The blading is made up and inserted in half rings, and Fig. [30] shows two rings of different sizes ready to be put in place. Fig. [31] shows a number of rows of blading inserted in the cylinder of an Allis-Chalmers steam turbine, and Fig. [32] gives view of blading in the same turbine after nearly three years' running.
The Governor
Next in importance to the difference in blading and balance piston construction, is the governing mechanism used with these machines. This follows the well-known Hartung type, which has been brought into prominence, heretofore largely in connection with hydraulic turbines; and the governor, driven directly from the turbine shaft by means of cut gears working in an oil bath, is required to operate the small, balanced oil relay-valve only, while the two steam valves, main and by-pass (or overload), are controlled by an oil pressure of about 20 pounds per square inch, acting upon a piston of suitable size. In view of the fact that a turbine by-pass valve opens only when the unit is required to develop overload, or the vacuum fails, a good feature of this governing mechanism is that the valve referred to can be kept constantly in motion, thereby preventing sticking in an emergency, even though it be actually called into action only at long intervals. Another feature of importance is that the oil supply to the bearings, as well as that to the governor, can be interconnected so that the governor will automatically shut off the steam if the oil supply fails and endangers the bearings. This mechanism is also so proportioned that, while responding quickly to variations in load, its sensitiveness is kept within such bounds as to secure the best results in the parallel operation of alternators. The governor can be adjusted for speed while the turbine is in operation, thereby facilitating the synchronizing of alternators and dividing the load as may be desired.
In order to provide for any possible accidental derangement of the main governing mechanism, an entirely separate safety or over-speed governor is furnished. This governor is driven directly by the turbine shaft without the intervention of gearing, and is so arranged and adjusted that, if the turbine should reach a predetermined speed above that for which the main governor is set, the safety governor will come into action and trip a valve which entirely shuts off the steam supply, bringing the turbine to a stop.