GB2127202A - Alarm device - Google Patents

Abstract

A personal alarm device has a canister 1 holding liquid 2 to produce gas under pressure in space 3. Depression of actuating cap 13 displaces hollow valve stem 8 to open valve 7 permitting compressed gas to escape past a diaphragm mounted at the throat of an acoustic horn in the cap, to produce a shrill noise. The initial fill of liquid is to a level just less than half the height of the canister, and tube 11 opens at a level above that of the liquid but extends a distance from the top of the canister at least equal to the height of the initial fill of liquid. Hence liquid cannot flow into tube 11 in any position of the device. <IMAGE>

Description

SPECIFICATION Alarm device The invention relates to an alarm device in which a small vapour cylinder or canister provided at one end with a normally closed vapour valve having an inlet in communication with the canister interior is fitted with an actuator (usually a depressible actuating cap) effective to release vapour through an outlet of the valve for operating a sound producing means (usually a vibratory diaphragm horn in the cap) that emits a piercing screech or scream.

Such a device, also known as a personal or portable or pocket alarm, is intended to scare away an attacker and summon help, and the invention aims to improve known such devices.

A major disadvantage of known vapouroperated alarm devices is that the alarm will not function reliably or at all unless the canister is held upright, i.e. with it s valve outlet at the top. This is because the vapour for operating the horn is stored in the canister in its liquid form, with vapour at its saturated vapour pressure occupying only the space not taken up by the liquid. Hence if the canister is tilted or inverted, as is inevitable in panic situations, the vapour space is remote from the valve and liquid enters the valve inlet instead of only vapour and this liquid prevents the diaphragm of the horn from vibrating properly and also causes the valve and diaphragm to freeze up as it vapourises.

According to one aspect of the invention, the valve inlet is connected to a tube which extends into the canister and is constructed and arranged in relation to the initial fill of liquid so that substantially only vapour will reach the valve inlet.

In one form of the invention, the tube, which may be of plastics material and is open at its unconnected end, is constructed to be of a length so that, when fitted to the valve, its open end terminates just less than half way along the canister interior, and the canister is filled with liquid, preferably dichlorodifluoromethane, at the saturated pressure of its vapour or higher, to a level just less than half the length of the canister interior. By means of this simple expedient, practically no liquid will enter the tube and hence reach the valve inlet, no matter what the inclination or inversion of the canister, because the open end of the tube will always communicate with the vapour space. Any droplets that might be splashed into the tube when the device is violently agitated vapourise in the tube before reaching the valve and there is little likelihood of freezing up.

Put more generally, the canister is provided with an initial fill of liquid to a level from the bottom of the canister interior less than half the canister length whereas the open end of the tube is central with respect to the cross section of the canister and terminates along the canister above the liquid level and at a distance from the canister top which is not less than the distance of the liquid level from the canister bottom, the last mentioned distance being not less than 40% of the canister length, or preferably being 45% + 3% or better still 45% of the canister length.Generalising further (regardless of regularity of cross section or longitudinal symmetry) the initial fill of liquid is not less than 40% of the canister capacity (or preferably it is 45% + 3% or better still 45% of the canister capacity) and the tube is open at its unconnected end at a location clear of the liquid in whatsoever position the device may be held. Thus, in the normal case of a cylindrical canister, the open end of the tube may extend half way along the canister length and even more, provided of course that in the upright position of the canister the open end of the tube still lies above the level of the initial fill.

According to a second aspect of the invention there is provided a combination suitable for assembling a device as described in the foregoing passages (only optionally including the liquid), wherein the tube in the assembled state has its open end at a distance of 50 + 8% from either end of the canister or preferably 50% + 5% or better still 50% + 2% of the canister length from either end. This then can readily leave a minimum 2% clearance between the open end of the tube and the level of the initial fill of liquid (as seen with the device upright).

Canisters with an open ended tube extending from the inlet of a discharge valve are known for aerosol dispensers but in that case the tube reaches close to the bottom of the canister and serves as a syphon for drawing the liquid or viscous canister contents into the valve under the pressure of a gas propellant.

In another form of the invention, the tube connected to the valve inlet is substantially rigid, is closed at its unconnected end and carries an unbalanced, i.e. eccentrically weighted, sleeve which is axially displaceable within limits along the tube and is rotatable with respect to the tube; a first port in the sleeve is adapted in one limiting position of the sleeve to communicate with a first passage in the tube leading to the tube bore, and a second port is adapted in the other limiting position of the sleeve to communicate with a second such passage; the canister is initially filled with liquid to a level so that only one of the ports in the sleeve is immersed when the canister is upright; and the free openings of the first and second ports of the sleeve are remote from the tube diametrically opposite the gravitational direction of the weights.In this construction, substantially only vapour will again reach the discharge valve at all inclinations of the canister.

