Abstract:
An inlet valve for a central vacuum cleaning system having a central vacuum motor connected to a piping network, is disclosed. The inlet valve includes a main body having an air inlet passageway formed therethrough and a pipe connector to connect the air inlet passageway of the inlet valve to the vacuum piping. An outer door is provided which is pivotally mounted to the main body on an opposite side to said connector and an inner door is provided which is pivotally mounted to said main body at one end between the outer door and the main body and seals the air inlet passageway when the inner door is in a closed position. A releasable latch is operatively connected to the outer door to keep the outer door and the inner door closed on the front of the valve when the inlet valve is not in use and a spring is provided to cause the inner door and the outer door to open upon the latch being released.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Canadian Patent Application No. 2,733,631, filed Mar. 10, 2011, the entire contents of which are hereby incorporated by reference. 
     FIELD OF THE INVENTION 
     This invention relates generally to central vacuum cleaning systems of the type that may be used to gather up dirt and debris from inside a building through a central suction motor and a network of vacuum suction pipes. More particularly, this invention relates to an inlet valve located on the vacuum piping to permit access to the suction within the piping. Most particularly, this invention relates to an inlet valve mounted on or adjacent to the floor of the type that may be used to remove dirt and debris gathered up to the device by sweeping or the like. 
     BACKGROUND OF THE INVENTION 
     Central vacuum cleaning systems are commonly used in modern home and commercial building construction. A central vacuum cleaning system typically includes a central vacuum motor, typically powered by electricity, which when activated creates a vacuum or suction. A connected network of rigid plastic pipes is located within the walls of the dwelling and in turn is connected to the central vacuum motor, the source of the vacuum. A removable debris collecting receptacle is provided as part of the central vacuum motor assembly. Accordingly, dirt and debris sucked into the pipe network is deposited in the removable receptacle which can be periodically emptied. The central vacuum motor is typically located in a remote location such as the basement or garage of a residential dwelling, where the noise of the vacuum motor is remote from the dwelling area, but the canister is still easily accessible for ease of emptying. The blowing action of the motor does not lift dust in the location being vacuumed as with a more conventional canister vacuum. 
     Wall mounted inlet valves are typically positioned on the vacuum piping network to permit flexible spiral wound hoses with rigid wand extensions to be connected to the source of vacuum. Typically, upon the hose cuff of the flexible hose being inserted into the inlet valve, a low voltage circuit is activated whereby the central vacuum motor is turned on. Some wands include an on/off switch to control the activation of the remote central vacuum motor. When the inlet valve is not in use a spring loaded cover or flap with a sealing gasket seals the opening in the inlet valve to prevent a loss of vacuum in the rest of the central vacuum system. 
     In addition to wall mounted inlet valves designed for hose attachment, more recently there have been developed floor or sweep inlet valves for directing the vacuum or suction adjacent to a floor surface. In this manner, debris swept up to the inlet valve can be removed through the vacuum inlet opening by the suction caused by the central vacuum motor. 
     One example of a prior floor type of inlet valve is Klassen, Canadian patent 2,104,484. This patent teaches a foot activated lever which when depressed by the user lifts a plug off of a downwardly directed vacuum pipe opening, closes a circuit to initiate suction and lifts a front gate on the device to create an inlet opening or passageway through which the dirt and debris can be drawn. However, this design is awkward because the user has to continually depress the lever, presumably with their foot, while at the same time trying to sweep around their foot to deliver the debris to the inlet opening and suction of the unit. If their foot is taken off of the lever this results in the door closing, the motor stopping and the plug sealing the rear opening of the device. While interesting this mode of operation is too awkward to be very practical. 
     Another prior device is Canadian Patent 2,123,179 to Graham. In this prior device a sweep inlet valve is provided also with a foot operated lever. However, rather than depressing the lever the user simply kicks the lever left or right. A double action spring acts to keep the lever positioned in one or the other positions. One position corresponds to an open and activated vacuum inlet, and the other position corresponds to a closed vacuum inlet with the motor turned off. This is a more practical approach than Klassen, but in Graham the front of the vacuum inlet is always open and the vacuum seal is only formed at the rear of the unit. Therefore, when installed in a floor trim or in a toe rail under a cabinet or the like the front opening is visible and can become caked with dirt, dust or the like, creating an unsightly appearance. In any event a permanently open front is not the most desirable look. 
