Modern Gasworks Practice

276 MODERN GASWORKS PRACTICE In the same way that the station governor ensures a steadiness of pressure in the consumers’ services, whatever may be the demand, so should the retort-house governor ensure a constant vacuum in the hydraulic main, whatever the volume of gas coming away from the retorts. The intensity of vacuum desired is obtained by means of “ loading ” on similar lines to the method prevailing with. station governors. Before the introduction of this apparatus the required. vacuum on the foul main, was obtained. by regulation of the speed of the exhauster ; . whereas the uniformity of the “ draw ” was coirtrolled. as effectively as possible, but not without considerable difficulty, by means of the ordinary type of exhauster-govemor working on the throttle of the engine or a by-pass. (For description, see Cliap. XV.) This method of regulation is still in vogue in those works where no retort-house governor is installed. The application of the retort-house governor requires some consideration in relation to the working of horizontal settings, owing to the operation of gasmaking being necessarily intermittent, and to the inipracticability of charging the whole beuch of retorts at the same moment. For instance, if a single retort beuch, working into a common hydraulic main, is considered, it will be seen that, owing to the different periods at which the distinct rows of retorts have been charged, there will be a large volume of gas coming away from some dip pipes, whereas those retorts in which. the charges are nearly sperrt will be yielding little or no gas. But the object of the retort-house governor being to maintain. a constant “ pull ” whatever the quantity of gas coming away (and providing all dip pipes are equally sealed), there will be a similar vacuum on each. retort; that is to say, there is every likelihood of drawing waste furnace gases up the pipes from tliose retorts where the charge is sperrt. Under the circumstances, the ideal would be to charge up an entire set, or series of settings, at one time (instead of carrying out the ordinary practice of travelling through the whole length. of the bench on a definite row of retorts), and to interpose a retort-house governor for each unit so worked. The vacuum could then. be gradually reduced as the period of carbonization on each distinct section advanced. Such. procedure, however, is scarcely possible in practice. Owing to the faet that the retort-house governor works in connection with a system of mains under a vacuum, the holder bell—or otter reservoir—in communi- cation witli the main re-ceives 110 support from the gas, consequently buoyancy has to be imparted to it by other means. In general, these governors may be divided into two groups, namely— (a) those deriving their buoyancy from a system of air floats within. the holder bell, and being regulated by direct loading of th e latter;