A smoke barrier is disclosed in our earlier Applications GB 2272836 and GB 2312842. These barriers each comprises an apertured plate slidable relative to a complementary apertured grill to open and close the openings of the grill. The plate is held by an electromagnet or solenoid in its open position and falls under gravity to its closed position when the electromagnet or solenoid is rendered inactive in the event of fire or smoke. One disadvantage of this earlier barrier is the requirement to supply electricity to the electromagnet or solenoid.

GB-PS-2161918A discloses a ventilator which is closeable to inhibit the spread of smoke and fire. In this document, electromagnets are provided to retain the ventilator in its closed position. The ventilator disclosed therefore suffers from the same disadvantages as mentioned above. A similar electro-magnetically controlled grill is disclosed in GB-PS- 2213719A.

The present invention sets out to provide a ventilator grill which operates automatically in the event of elevated temperatures to prevent the passage of flames and/or smoke and which is not electrically operated.

In one aspect the present invention provides a ventilator comprising a stationary grill having openings through which air can flow and a sliding sealing plate positioned adjacent the grill and having openings which register with the openings of the grill when the ventilator is in an open configuration and lands between the openings which register with the openings of the grill when the ventilator is in its closed configuration, and means for imparting sliding movement to the sealing plate automatically in response to a predetermined elevated temperature, the movement imparting means comprising a spring of bi-metallic material connected between the stationary grill and the sliding plate which operates to resist movement of the sealing plate to retain the grill in its open configuration below a specified temperature and whose length increases at elevated temperatures to move the sliding plate relative to the stationary plate initially partially to close off the openings formed in the stationary plate and ultimately to fully close off these openings, movement of the sliding plate being reversed as the ambient temperature returns to below the specified temperature.

Preferably, the properties of the spring are such that its length increases progressively between, say, 30°C and, say, 75°C at which temperature the openings of the stationary grill are fully closed.

By a"bi-metallic material"is meant one whose length varies directly in proportion with the temperature to which it is subjected, the variation being relatively significant between a predetermined start and finish temperature. Bi-metallic materials enjoy this characteristic.

The invention will now be described by way of example only with reference to the accompanying diagrammatic drawing in which the sole Figure is a side view in section of a ventilator in accordance with the invention.

As will be seen from the drawing, the ventilator grill comprises an outer stationary grill panel 1 formed with a plurality of elongate openings 2 through which air can normally pass, from one side of the ventilator grill to the other. Inclined louvres 5 are sited above each opening 2. Positioned behind the stationary panel 1 is a sliding plate 3 also formed with a plurality of openings 4 of position and size which complement those of the stationary panel 1. The respective openings are so positioned that those of the sliding plate 3 register with those of the panel 1 when the ventilator is in its open configuration and lands 6 between the openings of the plate register with the openings of the panel 1 when the ventilator is in its closed configuration. A block 7 including an array of through- passages 8 is positioned behind the sliding plate 3 and remote from the stationary grill panel 1.

Secured to the rearwardly extending wall 9 of the grill is a collar 10 within which is positioned a spring 12 produced from a bi-metallic material. The end of the spring 12 remote from the wall 9 is mounted on an annular plate 14 secured to the upper end of a rod 11. The end of the rod 11 remote from the collar 10 seats on a flange plate 15 secured to the sliding plate 3. Thus, any elongation of the spring 12 imparts downward movement to the rod 11 and thence to the sliding plate 3 through the flange 15.

The spring 12 is selected so that its length increases at elevated temperatures from an initial length at which the grill is in its open configuration with the respective openings in register and a second position in which the openings of the stationary panel 1 are closed by the lands 6 of the sliding plate 3. In one example the spring is selected whereby its length progressively increases between 30°C and 75°C at which the ventilator grill is respectively in its open and closed positions. Of course, between these temperatures there is a progressive closing or opening of the openings.

In operation, the grill is conventionally mounted within a wall, panel or the like.

Normally, the grill is in its open position in which the openings 2,4 of the panel 1, and plate 3 are in register, the spring 12 operating to hold the sliding plate 3 in its raised position. In the event of fire, the consequent elevated temperature causes the length of the spring to increase thereby moving the plate 3 downwardly initially partially to close the openings 2 and finally fully to close off these openings. As the ambient temperature falls, so the spring moves the sliding plate 3 relative to the stationary panel 1 until the ventilator adopts its open configuration.

It will be appreciated that the foregoing is merely exemplary of ventilators in accordance with the invention and that various modifications can readily be made thereto without departing from the true scope of the invention disclosed in this application.