     A further prior inlet valve is to Mantyla, Canadian patent 2,279,770. In this prior patent a valve cover plate or door is provided on the front of the unit which is held in sealing engagement to the main body by an arched latch mechanism. In this way the unit is always closed when not in use and provides an improved aesthetic appearance. By lifting the latch with their toe, the user frees the door which is biased to an open position to provide access to the vacuum source. The opening of the door also closes a low voltage circuit to activate the central vacuum motor. However, this prior design includes an arched latch mechanism which stands proud of the surface of the unit to considerable degree. Therefore, it projects slightly out from the baseboard somewhat which in some cases may be considered undesirable. 
     Other floor or other types of inlet valves are shown in the following additional U.S. Pat. Nos. 2,810,028, 3,027,587, 3,027,588, 3,655,927, 3,676,986, 5,083,704, 5,205,013, 5,279,016, 5,408,721, 5,504,967, 6,108,858 and Canadian patent 2105554. 
     What is desired is a floor or sweep inlet valve for connection to a central vacuum system that overcomes one or more of the deficiencies of these prior designs. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a sweep inlet valve which is of a sleek outer design and does not project as obtrusively from the floor surface or wall surface in which it is mounted as the prior art. The present invention is also directed to a design which completely covers the vacuum opening when not in use presenting a clean, finished appearance with surface texturing if desired, rather than leaving a gaping hole or permanent opening as in some of the prior art. The present design is also one which is easily turned on or off by a single contact by the foot of the user without the need for continuous contact with the unit in order to maintain power, the vacuum opening, or any other aspect required to operate the unit. 
     In particular, this invention is directed to an inlet valve for a central vacuum cleaning system having a central vacuum motor connected to a piping network, the inlet valve comprising: 
     a main body having an air inlet passageway formed therethrough and an outlet connector to connect the inlet valve to said vacuum piping; 
     an outer door pivotally mounted to said main body over an inlet side of said air inlet passageway on an opposite side of said main body from said outlet connector; 
     an inner door pivotally mounted to said main body, said inner door being positioned between said outer door and said main body and covering an inlet side of said air inlet passageway when in a closed position, said inner door being mounted to said outer door wherein said inner and outer doors pivot open and closed together; 
     a releasable latch operatively connected to said outer door to keep said outer door closed and said inner door on an inlet side of said air inlet passageway when said unit is not in use; and 
     a spring to cause said inner door and said outer door to open upon said latch being released. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Reference will now be made, by way of example only, to drawings in which depict preferred embodiments of the present invention and in which; 
         FIG. 1  is a perspective view of the present invention from below and to one side in a doors open position; 
         FIG. 2  is a rear exploded view of the embodiment of  FIG. 1 ; 
         FIG. 3  is a true cross-section view of the embodiment of  FIG. 1  along lines  3 - 3 ; 
         FIG. 4  is a cross-sectional perspective view of the embodiments of  FIGS. 1 and 2  in a doors closed position; 
         FIG. 5  is an exploded view of the present invention from above and in front; 
         FIG. 6  is a front view of  FIG. 4 ; 
         FIG. 7  is a front view of the embodiment of  FIG. 1  with the outer door removed; 
         FIG. 8   a  is a side cross-sectional view showing the outer door cam slot in more detail in a doors closed position; 
         FIG. 8   b  is the view of  8 a in a doors open position; 
         FIG. 9  is an exploded rear view of a second embodiment of the present invention having a touch operated outer door; and 
         FIG. 10  is an exploded front view of the second embodiment of  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows an inlet valve for a central vacuum cleaning system according to the present invention. The inlet valve includes a main body  10  with an air inlet passageway  12  ending in an outlet spigot pipe connection  14  on a rear face of the main body  10 . The main body defines an air passageway through the main body as shown. An outer door  16  is hinged along a top edge of the main body  10  to permit the outer door  16  to pivot between an open and a closed position and includes door spline walls  18  at each side edge. These door spline walls  18  slide through an opening between low debris walls  20  in the main body as the outer door opens and closes. The door spline walls  18  help to define a front opening on the air passageway through the main body to, among other things, more precisely focus the suction. A cam opening  22  is formed in each door spline wall  18 . A button latch assembly  24  is mounted to the outer door  16  and accessible through an opening  26 . The button latch assembly  24  interacts with a latch mechanism  28  on the main body  10 . 
