Patent Publication Number: US-6669056-B2

Title: Foaming device

Description:
FIELD OF THE INVENTION 
     The present invention relates to a foaming device capable of generating foam by mixing a quantity of liquid with a volume of air, in accordance with the preamble of claim 1. 
     BACKGROUND OF THE INVENTION 
     It is known that in the field of devices for generating foam by mixing a foam-generating liquid with air, the need to optimize foam formation is increasingly felt. 
     One solution currently used in the field of foam-generating devices, particularly devices using two pumping members (one for expelling a quantity of liquid and the other for compressing and expelling a volume of air), requires that the said devices be produced in such a way that they expel a constant rate of flow of air during the escape of the foam. 
     In this context, “rate of flow of air” means the variation in the volume of air expelled as a function of the displacement of an air piston which deforms (compresses) the chamber in which the air to be expelled is contained. 
     The above solution has the disadvantage of expelling an airflow that does not completely mix with the liquid. In other words, at the beginning of the compression of the device, the airflow that invests the liquid is too great for the available liquid. 
     An example of a foam-generating device with an air chamber enclosed in a compressible bellows (shaped appropriately to ensure the escape of the air in a constant air/liquid ratio) is disclosed in U.S. Pat. No. 5,462,208. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the problem of devising a foaming device that has structural and functional characteristics such as to satisfy the abovementioned requirements and at the same time obviate the problems discussed with reference to the prior art. 
     This problem is solved with a foaming device in accordance with claim 1, capable of generating foam by mixing a quantity of liquid with a volume of air. 
     Further characteristics, and the advantages, of the device according to the present invention will become clear in the following description of a preferred embodiment thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The description is given by way of non-limiting guidance, with reference to the accompanying figures, in which: 
     FIG. 1 shows a cross section through a foaming device fitted to a tank and with a cap; 
     FIG. 2 shows an enlarged cross section through the foaming device of FIG. 1; 
     FIG. 3 shows an enlarged cross section through the foaming device of FIG. 1 when deformed at maximum compression; 
     FIG. 4 shows detail A from the device of FIG. 3, enlarged and in a deformed condition assumed during expulsion of air; 
     FIG. 5 shows detail B from the device of FIG. 3, enlarged and in a deformed condition during aspiration of air; 
     FIG. 6 shows detail C from the device of FIG. 3, enlarged and in a deformed condition during aspiration of air; 
     FIG. 7 shows an enlarged perspective view of a foaming member; 
     FIG. 8 shows a cross section through another embodiment of the foaming device, fitted to the tank and with the cap, and 
     FIG. 9 is a graph showing the reduction in the volume of an air chamber of the foaming device of FIG. 1 or FIG. 8 against the stroke of an air piston of the said device. 
    
    
     DETAILED DESCRIPTION 
     The number  1  refers to a foaming device capable of generating foam by mixing a volume of air A′ with a quantity of liquid L′. 
     The device  1  can be fitted to a tank  2  designed to contain the liquid L during transportation and during use of the device  1 , thus ensuring that it is not lost or contaminated with dust or the like. 
     The tank  2  is bounded by essentially cylindrical side walls  3  that extend along an axis of symmetry X—X, from an upper end  3 ′ to a lower end  3 ″ . At the said lower end  3 ″, the tank  2  is provided with a bottom  4 , while at the upper end  3 ′ it is provided with closing means  5 . 
     The bottom  4 , of deformable resilient material, is fitted removably to the tank  2  and is roughly dish-shaped. The said bottom  4  also includes a gripping lip  4 ′ in the form of a cylindrical wall which, together with the outermost wall of the bottom  4 , provides a gripping space  4 ″. 
     Near the bottom  4 , on the inside of the tank, is one end of an aspiration tube  6 , the other end of which fits inside an aperture  7  formed in the closing means  5  of the tank  2 . 
