This invention relates to a powder type fire extinguisher. In such extinguishers, a powder contained in a chamber in the extinguisher is driven out of the chamber by compressed gas when a container holding the gas is opened. 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, and thus that the powder is fully fluidized inside the chamber before any output from the chamber occurs.
In DE-A-1434959 there is disclosed such a fire extinguisher, in which the valve controlling the compressed gas escape is activated by a manual lever operable in two stages. Since the second stage is also under manual control, it cannot be ensured that the powder has been sufficiently fluidized before any output commences.
According to the invention, there is provided a fire extinguisher for discharging powder, having a chamber for holding the powder, a container for compressed gas, a powder outlet from the chamber and means for opening the gas container to allow compressed gas to enter the chamber and drive the powder out of the outlet, wherein a valve is provided in the outlet, the valve having a valve member movable onto and off a seat in a valve housing to close or open the outlet, characterised in that the valve member is movable by pressure on opposed faces of the member, that the area of the valve member face exposed to pressure from the chamber is greater than the area of the other face, and in that 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 fluidized 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 fluidized powder to pass out.
Preferably, the extinguisher has a head fitting which includes an outlet passage and which supports a cylinder containing the compressed gas and a mechanism for puncturing the cylinder to allow the gas to escape into the chamber and which also contains passages for directing the escaping gas through a tube to the bottom of the mass of powder in the chamber and to said other face of the valve member.
The valve is preferably mounted in the outlet passage in the head fitting.
The valve may be a poppet valve and said other face may be formed by the end of the valve stem. The valve stem may be arranged above the head and the head itself may be acted upon by the pressure in the chamber.
The valve head may present a rounded face to the chamber, to offer minimal resistance to the flow of powder when the valve is open.
The outlet passage may be continued upstream of the valve, into the chamber, by an elongate tube.
The invention also provides a method of controlling the output from a fire extinguisher for discharging powder, characterised in that a valve is placed in the powder outlet from 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 invention will now be further described, by way of example, with reference to the accompanying drawings, in which:
The head fitting 10 shown in Figure 1 is for fitting into the neck of a cylindrical powder container in a conventional manner. The container itself is not shown, and can be conventional. Any suitable method of fastening the fitting into the container neck can be used. In Figure 1, a flange 12 limits the insertion of the fitting into the container neck.
The fitting has a socket 14 for receiving a cylinder of compressed gas. A conventional firing mechanism (not shown) will be 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 valve shown in Figures 3 and 4 fits into the lower end 20 of the passage.
Looking now at Figure 2, the socket 14 for the cylinder and the lower end of the outlet passage can be seen. 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 24 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.
The valve shown in Figures 3 and 4 has a housing 30 with a valve seat 31 and a valve member 32 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. 0-ring seals 46 and 48 respectively seal the valve housing in the outlet passage 16 and 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 daN/cm2 (750-1000 psi). Gas passes down a tube fitted in socket 22 to fluidise the powder and to build up the pressure inside the chamber. 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. The pressure acting on the lower side of the valve head 34 is gradually building up as the powder is becoming fully fluidized, but initially is substantially lower than the pressure above the valve.
At a certain stage, once the powder is fully fluidized, and is ready to be driven out of the chamber, the pressure on the bottom of the valve will become equal to that above. Since the area of the valve head presented to pressure from below is greater than the area of the stem presented to pressure from above there will be a net opening force acting on the valve member, and the valve will open to allow the fluidized powder to flow through the pipe 50 and out. This stage is typically reached about 2 seconds after operation of the firing mechanism.
Figure 4 shows that the cross-sectional area occupied by the part of the housing containing the bore 18 is kept small, so as not to unduly reduce the cross-sectional area of the outlet passage in this region.