»O CP
MODERN GASWORKS PRACTICE
As regards the crown rest, this cousists of a series of radiating rafters carried on columns erected in the tank and comiected together by purlins to form a skeleton framework of the same camber as the dorne. The frame is frequently constructed from timber, although. light sections of rolled Steel may be economically employed. The design is simple and may be seen in Figs. 388 and 407. An important considera-tion is that of arranging for the bracing of the columns, which are usually of some considerable height, particularly in the cases of the flat-bottomed steel tanks
A complete diagram of a telescopic gasholder with guide-framing is given in Fig. 405.
An interesting feature of some of the earlier gasholders was the housing which was erected over and around them as a means of protection. A notable example of the covered gasholder is that at the Tegel works of the Berlin municipality (Fig. 406). The building is an architectural work of brilliance, being 300 feet in height and overlooking the whole of the northern part of the city. The capacity of the holder is nearly 8 million cubic feet, and the cost complete with house was £107,000. An unusual feature is the lead-covered oil storage reservoir in the middle of the tank.
SPIRALLY GUIDED GASHOLDERS
The spirally guided gasholder, the proposal of Mr. W. H. Y. Webber and the invention of Mr. W. Gadd (Fig. 379) with which an external guide-framing is wholly
Fia. 409.—Housed Gasholdeks, Vienna Gaswokks.