     At the upper end  3 ′ of the tank  2 , the closing means  5  comprise a base  8  shaped as a series of vertical cylindrical walls  8 ′ and annuluses  8 ″ which give it a conical profile. 
     The base  8  is pierced by a plurality of holes  9  that allow communication between the tank  2  and the external environment via a renewing pass  10  (in FIG. 2) whereby the air in the tank  2  is renewed. 
     The closing means  5  also include a containment cylinder  11  integral with the base  8  and forming one piece with the side wall  3  of the tank  2 , to which it is connected by a shoulder surface  12  of curvilinear sections. Internally, the said containment cylinder  11  has an essentially annular stop edge  17 . 
     Where the shoulder surface  12  meets the side walls  3  of the tank it forms a supporting ledge  13  to support a cap  14 , which can be placed on the device  1  when the said device  1  is not likely to be used. 
     Referring to FIG. 2, the containment cylinder  11  forms a space  15  that houses an envelope  16  attached to it by male/female attachment to the base  8  of the closing means  5  of the tank  2 . 
     Attachment of the envelope  16  to the base  8  is via an annular base  19  with an undercut portion  20  engaged with the series of vertical cylindrical walls  8 ′ and annuluses  8 ″ of the base  8  of the closing means  5 . 
     The said annular base  19  and the said undercut portion  20 , and also the series of vertical cylindrical walls  8 ′ and annuluses  8 ″, represent a preferred embodiment of means of attachment. 
     The annular base  19  terminates, in a preferred embodiment of the device  1 , in an annular lip  21  which diverges downwards and engages, deforming elastically as it does so, with an annular cavity defined by the series of vertical cylindrical walls  8 ′ and annuluses  8 ″ of the closing means  5 . The annular lip  21  forms, in a preferred embodiment, a renewing valve  21 ′ through which the air in the tank is renewed. The said renewing valve  21 ′ for the renewal of air in the tank is a non-limiting example of an embodiment of the means of renewing the air in the tank. 
     The envelope  16  also includes a resiliently deformable diaphragm  22 , preferably cup-shaped, which encloses an air chamber  23 , and a tubular core  26 , which houses one end of the aspiration tube  6  and is integral with and concentric with the diaphragm  22 . 
     The diaphragm  22  preferably comprises a supporting surface  22 ′ whose shape is essentially that of a flat circular annulus, and a surface  22 ″ which is concave towards the air chamber. The concave surface  22 ″ of the diaphragm  22  is provided with an anchoring ring  24  on the outside edge and an inner ledge  25  not far from the inside edge of the diaphragm  22 . 
     The tubular core  26  is surmounted by a cup-shaped head  27  that acts as a piston  27 ′ for the liquid: said head has a sealing lip  28  with diverging walls and an essentially frustoconical projection  29 . The projection  29  contains a cut  30  approximately at right angles to an axis Y—Y of symmetry of the tubular core, which preferably coincides with the axis X—X of symmetry of the tank. 
     Above the cut  30  is a closing lip  47  integral with the frustoconical projection  29 . 
     The closing lip  47  acts as a non-return valve  46  on a path of aspiration of the liquid  44  that allows communication between the tank  2  and a liquid chamber  42 . 
     As shown in FIG. 3, the cup-shaped head  27  of the envelope  16  is functionally connected with an intermediate element  31  comprising an annular band  32  and a liquid cylinder  33 , these being preferably made in one piece. 
     The annular band  32  of the intermediate element  31  comprises, in a preferred embodiment, a first annulus  32 ′ and, concentric and integral with the first annulus  32 ′, a second annulus  32 ″. The annuluses are arranged on parallel planes at different heights. 
     The second annulus  32 ″ comprises, in another embodiment of the device, an upper annular projection  40  and a lower annular projection  41 . The said projections run around the edge of the second annulus  32 ″, the first above and the second below the said second annulus. The lower projection  41  engages with the inside ledge  25  of the diaphragm  22 . 
