a circular arc and two facing lateral walls  36 . Each of these lateral walls  36  comprises a retaining boss  37 , the two bosses  37  being disposed face-to-face.  
      The portion of the groove  14  visible in  FIG. 7  forms a locating member adapted to receive the tube  6  when the latter is pressed into it and to enable sliding of the tube relative to the longitudinal axis along which it extends, in other words parallel to itself.  
      Note that when the tube  6  is pressed into this portion of the groove  14  (see  FIG. 9 ) to obtain the assembly shown in  FIG. 7 , the tube  6  first slides down the lateral walls  36 , until its lower passage comes into contact with the bosses  37 , which creates a hard point to be overcome in order to press the tube  6  all the way in. The user then continues to press in the tube  6 , which elastically deforms the lower passage of the tube, which then takes up a position facing the bottom  35 . The web  7  of the tube  6  takes up a position between the two bosses  37 , which retains the tube  6  in the direction of the portion of the groove  14  shown in  FIG. 7 .  
      Although the lower passage of the tube  6  is retained in its housing by the bosses  37 , a clearance remains between the tube  6  and the locating member, which allows the sliding previously referred to (see  FIG. 10 ).  
      The tube  6  is also removed by elastically deforming the lower passage of the tube  6 , which likewise overcomes the hard point.  
       FIG. 8  shows in section the position of the tube  6  as just described.  
       FIG. 11  is a perspective view of the pump head  11  in the  FIG. 3  configuration.  
       FIG. 12  shows the pump head  11  when the mobile jaw  15  has been fitted; this figure shows the jaw separated from the cover  12 , in order to show the cooperation of the mobile jaw  15  with the components mounted on the pump head  11 .  
       FIG. 13  is a view in section of the assembly shown in  FIG. 12  and shows in particular the mounting of the plate  27  on the pump head  11 .  
      The plate  27  is fastened to a drive shaft  38  that is mounted on bearings and rotates relative to the pump head  11 . The shaft  38  is fastened to a gear  39  meshing with a worm gear  40  that is driven in rotation by a motor (not shown).  
      FIGS.  14  to  16  are plan views of the assembly shown in  FIG. 12  in three particular positions of the mobile jaw  15  defined by the eccentric finger  28 , that is to say by the angular position of the plate  27 .  
       FIG. 14  shows the eccentric finger  28  in a position allowing the mobile jaw  15  to be fitted to the pump head  11 .  
      In  FIG. 15 , the mobile jaw  15  is in the same position as in  FIG. 14  but the eccentric finger  28  is in a position in which it locks the mobile jaw  15  and prevents it from being extracted from the pump head  11 .  
       FIG. 16  represents the mobile jaw when closed by the eccentric finger  28 .  
      The successive positions represented in FIGS.  14  to  16  are not visible from the outside in normal use of the pump  1 , this region being covered by the cap  12  that is normally fitted over the jaw  15 .  
      FIGS.  17  to  19  are various views of the counter-member  24  that is mounted on the pump head  11 .  
      Referring to  FIG. 19 , the counter-member comprises an upper test body  41 , a lower test body  42 , and two flanges  43  which connect the test bodies  41 ,  42  to each other and whose shape follows the contour of the test bodies  41 ,  42 .  
       FIG. 18  shows the shape of the flanges  43  forming the lateral walls of the counter-bearing  24 . The flanges  43  are rigidly fixed to each of the test bodies  41 ,  42  by a locating pin  44  and a fixing screw  45 .  
      The  FIG. 17  bottom view also shows the surface of the lower test body  42  that is fixed to the pump head  11 . This surface incorporates a cable orifice  46  between two tapped bores  47  in respective bosses  48 .  
      The counter-member  24  further comprises an upper contact member  49  and a lower contact member  50  rigidly fixed to the upper test body  41  and the lower test body  42 , respectively.  
      Given the position of the pins  44  and the screws  45  securing the test bodies  41 ,  42  to the flanges  43 , the test body  41 ,  42  may be deformed when a force is applied to the contact members  49 ,  50 .  
      FIGS.  20  to  22  are views of the counter-member  24  analogous to FIGS.  17  to  19 ; here the counter-member  24  comprises a resilient seal  51  that fills up the interstices between the flanges  43  and the test bodies  41 ,  42  fitted with their contact members  49 ,  50 . The resilience of this seal provides the sealing effect and at the same time allows relative movement of the test bodies  41 ,  42  and the flanges  43 . The material of the resilient seal  51  must have a negligible stiffness compared to that of the test bodies  41 ,  42  and the flanges  43 . The test bodies  41 ,  42  may be made from a high strength martensitic stainless steel, for example, conforming to the French standard AFNOR Z40 CNV 14, and tempered/annealed to an HRC hardness of  45 , whereas the flanges  43  and the contact members  49 ,  50  may be made of ordinary stainless steel; in this case the resilient seal  51  may be made of silicone. Generally speaking, all interstices and orifices between the test bodies  41 ,  42 , the contact members  49 ,  50  and the flanges  43  may be filled in by this kind of seal, to obtain a perfect seal.  
