When the turbine is required to exhaust against a back pressure of one or two pounds a slightly different arrangement of piping must be made. The water in this case must be allowed to circulate through the glands in order to keep the temperature below 212 degrees Fahrenheit. If this is not done the water in the glands will absorb heat from the main castings of the machine and will evaporate. This evaporation will make the glands appear as though they were leaking badly. In reality it is nothing more than the water in the glands boiling, but it is nevertheless equally objectionable. This may be overcome by the arrangement shown in Fig. [49], where two connections and valves are furnished at M and N, which drain away to any suitable tank or sewer. These valves are open just enough to keep sufficient circulation so that there is no evaporation going on, which is evidenced by steam coming out as though the glands were leaking. These circulating valves may be used with any of the arrangements above described.
FIG. 49
The Governor
On the right-hand end of the main shaft in Fig. [34] there will be seen a worm gear driving the governor. This is shown on a larger scale at A (Fig. [50]). At the left of the worm gear is a bevel gear driving the spindle D of the governor, and at the right an eccentric which gives a vibratory motion to the lever F. The crank C upon the end of the shaft operates the oil pump. The speed of the turbine is controlled by admitting the steam in puffs of greater or less duration according to the load. The lever F, having its fulcrum in the collar surrounding the shaft, operates with each vibration of the eccentric the pilot valve. The valve is explained in detail later.
FIG. 50
This form of governor has been superseded by an improved type, but so many have been made that it will be well to describe its construction and adjustment. The two balls W W (Fig. [50]) are mounted on the ends of bell cranks N, which rest on knife edges. The other end of the bell cranks carry rollers upon which rest a plate P, which serves as a support for the governor spring S. They are also attached by links to a yoke and sleeve E which acts as a fulcrum for the lever F. The governor is regulated by means of the spring S resting on the plate P and compressed by a large nut G on the upper end of the governor spindle, which nut turns on a threaded quill J, held in place by the nut H on the end of the governor spindle and is held tight by the lock-nut K. To change the compression of the spring and thereby the speed of the turbine the lock-nut must first be loosened and the hand-nut raised to lower the speed or lowered to raise the speed as the case may be. This operation may be accomplished while the machine is either running or at rest.