     The said annular band  32  of the intermediate element  31  provides an annular space  34  bounded by the first annulus  31 ′, the second annulus  32 ″ and the upper annular projection  40 . 
     The annular band  32  contains a plurality of holes  35  for expulsion of the volume of air A′ (in FIG.  4 ), these preferably being in the first annulus  32 ′ and allowing communication between the air chamber  23  and a path of expulsion of the air  36  into a mixing chamber  37  in which the volume of air A′ is mixed with the quantity of liquid L′. 
     Additionally, the annular band  32  contains a plurality of air aspiration holes  38  (in FIG.  5 ), preferably in the second annulus  32 ″, so that an air aspiration path  39  can communicate with the air chamber  23 . 
     The liquid cylinder  33  contains the liquid chamber  42 . This is separated from the air chamber  23  by the sealing lip  28  of the envelope  16  which presses against the walls of the liquid cylinder  33 . The liquid chamber  42  is preferably bounded not only by the liquid cylinder  33  and cup-shaped head  27  but also by a transverse expulsion wall  43  at one end of the liquid cylinder  33 . 
     In a preferred embodiment, the cut  30  in the cup-shaped head  27  gives communication between the liquid chamber  42  and the space inside the tubular core  26  of the envelope, through the liquid aspiration path  44 . 
     A non-return valve  46  is positioned on the liquid aspiration path  44 . The said non-return valve  46  is produced, in a preferred form of the device  1 , by a flexible lip  47  belonging to the cup-shaped head  27  and positioned above the cut  30  and integral with the frustoconical projection  29 . 
     The non-return valve  46  is only a preferred, non-limiting example of means of controlling the flow of liquid during expulsion. 
     The transverse expulsion wall  43  of the liquid cylinder  33  is preferably pierced by a plurality of holes  48  for expulsion of the liquid and defines, together with a portion of the liquid cylinder  33 , a liquid expulsion chamber  49 . 
     The liquid chamber  42  is in communication, via the liquid expulsion holes  48  and a liquid expulsion path  50 , with the mixing chamber  37 . The liquid expulsion path  50  is separated from the air expulsion path  36  by the liquid cylinder  33 , as far as the mixing chamber  37  where the said paths come together. 
     A liquid expulsion valve  51  is positioned on the liquid expulsion path  50 . 
     The said liquid expulsion valve  51  is preferably a resiliently deformable flap  52  which is housed in the expulsion chamber  49  and provided with elongate walls  52 ′ which press and deform against the walls of the expulsion chamber  49 . The liquid expulsion valve  51  described is a preferred, non-limiting example of an embodiment of means of sealing the foam. 
     In one preferred embodiment, the intermediate element  31  is attached to an essentially hollow air piston  53  comprising a upper cylindrical body  54  and a lower cylindrical body  55 , the diameter of the latter being greater than that of the upper cylindrical body  54 , and these two bodies  54  and  55  being joined by an annular surface  56 . The said upper cylindrical body  54  is preferably joined to the said annular surface  56  by a frustoconical wall  57 . 
     The air piston  53  slides inside and is connected to the containment cylinder  11  by means of a guide projection  58  on the lower cylindrical body  55 , on the outside of the latter, which abuts against the stop edge  17  of the containment cylinder  11 . 
     The lower cylindrical body  55  preferably comprises an annular tooth  59  located on the inside of the said lower cylindrical body in abutment with the anchoring ring  24  of the diaphragm  22 . The diaphragm  22  is locked, near its edge, between the intermediate element  31  and the air piston  53 , by the annular tooth  59  on the air piston  53  in abutment against the anchoring ring  24  of the diaphragm  22 , and by the lower annular projection  41  of the intermediate element in abutment against the ledge  25  on the inside of the diaphragm  22 . 
     In a preferred embodiment, the annular surface  56  of the air piston  53  comprises a plurality of essentially radial grooves  60  running from the periphery towards the centre of the said annular surface and interrupted at a plurality of through holes  61  passing through the said annular band. 
