Patent GB-684871-A (GB)
Title: Fire-detector
IPC: G08B17/04
Filed: 1950-07-24
Abstract: 684,871. Fire alarms. TECALEMIT SOC. ANON. July 24, 1950 [Aug. 2, 1949], No. 18478/50. Class 118 (i) [Also in Group XIII] A fire detector comprises a receptacle balanced on a horizontal pivot and containing a movable mass, tubes on each side of the mass being so connected to the area under protection that a sudden increase of temperature causes a difference of pressure between the tubes which shifts the mass and so trips the alarm. Fig. 1 shows a V-shaped glass tube a containing mercury and balanced on a horizontal pivot so that unequal heating of the two arms of the tube displaces the mercury and thereby shifts the centre of gravity to trip a connection to an alarm. The sensitivity of the balance of the tube is adjusted by moving a weight d along a rod c carried by a metal mounting for the tube. It can also be modified by arranging one limb at a steeper gradient than the other. The activating limb is connected to an exploration tube in the premises fitted with the detector, while the responsive limb is connected to a further tube communicating with the exploration tube so that normal rises in temperature will not actuate the device. The exact position of the device may be indicated by connecting it to a resistance or a rheostat. In a modification, Figs. 7 and 8, the device consists of two receptacles 1, 2 connected by a siphon tube 3. The receptacles are housed in sockets 4, 5 connected by a bar 6. The socket 4 pivots in bearings 8, 9, in a fixed support 10. The activating receptacle 1 is connected to a tube 14 while the responsive receptacle is connected to a tube 16 communicating with the tube 14 through an expansion chamber 18 and a pressure-equalizing device 19. The balance of the receptacles is adjusted by means of a weight 12 attached to the socket 4. Keyed to the pivot pin 7 is a cam member 20 on which rests a link 23 with a fixed pivot 22 and connected to a link 25 to form a toggle. The link 25 is pivoted on the vertical arm 27 of a bell-crank .lever 28 which can rock about a pivot 29 and has a horizontal arm 30 'carrying a pin 31 engaged in the forked end 32 of a lug 33 rigid with a sector 34 mounted on a pivot 35. Over the sector 34 passes a cable 40 carrying a weight 41. Anchored to the frame of the device is a spring 36, which restores the bellcrank lever to the position of .engagement of the pin 31 in the fork 32. A fixed stop 38 limits the swing of the bell-crank lever. Means may be provided for winding up the weight 41 for setting purposes. Upon'an abnormal rise in temperature, the pressure in the tube 14 rises and mercury is forced out of the vessel 1 and through the siphon tube 3 thereby upsetting the balance of the device. The cam 20 breaks the toggle 23, 25 whereupon the bell-crank lever is displaced and the pin 31 disengaged so that the weight 41 falls. This fall may be used to operate a fire-extinguisher. Air displaced from the receptacle 2 flows into the expansion chamber 18. The arrangement 19 is a tubular coil compensating for normal increases in temperature within the premises. Specification 607,409, [Group XXXVII], is referred to.