Known alarm devices operating with vapour canisters suffer from a further disadvantage in that the actuating cap for the discharge valve must be held depressed against the pressure of the vapour in the canister and any biasing spring for the valve. This is clearly not always feasible in an attack.

According to a further aspect of the invention, therefore, the cap and canister are provided with interengageable formations which enable the cap to be locked in the depressed condition so that the sound producer or horn continues to operate until the cap is deliberately unlocked or the liquid in the canister is exhausted.

In a preferred form of the invention, the alarm device comprises a canister containing a volatile liquid to an appropriate canister height and vapour in the space not occupied by the liquid, a normally closed discharge valve in the top of the cannister communicating with the vapour space through an open-ended tube terminating an appropriate distance down the canister, which valve can be opened by means of a displaceable hollow valve stem that projects from the canister so as to permit vapour to escape through the stem when the stem is displaced, and an actuating cap which can be placed on the canister top to engage the valve stem and which contains a frustoconical acoustic horn defining a throat and mouth of which the throat carries a diaphragm and the mouth is in register with a sound and vapour outlet in the cap, the arrangement being such that, when the cap is in place on the cannister, the diaphragm is disposed adjacent to the projecting valve stem and the cap is depressible to displace the stem and open the valve, whereby the escaping vapour causes the diaphragm to vibrate and generate a noise emitted through the sound outlet with the vapour.

Further features of the invention will be described with reference to examples shown in the accompanying drawings, wherein: Figures 1 and 2 are sectional side elevations of an alarm device in the inoperative and operative cap positions respectively; Figure 3 is an enlarged section of the cap and only parts of the cannister of Fig. 2; Figure 4 is a fragmentary sectional elevation of a different embodiment of alarm device; and Figure 5 is cross-section on line A-A in Fig.

4.

Referring to Figs. 1 and 2, the alarm device comprises a cannister 1 filled with liquefied dichlorodifluoromethane 2 to less than half height and its vapour at saturated vapour pressure in the space 3. The top of the cannister has a metal closure 4 which defines a rim with a lip 6 (see Fig. 3) and contains a normally closed discharge valve 7 for vapour.

The construction of the valve is not critical to the present invention and is known for aerosol containers. However, it should be noted that the valve member terminates in a displaceable hollow stem 8 which projects through the closure 4 and defines the valve outlet through which vapour is discharged, whilst the valve inlet is defined by a hollow spigot 9 to which an open-ended tube 11 is attached. This tube has a length so that its unattached open end 1 2 is disposed just less than half way down the canister.The proportions in the example of Figs. 1 to 3 (readily obtained by measurement of the accompanying drawings) show the length of the tube 11 to be 46% of the length of the canister, the height of the liquid to be 45% of the canister length and the volume of liquid to be also 45% of the canister volume; the effective canister length has been taken to end midway of the height of the canister closure 4. Clearly, minor variations in these proportions, say + 5% of the canister length (though preferably less) would not much matter, and also manifestly it would not matter if the tube 11 were slightly longer, say 50% + 8% of the canister length (though preferably nearer 50%), provided of course in all cases that the open end 1 2 is above the level of the initial fill of liquid with the canister in the upright position.

A removable flexible plastics cap 1 3 is placed over the top closure 4 and will now be described with reference to Fig. 3. A skirt 1 4 of cap 1 3 is of circular cross section and slidable on the canister. The body 1 6 of the cap is slightly elliptical, with the minor axis in the plane of Fig. 3. In the zone of this minor axis and just above the skirt 14 the cap body 1 6 is provided with two diametrically opposed arcuate ribs 1 7 of substantially triangular cross section defining a bevelled face 1 8 and a radial shoulder 19.It will therefore be clear that, if the cap is pressed down on the canister, its body 1 6 will flex to enable the ribs 1 7 to ride over the rim of canister closure 4 and snap into place behind it, the cap being then locked in place because the lip 6 abuts the shoulders 1 9. However, the cap 1 3 can be deliberately removed from the canister because, if the body is compressed by applying finger pressure along its major axis (at right angles to the plane of the paper in Fig. 3), the effect will be to expand it along the minor axis and thereby move the ribs 1 7 apart sufficiently to clear the lip 6, the cap being pulled off at the same time. Striations, knurling or other grip-enchancing formations may be provided on the outside of the cap body at or near its major axis to indicate to the user where the body should be squeezed to remove it.

