Modern Gasworks Practice

THE STORAGE OF GAS 625 1. Holders guided by wire cables. (Now obsolete.) 2. Holders guided by ordinary distinct vertical guide-framing, with or without “ flying lifts.” A typical holder with braced guide-framing is shown in Fig. 377. A telescopic holder with “ flying ” lift is seen in Fig. 378. 3. Spirally guided holders (left or right liand, or a combmation of both). The guides, so far as the beil is concerned, may be either internal or external. Fig. 379 shows a spirally guided gasholder. 4. Holders with a floating roof, generally known as the Nuremberg type. The cable-guided holder, th.ough of historical interest, can scarcely be con-sidered under the heading of modem structures. Holders of this type are still in use, the largest of the kind being in operation at Middlesbrough. This holder has three lifts (the outer of which is 185 feet in diameter) and a total capacity of 2| million cubic feet. Theoretically, at least three cables are necessary for a single-lift holder. One extremity of each is a.ttached to the upper edge of the tank, the cable is then led round a pulley fixed to the top curb of the gasholder and afterwards passes over the top of the beil to a second pulley attached to the top curb at a distance of about one-third of the circumference from the first pulley. The cable is tlien led downwards and around a third pulley fitted to the bottom curb of the holder, its other extremity being fastened to the top of the tank. Thus, as the bell rises or falls each. cable is maintained in a taut condition. THE DESIGN OF GASHOLDERS By far the most common. type of gasholder is the single or multiple “ lift ’’ vessel guided by a number of columns spaced circumferentially around the top of the tank at distances of from 15 to 30 feet apart. The columns are adequately braced together by horizontal gilders and diagonal ties, the gilders for large holders being built up from steel sections, whilst the ties (which are in tension only) may be made from plain round or flat steel bars. In the past, it was customary to erect massive cast-iron. columns which carried a guide rail and ensured the rigid guiding of the holder. A heavy cast-iron or wrought-iron trellis cross girder extended from apex to apex of the columns, whilst tie-rods of umisual length completed the framework. To-day, the cast-iron frame lias been entirely superseded by that composed of comparatively light columns constructed from rolied mild-steel sections. For the smaller holders (say up to 750,000 cubic feet capacity) the standards may advantageously be plain rolied steel joists at centres of from 15 to 18 feet, stayed up by a smaller size of the same section for the horizontal cross struts. Each panel would then be tied together by circular rods arranged diagonally, and meeting in the centre of the panel. At the iunction of the ties a centre ring, permitting of adjustment, may be used, but modem practice tends towards adjustment at the standards. Centre rings, moreover, are inclined to spring, and are often absurdly weak in. con> parisou with the bars. Particulars of the guide-framing for a holder of this kind are given in Fig. 388. s s