Patent Publication Number: US-6702187-B2

Title: Air diffuser

Description:
FIELD OF THE INVENTION 
     THIS INVENTION relates to diffusers. 
     BACKGROUND TO THE INVENTION 
     The term “diffuser” is used to designate those devices which, in air conditioning systems, are employed for the purpose of regulating flow of air, which may be heated air or cooled air, from air conditioning ducting into a room. 
     Various conditions occur in an air conditioned room depending on whether the outside temperature is above that at which the room is to be maintained or below that at which the room is to be maintained. 
     In “Summer” conditions cooled air is fed from the air conditioning plant to the diffuser. If the room temperature is below that at which it is desired to maintain it, because cooled air has previously been fed in, then the diffuser must remain closed to prevent further cooled air entering the room. 
     As the room heats up a room temperature sensing element must detect this and open the diffuser to allow more cooled air into the room. The diffuser thus opens and closes as the room temperature varies. 
     In “Winter” conditions heated air is fed to the diffuser. If the room is above the requisite temperature, because heated air has previously been fed into the room, the diffuser must remain closed to prevent further heated air entering. As the room cools down, the room temperature sensing element must detect this and open the diffuser to allow more heated air in. The diffuser consequently opens and closes as the room temperature varies. 
     In the specification of our South African patent 96/4791 (U.S. Pat. No. 5,647,532 and Australian Patent No. 700908) there is disclosed a diffuser which has a single room temperature sensing element which closes a diffuser when the room is too cold (in Summer conditions) and also closes the diffuser when the room is too hot (in Winter conditions). This avoids the use of complex constructions involving two or more room temperature sensing elements. The present invention seeks to provide an improved diffuser using a single room temperature sensing element. A modification of this diffuser is disclosed in our South African Patent No. 2000/1891 (U.S. Pat. No. 6,254,010 and Australian Patent Application No.28880/00) 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to one aspect of the present invention there is provided a diffuser for controlling flow of air in an air conditioning system, the diffuser including an air flow control baffle, a first temperature sensitive element for sensing room temperature variations and including a body and a piston which move relatively to one another in response to temperature variations, a second temperature sensitive element for sensing duct temperature variations and including a body and a piston which move relatively to one another in response to temperature variations, a housing, the body of one of said elements being fixed to said housing, a pair of links having inner ends and outer ends, the links being pivotally mounted on said housing at their inner ends and having their outer ends connected to said baffle, the links protruding outwardly from said housing, each link having a first cam surface on one side of its pivotal mounting and a second cam surface on the other side of its pivotal mounting, a control element having a first surface for bearing on said first cam surfaces and a second surface for bearing on said second cam surfaces, the body of the other temperature element being fast with said control element, spring means for urging said first surface towards the first cam surfaces, and a rod opposite ends of which bear on said pistons to prevent the pistons moving towards one another, the spring means, by acting on the body of said other element, holding the pistons against movement away from the ends of the rod. 
     According to a further aspect of the present invention there is provided a diffuser for controlling flow of air in an air conditioning system, the diffuser comprising first and second temperature sensitive elements for respectively sensing room temperature and duct temperature variations, the elements being axially aligned, a link for displacing an air flow control baffle, and a control structure for displacing said link in dependence on sensed room temperature thereby to displace said baffle and vary air flow, said control structure having a first component which acts on the link when said second element is detecting cooled air and a second component which acts on the link when the second element is detecting warmed air. 
     According to another aspect of the present invention there is provided a diffuser for controlling flow of air in an air conditioning system, the diffuser including an air flow control baffle, a first temperature sensitive element for sensing room temperature variations and including a body and a piston which move relatively to one another in response to temperature variations, a second temperature sensitive element for sensing duct temperature variations and including a body and a piston which move relatively to one another in response to temperature variations, a housing, the body of the first element being fixed to said housing, a pair of links having inner ends and outer ends, the links-being pivotally mounted on said housing at their inner ends and having their outer ends connected to said baffle, the links protruding in opposite directions to one another from said housing, each link having a first cam surface on one side of its pivotal mounting and a second cam surface on the other side of its pivotal mounting, a control element having a first upwardly facing surface for bearing on said second cam surfaces and a second downwardly facing surface for bearing on said first cam surfaces, the body of the first temperature element being fast with said control element, spring means for urging said second downwardly facing surface towards the first cam surfaces, and a rod opposite ends of which bear on said pistons to prevent the pistons moving towards one another, the spring means, by acting on the body of the second element, holding the pistons against movement away from the ends of the rod. 
