Modern Gasworks Practice

438 MODERN GASWORKS PRACTICE The annular condenser shown in the figure is the improved Walker type, and may be composed of any number of tubes. It will be noticed that the inner cylinder is coned, so as to increase the annular space at the bottom. In this way stoppage due to tarry deposits is avoided. The base of the annular space is also given a fall, so that tar may run away readily to the seal-pot. Annular condensers should, Fig. 267.—Vertical Condbnsbb. whenever possible, be fixed in a moderately sheltered position so that tliey are not exposed to the extremes of climatic conditions. As regards their size, one rule (given by R. and J. Dempster) states that the allowance of superficial cooling surface should be 150 to 200 square feet per 1,000 cubic feet of gas passing per hour.