       FIG. 23  is a side view of the counter-member  24  in longitudinal section, showing the shape of the test bodies  41 ,  42 .  
      Each of the test bodies comprises a base  52  from which extends a curved portion  53  which has at its end a dovetail mortise  54  in which a dovetail tenon  55  on the corresponding contact member  49 ,  50  engages. Each base  52  comprises transverse holes  56  for inserting the pin  44  and the screw  45  and an orifice  56 ′ for fixing a rear wall (not shown).  
      Each of the test bodies  41 ,  42  has a strain gauge  57  fixed to the inside wall of the curved portion  53 . The strain gauges  57  are adapted to measure deformation of the curved portion  53  to which they are fixed. Such deformation may occur when the counter-member  24  is fixed to the pump head  11  by screws inserted into the tapped holes  47  and a force is exerted on one of the contact members  49 ,  50 .  
      Note that deformation of the curved portion  53  of one of the test bodies is independent of deformation of the curved portion  53  of the other test body, since the test bodies  41 ,  42  are connected only at their base  52 , via the flanges  43 .  
      The strain gauges may be connected into a Wheatstone bridge, for example, in a manner that is well known in the field of mechanical engineering.  
      Cables (not shown) passing through the orifice  46  connect each of the gauges  57  to the control circuitry of the pump  1 .  
       FIG. 24  is a diagrammatic representation of a processing unit  58  connected to the counter-member  24  and various components of the pump  1 , such as the motor driving the rotor  26 , the motor driving the eccentric finger  28 , input peripherals such as the keys  10 , and output peripherals such as the display  9 .  
      The processing unit  58  comprises a module  59  for compensating creep of the tube  6 , a module  60  for controlling closing of the mobile jaw  15 , and a module  61  for filtering pulsation of the pump  1 .  
      The functions of the processing unit, whose operation is explained hereinafter, may be provided by appropriate electronic circuitry or by an appropriately programmed data processing device.  
      The peristaltic pump  1  that has just been described operates in the manner indicated hereinafter.  
      When the pump  1  is started, the mobile jaw  15  is in the position shown in  FIG. 15 , which corresponds to the position of the cap  12  shown in  FIGS. 9 and 10 , and the rotor  26  is also in the position shown in  FIG. 15 , with the flat  32  disposed so that a rectilinear passage is formed between the rotor  26  and the jaw  15 . The locating members of the cap  12  are then aligned with this rectilinear passage.  
      First of all, a tube  6  is fitted to the pump  1 . To this end, as shown in  FIG. 9 , the user holds the tube  6  in both hands and inserts it into the groove  14 . Because of the bosses  37 , this pressing in maneuver has to overcome a hard point, as previously explained, for the tube  6  to reach the appropriate position in the locating members formed at each end of the groove  14 , as shown in  FIG. 7 .  
      Referring to  FIG. 10 , the user may then slide the tube  6  laterally, in either direction, to adapt the length of tube available on either side of the cover  12  as a function of the accessories to which the tube  6  is connected (see  FIG. 1 ).  
      Once this operation has been effected, intervention of the user insofar as the positioning of the tube  6  in the pump  1  is concerned is no longer necessary.  
      Using the control keys  10 , the user indicates that he wishes to start the pump  1 , which drives rotation of the plate  27  via its drive system until the mobile jaw  15  reaches the position shown in  FIG. 16 , in which the tooth  18  of the jaw  15  clamps the web  7  of the tube  6  against the immobilizing pin  25 .  
      When this position is reached, the motor stalls and draws a higher current. When this consumption peak is detected, the motor is stopped.  
      As the jaw  15  closes, the tube  6  is wrapped around the rotor  26  and at the same time slides as required in the locating members of the cap  12 .  
      The tube  6  is finally held on either side of the rotor  26  by the cooperation of the tooth  18  and the immobilizing pin  25 , on the one hand, and by the cooperation of the bearing member  19  and the counter-member  24 , on the other hand, which lightly grip both passages of the tube  6 .  
      The mobile jaw  15  is held in this closure position because of the irreversible nature of the system comprising the wheel  39  and the worm  40 . The pitch and the helix angle of these components are chosen, in a manner that is well known in the art of mechanical engineering, so that rotation of the worm  40  drives the wheel  39  but rotation of the wheel  39  is not able to drive rotation of the worm  40 .  
      When the tube  6  has been inserted in this way, the rotor  26  may be rotated to start circulating the fluid contained in the tube  6  thanks to the movement of the rollers  30 .  
