Modern Gasworks Practice

266 MODERN GASWORKS PRACTICE sists of combining the usually distinct apparatus of tar-tower and retort-house govemor. The tower is made considerably higher than is general, and the upper portion contains a special receptacle which takes a floating bell of greater diameter than the tower proper. The bell chamber is closed by a cover plate ha ving a centrally disposed hole through which a rod passes, by means of which the govemor may be adjusted. Immediately below the bell chamber is the gas inlet. The subsequent passage of the gas may be seen from the section given in Fig. 185. The governor valve serves to throttle the passage of the gas should the vacuum increase above the normal, while, should the vacuum decrease, the valve is raised, with a consequeufc I Running Socket Tar Flu&h Cock Tar Overflow to Well Liquor Run-ofT Cock increase in the area of the gas passage, due to the increase in pressure of the gas on the bell. Düring the last few years there has been a growing tendency to erect tar towers built up from mild steel plates and sections. It is somewhat difficult to understand why this should be done, for the ordinary cast-iron pipe cannot be excelled, and is extremely cheap. Possibly, the steel tower was originally introduced owing to the ob-jection to sending cast-iron work long distances, when it is liable to rough handling and damage. The experience of J. G. New-bigging in Connection with ammonia losses may be mentioned, as bearing out the arguments that the internal or external seals with tar towers are unnecessary and actually wasteful, and that it is far preferable to take It had been Mr. Newbigging’s general Fig. 183.—Seal Regulation by Tar Overflow. the liquor direct to an effectively sealed pot. custom to run liquor into his mains from an overhead tank, when striking differences in the amount of free and fixed ammonia led him to make investigations. Two deductions were made, the first being that ammoniacal liquor constantly overflowing the weir valves was in such a state that free ammonia was being driven off in large quantities, and, consequently, any exposure to either an air current in tlie pipe line or to the atmosphere meant a probable source of serious loss. To overcome such drawbacks, water, instead of liquor, was used for flushing the hydraulic mains, and in this männer ammonia loss was curtailed, owing, it is said, to a lower percentage of free ammonia in the liquor overflowing the weir valves. In view of these results, it might appear advisable to admit water instead of the usual trickle of liquor to the hydraulic mains, but the author considers the practice undesirable.