—Frequently no heed is paid to the collection of the dust. Sometimes a dust chamber is arranged to intercept it on the far side of the fan, or attempt is made to blow the dust into a tank of water. The fine dust of which we are speaking cannot be satisfactorily collected by either of these methods, nor even by a cyclone separator, so useful for the collection of many kinds of dust. In lead works generally, the dust removed by the fan is best collected in filter-bags made of some porous fabric. Various efficient filters constructed on these lines by Messrs. Henry Simon, Ltd.; Messrs. Beth and Co., Ltd.; and the Sturtevant Engineering Company, Ltd., are on the market.
Fig. 6 shows an arrangement of piping with balanced telescopic joints fitted to a Sirocco dust fan for removal of dust, in an electric accumulator works, when scooping out litharge from a cask into the receptacle prior to emptying the weighed quantity into the mixing machine, also under a hood connected with the exhaust system. (Illustration supplied by Davidson and Company, Limited, Belfast.)
In collecting the dust, care must be taken to provide an adequate outlet for the spent air, so as to prevent creation of a source of friction in front which might destroy the effectiveness of the installation.
Fig. 7.—Exhaust Ventilation on the Patent “Pentarcomb” Principle applied to Linotype and Monotype Machines in Printing Works, as installed by the Zephyr Ventilating Company, Bristol.
P, Patent “pentarcomb” for equalizing exhaust; V, patent “pentarcomb” for general ventilation; D, main and branch ducts; F, fan; U, upcast from fan; M, hoods over metal-pots of monotype machines, constructed to raise and lower, and swing out and in with metal-pot; L, hoods over metal-pots of linotype machines, constructed to raise and lower.
In the illustration “pentarcomb” grids connect the branch ducts over the metal-pots of mono and linotype machines with the main duct. The “pentarcomb” grids are arranged also elsewhere in the main duct itself to assist in the general ventilation of the workroom. The hoods over the metal-pots are constructed to be raised and lowered, and to swing out and in radially with the melting-pot arm. (Drawings supplied by the Zephyr Ventilating Company, Bristol.)
In order to secure equality of flow from a number of branched ducts, the Zephyr Ventilating Company apply a special grating of curved and slanting inlets—the “pentarcomb”—to each branch duct. The air passing through the comb is split up into numerous small columns, and the inclination of the curve which each is made to take is such as to reduce friction to a minimum. By means of this device we have found, in a trunk with twenty branches, the draught at the one farthest from the fan as serviceable as that next to it. The method is illustrated applied locally to remove the fumes from linotype machines, and generally in the main duct for removal of foul air near the ceiling.
Where electricity is available as a motive power for driving the fan, some modification in the views expressed as to the curvature of the pipes and system of installation can be allowed. In a red lead plant, for instance, it may be desirable to have the pipes leading to the sifter or packing machine with sharp angles, so as to prevent tendency of such heavy dust to collect in them. The electric current allows a fan to be installed at any point desired; and if applied with knowledge that the increased friction due to an acute angle has to be overcome, the result may be quite satisfactory.