The cap body 1 6 contains a moulded plastics insert 21 with a tight fit. The insert embodies a frustoconical acoustic horn 22 which defines a mouth 23 aligned with a sound and vapour outlet 24 in the cap body and a throat portion 26 surrounded at a spacing by a collar 27. This collar is provided with a throughgoing stepped socket 28 in which the hollow valve stem 8 is engaged up to the step 29 when the cap 1 3 is in place over the top of the cannister. The socket 28 opens into the space between the collar 27 and throat portion 26. A concave, preferably V-shaped shoulder 31 is formed inside the collar 27 in line with the end of throat portion 26 to support a vibratable diaphragm 32 across the end of throat portion 26.The diaphragm 32 which may be of metallised Melinex (RTM), is permanently clamped in position in a stretched condition by a hollow plastics plug 33 which has a rim complementary in shape to the shoulder 31 and which is force fitted in the collar 27 or cemented or welded therein or held in place by peening over the collar.

Hiterto, a diaphragm was merely adhered to the throat of the horn and the present construction is not only more reliable but also enables the diaphragm to be held taut and produce a louder noise.

In operation, the cap 1 3 is depressed to displace valve stem 8 and open valve 7. If, as will be usual, the cap is depressed far enough for the ribs 1 7 to engage behind the rim of cannister closure 4 as is shown in Fig. 2, the cap will be locked in place with the valve remaining open. While valve 7 is open, pressurised vapour is discharged through stem 8 and socket 28 into the space between the collar 27 and throat portion 26. As the vapour forces its way between the diaphragm and throat portion, it vibrates the diaphragm and a shrill shrieking noise is generated and emitted through sound outlet 24.

Substantially only vapour escapes through valve stem 8 because end 1 2 of tube 11 is disposed in the vapour space 3 of the cannister and more liquid vapourises immediately some of the vapour has been expelled. If, in panic, the device is dropped, it will continue to function J -cause the cap is locked on.

Should the cannister be tilted, the tube end 1 2 will remain in the vapour space. For example, if the cannister of Fig. 2 is placed on its side, it will be evident that, by reason of the less than half filling, the liquid will have flowed to take up a level below the tube 11.

Again, if the cannister were to be inverted, the end 12 of tube 11 would not be im mersed in the liquid. The device is reusable by replacing the cannister when exhausted.

The embodiment of Figs. 4 and 5 differs as regards the means for ensuring that substantially only vapour enters inlet spigot 109 of the valve of cannister 101. The tube 111 is substantially rigid and has a shoulder 41 near the valve end and a shoulder 42 at the other end, which is closed, defining respective stops for limiting axial displacement of a sleeve 43 which is easily slidable as well as rotatable on the tube. In its illustrated lower limit of displacement, a port 44 in sleeve 43 is in registry with a circumferential groove 46 in tube 111, the groove communicating with the bore of the tube through at least one hole 47.

In its upper limiting position, a port 48 in sleeve 43 is in registry with a circumferential groove 49 similarly communicating with the tube bore through a hole 51. The spacing between groove 49 and port 48 in one limiting position is therefore equal to the distance by which the sleeve can slide to the other limiting position. The openings of both ports extend to positions remote from the tube 111.

The sleeve 43 is weighted at a position diametrally opposite to the ports 44 and 48, in the illustrated version by being formed with two sector-shaped unbalancing projections 52. The same effect can be achieved with a sleeve which is of constant cross-section along its length but is excentrically mounted to provide more material on the side opposite to the ports. Vapourisable liquid 102 is introduced in the cannister to a level below the port 44 when cannister 101 is upright, the remainder being vapour space 103.

It will be seen that, in the Fig. 4 cannister position, vapour will reach the valve from the vapour space 103 through port 44, groove 46 and hole 47 but no liquid can enter the tube because port 48 is out of registry with groove 49. If the device were to be inverted, sleeve 43 would slide to its other limiting position adjacent to the shoulder 41 and port 48 would now be in the vapour space whilst port 44 is blocked. If the device were tilted clockwise, the liquid 102 would seek its lowest position and would immerse port 44 were it not for the fact that sleeve 43 easily turns on the tube under gravity because of the eccentric weights constituted by the projections 52. Consequently, port 44 will be turned so as again to be disposed in vapour space.The combination of rotary and rectilinear sleeve mobility ensures that one or the other port will always be in the vapour space of the cannister. Although this construction is more expensive, it enables more liquid to be introduced in a given cannister size as compared with the previously described embodiment and hence the alarm can operate longer or be used more often before the cannister needs to be replaced. Of course the locking on feature of the cap and the improved mounting of the diaphragm can also be used in this embodiment.

The combination of improved features according to the present invention makes itself particularly evident in comparison with known devices if the alarm device is dropped on its side after actuation, which would be the most common situation when the user is fending off an attacker, because it will not stop to function as hitherto. The valve remains open because the cap can be locked on; liquid is prevented from entering the valve because of the tube 11 or 111; and the device remains effective even if the sound outlet 24 happens to be facing the ground because the advantageous manner of mounting the diaphragm enables louder noise to be emitted than hitherto.

