US20160221744A1

US20160221744A1 - Dispenser head

Info

Publication number: US20160221744A1
Application number: US14/608,332
Authority: US
Inventors: Stefan COPPUS; Goslin Van Herpen; Theo OSTENDORF
Original assignee: Tremco Illbruck Productie BV
Current assignee: Tremco Illbruck Productie BV
Priority date: 2015-01-29
Filing date: 2015-01-29
Publication date: 2016-08-04

Abstract

A dispenser unit comprising a dispenser can and a dispenser head which is provided with a delivery tube. The delivery tube has a longitudinal section with a lumen tapering in flow direction and a tube-like extension having an approximately constant inner diameter which corresponds to the smallest diameter of the adjacent section with the tapering lumen. A plug whose cross-sectional dimensions correspond to the lumen of the extension so that the discharge tube can be sealed by receiving the plug in its discharge opening. The length of the constant diameter extension is so chosen that in case of clogging small sections of the extension can be cut off to reopen the delivery opening of the delivery tube.

Description

The invention relates to a dispenser head for opening a valve of a dispenser can and dispensing a fluid under pressure of a propellant medium from the can, wherein the dispenser head is provided with a base for mounting the dispenser head on the can, the dispenser head being provided with a seat adapted to tightly fit to the valve of the can and with an orifice being in fluid connection with the valve seat, wherein the dispenser head furthermore is provided with a delivery tube dispensing a fluid under pressure of the propelling medium when the tube is connected with the orifice of the dispenser head in fluid tight manner, said delivery tube having a first end being arranged at the dispenser head orifice and a second end comprising a discharge opening from which the can content is dispensed, the tube comprising at least one longitudinal section between both said ends with a lumen which is tapering towards the discharge opening.
Canned fluids to be dispensed by the dispenser head—and also covered by the present invention—especially are common in the field of construction, for instance for sealing joints at the place of construction, without being restricted thereto. For example, such foam compositions may be polyurethane foams or latex foams or the like.
WO 2005/120987 A1 discloses a delivery tube for such dispensing head, the free cross-sectional area of this delivery tube being progressively reduced, i.e. having a lumen tapering towards the dispensing opening along the length of the delivery tube thereby obtaining an increased foam volume.
It is quite common that a dispenser unit comprising head and can is only partially emptied with the consequence that when taking up the dispenser unit for the next use, which may be days later, the discharge opening of the delivery tube is blocked by dried foam or the dried composition from which the foam is generated. In this context and in general according to the present invention, the phrase “dried” foam or composition also covers “cured” foam or composition. However, cutting off the clogged free end section of the tube would shorten the length of the section of the delivery tube having the tapering lumen with the consequence that the effect of this design—increasing the foam volume—would be impaired. Furthermore, cutting off the clogged free end section of the delivery tube would result in a larger diameter of the progressively tapering lumen at the discharge opening of the tube so that the discharge opening cannot be closed and sealed by the plug anymore to prevent further drying or curing of the foam composition that is present in the tube. In fact, the said plug has a given diameter to fit into the tube end in its initial shape so that the said plug would have a too small diameter to close and seal the tube having a cut-off end portion. The other way around, a plug having a diameter to fit and seal the tube having a cut-off end portion would be too large to fit into the discharge opening of the originally provided tube. Accordingly, in case the tube is clogged by dried foam, a new tube must be provided, which is expensive and inconvenient.
The object to be achieved by the present invention is to provide a delivery head with a delivery tube which avoids the above-discussed drawbacks by employing means which are easy to handle and do not or only by a negligible amount increase production cost, and which still provides an increased volume of dispensed foam due to the tapering lumen of the discharge tube.
The foregoing objects and improvements are attained by a dispenser head comprising a delivery tube according to claim 1 or by a respective delivery tube adapted to be mounted at a respective dispenser head, the tube comprising at least one longitudinal section with a lumen which is tapering towards the discharge opening and which is provided with a large inner diameter at a first end portion and a narrow inner diameter at a second end portion, namely narrower than the large inner diameter, wherein the first end portion of the lumen is directed towards the dispenser head orifice and the second end portion is directed to the discharge opening of the tube, and a tube-like extension positioned between the second end of said at least one longitudinal section and said discharge opening, wherein the discharge opening is provided at the free end of the extension, the extension having an approximately constant inner diameter equaling to at least the smallest diameter of said longitudinal section, the minimum length of said extension being chosen such that it can receive and hold a plug having a cross-sectional shape suitable to completely fill the discharge opening thereby effectively sealing said discharge opening. Preferred embodiments are defined by the dependent claims.
According to the invention, the extension of the delivery tube may predominantly or only have the function to serve as seat for the plug, so that the extension can be correspondingly short so that the presence of the extension will have no or only a negligible effect on the function of the progressively tapering section of the delivering tube, namely to increase the foam volume. Accordingly, the extension for instance may have a length of only a few millimeters, especially lower than about 10 mm.
However, the extension may as well be dimensioned such that in case the discharge opening of the delivering tube is clogged its length provides the possibility to cut off at least one short section of the extension thereby removing the clogged range while still retaining a length of the extension long enough to provide a proper seat for the plug. In such cases cutting off the free end of the extension with the clogging substance is a solution being highly preferred for practical reasons. Preferably, the extension is dimensioned in length so that at least two or more sections of the extension can be cut off while still retaining a length of the extension long enough to provide a proper seat for the plug, wherein each section may have a length of about ≧2.5 mm or of about ≧5 mm, without being restricted thereto.
