Patent GB-749597-A (GB)
Title: Improved means for detecting and suppressing explosions
IPC: G08B17/06
Filed: 1953-04-09
Abstract: 749,597. Photo-electric fire detectors. GRAVINER MANUFACTURING CO., Ltd., WILKINSON SWORD CO., Ltd., and MATHISEN, A. April 1, 1954 [April 9, 1953; May 22, 1953; Sept. 11, 1953], Nos. 9618/53, 14477/53 and 25237/53. Class 40 (3). Explosions are suppressed by photo-electric means which respond to illumination from an incipient explosion to shatter a frangible container of liquid suppressant. The invention is described with reference to suppressing explosions in an aircraft fuel tank comprising a flexible rubber bag 10 which fits within a tanksupporting structure adjacent the skin of the fuselage or the wing of the aircraft which is stiffened by stringers. A thin skin between the inner flanges of the stiffeners forms the tank supporting plating. Alternatively this thin skin may form the tank. A photo-electric detector 11a is mounted in one upper corner of the tank while detector 11b is mounted in the diametrically opposite lower corner. Thus if one cell is covered by fuel the other may be uncovered. The suppressant containers are in the form of two cylindrical tubes 12a, 12b extending throughout the tank. The connecting wires are embedded in the rubber walls of the tank. Spherical containers may be used as shown dotted. The suppressant may be methyl bromide or dibromo difluoro-methane. Alternatively a hydrocarbon liquid, e.g. iso-pentane, may be used which enriches the mixture beyond the explosive range. Circuit arrangements.-In the arrangement of Fig. 4 a photo-multiplier tube is arranged to be responsive to the incipient explosion. The cathode o and the dynodes 1 to 9 of the multiplier tube are fed fron the secondary of transformer 21, the primary of which is supplied with 115 volts, 400 cycles. The collector anode 10 is connected to the positive terminal of a D.C. supply, the negative terminal of which is earthed, the last dynode 8 being also earthed. A cold cathode tube 23 normally held non- conductive by a bleeder chain consisting of a 7 and 11 Megohm resistor is effectively shortcircuited and a 4-microfarad condenser discharges through the valve detonating the explosive charges 24 in its cathode circuit. In the arrangement of Fig. 5 (not shown) a single vacuum or gas-filled photo-cell is used, the cell being arranged to short-circuit part of a bleeder chain, thus rendering a cold cathode triode conductive. This triode short-circuits an element of a further bleeder chain, thus rendering conductive a cold cathode tetrode with detonators in the cathode circuit. An arrangement is described (with reference to Fig. 6 (not shown)) in which an A.C. fed photocell is arranged to trigger an A.C. fed thyratron. In the modification of Fig. 7 the grid of a triode 51 is free until the photo-cell 50 becomes conductive, thus applying a negative potential to the grid and rendering the valve noh-conductive. An anode relay 52 is then de-energized and detonators 53 are fired. In further modifications, Figs. 9, 10 and 11 respectively (all not shown), a magnetic amplifier is supplied by a barrier layer cell to energize a relay and fire the detonators, a number of barrier layer cells are used to form a mosaic and trigger a cold cathode tube, and a barrier layer cell is used, with a transistor as amplifier. The transistor may also be used as the detector. Specifications 582,312, 643,188, 682,988, 702,919, 749,583 and 749,591, [all in Group XXI], are referred to.