GB2408684A

GB2408684A - Powder fire extinguisher

Info

Publication number: GB2408684A
Application number: GB0328372A
Authority: GB
Inventors: Roger Carr
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-12-06
Filing date: 2003-12-06
Publication date: 2005-06-08
Anticipated expiration: 2023-12-06
Also published as: GB2408684B; GB0328372D0

Abstract

A powder fire extinguisher has a powder filled chamber, a compressed gas canister, a powder outlet 72 by which powder can leave the chamber and means for releasing compressed gas from the canister into the chamber to mix with and fluidise the powder. A Valve 42 in the outlet controls the discharge of fluidised powder, and comprises a closure member 44 slidable in a passage in which it is a sloppy fit. The closure has opposed faces on which gas pressure can act to move the closure between two valve seatings such that when the compressed gas is first released the closure engages one of the seatings to prevent fluidised powder from leaving the chamber, but after gas pressure has been fully established the closure is forced away from the one seating 60 to engage with the other to allow powder discharge to occur via a gap between the closure and the one seating. Sealing means 80 between the closure and the said other seating prevents powder from passing between the closure and the said other seating to occupy the space between the closure and the passage wall. The stem or the wall of the passage is profiled to cause a whistling sound as air passes therethrough. Spring means may be provided which acts on the closure in a direction to move it away from the said one seating 60.

Description

1 2408684 Title: Improved powder extinguisher discharge valve

Field of invention

This invention relates to a powder type fire extinguisher. In such extinguishers, a dry powder contained in a chamber in the extinguisher is driven out of the chamber by compressed gas when a cylinder containing the gas is opened.

Background to the invention

To achieve a satisfactory output, it is necessary to ensure that the compressed gas does not escape directly through the outlet without entraining the powder. To this end steps are taken to ensure that the powder is fluidised inside the chamber before any output from the chamber occurs.

A valve which achieves this is described in GB 2,148,114. Here the valve is described as being incorporated into a fire extinguisher of the powder type, having a chamber for holding the powder, a container for compressed gas, a powder outlet from the chamber an means for opening the gas container to allow compressed gas to enter the chamber and drive the powder out of the outlet. The valve is provided in the outlet and has a valve member movable, by pressure on opposed faces of the member, onto and off a seat in a valve housing, to close or open the outlet. The area of the face of the valve member which is exposed to pressure from the chamber is greater than the area of the other face, and a passage is provided from the gas container to the valve housing to allow compressed gas to act on said other face of the valve member directly the container is opened.

In this way, the valve is held closed while the compressed gas brings the powder into a fluidised state and while the pressure in the chamber builds up. Once the pressure in the chamber is equal to the pressure acting on said other face of the valve member, the difference in areas of the valve member faces exposed to pressure will cause the valve to open fully to allow the fluidised powder to pass out.

The arrangement proposed by GB 2,148,114 provided a method of controlling the output from a powder type fire extinguisher, wherein the valve is placed in the powder outlet rom the extinguisher, and, on opening of a source of compressed gas to expel the powder, the gas is introduced to a space where it exerts a force on the valve to hold the valve closed while the pressure in the powder chamber builds up to a level at which satisfactory output can take place, and when this level has been reached, the pressure in the chamber exerts a force on the valve which opens the valve to allow the powder to be expelled.

The arrangement is shown in and described with reference to the drawings of GB 2,148,114 and comprises an extinguisher head 10 shown in Fig 1 for fitting onto the neck of a cylindrical powder container in a conventional manner. The container iteself is not shown.

A flange 12 limits the insertion of the fitting into the container neck.

The head fitting has a socket 14 for receiving a cylinder of compressed gas. A conventional firing mechanism (not shown) is provided on the outside of the fitting to allow the cylinder to be punctured when the extinguisher is to be used.

An outlet passage 16 extends through the fitting. A conventional nozzle to direct the flow can be attached to the outer end 18 of the passage.

The socket 14 for the cylinder and the lower end of the outlet passage can be seen in Fig 2.

Also visible is a socket 22 for a tube (not shown) which extends from the head fitting to near the bottom of the chamber. A passage 23 for compressed gas leads from the socket 14 to the socket 22, and another passage 26 leads from socket 22 to the lower end 20 of the outlet passage 16.