Although these advantages are obtained no matter what the cannister dimensions might be, it might be mentioned that, in practical tests an alarm device of the Figs. 1 to 3 construction with a cannister having outer dimensions of about 35 mm dia. and 98 mm length emitted a countinuous scream of 105 decibels for 1.5 minutes before the cannister was exhausted.

It will be appreciated that the invention in not confined to use with alarm devices having a vibratory diaphragm horn in the cap but extends to alarm devices employing other means for the production of the sound.

Although the embodiments of the invention described above have cylindrical canisters, it would be feasible to use canisters that are non-circular in section (e.g. polygonal prismatic) and/or that are not of constant section (e.g. spherical or even conical).

Claims (11)

1. An alarm device having a liquified vapour canister provided at one end with a normally closed vapour valve, an inlet of the valve being in communication with the canister interior, an actuator effective to release vapour through an outlet of the valve for operating a sound producer that emits a piercing noise, a tube connected to the valve inlet and extending into the canister, and a fill of liquid (preferably dichlorodifluoromethane, at the saturated pressure of its vapour or higher), the initial fill of liquid and the construction and arrangement of the tube being such that substantially only vapour will reach the valve inlet.

2. Device according to claim 1 wherein the tube is constructed to be of a length so that, when fitted to the valve, its open end terminates just less than half way along the canister interior, and the canister is filled with liquid to a level just less than half the length of the canister interior.

3. Device according to claim 1 wherein the cannister is provided with an initial fill of liquid to a level from the bottom of the canister interior less than half the length of the canister interior, the tube is open at its unconnected end, and its open end is central with respect to the canister cross-section and terminates along the canister above the liquid level and at a distance from the canister top which is not less than the distance of the liquid level from the canister bottom, the last mentioned distance being not less than 40% of the canister length, or preferably being between 45% + 3% and better still 45% of the canister length.

4. Device according to claim 1 wherein the initial fill of liquid is not less than 40% of the canister capacity or preferably 45% i 3% or better still 45%, and wherein the tube is open at its unconnected end at a location clear of the liquid in whatever position the device may be held.

5. Device according to claim 1 wherein the tube connected to the valve inlet is substantially rigid, is closed at its unconnected end and carries an unbalanced sleeve which is axially displaceable within limits along the tube and is rotatable with respect to the tube; a first port in the sleeve is adapted in one limiting position of the sleeve to communicate with a first passage in the tube leading to the tube bore, and a second port is adapted in the other limiting position of the sleeve to communicate with a second such passage; the canister is initially filled with liquid to a level so that only one of the ports in the sleeve is immersed when the canister is upright; and the free openings of the first and second ports of the sleeve are remote from the tube diametrically opposite the gravitational direction of the weights.

6. An alarm device having a liquified vapour canister provided at one end with a normally closed vapour valve and with a depressible actuating cap effective to release vapour through an outlet of the valve for operating a sound producer that emits a piercing noise, the cap and canister being provided with interengageable formations which enable the cap to be locked in the depressed condition so that the sound producer continues to operate until the cap is deliberately unlocked or the liquid in the canister is exhausted.

7. Device according to claim 6 wherein the cap has a skirt of circular cross-section slidable on the canister and a body that is slightly elliptical, the formations on the cap for engagement with those on the canister being provided at the minor axis of the ellipse, the arrangement being such that compression of the cap body by finger pressure at the major axis of the ellipse expands it along the minor axis enabling the formations to be disengaged.

8. Device according to claim 6 or claim 7 in combination with the device according to any of claims 1 to 5.

9. The combination of integers suitable for assembling a device according to any preceding claim (whether or not it includes the liquid) wherein the tube in the assembled state has its open end end at a distance of 50% i 8% of the canister length from either end of the canister or preferably 50% i 5% or better still 50% i 2% from either end.

10. Device according to any preceding claim having an actuator in the form of a depressible actuating cap which contains a frustoconical acoustic horn defining a throat and mouth of which the throat carries a diaphragm and the mouth is in register with a sound and vapour outlet in the cap, the arrangement being such that,when the cap is in place on the canister, the diaphragm is disposed adjacent to a projecting valve stem and the cap is depressible to displace the stem and open the valve, whereby the escaping vapour causes the diaphragm to vibrate and generate a noise emitted through the sound outlet with the vapour.

11. An alarm device substantially as shown in and hereinbefore described with reference to Figs. 1 and 2 or Figs. 4 and 5, in each case with or without the features more particularly shown in and described with reference to Fig. 3, of the accompanying drawings.