To make the above-said solution available means that the extension has to be longer than would be necessary just for receiving the plug. Tests have shown that calculating the length of the extension such that it also considers the necessity to cut off a short length of the free end section of the extension to re-open the delivering tube would not result in relevant impairment of the effect of the progressively tapering section on the volume of the foam. Since re-use of an only partially emptied dispenser unit often will not happen more than once or twice, the initial length of the extension can be correspondingly calculated.
Preferably, the constant diameter extension has a length at least equal to the length of the closure plug, so that even in case one or more sections of the extension is cut off, plug can cooperate with the extension over the entire length of the plug without worsening the sealing properties of the plug.
Preferably, independent from or in combination with the above captioned feature, the constant diameter extension has a length of at least about 5 mm or at least about 10 mm or at least about 15 mm, most preferred the length of the constant diameter section preferably amounts up to about 40 mm or up to about 30 mm, more preferably only up to about 20 mm or even only up to about 15 mm. This has been found to be a preferred cut-off-length in view of the length of the foam composition that is cured or solidified in the tube during the period of non-use when the can is used by craftsmen in the field of construction.
In general according to the present invention, the term “about” when referring to a measurable value such as an amount, distance or volume, and the like, is meant to encompass variations of ±20%, preferably ±10%, more preferably ±5%, even more preferably ±1%, and yet even more preferably ±0.1% from the specified value, as such variations are appropriate to perform the disclosed methods.
Preferably the length of the extension having a constant inner diameter is chosen such that it provides the possibility of shortening the extension without interfering with the adjacent section having a tapering lumen. Especially, the constant diameter extension may have a length essentially not adversely affecting a foam volume of a predefined aliquot of the pressurized can content, when the can content is dispensed from the can by the propellant medium. Accordingly, the length of the constant diameter section preferably is adapted so that the foam volume is diminished by the presence of the constant diameter section of not more than about 12 vol.-% or of not more than about 8 vol.-% or not more than about 6 vol.-% of the dispensed foam composition or even of not more than about 4 vol.-% or of not more than about 2 vol.-% of the foam volume, respectively, in relation to the foam volume achieved under same dispensing conditions without the constant diameter section at the tube.
It has been found in diligent studies that to keep interference low or at least essentially negligible, preferably the constant diameter extension has a maximum length of about ≦33% or more preferably about ≦25% or ≦about 20% of the tube length, especially about ≦17% of the length of the tube. Especially, the constant diameter extension may have a maximum length of about ≦33% or more preferably about ≦25% or about ≦20% of the length of the tapering section of tube, especially about ≦17% of the length of the tapering section. In diligent studies this has been shown to be favorable especially when applying canned polyurethane foam compositions or canned latex foam compositions as used in the field of construction, though not being restricted thereto. The length of the extension may be ≧about 2% or ≧about 4% of the tube length, preferably or ≧about 6% or ≧about 8% or more preferably ≧about 10% of the tube length, for instance about 12% to 16% of the tube length. The “tube length” in this respect is the entire tube length including the mounting section to mount the delivery tube at the dispenser head. Especially, in a more restrictive approach, the “tube length” in this respect may be the length of the tube without the mounting section.
The mounting section is considered to be the section of the tube which is overlapping with the corresponding mounting section of the dispenser head when the tube is mounted at the head, e.g. when the tube is threaded or pressed over or into a sleeve-like mounting portion of the dispenser head.
Accordingly the length of the mounting section may be the length of the tube being provided with a thread for mounting the tube at the dispenser head.
Preferably the constant diameter extension has a length being about 2-times to about 25-times the inner diameter of the discharge opening, which has been found to be favorable to not adversely affect the dispense of the foam, especially with respect to dispensing velocity and foam volume.
Since the delivery tube including this extension is normally made of plastic material like for instance LLDPE, cutting off a longitudinal segment of the extension can be done by means of a simple tool like pincers or pliers or even a knife.
The dispenser tube may have a total length from about 6 cm to about 30 cm, more preferred from about 8 cm to about 25 cm or from about 10 to about 20 cm, especially about 15 cm, so that the tube length is adapted to most common applications of the canned composition, especially with respect to seal a joint between two constructional parts by dispensing the foam into the joint.
The tapering section of the dispenser tube is provided with an end portion having a large inner diameter at a first end section of said lumen and a narrower inner diameter at a second end section of said lumen, wherein the first end section is arranged adjacent to the dispenser head orifice and the second end portion more distant from the dispenser head orifice and is attached to the constant diameter extension. The lumen of the longitudinal tapering section preferably is tapering continuously over its length, so that each cross-section of the lumen being more close to the delivery end of the tube than another cross-section is narrower (smaller in its cross-section area) than the said other cross-section. Preferably, the lumen is tapering without step-like change of the cross-section diameter. Preferably, the tapering section tapers continuously, i.e. there are no constant diameter sections within the tapering section, which however might be present in some instances.