     In another embodiment of the device  1 , the through holes  61  (shown in FIG.  5 ), located on the air aspiration path  39 , are intercepted by an air aspiration valve  62 , which is typically a second annular portion  63 ″ of a resiliently deformable ring  63 . The said ring  63  also includes a first annular portion  63 ′, which intercepts the air expulsion holes  35 . 
     The first portion  63 ′ of the ring  63  acts as an air expulsion valve  64 . 
     The air aspiration valve  62  and the air expulsion valve  64  represent a preferred, non-limiting embodiment, the first as a means of controlling the incoming flow of air and the second as a means of controlling the outgoing flow of air. 
     With reference to FIG. 1, the air piston  53  is surmounted, in another embodiment of the device  1 , by an essentially hollow head  65  comprising, as a minimum, an outer cylindrical wall  66 , an inner cylindrical wall  67  (these walls  66  and  67  being preferably concentric), and a transverse pipe  68  that extends essentially at right angles to the axis Y—Y. 
     The said head  65  is connected to the upper cylindrical body  54  of the air piston  53  by attaching together the upper cylindrical body  54  of the air piston  53  and the inner cylindrical wall  67  of the head  65 . 
     Preferably, the outer cylindrical wall  66  of the head  65  extends down and rests on the annular surface  56  of the air piston  53 . 
     The transverse pipe  68  inside the head  65  can receive a foaming member  69  (FIG. 7) comprising a grid  70  with a plurality of passageways  71  dividing the foaming member  69  into an upper zone  72  and a lower zone  73 , the said passageways  71  being such as to allow communication between the said upper zone and the said lower zone. 
     The foaming member  69  also includes one or more bases  74 , each provided with an aperture  75  entirely contained either within the upper zone  72  or within the lower zone  73  of the said foaming member  69 . 
     In addition, the foaming member  69  includes one or more intermediate projections  76  entirely contained either within the upper zone  72  or within the lower zone  73  of the foaming member  69 . 
     The intermediate projection  76  and the transverse pipe  68  define a labyrinth path  77  that passes through the grid at at least two points followed by the quantity of liquid L′ mixed with the volume of air A′ for complete and uniform generation of the foam. 
     The device  1  according to the invention is capable of generating foam by mixing the volume of air A′ with the quantity of liquid L′. 
     In the initial or rest configuration of the device  1 , illustrated in FIG. 2, the head  65  is in the fully up position in which it is supported by the air piston  53 . 
     The device  1  is permanently being pushed towards the said initial or rest configuration by the diaphragm  22 , which is of a resilient material. The said diaphragm  22  exerts a force which, in the initial or rest configuration, pushes the guide projection  58  of the lower cylindrical body  55  towards the stop edge  17  of the containment cylinder  11 , supporting the air piston  53  in an upper limit position. The said diaphragm  22  is preferably elastically preloaded, even with the air piston  53  in the said upper limit position. 
     When the device  1  is used for the first time, the air chamber  23  contains the volume of air A′, while the liquid chamber  42  does not contain the quantity of liquid L′, which must first be drawn up from the tank  2 . 
     Pushing the head  65  down, generally by hand, against the permanent effect of the cup-shaped diaphragm  22  has the effect of expelling air, but no liquid L′ is expelled from the liquid chamber  42  as the latter is initially empty. 
     When pushed down, the head  65  connected to the air piston  53  moves the said air piston down, in a direction roughly parallel to the axis Y—Y and/or X—X, guided by the containment cylinder  11 . The air piston can be moved from the upper limit position, described above, to a lower limit position, in which the lower cylindrical body  55  interferes with the base  8  of the closing means  5 . 
     The air piston  53  also takes down with it the intermediate element  31  which, together with the air piston  53 , anchors the edge of the diaphragm  22 . 
