Patent GB-407766-A (GB)
Title: Improvements in and relating to electric safety lamps
IPC: F21V25/06
Filed: 1932-10-31
Abstract: 407,766. Electric safety-lamps. RAVE, C., 1A, Ziegelei, Luckenwalde, Germany. Oct. 31, 1932, No. 30680. Convention date, Aug. 11. [Classes 39 (ii) and 75 (iv).] In an electric safety-lamp for use in mines &c., with a protecting-bell enclosing a protective medium which directly surrounds the lamp bulb, spring means are provided for disconnecting a contact on the lamp bulb from the source of current when the protecting-bell is broken and, in case the lamp bulb is also broken, provision is made for positively delaying access of explosive air to the filament by means of the protective medium until the filament has been extinguished or cooled. The lamp 1, Fig. 1, is screwed into a socket 12, preferably of insulating-material which is inserted through a circular opening in a rubber disc 13 forming an air-tight joint for the protective bell 5 which is secured to a cover member 16 by a cap-nut or ring 32, these members also being secured to a casing 19 by a cap-nut 33. The socket 12 is secured to the rubber disc 13 by a rear cap 14, so that these members have a limited movement within an aperture in the member 16 and assume their upper position when the bulb 1 is inserted and the bell 5 filled with water. In this position the lamp circuit is closed by its central contact bearing on a conducting-rod 37, while the edge of its metal shell 29 bears against the edge of a metal cylinder 28 which is pressed downwardly by a spring 26. Above the lamp bulb is a float 2 which preferably acts as a reflector and contains an upper airtight chamber 42, the lower chamber 2<1> being formed with a narrow annular bottom opening 3 and a series of openings 4 near its top edge. This lower chamber becomes filled with water which flows out through the annular opening when the bell 5 is broken, thus surrounding the bulb with a veil of water which excludes air from openings in the bulb until the filament is cooled. In a modification, Fig. 2, the protective medium comprises a gas under a pressure sufficient to maintain the bulb upon its spring seating, the bulb being enclosed within a cap 7 of transparent flexible material such as that known under the Registered Trade Mark " Cellophane." Due to the gaseous pressure the cap 7 is normally spaced uniformly from the bulb, so that an object breaking the bell 5 also forces the cap against the bulb and temporarily seals any aperture produced in the latter, allowing the filament to cool to ensure safety. This construction may be modified by providing a liquid filling within both the " Cellophane " cap and protective bell and inserting a spacing- member between the apex of the bulb and bell to hold the flexible cap away from the bulb. In a further modification the protective bell is reinforced by a wire net embedded therein, so that the glass only cracks or splits when fractured and prevents a liquid filling from escaping too quickly. Alternatively an ordinary glass protective bell may contain a liquid filling together with bodies which, on the protective bell being broken, produce gases or froth which shut off the incandescent lamp from the outer air. For example bicarbonate in tablet form with a core of tartaric acid is introduced with an addition of saponin or liquoriceroot extract into the protective bell, the internal pressure being sufficient to prevent the evolution of gas or froth until the protective bell is broken. A protective gas may also be produced by introducing into the bell a liquid such as methyl bromide which will evaporate rapidly when the bell is fractured, and delay access of air to the filament. Another way of delaying the access of air comprises filling the bell with a viscous or jelly-like mass, for example by adding gelatine, glue, starch, or syrup-like substances to the liquid filling.