The tapering section may taper in a uniform manner (constant tapering angle over the length of the tapering section) or non-uniform (with different tapering angles over the length of the said section).
Especially, the tapering angle may be larger at the first end of the lumen and may decrease in direction to the second end of the lumen, for instance stepwise or with decreasing relative amount.
Irrespective of the tapered design of the tapering section, the ratio of the diameters of the lumen at its first end to that of its second end may be ≧about 1.25 or ≧about 1.5, preferably ≧about 2 or ≧about 2.5, especially about 3. Said ratio may be ≦about 6 or ≦about 5 or preferably ≦about 4 or ≦about 3.5. This achieves rapid dispense velocity in combination with high foam volume of the dispensed can content.
According to the invention, in general, the “tapering” of the tapering section is given with respect to the lumen of the tapering section. Furthermore, in general the tapering angle is the inclination angle of the inner wall of the tube defining the lumen to the longitudinal axis of the tube.
The total length of the tapering section may be ≧about 50% or ≧about 67% or preferably ≧about 75% of the total length of the tube, especially ≧about 80% or ≧about 85% of the total length of the tube, without being restricted thereto.
Preferably the length of the extension in addition to the length of the total length of the tapering section is equal to the total length of the tube, but there may be—though not preferred—further tube sections, especially at the end portion of the tube opposite to the extension, like for instance a non-tapering mounting section of the tube or the like.
The tapering longitudinal section may comprises at least two sub-sections with different tapering angles, the tapering angle of the first sub-section adjacent to the extension being smaller than the tapering angle of the other (second) sub-section with a tapering lumen. The tapering angle of the first and the second sub-section may be constant over its length respectively. The ratio of the tapering angle of the first sub-section to that of the second sub-section may be ≧about 1.5 or ≧about 2, especially ≧about 3, said ratio may be ≦about 20 or ≦about 10, for instance about 5-7. The ratio of the first to the second sub-section may be about 10:1 to about 1.25:1 or about 6:1 to about 1.35:1, especially about 4:1 to about 1.5:1, for instance about 2:1 (the length of the second sub-section is measured without the tube section engaging the part of the dispenser head for fastening the tube in its position to dispense the can content). This has been found to be favorable to achieve a large volume of dispensed foam, especially in connection with the constant diameter section.
Preferably, the plug is adapted to be arranged in frictional connection with the extension when being in sealing engagement within the extension.
The plug may have an end portion which is tapered towards the free end of the plug by way of which the plug is easier inserted in the discharge opening of the tube.
Preferably, the plug is fastened by a detachable a one-piece-connection with the dispenser head, so that that the plug is secured at the dispenser head to avoid the loss of the plug. The plug preferably is fastened at a tamper evident device of the dispenser head but may be fastened at any other area or portion of the head.
Preferably, the dispenser head may comprise a manually operable actuation means, preferably designed as a lever, for actuating the valve of a can when the dispenser head is mounted at the can, wherein the head comprise a tamper evident device positioned between the actuation device and an outer casing of the head. The plug may be fastened at this tamper evident means.
A fastening device for fastening the tube at the head when the tube is not in use may be provided. The fastening device may be manually detachable from the head or may be integral with the dispenser head. The tamper evident device can be formed with a means for fastening the delivery tube when the tube is not arranged at the dispenser head for dispensing the can content, e.g. during transport of the head which may be mounted at the can, what also improves easy handling and easy manufacture of the head. However, the fastening device in principle may be provided at any other area or portion of the head. The means for fastening the tube at the head may be designed as a projection which is shaped that it can be inserted in the end of the delivery tube with the larger inner diameter or, vice versa, that this end can be slid over the second projection. The second projection may separate from the first projection. Alternatively the first and the second projection may be attached to each other, for instance arranged adjacent to each other, wherein the plug is designed as an extension of the projection.
Most preferably, the plug for closing the tube is arranged nearby or adjacent to the fastening device for the tube or even at said fastening device. The plug for closing the discharge opening can also be provided as part of a tamper evident device. The tamper evident device may be formed with a projection being shaped and dimensioned such that it constitutes a plug which can be inserted in the lumen of the free end of the extension. This arrangement has the advantage that the plug as part of the larger tamper evident device is easier to handle than an item consisting of nothing but the plug. The plug may be arranged at the fastening device, for instance at the free end of the projection be designed as the fastening device.
A plug as described above can be obtained by cutting off a segment from an accordingly dimensioned and shaped—preferably cylindrically—profile of plastic material.
The plug may be formed with an end portion which is tapered towards the free end of the plug by way of which the plug is inserted in the discharge opening.
Furthermore, the invention is related to a dispenser unit comprising a head according to the present invention and a pressurized can, wherein the can comprises a valve for dispensing the can content and the can valve is adapted to be connected with the valve seat of the dispenser head in an air tight manner.
The dispenser tube has been described in combination with the dispenser head, but it is to be understood that the tube with all features of it according to the present invention also is disclosed independent from the head, though the tube is adapted to be mounted at a related dispenser head.
The fluid of the can, which is dispensed thought the dispenser head and through the delivery tube especially may be a foam composition like a polyurethane foam or other polymer foam, though not being restricted thereto.