As shown in Figs 3 and 4 the valve has a housing 30 with a valve seat 31 and a valve member 32 is movable in the housing. The valve member has a head 34 and a stem 36 and the stem is guided in a bore 38 in the housing. the top of the housing 30 is a tight fit in the lower end 20 of the outlet passage, and a key portion 40 fits in a keyway 42 in the head fitting. The engagement between the key 40 and the keyway 42 ensures that the passage 26 lines up with a passage 44 in the valve housing, so that gas pressure can pass from the cylinder socket 14 to the bore 38 in which the valve stem 36 slides.

Am O-ring seal 46 seals the valve housing in the outlet passage 26 and an O-ring seal 48 seals the valve stem 36 in the bore 38.

In operation, puncturing of the compressed gas cylinder by the firing mechanism causes gas to be forced through passages 24 and 26, typically at a pressure of 50-75 bar (750- 1000 psi).

Gas passes down a tube fitted in socket 22 to fluidise the powder and to build up pressure inside the chamber.

At the same time, gas also passes into passage 44 to act on the top of the valve stem 36.

As a result, the valve member 32 is forced downwards against the seat 31 to close the valve.

Initially the pressure acting on the underside of the head 34 is substantially lower than the pressure above the valve. However this pressure gradually builds up as the powder becomes fully fluidised.

The area of the valve head presented to pressure from below is greater than the area of the stem presented to pressure from above. Therefore there will be a net opening force acting on the valve member. Once the powder is fully fluidised, and the pressure on the underside of the valve head 34 becomes equal to that above, the valve opens to allow the fluidised powder to flow through the pipe 50 and out. This stage is typically reached about 2 seconds after operation of the firing mechanism.

A problem has arisen in practice due to the 2 second delay before powder issues from the nozzle.

In consequence, in order to alert the user to the fact that the extinguisher is functioning and will shortly discharge, it has been proposed to omit the O-ring 48 and make the closure part 36 a sloppy fit in the passage 38. This has meant that a small volume of gas has been able to escape between 36 and 38 until the closure rises and the head 34 closes off the lower end of passage 38. The sound of the escaping gas has indicated to the user that the gas cylinder in the extinguisher has been reliably punctures and that discharge is imminent.

Unfortunately this has resulted in powder becoming lodged between 36 and 38 and this can result in subsequent unreliable operation of the extinguisher. This happens if the powder lodged between 36 and 38 from an earlier discharge prevents the stem 36 of the closure from sliding in 38, and therefore prevents it from opening when the extinguisher is next used, after the spent gas cartridge (from the first discharge) has been replaced.

It is an object of the present invention to provide an improved discharge control valve for use in a powder fire extinguisher head which overcomes this problem.

Summary of the invention

According to one aspect of the present invention in a powder fire extinguisher having a powder filled chamber, a compressed gas canister, a powder outlet means by which powder can leave the chamber, means for releasing compressed gas from the canister into the chamber to mix with and fluidise the powder, and valve means in the outlet for controlling the discharge of fluidised powder through a nozzle, and wherein a valve closure member is provided slidable in a passage in which it is a sloppy fit, which has opposed faces on which gas pressure can act to move the closure between two valve seatings such that when the compressed gas is first released the closure engages one of the seatings to prevent fluidised powder from leaving the chamber, but after gas pressure has been fully established the closure is forced away from the one seating to engage with the other to allow powder discharge to occur via a gap between the closure and the one seating, sealing means is provided between the closure and the said other seating to prevent powder from passing between the closure and the said other seating to occupy the space between the closure and the wall of the said passage in which the closure slides. When the closure is disengaged from the said other seating, gas can pass between the closure and the said passage while the powder is becoming fluidised.

Preferably the sealing means comprises an O-ring seal.

Typically the passage and closure are moulded from plastics material such as an acetal resin and the O-ring is formed from nitrite rubber typically having a shore hardness of 70.

Where the closure comprises a stem portion which slides in the said passage and an enlarged head at one end of the stem for engaging the two seatings, the O-ring is preferably a close fit around the stem portion of the closure, and is located at the end of the stem adjacent the enlarged head.

Preferably the opposite end of the stem portion of the closure comprises one face of the closure while the enlarged head at the other end of the stem comprises the other face of the closure, the smaller cross-section of the stem thereby creating the smaller face, so as to produce the differential force acting on the closure when the pressure on both faces becomes equalised.

According the another aspect of the invention it has been found beneficial to create a concave depression in the end of the stem portion of the closure remote from the enlarged head thereof.

