This invention relates to ventilators, more particularly, casement ventilators in roofs, and is concerned with mechanisms for opening and closing them in response to fire alarms and/or

building management systems It is known for a casement ventilator to have gas springs connected between a fixed frame and a movable panel hinged thereon to effect opening of the ventilator, pneumatic cylinder-and-piston units (hereinafter referred to simply as "pneumatic units") also being connected between the fixed frame and the movable panel to effect closing ofthe ventilator, and a latch to lock the ventilator closed urged into automatic locking position by the piston of an air cylinder against the urge of a mechanical spring that serves for releasing the latch and opening ofthe ventilator when air from a power line to the air cylinder is cut off in response to a signal from a fire alarm and/or a building management system and/or other control system Closing of the ventilator is effected by the pneumatic units, against the force ofthe gas spπngs, in response to an appropriate signal from the building management system The rating of the gas spπngs is determined by the weight of the movable panel plus a theoretical snow-plus-wind loading, and if the ventilator panel is glazed then the glass adds further to the theoretical loading and, with double- glazing, very appreciably more, so much so that the gas springs have to be so highly rated that they may damage the movable panel (e g shattering the glass) and/or the hinges because ofthe violence ofthe opening movement Furthermore, the rating of the pneumatic units must be such that they can close the ventilator against the force ofthe gas springs, and can hold the ventilator closed until the latch is re-engaged upon restoration ofthe air supply to its operating air cylinder No account can be taken of assistance to closing of snow or wind, consequently, with an air power line of limited pressure the diameter ofthe cylinders ofthe pneumatic units may become such that, in order to

accommodate them between the fixed frame and the movable panel, the size ofthe fixed frame (especially its width) has to be such as to detract appreciably from the effective ventilation area within it

The object of the invention is to overcome the above mentioned disadvantage According to the present invention, a casement ventilator ofthe type described above is characterized in that the pneumatic units are double-acting, so as to be able to assist the gas springs in the initial opening of the ventilator, and in that an air receiver is charged through a non-return valve from the power line upon closing of the ventilator and provides air for the opening movement of the pneumatic units Because the pneumatic units assist the gas springs to open the ventilator, the rating ofthe gas springs can be reduced and the rating of the pneumatic units can also be reduced because they have to overcome only the lesser force of the gas springs to close the ventilator Consequently, the diameter ofthe cylinders ofthe pneumatic units can be minimised and likewise the size of the fixed frame, with, therefore, maximising ofthe effective ventilation area. Because the pneumatic units are required to assist only initial opening ofthe ventilator, the air receiver does not need to be of large capacity, so it can have such a diameter that it can be

accommodated within the fixed frame

The receiver is preferably connected with the pneumatic units via an air line from between the non-return valve and the receiver, and the air line includes a change- over valve (e.g. a 5/2 Air Pilot Valve) with a pilot supply from the power line urging the change-over valve into the

"pneumatic-units closing-movement" condition against a spring biassing the change-over valve towards the "pneumatic-units opening-movement" condition, whereby the whole enhanced system can be operated from a single existing power line

Speed controllers may be provided between the change-over valve and the respective ends

of the cylinders of the pneumatic units, to control the rate of opening and closing respectively ofthe ventilator, or (preferably) the change-over valve may be provided with exhaust restπctors, preferably with silencers

A device that shuts off air at a predetermined temperature (e g a Shaped Metal Alloy

device) is preferably incoφorated in the power line to cause opening of the ventilator when that temperature (e g , 72°C) is exceeded, and the device automatically resets to re-open the power line when the temperature returns to normal

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which - Figure 1 is a diagrammatic small-scale plan of a casement ventilator in accordance with the invention,

Figure 2 is a section across the ventilator taken from the line II-II of Figure 1 and with the ventilator panel shown partially opened, and

Figure 3 is a circuit diagram incorporating the controlling devices for the pneumatic unit and latch cylinder indicated in Figure 1 and shown in Figure 2

The casement ventilator shown in Figures 1 and 2 has gas spπngs 10 connected between a fixed frame 11 and a movable panel 12 hinged thereon at 13 to effect opening ofthe ventilator, pneumatic cylinder-and-piston units 14 (hereinafter referred to simply as "pneumatic units 14") also being connected between the fixed frame and the movable panel to effect closing of the ventilator, and a latch 15 to lock the ventilator closed (by engagement with a projection 16 on the movable panel 12) urged into automatic locking position by the piston 17 of an air cylinder 18 (see Figure 3) against the urge of a mechanical spπng 19 that serves for releasing the latch 15 and opening of the ventilator when air from a power line 20 is cut off in response to a signal from a

fire alarm and/or a building management system and/or other control system, such as the device

21 shown in Figure 3 that shuts off the air at a predetermined temperature (e g a Shaped Metal Alloy device) to cause opening of the ventilator when that temperature (e g 72 °C) is exceeded, and the device 21 automatically resets to re-open the power line when the temperature returns to normal In accordance with the present invention, the pneumatic units 14 are double-acting, so as to be able to assist the gas spπngs 10 in the initial opening of the ventilator, and an air receiver

22 is charged through a non-return valve 23 from the power line 20 upon closing ofthe ventilator and provides air for the opening movement ofthe pneumatic units The receiver 22 is connected with the pneumatic units 14 via an air line 24 from between the non-return valve 23 and the receiver and the air line 24 includes a change-over valve 25 (e g a 5/2 Air Pilot Valve) with a pilot supply, indicated by the broken line 26, from the power line 20 urging the change-over valve into the "pneumatic-units closing-movement" condition against a spπng 27 biassing the change¬ over valve towards the "pneumatic-units opening-movement" condition (in which condition the change-over valve 25 is shown in Figure 3), whereby the whole enhanced system can be operated from a single existing power line

The change-over valve 25 is provided with exhaust restπctors 28, with silencers 29, to control the rate of opening and closing respectively of the ventilator Alternatively, speed controllers may be provided between the change-over valve and the respective ends of the cylinders 30 ofthe pneumatic units 14, as indicated by the broken line boxes 31 in Figure 3 Because the pneumatic units 14 assist the gas springs 10 to open the ventilator, including the load of double-glazing 32 ofthe panel 12, and any snow-plus-wind loading, the rating ofthe gas spπngs can be reduced (as compared within existing ventilators ofthe known kind) and the rating ofthe pneumatic units can also be reduced because they have to overcome only the lesser

force of the gas springs to close the ventilator Consequently, the diameter of the cylinders 31

ofthe pneumatic units 14 can be minimised and likewise the size of the fixed frame 1 1 (in which they are housed), with, therefore, maximising of the effective ventilation area

Because the pneumatic units are required to assist only initial opening of the ventilator,

the air receiver 22 does not need to be of large capacity, so it can have such a diameter that it can

be accommodated within the fixed frame 1 1 , as indicated in Figure 1 and shown in Figure 2