The annular space surrounding this feed-hopper generally forms a chamber for receiving the gas produced, as in the Winterthur (Fig. 92), the Bollinckx (Fig. 98), and the Taylor apparatus (Fig. 99).
In generators having an internal vaporizing-tank, this tank itself serves as a feed-hopper, which is the case in the Deutz apparatus (Fig. 106) and Wiedenfeld generator (Fig. 95).
Connection of Parts.—In order to facilitate the thorough cleaning of the retort, preference is given to removable charging-boxes and feed-hoppers. These are features of apparatus of the Bollinckx type (Fig. 98), in which the charging-box is secured to the generator by means of its yoke and by catches provided with knobs, and also of apparatus of the Winterthur kind (Fig. 92), having a charging-box pivoted about a vertical axis, or apparatus of the Duplex type (Fig. 110), in which the charging-box can swing about a horizontal hinge.
Air Supply.—We have seen that, when starting the generator, the gas is produced with the aid of a fan. This fan may be operated mechanically, but is generally operated by hand.
It is customary to convey the air-blast through a pipe leading to the ash-pit, as in the Winterthur apparatus (Fig. 92). Often, however, the air supply pipe is directly branched on that which leads from the vaporizer to the ash-pit, as in the Deutz apparatus (Fig.
106). In this case a set of valves or dampers permits the disconnection of the fan or its connection with the ash-pit.
Fig. 110.—Duplex charging-hopper.
In some apparatus an air inlet is provided immediately adjacent to the ash-pit. This arrangement is faulty for the reason that it gives rise to gaseous emanations which take place by reaction after each suction stroke of the engine. Furthermore, it is advisable that the air supplied below the ash-pit be as hot as possible. For this reason the employment of preheaters is desirable. The dry air forced in by the fan stimulates combustion, and the hot gas produced and mixed with smoke escapes through a separate flue, generally arranged beyond the vaporizer and serving as a chimney. This chimney should in all cases be extended to the outside of the building, and should never terminate in
a brick chimney or similar smoke-flue. The direct escape of such gas and smoke through a telescopic chimney above the charging-box has been generally abandoned in modern structures.