     According to yet another aspect of the present invention there is provided a diffuser for controlling flow of air in an air conditioning system, the diffuser including an air flow control baffle, a first temperature sensitive element for sensing room temperature variations and including a body and a piston which move relatively to one another in response to temperature variations, a second temperature sensitive element for sensing duct temperature variations and including a body and a piston which move relatively to one another in response to temperature variations, a housing, the body of the second element being fixed to said housing, a pair of links having inner ends and outer ends, the links being pivotally mounted on said housing at their inner ends and having their outer ends connected to said baffle, the links protruding in opposite directions to one another from said housing, each link having a first cam surface on one side of its pivotal mounting and a second cam surface on the other side of its pivotal mounting, a control element having a first downwardly facing surface for bearing on said first cam surfaces and a second upwardly facing surface for bearing on said second cam surfaces, the body of the first temperature element being fast with said control element, spring means for urging said second upwardly facing surface towards the second cam surfaces, and a rod opposite ends of which bear on said pistons to prevent the pistons moving towards one another, the spring means, by acting on the body of the first element, holding the pistons against movement away from the ends of the rod. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: 
     FIG. 1 is a vertical section through a diffuser in accordance with the present invention; 
     FIG. 2 is a vertical section through part of the diffuser of FIG. 1, FIG. 2 being to a larger scale than FIG. 1; 
     FIGS. 3 to  5  are vertical sections through the diffuser part of FIG.  2  and show the diffuser in different operative conditions; 
     FIG. 6 is a vertical section through a second embodiment of the diffuser in accordance with the present invention; 
     FIG. 7 is a vertical section through part of the diffuser of FIG. 6, FIG. 7 being to a larger scale than FIG. 6; 
     FIGS. 8 to  10  are vertical sections through the diffuser part of FIG.  7  and show the diffuser in different operative conditions; 
     FIG. 11 is a vertical section through a third embodiment of the diffuser in accordance with the present invention; 
     FIG. 12 is a vertical section through part of the diffuser of FIG. 11, FIG. 12 being to a larger scale than FIG. 11; 
     FIGS. 13 to  15  are vertical sections through the diffuser part of FIG.  12  and show the diffuser in different operative conditions; 
     FIG. 16 is a pictorial view of the part of FIGS. 12 to  15 ; and 
     FIG. 17 is a section illustrating a modification of the diffuser part of FIGS. 12 to  16 . 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Referring firstly to FIG. 1 the diffuser  10  illustrated comprises a short vertical duct  12  which is connected at its upper end to the ducting D through which cooled air or heated air flows to the diffuser depending on the cooling or heating requirements which prevail. At the lower end of the duct  12  there is a truncated cone  14  which is mounted with its smaller end uppermost. At the wider lower end of the cone there is a trim disc  16  which conceals a vertically extending tube  18  which constitutes a housing of the diffuser  10 . The trim disc  16  is constituted by a sheet of metal with an upturned rim. The lower end of the cone  14  is square or circular in shape and is bounded by a horizontal rim. This rim rests on the hangers (not shown) that are used to support the false ceiling in a building. The duct  12 , ducting D and cone  14  are not shown in FIGS. 2 to  5 . 
     The operating mechanism of the diffuser is shown in detail in FIGS. 2 to  5  and comprises two thermally sensitive elements  20 ,  22  which in the art are often referred to as “pills”. Each element  20 ,  22  comprises a body  24  in which there is a wax that melts at a predetermined temperature and thereafter expands. One end of the body  24  is closed and the other end of the body  24  has an opening therein. Between the wax and the open end of the body there is a piston. The piston moves in the body  24  as the wax expands and contracts. 