According to a further feature of the invention the surface of the stem, or the said remote end thereof, or the wall of the passage within which it slides, is configured so as to cause the movement of the air thereover (or between the closure an the passage) to create a whistling sound. In use the sound will occur after the gas canister is punctured but will stop as soon as the powder starts to discharge.

The O-ring may be located in a rebate in the wall of the stem or in an annular depression in that face of the enlarged head around the junction between it and the stem which protrudes therefrom, or may be held captive in an annular rebate in the end of the passage defining the said one seating against which the enlarged head of the closure engages after pressures on opposite faces of the closure are equalised and the closure moves to release the fluidised powder.

Spring means may be provided which acts on the closure in a direction to move the enlarged head and O-ring seal into contact with the said one seating. Typically the spring means comprises a helical compression spring having a low spring rate which is readily overcome by the initial pressure differential so as not to prevent movement of the closure towards the said other seating, but when the pressures are equalised, acts to return the closure to its original position.

The invention will now be described by way of example with reference to the accompanying drawings in which: Fig 1 is a cross-sectional elevation through a fire extinguisher head constructed as an embodiment of the invention, and Figs 2 and 3 show the flow control valve of the head of Fig 1 to an enlarged scale with the closure in its two positions.

In the drawings, the fire extinguisher head comprises a moulded body 10 having a large diameter flange 12 by which it can be screwed to the open upper end of a powder filled container (not shown).

Centrally of the body 10 is a second connection 14 adapted to be screwed to the upper end of a gas canister (not shown), by means of an internally screw threaded socket 16.

Centrally of the latter is a plunger mechanism comprising a push rod 18 from the lower end of which protrudes a piercing pin 20 of know type, which if moved sharply in a downward direction pierces the thin metal closure to the gas canister to allow gas under pressure to leave the canister and pressurise the interior of the body 10 and thereby the powder container (not shown).

A two part handle 22, 24 allows the push rod 18 to be forced in a downward direction when it is required to operate the extinguisher. To this end the part 24 is fixed to and in fact integrally formed with the body 10 and the part 22 comprises a pivotal lever, which pivots relative to fixed part 24 about a pin 26 and extends over the upper end 28 of the rod 18, so that if pressed down relative to the fixed part 24 an internal moulding 30 engages the end 28 of the rod 18 and forces it in a downward direction.

The rod 18 is normally held at the upper end of its travel by a spring 32 acting between a shoulder of the cylindrical insert 34 at its lower end and an annular shoulder 36 at the lower end of the upper part of the rod 18.

To the side of the central part of the body 10 is located a side housing 38 formed with a cylindrical hollow interior into which protrudes at an angle and arm 40, the upper end of which supports an inner hollow cylindrical housing 42 which serves as a guide for a poppet valve closure 44. The upper end of the hollow interior housing42 is denoted by reference numeral 46 and this communicates with the interior of the connection 14 via passages 50, 52, 54 and 56. In this way when the interior 16 of connection 14 becomes pressurised with gas (typically carbon dioxide) this immediately pressurises the upper end 46 of the housing 42 which causes the valve closure 44 to move downwardly, until the enlarged head 58 at its lower end engages a frusto-conical valve seating 60 formed internally of a cylindrical tubular extension 62 which is screwed into the lower end of the side housing 38 and defines a chamber 65 which accommodates the enlarged head 58 of the closure 42. A syphon tube 64 is secured into the tubular extension 62. Only the upper part of tube 62 is shown. The tube actually extends downwardly to an open lower end which communicates with a region at the lower end of the interior of the powder filled container (not shown).

In operation, on initial breaking of the seal by pin 20, the high pressure gas acts on both the upper end of the powder charge and the upper end of 42. Since the powder charge effectively slows down the pressure front, the pressure in chamber 65 will not rise as fast as that in 46, and it is this pressure dif ferential which causes closure 42 to move downwardly. Once 58 engages 60, powder is prevented from passing from chamber 65 into the chamber 68 and from there via 70 to the outlet nozzle 72. In know manner the operator is able to control the discharge of powder since communication between 70 and 72 is only established while rod 18 is pushed down so that an O-ring 74 carried by an enlarged section 76 of the rod 18 has disengaged from a cylindrical sleeve guide 78, to create an annular opening through which fluidised powder can pass to 72. If the handle part 22 is allowed to lift under the action of spring 32 acting through the rod 18, the O- ring 74 once again closes off the communication between 70 and 72, thereby shutting off the discharge of powder.