      When the pump  1  is operating, the safety of the user is ensured by the fact that the mobile jaw  15  is in the  FIG. 16  position, that is to say in a position in which removal of the combination of the mobile jaw and the protective cap is prevented by the eccentric finger  28  and the shoulder  22 ′ in the oblong hole  22  in the mobile jaw  15 . It is also impossible to remove the cap  12  when the mobile jaw  15  is in the  FIG. 15  position, that is to say when the rotor  26  is not moving but the pump  1  is powered up.  
      On the other hand, when the pump  1  is powered down, the eccentric finger  28  resumes the position shown in  FIG. 14 , which releases the combination of the mobile jaw and the protective cap, for example to allow cleaning of the components of the pump head  11 .  
      The pump  1  further comprises means for obtaining, via the counter-member  24 , information relating to the tube  6  and to the circulating fluid and to operate accordingly on the pump  1 .  
      The counter-member  24  is connected to a processing unit ( FIG. 24 ) that stores in a memory a signal-pressure coefficient and is adapted to derive the pressure of the fluid circulating in the tube  6  from this signal-pressure coefficient and the voltage delivered by the strain gauges  57  (which is representative of the deformation of the corresponding curved portion  53 ).  
      Once the tube has been fitted, and with the pump head in the  FIG. 16  position, the processing unit first verifies the presence of the tube  6  and its correct placement. To this end, deformation of the curved portions  53  must be confirmed by confirming that the distance between the counter-member  24  and the bearing member  19  of the jaw  15  in the closed position is less than the width of the tube  6  (see  FIG. 23 ).  
      If the presence of the tube  6  is not detected, the pump  1  does not start and displays an error message.  
      Once the tube has been positioned correctly and the pump is operating, the processing unit  58  supplies to the output peripherals the instantaneous pressure of the fluid in each of the passages of the tube  6 , independently of each other.  
      The signal-pressure coefficient is determined empirically, during a preliminary calibration phase, by installing a tube with known characteristics in the pump  1  and applying to it a known pressure. The voltage delivered by the strain gauges  57  is then read off; the pressure corresponding to this value being known, the coefficient may be determined. It may be determined for each new tube used. An average value may be obtained by subjecting a plurality of tubes to this test and determining from the test results a mean coefficient valid for all the tubes.  
      The processor unit  58  may use the measured pressure of the fluid in the tube  6  for the following supplementary applications.  
      The processing unit  58  includes a module  59  for compensating creep of the tube  6 , which improves the reliability of the measurements. To this end, at regular intervals, for example every 20 milliseconds, the module  59  measures the voltage supplied by the strain gauges  57  and effects a dynamic calibration, from one measurement to the next, taking the lowest voltage as the reference value for calculating the zero pressure.  
      The processing unit  58  also includes a module  60  for controlling closure of the mobile jaw  15  that is adapted to regulate the speed of the mobile jaw  15  when it moves from its open position to its closed position, leading to compression of the tube  6  between the bearing member  19  and the counter-member  24 . Tightening the mobile jaw  15  too quickly disturbs the pressure measurement, because of the elasticity of the tube  6 .  
      The module  60  may therefore slow down the closing of the mobile jaw (i.e. slow down the motor of the eccentric finger  28 ) if the pressure measurement is disturbed.  
      The module  60  may further be programmed to start the closure of the mobile jaw  15  at a high speed and then to clamp the tube  6  at a lower speed, once the tube  6  reaches the vicinity of the counter-member  24 .  
      The processing unit  58  further comprises a module  61  for filtering pulsation of the pump  1 . The movement of the rotor  26  acting on the tube  6  during the operation of the pump  1  causes cyclic disturbances to the pressure measurement, these disturbances depending on the rotation frequency of the rotor  26 .  
      The module  61  applies electronic filtering, for example by means of a low-pass RC filter setting a cut-off frequency.  
      In the present example, the rotation speed of the rotor  26  is 240 rpm and the rotor comprises three rollers, which corresponds to an angular frequency of 12 Hz. A cut-off frequency of 1.5 Hz may then be defined by an appropriate RC filter; this value gives good results.  
      The processing unit  58  may also slave the rotation speed of the rotor  26  to the measured pressure of the fluid in the tube  6 . For example, if the processor unit  58  has information relating to the permitted maximum pressure in the tube  6 , the rotation speed of the pump may be increased to the maximum and then reduced on demand, if the pressure in the tube  6  approaches its permitted maximum value.  
      Similarly, by indicating abnormal variations in fluid pressure, the processing unit  58  may detect incorrect flow of the fluid in the tube  6 , linked to clogging of the tubes, for example.  
      Variants of the device may be envisaged that do not depart from the scope of the invention. In particular, the tube  6  may comprise a single passage or more than two passages, the counter-member comprising as many test bodies as there are passages.