In the following an exemplary embodiment of the invention will be explained with reference to the enclosed drawings in which:

FIG. 1 is a longitudinal section of a dispenser head;

FIG. 2 is a side view of a delivery tube;

FIG. 3 shows a section along line A-A in FIG. 2;

FIG. 4 is a view according to FIG. 1a of a modified dispenser head;

FIG. 5 is a longitudinal section of a dispenser head according to FIG. 1 schematically showing the mounted delivery tube.

With reference to FIG. 1, a dispenser head 10 and a can 12 on which the head 10 is mounted form a dispenser unit for generating foam from a fluid with which the can is partially filled. The dispenser head is provided with a base 11 by means of which the dispenser head is mounted on the can.
The can comprises a valve (not shown) which is operated by means of an actuating device designed here for example as a lever 14 pivotably attached to the head. The actuating lever 14 is provided with an adapter 16. A passage 17 extending through adapter and lever constitutes a connection between the valve attached to the can, comprising valve seat 17 a to fluid tightly engage the can valve 12 a, and mounting means 17 b to mount the dispenser tube. The mounting means here for example are designed comprising an opening 28 a in the actuating lever 14 for receiving the mounting section 20 of a delivery tube 22. The discharge tube at its free end is provided with a discharge opening 23, such as shown in FIG. 2 and FIG. 3. FIG. 5 schematically shows the disperser head according to FIG. 1 and the delivery tube 22 according to the present invention being mounted at the dispenser head. When the tube is mounted the free end 22 a of the tube 22 may abut against the base 28 c of recess 28 b, terminated by opening 28 a (FIG. 1), to provide a tight and defined mounting state of the tube. The delivery tube may be designed according to FIGS. 2 and 3.
With further reference to FIGS. 2 and 3, the mounting section 20 of the delivery tube to be connected with the dispenser head 10 is provided with an internal thread 24 by means of which the delivery tube may be attached to the adapter 16. For this purpose the adapter 16 comprises an annular seat 26 for receiving mounting section 20 which seat coaxially encircles passage 17 and its orifice 18. A sleeve-like component 28 separating seat 26 from passage 17 is provided with a thread 27 on its outer circumferential surface 29 which thread—when the delivery tube is attached to head 10—cooperates with the internal thread 24 of mounting section 20 of the delivery tube thereby obtaining a fluid-tight connection. The can content is passing orifice 18 of the dispenser head to pass into the tube, wherein in this embodiment the orifice 18 is provided at the free end of the sleeve 28 but may be provided in other suitable manner.
The mounting means 17 b of the dispenser head 10 for mounting the tube are provided with a circumferentially closed flange 17 c encircling the recess 28 b receiving the mounting section 20 of the tube. Especially, the flange 17 c may be circumferentially closed, i.e. without windows or through holes, to prevent the tube from deforming cross-sectionally when positioned in its mounting position, especially during dispense of the can content. The inner surface of the flange 17 c may abut against the outer surface of the mounting section of the mounted tube to securely preserve its shape and to avoid any can content leaks at the mounting means which would hamper an exchange of the tube.
The delivery tube 22 comprises a tapering longitudinal section 33 between both said ends 22 a,22 b of the tube, wherein the tapering longitudinal section 33 is provided with a lumen 38 which is tapering towards the discharge opening 23 and which is provided with a first end portion 38 a having a large inner diameter and a narrow inner diameter at a second end portion 38 b of said lumen, wherein the first end portion 38 a directed to the dispenser head orifice for dispensing the can content, especially is arranged adjacent to the dispenser head orifice 18, and the second end portion 38 b is directed to the discharge opening of the tube. A tube-like extension 36 having a constant inner diameter is positioned between the second end portion of the 38 b of the lumen 38 and the tube end 22 b. Especially, the tube discharge opening 23 is arranged at a free end of the extension 36. Evidently, the first and second end portions 38 a, 38 b of the lumen are arranged at the first and second end portions 33 a, 33 b of the longitudinal section.
Accordingly, the delivery tube 22 with longitudinal axis 22′ comprises three sections, namely a first tapering section 30, a second section 32 and a third section 36 (namely constant inner diameter extension 36).
Furthermore, a mounting section 20 is provided, which also may taper but which is not considered as part of first tapering section 30 to the extent to which the mounting section is engaging the outer surface of the annular seat 26.
The lumen 38 of the longitudinal section is tapering continuously over its length. So the total lumen 38 provides lumens 39, 41 (sub-lumens) of the first and second sections 30, 32, respectively, as discussed below.
The inner diameter of the lumen at its narrow end portion 38 b is about ¼ of the inner diameter of the lumen at its wide end portion 38 a.