     The trim disc  16  has slots in it to allow room air to enter the space above the trim disc  16  and circulate around the thermally sensitive element  20 . 
     A rod  26  extends from the element  20  to the element  22 , the ends of the rod  26  entering the bodies  24  via said openings. The ends of the rod  26  are in contact with the pistons. When the wax of either element expands it pushes the respective piston in the direction which moves more of the rod  26  out of the respective body  24 . A spring  28  is provided for moving the rod  26  back into the bodies  24  when the wax contracts on cooling. 
     A one-piece bobbin  30  with a bore  32  passing therethrough is provided. The rod  26  passes through the bore  32 . The bobbin  30  includes two discs  34  and  36 . The discs  34  and  36  are spaced apart in the vertical direction. Below the disc  34  the bobbin is in the form of a vertically elongate sleeve  38  in the bore  32  of which the rod  26  slides. The lower portion of the bore  32  in the sleeve  38  is tapped and the upper end of the element  20  is screwed into the sleeve  38 . The body  24  of the element  20  and sleeve  38  thus move together. 
     The bobbin and disc  34  and  36  form a control structure. 
     The lower end of the tube  18  is closed by an end cap designated  40 . The cap  40  comprises a cylindrical side wall  42  which has an external step in it at  44 . Above the step  44  the side wall has external threading  46  and the lower end of the tube  18  has corresponding internal threading. Below the step  44  the end cap has a ring of holes  48  in it to promote air flow over the element  20 . The cap  40  is open at its lower end and has a transverse wall  50  at its upper end. The wall  50  has a central opening  52  through which the sleeve  38  passes with clearance. 
     The spring  28  is located between the transverse wall  50  of the cap  40  and the underside of the disc  34 . One function of the spring  28  is to hold opposite ends of the rod  26  in contact with the pistons of the elements  20  and  22 . In one constructional form the end sections of the rod  26  fit into the bodies  24  and there are shoulders between these sections and the remainder of the rod. The shoulders limit penetration of the rod into the bodies  24 . 
     The discs  34  and  36  are connected by a column designated  54 . In horizontal section the column  54  is rectangular, the bore  32  passing through the column  54 . 
     The upper end of the tube  18  is closed by an end cap  56 . The end cap  56  can be screwed into the tube  18 , can be glued in or can be a push fit therein. The cap  56  has a vertically extending bore  58  therein which is tapped. The body  24  of the element  22  is screwed into the bore  58 , the element protruding upwardly from the cap  56  into the ducting D. 
     A sleeve  60  is pressed over the upper end of the element  22  and conceals part of the body  24  of the element  22 . By turning the element  22  with respect to the cap  56 , the element  22  is displaced vertically thereby to adjust the set point of the diffuser. 
     The tube  18  has two diametrically opposed openings  66  therein. Two operating links  68  pass through the openings  66 . The links  68  are pivotally mounted on the tube  18 . The pivots consist of pins  70  spanning across the interior of the tube  18 . 
     Hangers  72  (FIG. 1) are pivotally mounted at  74  on the outer ends of the links  68  and pass through holes  76  in an airflow control baffle  78 . Each hanger  72  is in the form of a spring which is fabricated using resiliently flexible wire. As seen in FIG. 1, each hanger  72  has a central coil  80  and two arms  82  and  84 . The hangers  72  pull the links  68  and baffle  78  towards one another. 
     The baffle  78  is disc-like and its periphery is close to the inner face of the cone  14  when the diffuser is closed (as shown in FIG.  1 ). The lower ends of the arms  84  of the hangers  72  pass through the baffle  78  and are bent over to form hooks which lie below the baffle  78 . The baffle  78  rests on the hooks and is supported thereby. 
     Each link  68  has two cam surfaces. The first cam surface  86  of each link  68  is on the top edge of the link and co-operates with the underside of the disc  36 . The second cam surface  88  of each link  68  is on the bottom edge of the link and co-operates with the top surface of the disc  34 . The surfaces  86  are radially inwardly of the pivot pins  70  and the surfaces  88  are radially outwardly of the pins  70 . 
