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of the enormously high speed of this turbine is eliminated.
The governor is of the centrifugal type, although differing greatly in detail from the ordinary fly ball governor, as will be seen by reference to Fig. 149. It is connected directly to the end of the gear wheel shaft. Two weights B are pivoted on knife edges A with
hardened pins C, bearing on the spring seat D. Eis the governor body fitted in the end of the gear wheel shaft K and has seats milled for the knife edges A. It is afterwards reduced in diameter to pass inside of the weights and its outer end is threaded to receive the i djusting nut I, by means of which the tension of the spring, and through this the speed of the turbine, is adjusted. When the sp’ed accelerates, the weights,
affected by centrifugal force, tend to spread apart, and pressing on the spring seat at D push the governor pin G to the right, thus actuating the bell crank L and cutting off a part of the flow of steam.
It has been found necessary with this turbine, when running condensing, to introduce a valve termed a vacuum valve, also controlled by the governor, as it has been found that the governor valve alone is unable to hold the speed of the machine within the desired limit. The function of the vacuum valve is as follows: The governor pin G actuates the plunger H, which is screwed into the bell crank L, but without moving the plunger relative to said crank. This is on account of the spring M being stiffer than the spring N, whose function is to keep the governor valve open and the plunger H in contact with the governor pin. When a large portion of the load is suddenly thrown off, the governor opens, pushing the bell crank in the direction of the vacuum valve T.
This closes the governor valve, which is entirely shut off when the bell crank is pushed so far that the screw () barely touches the vacuum valve stem J. Should this not check the speed sufficiently, the plunger H is pushed forward in the now stationary bell crank and the vacuum valve is opened, thus allowing the air to rush into the space P in which the turbine wheel revolves, and the speed is immediately checked.
The main shaft and dynamo bearings are ring oiling. The high-speed bearings on the turbine shaft are fed by gravity from an oil reservoir, and the drip oil is collected in the base and may be filtered and used over again.
The fact that the steam is used in but a single stage or set of buckets and then allowed to pass into the
exhaust chamber might appear at first thought to be a great loss of kinetic energy, but, as has been previously stated, the static energy in the steam as it enters the nozzles is converted into kinetic energy by its passage through the divergent nozzles, and the result is a greatly increased'volume of steam leaving the nozzles at a tremendous velocity, but at a greatly reduced
pressure-practically exhaust pressure—impinging against the buckets of the turbine wheel and thus causing it to revolve.
Efficiency tests of the De Laval turbine show a high economy in steam consumption, as, for instance, a test made by Messrs. Dean and Main of Boston, Mass., on a 300 H. P. turbine, using saturated steam at about 200 lbs. pressure per sq. in. and developing 333 Brake
H. P., showed a steam consumption of 15.17 lbs. per B. H. P., and the same machine, when supplied with superheated steam and carrying a load of 352 B. H. P., consumed but 13.94 lbs. per B. H. P. These results, compare most favorably with those of the highest type of reciprocating engines.
Fig. 150 shows a cross section of a 300 H. P. De Laval wheel, showing the design necessary for withstanding the high centrifugal stress to which these wheels are subjected. All De Laval wheels are tested to withstand the centrifugal stress of twice their normal velocity without showing signs of fatigue.
The following table gives the sizes and weights of some of these turbines, together with revolutions per minute of the turbine shaft and the main shaft.