     Also shown is an inner door  30 . The inner door  30  includes a cam follower  32  at each side edge which fits into the cam openings  22  in the door spline walls  18  of the outer door  16 . The inner door  30  also includes a flat gasket  34  to seal against the main body  10 . Most preferably the flat gasket  34  is an overmolded gasket which is secured in openings (not shown) within the inner door  30  such that the flat gasket  34  projects on both the outside and the inside of the inner door  30 . The outside face of the flat gasket is herein indicated with number  36 . Most preferable the flat gasket  34  provides a sealing surface to seal against a sealing edge  38  on the main body  10  when the inlet valve is not in use but there is suction in the system because some other outlet is in use. The inner door  30  also carries a contour molded gasket  40  to seal the air passageway through the body when the inlet valve is in use to prevent a loss of vacuum around the inner door  30 . The operation of these elements will be explained in more detail below. The inner door  30  is pivotally hinged to the main body  10  in a manner described in more detail below. 
     Turning now to  FIG. 2 , the outer door  16  has outer door hinges  42  by which it can be hingedly mounted to the main body  10 . The inner door  30  is mounted to the main body  10  by means of inner door pivot points  44 , which define an inner door hinge axis. Inner door pivot points  44  are mounted into holes  46  in the main body  10 . As well inner door spring cam shafts  48  fit into curved slots  50  on the main body  10 . The inner door  30  is provided with door guide pads  52  (see  FIG. 5 ) located on an outer face  54  of the inner door  30  to ensure that the outer door  16  slides smoothly and without catching across the inner door  30  when the doors are being opened or closed. The cam followers  32  of the inner door  30  fit into the cam openings  22  of the door splines  18  of the outer door  16 . The action of the cam followers  32  is described in more detail below. 
     As shown in  FIG. 3 , when the inner and outer doors are opened, they help define an air suction mouth area  56  which leads to a throat area  58  defined over an air foil  60 . As can be seen by the air flow lines F the air flow, created by the suction of the central vacuum motor, is caused to accelerate through the throat area  58  to help lift dirt and debris over the air foil  60 . The air suction area  56  is defined by the inner door lower edge  62 , the outer door splines  18 , and the floor  64 . 
       FIG. 4  shows a view from behind of the preferred form of the invention of  FIGS. 1 and 2 . In  FIG. 4  strengthening ribs  66 , which may be placed in a grid pattern, can be seen on the outer door  16 . As will be appreciated by those skilled in the art, the strengthening ribs  66  provide a rigid plastic door with a lower total amount of plastic than a solid door. Therefore the strengthening ribs  66  are useful for stiffening the door without requiring large additional amounts of plastic and provides a material and cost saving feature for the present invention. It will also be appreciated that other rib patterns (honeycomb) are comprehended by the present invention. It will also be appreciated that as the inner door  30  is making the sealing connection with the inlet opening of the main body  10 , the outer door  16  can have a more relaxed dimensional tolerance than the inner door  30 . 
     A spring assembly is used to bias the inner and outer doors to an open position. As shown, there are provided the following support elements to complete the spring assembly. On the main body  10  there is provided a top wire terminal  68  and a cable trap hole  70 . The guide wall  72  of the main body  10  helps to hold the spring (not shown) in place. A lower wire terminal  74  is provided as well. 
       FIG. 4  also shows, in more detail, the air foil  60 . The throat area  58  is defined by curved walls  76  and the air foil  60 . The purpose of the curved walls  76  is to focus the suction in a region close to the floor next to the sweep inlet valve to encourage the removal of dirt, debris and the like that are swept up to the unit. The air foil  60  helps to encourage efficient removal of debris and sweepings by means of its shape. As well, the outer door hinge  42  is clearly illustrated in  FIG. 4 . Also shown is the front debris ramp  78  on the main body  10 . A slight incline has been found to provide good results, with the range being between 5 and 20 degrees. The most preferred incline is an 11 degree incline for this embodiment. 
