Modern Gasworks Practice

624 MODERN GASWORKS PRACTICE THE VARIOUS TYPES OF GASHOLDERS The chief distinction between the various forms of holders is to be found, not so much in the formation of the floating bell but in the manner adopted for guiding the bell, and in the construction of the tank containing the water. The function of the water is primarily that of providing an. elastic gas-tight seal in which the bell may rise or fall; in addition, it receives the whole of the yressure thrown by the weight of the bell, and in this way forms the necessary resistance by means of ■which the bell is raised or the gas expelled. Fig. 379.—Spirally Guided Holder. In the first instance gasholders may be generally classified -under two distinct headings :— 1. Simple holders, in which the bell consists of one section or “ lift ” only. 2. Compound holders, in which the bell is composed of two, or a number of “ lifts,” arranged to telescope one into another when the holder is empty, or partly so. More broadly classified, the various descriptions of holders may be set down as follows :—■