     To inhibit heating or cooling of the element  20  by air entering the duct  12  from the ducting D, a sleeve (not shown) of thermally insulating material can be provided between the spring  28  and the sleeve  38 . 
     The element  20  senses room temperature and the element  22  detects duct temperature. On the assumption that cooled air is flowing in the ducting D, the piston of the element  22  is fully retracted. If it is further assumed that the room is cold, then the piston of the element  20  is also fully retracted, the wax in both elements  20  having contracted and possibly solidified. In these conditions the diffuser is as shown in FIG.  2 . The spring  28  presses on the underside of the disc  34  lifting the bobbin  30  and element  20  upwardly with respect to the rod  26  to the maximum extent permitted by the structure. 
     The links  68  are thus in their fully raised positions which means that the baffle  78  is close to the cone  14  and air flow is at a minimum. 
     As the room warms up, the wax in the element  20  expands and an upward thrust is exerted on the rod  26 . However, the rod  26  cannot move upwardly as its upper end is against the piston of the element  22 . Thus the body  24  of the element  20  moves downwardly with respect to the piston of that element. The bobbin  30  moves down with the body of the element  20 . When the disc  34  descends, the links  68  pivot downwardly about the pins  70 , the links  68  rolling on the cam surfaces  88 . The baffle  78  is thus lowered and cold air can flow between the baffle  78  and the cone  14 . This condition is shown in FIG.  3 . The disc  34  thus constitutes a component which acts on the links whilst the element  22  is detecting cooled air. 
     As the element  20  cools the reverse action occurs, the bobbin  30  lifting with the body  24  of the element  20  as the wax contracts. The diffuser thus returns to the condition of FIG.  2  and flow of cold air ceases. Thus room temperature is regulated. 
     In cool or cold atmospheric conditions, heated air flows in the ducting D and the wax in the thermally sensitive element  22  expands. The piston of the element  22  moves downwardly pushing the rod  26  in the same direction. 
     The lower end of the rod  26  pushes down on the piston of the element  20  shifting the entire element  20  and bobbin  30  downwardly. This is shown in FIGS. 4 and 5. FIG. 4 shows the position which the diffuser occupies when heated air is being supplied along the ducting D and the room is cold and FIG. 5 the position the diffuser occupies when heated air is being supplied and the room is warm. 
     It will be noted from FIG. 4 that the disc  34  has moved away from the links  68  and that the cam surfaces  88  are spaced from the disc  34 . The cam surfaces  86  now co-operate with the underside of the disc  36 . 
     As the element  20  heats up the wax in it expands and the piston is pushed in the direction which tends to move the rod  26  upwardly. However, the rod  26  is effectively fixed by the piston of the element  22  and thus the body of the element  20  moves down carrying the bobbin  30  with it. The disc  36  bears down on the cam surfaces  86  pivoting the outer ends of the links  68  upwardly. The baffle  78  is thus lifted towards the cone  14  reducing the supply of heated air. The links  68  are now as shown in FIG.  5  and the flow of heated air is a minimum. The disc  36  thus constitutes a second component which acts on the links whilst the element  22  is detecting warmed air. 
     As the room cools, the wax in the element  20  contracts. The piston thus tends to move downwards away from the lower end of the rod  26 . However, the spring  28  acts on the piston through the disc  34 , sleeve  38 , the body  24  and the wax holding it against the lower end of the rod  26 . The body C 24  of the element  20  thus moves upwards against the spring action allowing the outer ends of the links  68  to pivot downwards about the pins  70 , the links rolling on the cam surfaces  86 . The diffuser is now again as shown in FIG.  4 . 
     A change over from heated air in the duct  12  to cooled air causes the wax of the element  22  to contract bringing the disc  34  and cam surfaces  88  back into their co-operating relationship and separating the disc  36  and the cam surfaces  86 . 