       FIG. 5  discloses the button latch assembly  24  and latch mechanism  28  in exploded view. The button latch assembly  24  is mounted to the outer door  16  and includes a button  80 , with a latch striker  82 , two button springs  84  and  86 , a retainer plate  88 . The latch mechanism  28  is mounted in hole  29  in the main body  10 . The button latch assembly  24  and latch mechanism  28  interact in a known manner to permit the outer door  16  to be held in a closed position, when the latch mechanism  28  holds the latch striker  82  of the button  80 . When the button  80  of the button latch assembly  24  is depressed against the button springs  84 ,  86  the latch mechanism  28  releases the latch striker  82  to permit the outer door  16  to spring open to an open position. The back of the latch assembly  28  is best seen in  FIG. 4 . It will be appreciated that more or fewer button springs are comprehended by the present invention. The main body  10  is also shown with the inner door  30  and the outer door  16  in exploded view. The outer face  36  of the flat gasket  34  is shown on the inner door  30  to provide reasonable seal between the inner and outer door. This seal is to discourage dirt from getting into the space between the inner and outer doors and potentially disrupting the smooth functioning of the device, while a good seal is desirable it does not need to be airtight. In fact there are breaks in the seal to provide the door guide pads  52  previously described. Also shown are the inner door  30  pivot points  44  and the cam follower  32 . 
       FIG. 5  shows the outer door  16  with an opening  26  for the button latch assembly  24 . Also shown are the curved walls  76  in the main body  10  which direct the dirt and debris along a specific narrow flow path towards the open throat area  58  defined by the air foil  60  as previously discussed. From the rear (best seen in  FIG. 2 ) it can be seen that the curved walls  76  form a gasket channel or slot  94  which extends in a curved manner from the lower outer corners towards the upper middle. The gasket channel  94  is preferably provided with a rounded lower edge  96  to permit a sliding seal to be made thereagainst. This gasket channel or slot  94  in the front face of the main body  10  accommodates the contour molded gasket  40 . This contour molded gasket  40  is intended to prevent a loss of suction to behind the inner door  30  and so needs to be able to maintain a seal when the inner door  30  is in the fully open position. Essentially this contour molded gasket  40  is curved in shape to match the shape of the gasket channel  94  and follows along the contoured sealing edge  38  of the channel  94  of the main body  10  during the rotation of the inner door from the closed to the open position and vice versa. The contour molded gasket  40  is most preferably provided with a face seal to permit better sealing contact with the main body  10  in the open position. 
     As shown on the right hand side of the main body  10 , there is provided wire terminals or contacts  68  and  74 . Most preferable the wire terminals  68 ,  74  are of the spring loaded type so that wire connections can be easily made to the low voltage wires (not shown) without the need for tools or the like. A push nut  100  is provided to hold a plastic grommet  102  in place on the inner door spring cam shaft  48 , when it is located within a curved slot  50  on the main body  10  (see  FIG. 2 ). A door spring  104  is shown with spacer washers  106 ,  108 . The spacer washers are preferably electrically conductive and increase the electrical contact area for better reliability. The door spring  104  is held in place and exerts an opening bias on the outer door via the inner door spring cam shaft  48 . The door spring  104  acts on the inner door/outer door combination to cause the doors to open. When the latch striker  82  of the button  80  is held by the latch mechanism  28  the outer door  16  cannot move. When the latch striker  82  is released from the latch mechanism  28  the button latch assembly  24  and thus the outer door  16  to which it is mounted are freed and the door spring  104  causes the doors  16 ,  30  to open. As the cam followers  32  of the inner door  30  move along the cam openings  22 , the outer door  16  opens. As the door spring  104  opens the inner and outer doors, the position of the door spring  104  changes relative to the wire terminals  68 ,  74  and then, when the doors  16 ,  30  are open the door spring  104  closes the electrical contact by contacting the spacer washers  106 ,  108 , completing the low voltage circuit, to initiate the central vacuum motor and creating suction. It will be understood by those skilled in the art that the door spring  104  can be exerting force on the inner door  30 , the outer door  16  or both depending upon the configuration of the elements. However, good results have been obtained where the door spring  104  acts on the inner door spring cam shafts  48  of the inner door  30  and the outer door  16  is moved Open as the inner door  30  opens. 
