RETORT-BENCH APPURTENANCES 247
dotted), so that an ampie bearing on the lower portion of the flange of one mouth-piece and the tipper portion of the flange of the mouthpiece just below may be ob-tained. The arrangement givea in Fig. 153, although. frequently seen, is not to be
Fra. 151.—C. I. Brac-
KBT FOR SUPPORTING Bracing Rail FOR Rbtobt Mouthpieces.
Fig. 152.—C. I. Bbac-ket j?or Channel Iron Mouthpiece Bbaoing.
Fig. 153.—Single Bull-head Rail Support.
recommended, particularly in view of the faet that the main buekstays do not bear direct upon the brickwork of the beuch, an intervening space being left wtiich is filled in with. a false wall.
ASCENSION PIPES, BRIDGE PIPES, AND DIP PIPES
The point of chief importance with regard to the ascension pipe is, perhaps, its size. Present-day practice in this respect is towards ample area, so much so-that in many cases the pipes in. modern installations provide practically double th.& cross-sectional area considered sufficient a decade ago. In general, however, design may be considered on safe lines if carried out in. accordance with. the following:—
Size of Ascension Pipes
Works making under 10 million cubic feet per amium . . . 5-inch pipe.
Works making between 10 million and 200 million oubio feet per annum 6 „ „
Works making above 200 million cubic feet per annum . . . 7 „ „
This rule refers, of course, to retorts having an ascension pipe at each end, in. the case of “ through. ” settings. In some recent horizontal benches, ascension pipes of 8-inch diameter have been. fitted at each. end of th.e retort. The chief diffi-culty with. the larger pipes lies in inducing the attendants to clear them properly. For 7-inch pipes a 5|- or 6-indi auger is generally used, but above this size the augers become som.ewh.at unwieldy and difficult to handle, so that there is some temptation. to make use of them as little as possible. In the arrangement of ascension pipes it is necessary to keep them as far as possible from the centre of the setting, so that tliey are unafEected by the lieat of the combustion chamber. There is also the question of curvature, for tlie purpose of working round the upper mouthpieces. All abrupt benets must be rigidly avoided, otherwise endless trouble in cleaning the pipes and in.