     Referring now to FIG. 6, a second embodiment of the diffuser is designated  110  and comprises a short vertical duct  112  which is connected at its upper end to the ducting D through which cooled air or heated air flows to the diffuser  110  depending on the cooling or heating requirements which prevail. At the lower end of the duct  112  there is a truncated cone  114  which is mounted with its smaller end uppermost. At the wider lower end of the cone  114  there is a trim disc  116  which conceals a vertically extending tube  118  of the diffuser  110 . The trim disc  116  is constituted by a sheet of metal with an upturned rim. The lower end of the cone  114  is square or circular in shape and is bounded by a horizontal rim. This rim rests on the hangers (not shown) that are used to support the false ceiling in a building. 
     The operating mechanism of the diffuser  110  is shown in detail in FIGS. 7 to  10  and comprises two thermally sensitive elements  120 ,  122 . The duct  112 , ducting D and cone  114  are not shown in FIGS. 7 to  10 . 
     The trim disc  116  has slots in it to allow room air to enter the space above the trim disc  116  and circulate around the thermally sensitive element  120 . 
     A rod  126  extends from the element  120  to the element  122 , the ends of the rod  126  entering the housings  124 . The ends of the rod  126  are in contact with the pistons. When the wax of either element  120 ,  122  expands it pushes on the respective piston in the direction which moves more of the rod  126  out of the respective housing  124 . A spring  128  is provided for moving the rod  126  back into the housings  124  when the wax contracts on cooling. 
     A one-piece bobbin  130  (see also FIG. 7) with a bore  132  passing therethrough is provided. The rod  126  passes through the bore  132 . The bobbin  130  includes two discs  134  and  136 . The discs  134  and  136  are spaced apart in the vertical direction. Above the disc  134  the bobbin  130  is in the form of a vertically elongate sleeve  138  in the bore  132  of which the rod  126  slides. The upper portion of the bore  132  in the sleeve  138  is tapped and the lower end of the body  124  of the element  122  is screwed into the sleeve  138 . The body  124  of the element  122  and sleeve  138  thus move together. 
     The lower end of the tube  118  is closed by an end cap designated  140 . The cap  140  comprises a cylindrical side wall  142  which has an external step in it at  144 . Above the step  144  the side wall  142  has external threading  146  and the lower end of the tube  118  has corresponding internal threading. Below the step  144  the end cap  140  has a ring of holes  148  in it to promote air flow over the element  120 . The cap  140  is open at its lower end and has a transverse wall  150  at its upper end. The wall  150  has a central opening  152  through which the rod  126  passes with clearance. 
     The upper end of the tube  118  is closed by an end cap  156 . The end cap  156  can be screwed into the tube  118 , can be glued into the tube or can be a push fit therein. The cap  156  has a vertically extending bore  158  therein. The sleeve  138  slides in the bore  158  of the cap  156 . 
     A sleeve  160  is pressed over the upper end of the element  122  and conceals part of the body  124  of the element  122 . By turning the element  122  with respect to the cap  156 , the element  122  is displaced vertically thereby to adjust the set point of the diffuser  110 . 
     The spring  128  is located between the end cap  156  and the upper surface of the disc  134 . One function of the spring  128  is to hold opposite ends of the rod  126  in contact with the pistons of the elements  120  and  122 . In one constructional form, the end sections of the rod  126  fit into the bodies  124  and there are shoulders between these sections and the remainder of the rod  126 . The shoulders limit penetration of the rod  126  into the bodies  124 . 
     The discs  134  and  136  are connected by a column designated  154 . In horizontal section the column  154  is rectangular, the bore  132  passing through the column  154 . 
     The tube  118  has two diametrically opposed openings  166  therein. Two operating links  168  pass through the openings  166 . The links  168  are pivotally mounted on the tube  118 . The pivots consist of pins  170  spanning across the interior of the tube  118 . 
     Hangers  172  are pivotally mounted at  174  on the outer ends of the links  168  and pass through holes  176  in an airflow control baffle  178 . Each hanger  172  is in the form of a spring which is fabricated using resiliently flexible wire. Each hanger  172  (see FIG. 6) has a central coil  180  and two arms  182  and  184 . The hangers  172  pull the links  168  and baffle  178  towards one another. 
