EXHAUSTING MACHINERY
483
and are 5 feet in diameter. They are almost invariably driven by electricity, as shown in Fig. 295.
Methods of Driving
Some years ago it was the common practice to drive the larger ex-hausters by means of belting, but the metliod is now fast giving way to the direct-coupled system. The belt drive is objectionable owing to the possibility of the beit slipping, in which. case the exhauster may stop abruptly, on account of friction between the blades and the case. The cost of driving power is, of course, the chief con-sideration in the case of the small works, and as steam power is frequently not available in such cases, a gas engine drive through a countershaft and belting is the only alternative. An advan-tage attending this method is the possibility of driving liquor and other pumps from the same countershaft. (A recommendation for the use of the exhauster in small works—and one which can scarcely be gauged in terms of money —is that a greaterpres-
Fig. 295.— Eleotkically Driven Exhauster Installation.
sure may be maintained on the district mains, tlius the annual quantity of gas consumed may undergo augmentation.)
On the larger and medium-sized works, wliere an ample supply of steam is always at hand, exhausters are frequently driven by reciprocating or turbine steam