     The present invention is also directed to a design which completely covers the vacuum opening when not in use presenting a clean, finished appearance 
     In  FIG. 6  the outer face  110  of the outer door  16  is shown with the button  80 . As can be appreciated, the outer face  110  of the present invention presents a clean, finished appearance. As shown, the outer face  110  presents a smooth cover or exterior (which may be textured if desired) that will blend easily into wall boards or the like without leaving a gaping opening as in some of the prior art. Further while the button  80  is slightly proud of the front surface it can be gently curved or rounded to provide an easy to activate element (best seen in  FIG. 1 ). 
       FIG. 7  shows a further view of the present invention with the outer door  16  removed for ease of illustration. In this view, the outer door hinge pins  112  are shown running across the top of the main body  10  for coupling the outer door hinge  42 . The outer door hinge pins  112  are mounted between pairs of hinge pin support columns  114 . The outer door hinge pins  112 , outer door hinges  42 , and hinge pin support columns  114  form hinge assemblies. It will also be appreciated that each hinge assembly is in the nature of a snap fit coupling of the outer door hinge  42  onto the outer door hinge pin  112  on the main body  10 . In this way the outer door  16  can be removed from the main body  10  for ease of installation or service of the device in a base board or toe rail or the like (not shown). In  FIG. 7  the mounting screw holes  116  and  118  for the main body  10  are clearly shown and well exposed when the outer door  16  is removed for ease of access. A second set of holes  120 ,  122  can also be provided. Most preferably, the outer door  16  will be disengaged from the inner door  30  in the shipped form of the invention. The installer simply removes the device from the package, positions the unit on the mounting surface, connects the vacuum piping, and screws the main body  10  in place. Afterwards, the outer door  16  can be pressed closed, and there is enough play in the components to allow the cam followers  32  to press past the edge of the door spline walls  18  until they engage in the cam openings  22 . This is achieved by gently pressing the outer door  16  down onto the inner door  30 . In this way installation is quickly and easily completed. 
     As well,  FIG. 7  shows the width of the suction opening or chute opening  124 . Also shown are lower debris walls  20  which are low walls adjacent to the slots  126  through the main body  10  which house the door spline walls  18  of the outer door  16 . The debris lower debris walls  20  are simply to make it less likely that debris will become jammed into the slots  126  affecting smooth opening and closing of the inner and outer doors  30 ,  16 . 
     The connection of the invention to the vacuum piping is established in a conventional manner by placing a vacuum piping connector over the outlet spigot pipe connector  14  which is dimensioned to make a snug fit. Glue can be used if desired to complete the joint. In some installations there may be less room behind the invention to establish the connection to the vacuum piping. The present invention provides a short cut line  128  (see  FIG. 1 ) molded into the outlet spigot pipe connector  14 . The short cut line  128  can be used by the installer to reduce the length of the outlet pipe spigot connector  14  to reduce the depth of the invention to accommodate smaller installation spaces. 
     The operation of the present invention can now be more clearly understood. When the outer door  16  is in a closed position it is held in the closed position by means of the interaction between the button latch assembly  24  and the latch mechanism  28 . The flat gasket  34  is in contact with the edge of the main body  10  to maintain a seal all the way along the upper edge. The front  36  of the lower part of the flat gasket  34  on the inner door  30  seals a lower edge of the front of the vacuum opening. A user, who wishes to open the inlet valve of the present invention, simply taps the button  80  with their toe, causing the latch mechanism  28  to release the latch striker  82  thereby allowing the outer door  16  to spring open under the influence of door spring  104 . It will be appreciated that the door spring  104  continuously urges the doors  16 ,  30  into an open position, but is frustrated when the interaction of the button latch assembly  24  with the latch mechanism  28  latches the outer door  16  in a closed position. In other words, upon release of the button latch assembly  24  from the latch mechanism  28 , the outer door  16  is allowed to move to an open position by means of the door spring  104  acting on inner door spring cam shaft  48  on the inner door  30 . 
     As shown in  FIG. 8   a  when the doors are closed the cam follower  32  is located at a lower end of the cam opening  22 . As shown the cam follower  32  is in the form of a shaped post, with a lower outer curved surface that fits against the curved cam opening  22  at position  130 . As shown in  FIG. 8   b , with the doors open the cam follower  32  is now located towards the other end of the cam opening  22  at position  132 . The shape of the cam opening  22  is due to the inner door hinge axis being displaced from the outer door hinge axis. This results in a need to have the cam follower  32  move along an arc, relative to the outer door  16 , requiring the cam opening  22  to have a curved shape. 
