Modern Gasworks Practice

RETORT-BENCH APPURTENANCES 257 with a connection taken direct to the tower. The cover plates for the open side of the main are dished, and are sealed in shallow lutes, so as to reduce to a minimum the loss of ammonia. There is only one main per beuch, on the machinc side. All the ascension pipes are 8 inch.es in diameter. A recent attempt has been made to construct hydraulic mains from reinforced concrete. As an emergency measure during the late war, Martineau constructed ten of such mains for use at a French gasworks. The metallic reinforcement consisted of a network of J-inch round iron wire formed in squares 4 indies by 4 indies. The concrete walls had a thick- Fig. 171. Fig. 172. Meunibr’s Floats. ness of 2f inches, and the valve of the tar-outlet was let into the cement. A rebate along the tipper part of the main received the cover, formed of a slab of cement into which were set the inspection and cleaning boxes. Before being put into use, the interiør surface of the main, as also the lower side of the cover, was given three coats of hot tar. This was done in order to close up the capillary passages in the cement, and tlius prevent g,ny action of ammonia upon the metallic reinforcement—the con-tinuous flow of tar during the working maintaining this protective coating. The main was put into use without any mishap in the way of expansion or leakage. Test pieces of cement placed in it at the time of commencing operations, and exam-ined six months afterwards, showed 110 sign of any action, on tlie cement by the ammoniacal liquor. Martineau expressed himself as wholly satisfied with the result of the measure imposed upon bim by circumstances. The ten mains were constructed in six weeks at a cost of 60 per cent, less than the prevailing prices for steel mains. With regard to the gas take-oft from the hydraulic mains, this should be ar-ranged from the cover of the box, ratter than from the side, as is so frequently found. The method by which the hydraulic main is supported in its position above the retort beuch requires careful consideration. As the chief function of the main is to provide a seal, it is essential that it should be maintained on a perfectly even keel; hence the supports must be such, that they are entirely uninfluenced by any movement of the beuch which may take place when heating-up occurs. In the past it was a favourite practice to bed the main on brick piers or cast-iron standards erected immediately on top of the retort beuch; thus when any movement of the latter occurred the mains were thrown out of level. Modern fixings for hydraulic mains which render them entirely independent of the beuch movements are shown in Figs. 165 and 169. That shown at C, Kg. 169, is, perhaps, not so desirable as the other methods, as if tiglitening of the main, tie rods is necessary, the tipper portion . s