Fig. 118.—Pintsch vaporizer and scrubber.
In other cases, the water lies inside and the gas outside. In this latter case, a longitudinal baffle is employed to compel the gases to heat the tubes in their whole length, as in the Deutz producer (Fig. 117). In a general way it may be said that such a series of tubes
presents the disadvantage of becoming clogged up rapidly by the deposit of lime salts contained in water.
Fig. 119.—Benz vaporizer.
Fig. 120.—Koerting vaporizer.
If the set of tubes consists of fire-tubes, the deposit will form on the outer surface, that is, on a portion not accessible for cleaning. From this point of view, water-tubes are preferable, as they allow the deposit or scale to be removed through the tubular heads or plates. On the other hand, such water-tubes have the drawback that their exterior surfaces are readily covered with pitch and soot. The tubular vaporizers of the
Field type (Bollinckx, Fig. 98) are composed of a single sheet-iron tube or shell, in which the tubes are arranged, dipping into a chamber through which the hot gases pass. This arrangement insures a rapid production of steam, but the Field tubes are even more liable than the others to become covered with deposits.
It will be seen that these types of vaporizers should all present the following features: easy access, small quantity of the body of water undergoing vaporization, and large heating surface with small volume.