GB710602A - Gas alarm - Google Patents

Abstract

In gas alarms of the type in which the presence of a gas or gas mixtures likely to explode produces heat by catalysed oxidation near an expansion agent in the form of a volatile liquid in a sealed limb of a U-tube containing mercury which is thereby caused to move past electrical contacts connected with an <PICT:0710602/III/1> oral or other alarm system, the U-tube is provided with absorbing material in the upper part of one leg above a constriction, while the enlarged other leg of said U-tube is surrounded by insulating material kept in position by an outer glass cover. In the preferred embodiment illustrated, a volatile liquid is absorbed in an absorbent 1b enclosed in the left-hand limb of a U-tube above a constriction 1a, and surrounded by a catalyst 3a. When an explosive gas is present, heat is generated, the liquid volatizes and the mercury is forced past contacts B and A whereby circuits connected respectively with "ahead" and "full alarm" signals are completed. The insulation 1c and the surrounding glass sheath protect the right-hand limb from heat radiation. If the concentration of the gas is high so that the mercury column reaches the contact 4c a magnet coil 6 is energized and the core 9 attached to a double-armed lever is drawn into it. A screening cap 10, from which heat can only escape by means of openings in the top, is also attached to said lever and is thereby lowered over the catalyst on to a sealing support 2 and prevents further heating which might lead to bursting of the U-tube or have other harmful effects. On cooling, the mercury in tube 1 recedes, the coil is deenergized and the counter weight 8 raises the screening cap. Alternatively the use of a lever may be obviated by attachment of the screening cap to the core of a magnet coil arranged directly above it.