Modern Gasworks Practice

RETORT-BENCH APPURTENANCES 253 I Fig. 164.—The Bergmann Expansion Joint. on a perfectly even keel, a uniform seal may be best obtained by macliining a small portion of the upper face of the dip-pipe flange. When turning up the dip edges the distance (cZ), Fig. 162, can be made constant for all pipes. When the pipes are in position, ready to be permanently tightened down, a straight edge can be run along the turned portion of all flanges. So long as the straight edge remains level the dip pipes will tlion all be level at the lower edges, and any flanges not complying with the line of level can be tliere and then adjusted. This method is preferable to running a straight edge underneath the dips and inside the hydraulic main; and, if necessary. the dips throughout the whole house can be brought to a conimon level with. ease. When a retort beuch is picked-up from cold, some means must be provided for permittmg any slight movement of the ascen-sion and bridge pipes. This may be allowed for by making one of the socket joints (preferably that where the bridge pipe and dip pipe meet) of slag wool to a deptb. of about 2 inches in the socket. This will permit movement; and when the heats are fully raised, the remainder of the joint may be made with borings in the usual way. The Bergmann, expansion bell-joint (Fig. 164) has been in-troduced in order to pro vide for expansion. An annular packing of asbestos is placed between the pipe and the socket so as to make a gastight joint. Moreover, the lower portion of tlie socket forms an. annular recess which serves as a seal when the liquid accumulates there. THE HYDRAULIC MAIN Although there are still many cast-iron hydraulic mains in use, they arc now never erected where renewals or extensions are carriecl out. Mild, steel plates put together with. the aid of angle sections are the modern practice, the plates being from fV-inch. to /u-incli thick, the usual being f-inch. With. regard to covers, cast-iron is still in many cases employed with. tlie steel main, the reason being that owing to the numerous holes for dip pipes and bolts for flanges the steel cover is somewhat more costly, and is apt to spring unless stiffened. The steel hydraulic main is rarely made square in section, favourite designs being those of a O-shape or with semi-circular bottom as at A in Fig. 165. From every point of view, however, the type shown in Fig. 167 may be looked upon as the most effectual. The base is given a decided fall to the tar outlet pipe connecting with the tar main, or tower; and, in addition, the main, is sloped longitudinally to the same pipe, so that in elevation it is V-shaped. One of the most important features is the apron plate, as seen, which permits of the thorough cleaning away of pitch or otlior deposita which. may tend to block the tar-outlet pipe. A cock, as shown, should always be fitted to tlie tar pipe from each. box, so that in the event of the cast-iron pipe breaking, the cocks may be shut and the unsealing of the dip pipes prevented. If a weir valve is employed, so that gas and liqtior pass out of the box together, a tar shield, as shown