Fig. 81.—Root blower.
Compressors.—In some installations air is supplied by compressor under the high pressure of 70 to 90 pounds per square inch, and seem well adapted to the production of a gas of good quality. Moreover, neither
tar nor ammoniacal waters are produced. The Gardie producer may be considered typical of this class of apparatus (Fig. 82). The chief feature of this producer is to be found in simple washing and purifying apparatus. It may be well to state here that the compression of air at high pressure occasions some complications, and a considerable expenditure of power.
Fig. 82.—Gardie producer.
Exhausters.—Some designers have invented devices which draw gas into the generator whence it is supplied to the engines, these suction apparatus being connected with the blowers or used separately. But with the exception of a few special instances, such arrangements are not widely used—at least not for the production of motive power alone.
Whatever may be the arrangement employed for the
introduction of a mixture of air and steam under the grate of the generator, the blast-pipe as a general rule discharges toward the center of the apparatus. Still, in large producers it becomes desirable to provide a means for varying the quantity of air and steam within wide limits so as to regulate the heat of the fire. For that reason several outlets are symmetrically arranged below the fuel.
Fig. 83.—Sawdust purifier.