     During the movement towards the lower limit position, the air piston  53  and the intermediate element  31  expel the volume of air A′ from the air chamber  23 . 
     While the air piston  53  is proceeding downwards, taking the intermediate element  31  with it, the said intermediate element is sliding relative to the liquid piston  27 ′, which remains in a fixed position relative to the tank  2 , thus reducing the volume of the liquid chamber  42 . 
     When the head  65  is released, the effect of the cup-shaped diaphragm  22  is to return the device  1  to the initial or rest configuration, following the phases of aspiration of the liquid from the tank  2  into the liquid chamber  42  and of aspiration of air from the environment around the outside of the device  1  into the air chamber  23 . 
     The elastic force of the diaphragm  22  acts on the air piston  53 , pushing it upwards and tending to increase the volume of the deformed air chamber  23  and the volume of the liquid chamber  42 . The diaphragm  22  acts as elastic means in a preferred and non-limiting embodiment of the device  1 . 
     The tendency to increase the volume of the deformed air chamber  23  and the volume of the liquid chamber  42  generates a depression in the air chamber  23  and a depression in the liquid chamber  42 . 
     The depression in the liquid chamber  42  closes the liquid expulsion valve  51 , preventing communication between the liquid chamber  42  and the liquid expulsion path  50 , and opens the non-return valve  46 , allowing communication between the liquid chamber  42  and the tank  2 , via the liquid aspiration path  44 . 
     The depression in the liquid chamber  42  lifts the closing lip  47  of the frustoconical projection  29 , which lies over the cut  30 , off the said cut  30 , giving communication between the liquid chamber  42  and the liquid aspiration path  44 , allowing liquid to be drawn from the tank  2  into the liquid chamber  42 . 
     When the head  65  is again depressed, the liquid chamber  42  gradually fills with liquid until it contains a quantity of liquid L′ sufficient to generate the foam. 
     In the initial or rest configuration of the device  1 , with the liquid chamber  42  filled with a quantity of liquid L′ sufficient to generate foam, downward depression of the head  65  connected to the air piston  53  causes expulsion of the volume of air A′ and of the quantity of liquid L′. 
     Depressing the head  65  depresses the air piston  53 , which moves the intermediate element  31 . The intermediate element  31  and the air piston  53  clamp the edge of the diaphragm  22  so that the said diaphragm  22  can deform. 
     As the air piston  53  proceeds towards the lower limit position, the diaphragm  22  deforms. This initially affects that portion of the concave surface  22 ″ of the diaphragm  22  which is next to the supporting surface  22 ′. 
     In this initial stage of deformation, the change in the volume of the air chamber  23  is less than the change in the volume of the said air chamber later on in the deformation, when deformation occurs to portions of the concave surface  22 ″ progressively further away from the supporting surface  22 ′ of the diaphragm  22 . 
     As the air piston  53  proceeds downwards, the reduction in the volume of the air chamber  23  increases, as shown by the curve S in FIG.  9 . The reduction in the volume of the air chamber  23  coincides with the volume of air expelled. 
     “Rate of flow of expelled air” here means the variation in the volume of air expelled as a function of the downward displacement of the air piston. Consequently the straight line R in FIG. 9 describes the change in the volume of air expelled by a device with a constant rate of flow of air and the increasing curve S, characteristic of the foaming device  1  according to the invention, describes the change in the volume of air expelled by a device with an increasing rate of flow of air. 
     The diaphragm  22  deforms elastically under the action of the air piston  53 , compressing the air inside the air chamber  23 , increasing the pressure of the air in the air chamber  23 . 
     The increased air pressure in the air chamber  23  produces an increased air pressure in the annular space  34  connected to the air chamber  23  through the air aspiration holes  38 . This closes the air aspiration valve. In other words the increased air pressure in the space  15  exerts a force on the second portion  63 ″ of the elastic ring  63  against the annular surface  56  of the air piston  53 , covering and closing the through holes  61 . 
     The increased pressure of the air in the air chamber  23  opens the air expulsion valve  64 , expelling the volume of air A′ into the mixing chamber  37  via the air expulsion path  36 . In other words, the increased air pressure in the chamber  23  produces a force on the first portion  63 ′ of the elastic ring  63 , which deforms elastically away from the first annulus  32 ′ of the annular band  32  of the intermediate element  31 , assisted by the space left vacant by the frustoconical wall  57  of the air piston  53 . 
     The convex surface  22 ″ of the diaphragm deforms under the action of the air piston  53  and progressively drapes itself over the base  8  of the closing means  5 , shaped generally conically. 
     As the device  1  changes from the initial or rest configuration to a deformed configuration shown in the situation of maximum deformation in FIG. 3, the convex surface  22 ″ of the diaphragm  22  interferes with the vertical cylindrical walls  8 ′ and the annuluses  8 ″ of the base  8 , which guide the said convex surface as it deforms. 
     In the deformed configuration, the convex surface  22 ″ of the diaphragm  22  is received progressively in recesses  15 ′ of the space  15  between successive vertical cylindrical walls  8 ′. 
     The series of vertical cylindrical walls  8 ′ and annuluses  8 ″—and also the recesses  15 ′ in the space  15 , shaped so as to receive, in the deformed configuration of the device, the diaphragm  22  or portions of this diaphragm such as the convex surface  22 ″—represent a preferred and non-limiting embodiment of means for increasing the rate of flow of expelled air. 
     As the air piston  53  proceeds downwards, the intermediate element  31  slides relative to the liquid piston  27 ′, which remains in a fixed position with respect to the tank  2 , reducing the volume of the liquid chamber  42  and increasing the pressure of the liquid in the liquid chamber  42 . The sealing lip  28  of the tubular core  26  stays pressed against the walls of the liquid cylinder  33 . 
     The liquid passes through the liquid expulsion holes  48  into the expulsion chamber  49  and the increased pressure of the liquid in the liquid chamber  42  generates an increase in the pressure of the liquid in the expulsion chamber  49 . The increase of the pressure of the liquid in the expulsion chamber  49  opens the liquid expulsion valve  51 . In other words, the increase in the pressure of the liquid in the expulsion chamber generates a force which lifts the elongate walls  52 ′ of the flap  52  off the walls of the expulsion chamber, allowing the liquid to reach the mixing chamber  37 . 
     The increased pressure of the liquid in the liquid chamber  42  closes the non-return valve  46 . The increased pressure of the liquid elastically deforms the closing lip  47  of the frustoconical projection  29 , closing the cut  30  and preventing communication between the liquid aspiration path  44  and the liquid chamber  42 . 
     During the period of expulsion of the liquid and air, the quantity of liquid L′ and the volume of air A′ pass along the liquid expulsion path  50  and the air expulsion path  35 , respectively, remaining unmixed until they reach the mixing chamber  37 , in which the liquid expulsion path  50  and air expulsion path  35  come together. 
     The movement of the air and liquid through the foaming member  69  generates the foam which escapes into the environment outside the device  1  through the transverse pipe  68 . Inside the foaming member  69 , the volume of air A′ and the quantity of liquid L′ mix intimately along a labyrinth path  77  in which they cross the grid  70  with its passageways  71  one or more times. 
     When the head  65  is released, the device  1  returns to the initial or rest configuration, following aspiration of liquid from the tank  2  and aspiration of air from the environment outside the device into the air chamber  23 . 
     The elastic force of the deformed diaphragm  22  pushes the air piston  53  upwards, tending to increase the volume of the air chamber  23  and of the liquid chamber  42 . 
     The tendency to increase the volume of the air chamber  23  generates a depression of the air in this chamber. 