     The baffle  178  is disc-like and its periphery is close to the inner face of the cone  114  when the diffuser  110  is closed (as shown in FIG.  6 ). The lower ends of the arms  184  of the hangers  172  pass through the baffle  178  and are bent over to form hooks which lie below the baffle  178 . The baffle  178  rests on the hooks and is supported thereby. 
     Each link  168  has two cam surfaces. The first cam surface  186  of each link  168  is on the top edge of the link  168  and co-operates with the underside of the disc  134 . The second cam surface  188  of each link  168  is on the bottom edge of the link  168  and co-operates with the top surface of the disc  136 . The surfaces  186  are radially inwardly of the pivot pins  170  and the surfaces  188  are radially outwardly of the pins  170 . 
     To inhibit heating or cooling of the element  120  by air entering the duct  112  from the ducting D, a first sleeve of thermally insulating material  190  is provided above the element  120  and a second sleeve  192  is provided around the element  120 . 
     The element  120  senses room temperature and the element  122  detects duct temperature. On the assumption that cooled air is flowing in the ducting D, the piston of the element  122  is fully retracted. If it is further assumed that the room is cold, then the piston of the element  120  is also fully retracted, the wax in both elements  120  having contracted and possibly solidified. In these conditions the diffuser  110  is as shown in FIG.  7 . The spring  128  presses on the upper surface of the disc  134  urging the bobbin  130  downwardly with respect to the rod  126  to the maximum extent permitted by the structure. 
     The disc  134  bears down on the cam surfaces  186  of the links  168  which are thus in their fully raised positions. This means that the baffle  178  is close to the cone  114  and air flow is at a minimum. 
     As the room warms up, the wax in the element  120  expands and an upward thrust is exerted on the rod  126 . The upper end of the rod  126  is against the piston of the element  122  and the piston of that element  122  cannot, because of the wax, move with respect to the body  124 . Hence, the body  124  of the element  122  moves upwardly carrying the bobbin  130  up with it. When the disc  134  ascends, the links  168  pivot downwardly about the pins  170 , the links  168  rolling on the cam surfaces  186 . The baffle  178  is thus lowered and cold air can flow between the baffle  178  and the cone  114 . This condition is shown in FIG.  8 . 
     As the element  120  cools the reverse action occurs, the bobbin  130  descends with the body  124  of the element  122  as the wax contracts. The diffuser  110  thus returns to the condition of FIG.  7  and flow of cold air ceases. Thus room temperature is regulated. 
     In cool or cold atmospheric conditions, heated air flows in the ducting D and the wax in the thermally sensitive element  122  expands. However, the rod  126  cannot move downwardly as its lower end is against the piston of the element  120 . Thus the body  124  of the element  122  moves upwardly with respect to the piston of that element, carrying the bobbin  130  with it to the position shown in FIGS. 9 and 10. FIG. 9 shows the position which the diffuser  110  occupies when heated air is being supplied along the ducting D and the room is cold and FIG. 10 the position the diffuser  110  occupies when heated air is being supplied and the room is warm. 
     It will be noted from FIG. 9 that the disc  134  has moved away from the links  168  and that the cam surfaces  188  co-operate with the top face of the disc  136 . 
     As the element  120  heats up the wax in it expands and its piston is pushed in the direction which tends to move the rod  126  upwardly. Thus the body of the element  120  moves up carrying the bobbin  130  with it. The disc  136  bears upwardly on the cam surfaces  188  pivoting the outer ends of the links  168  upwardly. The baffle  178  is thus lifted towards the cone  114  reducing the supply of heated air. The links  168  are now as shown in FIG.  10  and the flow of heated air is a minimum. 
     As the room cools, the wax in the element  120  contracts. Its piston thus tends to move downwards away from the lower end of the rod  126 . However, the spring  128  bears down on the disc  134  forcing the bobbin  130  and the body of the element  122  downwardly so that the rod  126  follows the descending piston of the element  120 . Downward movement of the disc  136  allows the outer ends of the links  168  to pivot downwards about the pins  170 , the links  168  rolling on the cam surfaces  188 . The diffuser  110  is now again as shown in FIG.  9 . 