First and second sections 30 and 32 have tapering lumens 39, 41, respectively, with different tapering angles as can be taken from FIGS. 2 and 3 of the drawing. The lumen 39 of first tapering section 30 has a tapering angle larger than the tapering angle of lumen 41 of second tapering section 32 of the delivery tube, for instance the angle ratio may be about 5. Third section having the constant inner diameter extension 36 the free end 40 of which defines the discharge opening 23, has a lumen which constitutes an extension of the two sections 30 and 32 comprising a tapering lumen has a more or less constant inner diameter along its length. The diameter of the lumen of the extension is at least essentially equal or equal to the diameter of the lumen of the second end portion of the longitudinal tapering section, what might be given in general in the present invention.
The wall thickness of the tapering section is at least essentially constant over the length of the tapering section, so that the outer surface of the tapering section is at least essentially tapering as the inner surface of the tapering section or as the lumen. The wall thickness of the extension may be essentially constant over its length and may be essentially equal to the wall thickness of the tapering section. This, respectively, may be given in general with respect to the present invention.
According to the given embodiment, the total length of the tube is about 15 cm, the length of the first tapering section 30 is about 25% of the tube length, the length of the second tapering section 32 is about 50% of the tube length. The length of the extension or of the third section, respectively, is about 2 cm.
According to the given embodiment, the length of section 36 represents about 15% of the total length of delivery tube 22. In the embodiment of the enclosed drawing that portion of mounting section 20 which is positioned in seat 26 does not contribute to the effect of the tapered portion(s) of the delivery tube when delivery tube 22 is connected to head 10 since then the first portion of the delivery tube is formed by cylindrical passage 17. In this specific embodiment the length of the extension or third section 36 is about 13% of the total length of the tube. Since the length of the mounting section 22 of the tube is quite short, the length of the extension or third section 36 is here is about 15.5% of the total length of the tapering section of the tube without the mounting section. The mounting section of the tube here is the length of the tube being provided with thread 24 what is essentially equal to the length of annular seat 26 which is overlapping with the tube in its mounted state.
Section 36 is long enough to receive a closure member. The closure member in the given embodiment is designed as a plug 47 which is adapted to be inserted into the lumen of the delivery tube. The plug 47 has a diameter or cross section corresponding to the diameter or cross-section of the lumen to seal the tube when inserted in the lumen. Such plug is provided on a tamper evident device 42 which is originally positioned between the casing 44 of head 10 and actuating lever 14 as shown in FIG. 1. This device 42 made of a suitable plastic is formed in such a way that it comprises a projection 46 which is so dimensioned and shaped that it can be inserted through discharge opening 23 forming a plug 47 in the free end of section 36 having a corresponding inner cross-section. The plug 47 also can be designed or arranged in other form, for instance as a separate plug.
In addition the tamper evident device 42 can be provided with a second stump-like projection 48 which can serve for holding delivery tube 22 in which case the delivery tube is slid with its mounting section 20 over projection 48 which may have a correspondingly shaped cross-section, and held in this position by adequate fixing means before first use. It is to be understood that other fastening means to fasten the tube at the dispenser head can be provided, though the shown embodiment is a preferred one.
The length of third section 36 having a constant diameter is such that it provides the possibility of cutting off two or three short portions in case discharge opening 23 is clogged by dried or cured substance. In FIG. 3 reference number 50 indicates a possible cutting line along which a short portion 52 may be cut from extension 36 to free discharge opening from clogging material by thereby creating a new discharge opening which is free. The length of the extension or third section 36 in the embodiment of FIG. 3 provides the possibility to cut off more than one portion if this became necessary.
In view of the fact that the delivery tube will be made from elastic material like polyethylene some slight deviations from the respective set value will be unavoidable.
Extensive tests have shown that a tapering delivery tube can be provided with an additional extension section 36 having a constant inner diameter without markedly impairing the effects of the tapered length of the delivery tube on condition that the end section does not exceed a certain length relatively to the tapered section(s).
In the embodiment of FIG. 4, the dispenser head shows the same construction and features as the head of FIG. 1, despite the following features. Plug 54 for closing the discharge opening 23 and holder 56 for delivery tube 22 are provided on separate parts which are attached to the lateral outer surface of dispenser head 10 by means of webs 58, 60, respectively, so that at least the plug 54 they may be removed for use by simply manually breaking web 58.