     As the inner door  30  is urged outwardly, the outer door  16  is also pivoted about its hinge points and opens the air suction area  56  of the inlet valve. As the inner door  30  pivots open the flexible contour molded gasket  40  moves within the gasket channel  94  allowing the inner door  30  to change position without binding during opening and closing. In this way, when opened, the contour molded gasket  40  seals on sealing edges  38  and the sweepings are directed only through the throat of the unit and not into any other spaces. As the door spring  104  moves to the open door position, it closes a low voltage circuit between the wire terminals  68 ,  74  initiating the vacuum motor and suction through the main body  10 . As will now be appreciated, the main body  10  includes curved walls  76  which feed to a throat area  58  defined by an air foil  60 . As a result, the suction is directed, concentrated and the air flow maintained at an optimum speed to help the present invention achieve superior suction and hence removal of the debris located within the general area of the air suction area  56  of the inlet valve. 
     When the debris swept up to the unit has been sucked away, the user can simply push on the button  80  with their toe to cause the outer door  16  to close. This will close the inner door  30 , load up the door spring  104  and disengage the door spring  104  from the wire terminals  68 ,  74  causing the central vacuum motor to shut down. As the outer door  16  reaches the fully closed position the latch mechanism  28  will again engage and hold the doors  16 ,  30  in a closed position against the biasing force of the now reloaded door spring  104 . In some cases the inner door  30  might not be held closed onto the main body  10 , due to design tolerances of the plastic molded parts. However, even so the inner door  30  is able to retain suction because the activation of suction in the system, for example when another inlet valve is in use, will cause the inner door  30  to be sucked onto the sealing edges  38  of the main body  10  creating a tight seal and preventing a loss of suction. While the foregoing mode of latching and unlatching of the doors is the most preferred form of the invention, the present invention also comprehends that an electronic switch such as a solenoid or RF activated remote controlled switch, or even a buttonless door latch, can be used in place of the button latch assembly  24  and latch mechanism  28  discussed above. 
     A buttonless alternative embodiment of the present invention is shown in  FIGS. 9 and 10 . In this embodiment the whole door acts as the button, and so no separate button is required. In  FIGS. 9 and 10  like elements from the first embodiment are shown with like numbers. In this embodiment the latch striker  134  extends rearwardly from the outer door  16  as shown. To achieve a balance of forces on the doors, a passive flat spring  136  is mounted in a recess  138  and contacts the outer door  16  in a generally symmetrically disposed position to said latch striker  134 . The flat spring  136  is sized and shaped to allow the forces along the outer door to be evenly balanced to permit smooth operation of the doors. In this embodiment, a user simply taps on the door, in any location, to cause the latch striker  134  to be released from the latch mechanism  28 . Once released this embodiment functions the same as previously described, with the door spring  104  opening the device. To close the outer door  16 , the user simply presses on the outer door  16  in any location to cause the outer door  16  to close and the latch striker  134  to be captured by the latch mechanism  28 . Although it would be preferable to position the latch striker  134  in the middle of the door  16 , the air inlet passage way  12  and inner door  30  are in the way. Therefore, the present invention provides a latch striker  134 /latch mechanism  28  on one side of the unit, with the flat spring  136  on the other side. 
     As can now be appreciated the present invention provides a sleek unit, able to fit into small installation spaces and yet which provides a wide suction mouth area. Without limiting the invention to these dimensions, a preferred form of the unit is 299.7 mm long by 91.4 mm tall by 69 mm thick. The air suction area  56  is 216 mm wide at the floor  64 . It will also be appreciated that the present invention can be installed in a wall, or in a floor although the latter is believed less preferred as it creates a potential tripping hazard when the unit is open and in use. 
     It will be appreciated that the foregoing description is in respect of certain preferred embodiments of the present invention, but that other configurations are comprehended within the broad ambit of the appended claims. Some of these alterations and variations are discussed above and others will be apparent to those skilled in the art. For example, although in the preferred embodiment the door spring  104  acts on the outer door  16 , this is not essential. All that is required is for the inner and outer doors to be motivated by the door spring  104  so that when released the doors open, the electrical circuit is completed and the vacuum motor can start.