The Horizontal Steam Turbine For Stationary Plants 1920

and the successive sets of blading are grad- ually increased in size, being greatest at the exhaust end of the turbine. After the steam has passed through the last set of blades it leaves the turbine casing through the exhaust pipe (H4). Maximum efficiency of the turbine is se- cured with the use of superheated steam and a highvacuum. To secure the highest oper- ating efficiency it is necessary to remove the slight amount of air in the steam by means of a dry vacuum pump which may be in- dependently steam driven or operated by an electric motor. The air, which enters the boilers with the feed water, expands into a great volume in passing with the steam through the turbine. Small turbines are not usually provided with an independent conclensing apparatus. Large turbines usually employ an inde- pendent conclensing apparatus, where the steam, after it has passed through the last set of revolving disks, is conclensecl. The condensed steam is pumped from the con- denser to the boilers which convert it again into high pressure steam required for the operation of the turbine. Sometimes a turbine equipped with con- clensing apparatus operates non-condensing, the exhaust steam being used for commercial heating. In this event, the steam is ex- hausted into the heating line instead of pass- ing through the conclensing apparatus. TRANSMISSION OF POWER Direct Connected Turbines (Fig. 4) The power of a direct connected steam turbine is transmitted through a flexible coupling (F5) to an electric generator (Fi) or a fan, pulley, pump, etc., or to a shaft upon which a driving pulley is mounted. In the latter case the pulley transmits the turbine power inclirectly by belt to shafting or machines. Geared Turbines Turbines with bucket wheels of small diam- eter run at high velocity—as high as 30,000 r.p.m. High turbine speeds must be reduced to enable the machinery to which the turbine is coupled to operate. Fig. 8 illustrates a set of reduction gears. On the end of pinion shaft (A) is a flexible coupling (C) to which is coupled the end of the turbine rotor shaft (not shown). Gears (B) are cut on the pinion shaft (A) which is lubricated by ring-oiled bearings (D) at each end of the shaft. In mesh with the teeth of pinions (B) are the teeth of gears (F) mounted upon the gear shaft 6E). To the end of the gear shaft Fig. 8. Speed reduction gear (E) is fixed a flexible coupling (G) to which is coupled a generator shaft (not shown). The gear shaft (E) is supported by ring-oiled bearings (H). Fig. 9 represents a geared turbine con- nected to an electric generator. The covers of the turbine and gear casing are lifted, showing the relative position of the turbine rotor (L), the pinion shaft (A) and the gear shaft (E), with their respective gears (B and F). The coupling of the pinion shaft is in a housing (at C) while the coupling (G) of the gear shaft (E) is shown connected to a similar coupling on the end of the generator shaft (J). Bearings are shown at F2. The high speed of the turbine is thus reduced, by means of the difference in size of the respective gears, to the relatively low speed of the generator. For example, a turbine speed of 3,600 r.p.m. may be reduced to a driving shaft speed of 450 r.p.m. 10