Claims

1.-21. (canceled)

22. A dispenser head for opening a valve of a can containing a fluid and dispensing the fluid from the can under pressure of a propellant medium, the dispenser head comprising:

a base for mounting the dispenser head on the can,

a valve seat adapted to fit to the valve of the can in a fluid-tight manner,

an orifice in fluid connection with the valve seat, and

a delivery tube to dispense the fluid under pressure of the propellant medium when the tube is arranged at the orifice of the dispenser head in a fluid-tight manner,

the delivery tube having a first end arranged at the dispenser head orifice and a second opposite end of the tube having a discharge opening from which the fluid is dispensable, the delivery tube comprising:

at least one longitudinal section between the two ends of the tube, wherein the at least one longitudinal section has a lumen which tapers toward the discharge opening and which has a first inner diameter at a first end portion and a second narrower inner diameter at a second end portion, wherein the first end portion of the lumen is directed toward the dispenser head orifice and the second end portion is directed toward the discharge opening of the tube, and

a tubular extension positioned between the second end portion of the at least one longitudinal section and the discharge opening, the discharge opening being positioned at a free end of the tubular extension, the tubular extension having an approximately constant inner diameter equal to at least a smallest diameter of the tapering longitudinal section, and a minimum length of the tubular extension being selected to receive and hold a plug having a cross-sectional shape suitable to completely fill the discharge opening such that the discharge opening is effectively sealed.