     The depression of the air in the air chamber  23  opens the air aspiration valve  62 , allowing communication between the environment outside the device and the air chamber  23  via the air aspiration path  39 . In other words the depression of the air in the air chamber  23  lifts the second portion  63 ″ of the elastic ring  63  off the annular surface  56  of the air piston  53  and uncovers the through holes  61 . The second portion  63 ″ of the elastic ring  63  deforms and is received in the annular space  34  of the intermediate element  31 . 
     The depression of the air in the air chamber  23  closes the air expulsion valve  64  and prevents communication between the air mixing chamber  37  and the air chamber  23  via the air expulsion path  36 . In other words the depression of the air in the air chamber  23  presses the first portion  63 ′ of the elastic ring  63  against the first annulus  32 ′ of the intermediate element  31 , closing the air expulsion holes  35 . 
     At the same time the elastic force of the diaphragm  22  moves the intermediate element  31  upwards, which tends to increase the volume of the liquid chamber  42 . The tendency of the volume of the liquid chamber  42  to increase generates a depression in this chamber. 
     The depression inside the liquid chamber  42  is transmitted to the expulsion chamber  49 , which closes the liquid expulsion valve  51  and prevents communication between the liquid chamber  42  and the mixing chamber  37 , via the liquid expulsion path  50 . In other words the elongate walls  52 ′ of the flap  52  press against the walls of the expulsion chamber  49  and prevent communication between the liquid chamber  42  and the liquid expulsion path  50 . 
     The flap  52  with its elongate side walls  52 ′ is a preferred and non-limiting embodiment of means of sealing the foam. 
     Aspiration of liquid from the tank  2  generates a depression in the said tank  2  which opens the air renewal valve  21 ′ and draws air in from the environment outside the device  1  into the tank  2  via the air renewal path  10 . 
     The depression in the tank  2  lifts the annular lip  21  of the annular base  19  of the envelope  16  off one of the vertical cylindrical walls  8 ′ of the base  8  of the closing means  5 , allowing communication between the tank  2  and the environment outside the device  1  via the air renewal holes  9  and the air renewal path  10 . 
     Unusually, in the device  1  according to the invention, all of the quantity of air expelled from the air chamber  11  is mixed with the quantity of liquid. In other words the rate of flow of air when the diaphragm  22  first begins to deform is small enough for it to remain completely trapped by the liquid. As actuation of the device continues, the rate of flow of expelled air increases with displacement of the air piston, and continues to be sufficient for foam generation. 
     Furthermore, the device  1  according to the invention is able to expel practically the whole of the volume of air A′ present in the air chamber  23  when the latter is in its initial or rest configuration. 
     Further, the device  1  according to the invention exhibits the advantage of possessing a simplified structure which facilitates manufacture of the device and improves the operations of assembly of its component parts. In other words the device  1  consists of a small number of components but still generates foam effectively. 
     It is an advantage that the device  1  according to the invention is not subject to deterioration of its parts by the action of chemical attack on metal parts and such like by the foam-generating liquid employed. 
     Also, the structure of the device  1  avoids the contamination of the air chamber during use of the device with residues of liquid or previously formed foam and, at the same time, avoids contamination of the tank with foam. Additionally, no liquid is entrained outwards during use of the device or during transport. 
     Lastly, the structure of the device  1  makes the assembly rigid, in such a way that there is no looseness in the connections between the parts. 
     In another embodiment of the device  1  (FIG.  8 ), the cup-shaped head  27  of the tubular core  26  of the envelope  16  receives a moving part  90  capable of moving between a configuration of abutment against the tubular core  26  and a raised configuration in abutment against an end stop  91  on the cup-shaped head  27 . 
     The non-return valve  46  comprises, in the other embodiment of the device  1 , the end stop  91  and the moving part  90 . 
     Clearly, a person skilled in the art could, in order to satisfy contingent and particular needs, make numerous modifications and alterations to the foaming device described above that would all remain within the scope of protection of the invention as defined by the following claims.