The discharge can be started again if required (provided the pressure in the canister remains high enough), by simply pressing down on handle part 22.

The closure 44 is a sloppy sliding fit in the sleeve 42 so that with the enlarged head 58 shutting off the chamber 65 from 68, gas can continue to leak into the chamber 68, which since it now communicates with the nozzle 72 via 70, audibly confirms to the operator that the gas canister has been pierced and that the extinguisher will shortly discharge.

This leakage of gas is only possible if the O-ring 48 of GB 2,148,114 is omitted. However this means that when pressures in 65 and 46 are equalised (so that the force on 44 due to the pressure from below acting on the larger area of 18 is greater than that from above due to the same pressure acting on the smaller area of 44), and the closure 44 moves upwardly to allow powder discharge to occur, some of the fluidised powder can penetrate into the gap between 44 and 42 created by the sloppy fit of 44 in 42. The presence of this powder can affect the free movement of 44 in 42. Whilst this is of little consequence during the discharge procedure while fighting a fire, it can present problems after the extinguisher has been used once, and is recharged for re-use on another occasion by refilling the container with powder and fitting a new gas cylinder to 14. If 44 is now jammed in 42 due to the powder which has infiltrated, the closure 44 may not move down under the initial pressure differential between 68 and 65 so that the passage between 65 and 68 will not be blocked during that crucial initial 1-2 seconds needed for the powder charge to become fully fluidised. The result could be incorrect and unreliable discharge when used in an emergency situation.

To prevent this an O-ring seal 80 is fitted to 44 just above the shoulder 82 between the enlarged head 58 and the cylindrical spigot section of 44 which is slidably received in the guide 42. The presence of 80 means that when the closure 44 returns to its upper position gas and powder cannot penetrate into any gap between 44 and 42 possibly to remain and impede the subsequent free movement of 44 in 42.

Figs 2 and 3 show the closure and guide to an enlarged scale. In Fig 2 the closure is shown in the position which in it should be prior to the gas cylinder being pierced. This is also the position adopted by the closure after the pressure has equalised, after the initial 1-2 seconds of operation. In this position there is good communication between 65 and 68 via the annular space between the annular flange 84 of the enlarged head 58 and the frusto- conical seating 60.

Fig 3 shows the position 44 adopts for the 1-2 seconds immediately after piercing the gas canister and before pressures have equalized. Here the annular flange 84 engages the seating 60 so as to close off communication between 65 and 68.

The lower end of the cylindrical sleeve 42 may be chamfered as can be seen at 86 in Fig 3 so as to better accommodate the O-ring 80 when the closure 44 is in its upper position.

The O-ring 80 is shown as being a tight fit around 44, so that it will remain in position adjacent the shoulder 82 of the flange 84. However an annular groove in 44 and/or 82 may be provided to allow the O-ring to nest more intimately around the closure.

A helical compression spring may be fitted between the head 58 and the upper end of syphon tube 64. Such a spring is shown at 88 and the central surface of the underside of the head 58 may be recessed at 90 as shown in Figs 2 and 3, to receive and locate the upper end of the spring.

Claims

1. A powder fire extinguisher having a powder filled chamber, a compressed gas canister, a powder outlet means by which powder can leave the chamber, means for releasing compressed gas from the canister into the chamber to mix with and fluidise the powder, and valve means in the outlet for controlling the discharge of fluidised powder through a nozzle, and wherein a valve closure member is provided slidable in a passage in which it is a sloppy fit, which has opposed faces on which gas pressure can act to move the closure between two valve seatings such that when the compressed gas is first released the closure engages one of the seatings to prevent fluidised powder from leaving the chamber, but after gas pressure has been fully established the closure is forced away from the one seating to engage with the other to allow powder discharge to occur via a gap between the closure and the one seating, characterized by sealing means between the closure and the said other seating to prevent powder from passing between the closure and the said other seating to occupy the space between the closure and the wall of the said passage in which the closure slides, but when the closure is disengaged from the said other seating, gas can pass between the closure and the said passage while the powder is becoming fluidised.