23. The dispenser head according to claim 22, wherein the tapering longitudinal section comprises at least first and second sub-sections having different tapering angles, the tapering angle of the first sub-section adjacent to the tubular extension being smaller than the tapering angle of the second sub-section having a tapering lumen.

24. The dispenser head according to claim 22, wherein the tubular extension has a length that allows shortening of the tubular extension without interfering with the at least one tapering longitudinal section which is adjacent to the tubular extension.

25. The dispenser head according to claim 22, wherein the tubular extension has a length at least equal to a length of the plug.

26. The dispenser head according to claim 22, wherein the tubular extension has a length of at least about 10 mm.

27. The dispenser head according to claim 22, wherein the tubular extension has a maximum length of less than about 33% of a length of the delivery tube.

28. The dispenser head according to claim 22, wherein the tubular extension has a length essentially not adversely affecting a foam volume of a predefined aliquot of the fluid under pressure, when the fluid is dispensed from the can by the propellant medium.

29. The dispenser head according to claim 22, wherein the tubular extension has a length about 2 to about 25 times an inner diameter of the discharge opening.

30. The dispenser head according to claim 22, wherein the at least one tapering longitudinal section arranged adjacent to the tubular extension tapers over its length with an essentially constant tapering angle.

31. The dispenser head according to claim 22, wherein the plug is adapted to be arranged in frictional connection with the tubular extension when in sealing engagement within the tubular extension.

32. The dispenser head according to claim 22, wherein the plug is fastened by a detachable, one-piece connection with the dispenser head.

33. The dispenser head according to claim 22, wherein the plug has an end portion tapered toward a free end of the plug for insertion of the plug in the discharge opening.

34. The dispenser head according to claim 22, further comprising a tamper evident device, wherein the tamper evident device is provided with the plug adapted for insertion into the discharge opening.

35. The dispenser head according to claim 22, further comprising a manually operable actuator for actuating the valve of the can when the dispenser head is mounted on the can, and a tamper evident device positioned between the manually operable actuator and an outer casing of the dispenser head, wherein the tamper evident device is provided with the plug adapted for insertion into the discharge opening.

36. The dispenser head according to claim 22, further comprising a fastening device to fasten the delivery tube when not in use to dispense fluid from the can, wherein the fastening device is detachable from the dispenser head, and wherein the plug is arranged at or adjacent to the fastening device.

37. The dispenser head according to claim 36, wherein the fastening device has a projection whose cross-sectional shape is adapted to a cross-sectional shape of a mounting section of the delivery tube to mount the delivery tube to the dispenser head when the mounting section is in engagement with the projection.

38. The dispenser head according to claim 22, further comprising a manually actuated lever for actuating the valve of the can when the dispenser head is mounted on the can, the dispenser head having a tamper evident device positioned between the manually actuated lever and an outer casing of the head, and the tamper evident device having a projection whose cross-sectional shape is adapted to a cross-sectional shape of a mounting section of the delivery tube.

39. The dispenser head according to claim 22, wherein the delivery tube comprises plastic.

40. The dispenser head according to claim 22, further comprising a mount for mounting the delivery tube, the mount having a circumferentially closed flange encircling a recess for receiving a mounting section of the delivery tube.

41. A dispenser unit comprising a dispenser head according to claim 22 and a pressurized can, wherein the can comprises a valve for dispensing fluid content of the can, the valve being adapted to connect with the valve seat of the dispenser head in a fluid-tight manner.

42. A delivery tube adapted for mounting at a dispenser head for opening a valve of a can containing a fluid to dispense the fluid under pressure of a propellant medium from the can and through the delivery tube when the dispenser head is mounted on the can and is tightly fitted to the valve by a valve seat so that an orifice of the dispenser head is in fluid connection with the valve seat on one side and with the delivery tube on another side,

the delivery tube having a first end adapted to be arranged at the orifice in a fluid-tight manner and a second opposite end having a discharge opening from which the fluid is dispensable, the delivery tube comprising: