Modern Gasworks Practice

RETORT-BENCH APPURTENANCES 255 one uninterrupted mam extendmg over a num Fig. 167.—Modern Form of Hydraulic Main. Fig. 168.—Tar Shibld for Hydraulic Main. A Continental type of hydraulic main with. weir valve is illustrated in Fig. 169. The main is provided with cleaning boxes fitted with automatic sealing devices having hand-wheel, screw, and locking bow. The special design of tar shield, in. reality performing the duty of a tar box, will also be notioed. Hydraulic mains as now erected are either («) Distinet mains, i.e., one to every retort beuch, on either or both. sides; or (b) Continuous mains, i.e., ber of (usually six) retort benches. Although. the latter type is somewhat less expensive as regards first cost, the advan-tages lie on the side of the distiaet main, which is more easily adjusted. In addition, a single setting can be readily isolated, and easier control is assured. In many of the con-tinuous mains it is customary to avoid the use and expense of long foul mains by arrang-ing the gas take-ofE (or gas and liquor take-ofE over a weir valve) at the extreme end of one of the sections. ' This method has, of course, its advantages ; but one of the chief troubles with hydraulic mains is the oscillation of the liquor therein, so that the dips are alternately lightly and heavily sealed as the crests and depressions of the waves . pass around theni. As the “ draw ” on the hydraulic remains constant, the pressure or vaeuum in the pipes connecting with the retort is accordingly affeeted by considerable fluctuation. Wh en, however, the gas take-off is arranged at the end of a length. of continuous main, the “ draw ” from the exhauster appears to exert an influence on the surface of the long stream of liquor and to give rise to proiiounced wave-motion. Such is the effeet of liquor oscillation that various means have been devised to restrict it. Among these are Meunier’s floats (Fig. 171). The floats, made from wood, are placed in the hydraulic main at, or partially below, the surface of the liquor, and, by means of a series of holes about 1 inch in diameter, free egress is provided for the gas. It is stated that a far more uniform level of liquid is main-tained in the hydraulic, there is thorough contact be.tween the gas and liquid, and retort pressures are more constant. Attached to the floats are dip-pipe sleeves (Fig. 172), wherewith the seal of the pipes can be either mechanically or automati-cally controlled by means of rods passing through stuffing boxes, as sliown. The inventor states that with the application of the floats he has found an inerease in gas make of from 10 to 12 per cent., whilst the trouble from naphthalene is consider-