2. A powder extinguisher as claimed in claim I wherein the sealing means comprises an O-ring seal.

3. A powder extinguisher as claimed in claim 1 or 2 wherein the passage and closure are moulded from plastics material.

4. A powder exyinguisher as claimed in claim 3 wherein the plastics is an acetal resin.

5. A powder extinguisher as claimed in claim 2, 3 or 4 wherein the O-ring is formed from nitrite rubber.

6. A powder extinguisher as claimed in claim 5 wherein the nitrite rubber has a Shore hardness of 70.

7. A powder extinguisher as claimed in any of claims 2 to 6 wherein the closure comprises a stem portion which slides in the said passage and has an enlarged head at one end of the stem for engaging the two seatings, and the O-ring is a close fit around the stem portion of the closure, and is located at the end of the stem adjacent the enlarged head.

8. A powder extinguisher as claimed in claim 7 wherein the opposite end of the stem portion of the closure comprises a smaller face of the closure while the enlarged head at the other end of the stem comprises a larger face of the closure, so that in use an equal pressure on both faces produces a differential force acting on the closure.

9. A powder extinguisher as claimed in either of claims 7 and 8 wherein the end of the stem portion of the closure remote from the enlarged head thereof is formed with a concave depression.

10. A powder extinguisher as claimed in any of claims 7 to 9 wherein the O-ring is located in a rebate in the wall of the stem.

11. A powder extinguisher as claimed in any of claims 7 to 9 wherein the O-ring is located in an annular depression in that face of the enlarged head around the junction between it and the stem which protrudes therefrom.

12. A powder extinguisher as claimed in any of claims 7 to 9 wherein the O-ring is held captive in an annular rebate in the end of the passage defining the said one seating against which the enlarged head of the closure engages after pressures on opposite faces of the closure are equalised and the closure moves to release the fluidised powder.

13. A powder extinguisher as claimed in any of claims 7 to 12 wherein spring means is provided which acts on the closure in a direction to move the enlarged head and O-ring seal into contact with the said one seating.

14. A powder extinguisher as claimed in claim 13 wherein the spring means comprises a helical compression spring having a low spring rate which is readily overcome by the initial pressure differential so as not to prevent movement of the closure towards the said other seating, but when the pressures are equalised, acts to return the closure to its original position.

15. A powder extinguisher as claimed in any of claims 7 to 14 wherein the surface of the stem is configured or profiled so that the movement of air thereover or between the closure and the passage will create a whistling sound, whereby in use the sound will occur after the gas canister is punctured but will stop as soon as the powder starts to discharge.

16. A powder extinguisher as claimed in any of claims 7 to 14 wherein the surface of the said remote end of the stem is configured or profiled so that the movement of air thereover or between the closure and the passage will create a whistling sound, whereby in use the sound will occur after the gas canister is punctured but will stop as soon as the powder starts to discharge.

17. A powder extinguisher as claimed in any of claims 7 to 14 wherein the wall of the passage within which the stem slides is configured or profiled so that the movement of air between the closure and the passage will create a whistling sound, whereby in use the sound will occur after the gas canister is punctured but will stop as soon as the powder starts to discharge.

18. A powder extinguisher constructed arranged and adapted to operate substantially as herein described by way of example and with reference to the accompanying drawings.

Amendments to the claims have been filed as follows: 1. A powder fire extinguisher having a powder filled chamber, a compressed gas canister, a powder outlet means by which powder can leave the chamber, means for releasing compressed gas from the canister into the chamber to mix with and fluidise the powder, and valve means in the outlet for controlling the discharge of fluidised powder through a nozzle, and wherein a valve closure member is provided slidable in a passage in which it is a sloppy fit, which has opposed faces on which gas pressure can act to move the closure between two valve seatings such that when the compressed gas is first released the closure engages one of the seatings to prevent fluidised powder from leaving the chamber, but after gas pressure has been fully established the closure is forced away from the one seating to engage with the other to allow powder discharge to occur via a gap between the closure and the one seating, characterized by sealing means between the closure and the said other seating to prevent powder from passing between the closure and the said other seating to occupy the space between the closure and the wall of the said passage in which the closure slides, but when the closure is disengaged from the said other seating, gas can pass between the closure and the said passage while the powder is becoming fluidised.

2. A powder extinguisher as claimed in claim 1 wherein the sealing means comprises an O-ring seal.

13. A powder extinguisher as claimed in any of claims 7 to 12 wherein spring means is provided which acts on the closure in a direction to move the enlarged head and O-ring seal into contact with the said other seating.

14. A powder extinguisher as claimed in claim 13 wherein the spring means comprises a helical compression spring having a low spring rate which is readily overcome by the initial pressure differential so as not to prevent movement of the closure towards the said one seating, but when the pressures are equalised, acts to return the closure to its original position.