     A change over from heated air in the duct  112  to cooled air causes the wax of the element  122  to contract bringing the disc  136  and cam surfaces  188  back into their co-operating relationship and separating the disc  134  and the cam surfaces  186 . 
     Turning now to FIGS. 11 to  16 , these illustrate a modified form of the diffuser of FIGS. 6 to  10 . Where applicable like parts have been designated with like reference numerals. 
     The end cap  140  is replaced by an end cap  140 . 1  which has a side wall  142 . 1  and an intermediate transverse wall  150 . 1 . Above the wall  150 . 1  the end cap  140 . 1  has a short sleeve  194  which is internally threaded. The wall  142 . 1  and the sleeve  194  provide a well for receiving the sleeve  190  of thermally insulating material. The housing  124  of the element  122  is screwed into the sleeve  194  from below. 
     The bobbin  130 . 1  has a main section  196  which is internally tapped and into which the-housing  124  of the element  122  is screwed from above. It also has a smaller diameter lower section  198  which is externally threaded. The section  198  passes through a platform  200  and a nut  202  screwed onto the section  198  holds the platform  200  against the shoulder  204  which exists where the lower section  198  of the bobbin joins its main section  196 . 
     The disc  134  of FIGS. 6 to  10  is placed by a disc designated  134 . 1  which includes an internally tapped collar  206 . The disc  134 . 1  is screwed onto the section  198  below the nut  202 . It is the lower end of the collar  206  which co-operates with the surfaces  186  of the links  168 . The outer periphery of the disc  134 . 1  is knurled. 
     The rod designated  126 . 1  comprises an upper part  208  and a lower part  210 . The part  208  is stepped down at its lower end to form a threaded spigot  212  which is screwed into a tapped blind bore  214  in the part  210 . 
     The disc  136  is replaced by a disc  136 . 1  having an upstanding peripheral rim  216 . The upper edge of the rim  216  co-operates with the cam surfaces  188  and the outer periphery of the rim  216  is knurled. 
     The end cap  156  is replaced by a disc-like top cap  218  which is held in place by a circlip  220 . The spring  128  bears on the underside of the cap  218  and on the top surface of the platform  200 . 
     By rotating the disc  134 . 1 , it can be moved along the bobbin thereby to enable the cooling set point to be adjusted. Likewise, rotation of the disc  136 . 1  causes it to move along the bobbin thereby adjusting the heating set point. 
     A bracket  222  having a vertical section  224  (FIG.  16 ), and a horizontal section  226  (FIGS. 12 to  15 ) is provided. The section  226  has a hole in it through which the lower section of the bobbin passes, the section  226  being between the platform  200  and the nut  202 . Thus the bracket  222  rises and falls with the bobbin. 
     The bracket section  226  protrudes from the tube  118  through a vertically elongate slot  228  so that the section  224  is outside the tube  118 . The section  224  has two holes  230 ,  232  in it, the edges of the discs  134 . 1 ,  136 . 1  being visible through these holes. On the peripheries of these discs there are graduation marks which indicate set points. These marks can be seen through the holes  230 ,  232 . 
     To enable access to be had to the discs  134 . 1 ,  136 . 1 , openings are provided in the tube  118 . These openings are not shown in FIGS. 11 to  16  but are illustrated in FIG. 17, and are designated  234 ,  236 . 
     The diffuser of FIG. 11 etc operates in the same way as the diffuser of FIGS. 6 to  10 . 
     In FIG. 17 there is illustrated an arrangement in which the end cap  140 . 2  has a circumferential series of headed locking clips  238  around its upper end and the tube  118 . 2  has openings  240  for receiving these clips so that the end cap  140 . 2  “snap fits” onto the tube  118 . 2 . The holes  148 . 1  of FIGS. 11 to  16  are replaced by holes  148 . 2  which are closer to the lower end of the end cap  140 . 2 .