Steam turbines; a practical and theoretical treatise for engineers and students, including a discussion of the gas turbine . s which are operated automatically in emer-gencies. The device shown in Fig. 121 consists of a steel ring(13) placed around the shaft between the turbine and the gener-ator. This ring, which is held in place by stud bolts (4), isplaced in a slightly eccentric position, and the centrifugal forcedue to this unbalancing is counteracted by a helical spring (n). COMMERCIAL TYPES 239 When the speed increases, the centrifugal effort overcomes thespring and the ring moves into a
Steam turbines; a practical and theoretical treatise for engineers and students, including a discussion of the gas turbine . s which are operated automatically in emer-gencies. The device shown in Fig. 121 consists of a steel ring(13) placed around the shaft between the turbine and the gener-ator. This ring, which is held in place by stud bolts (4), isplaced in a slightly eccentric position, and the centrifugal forcedue to this unbalancing is counteracted by a helical spring (n). COMMERCIAL TYPES 239 When the speed increases, the centrifugal effort overcomes thespring and the ring moves into a still more eccentric position asindicated by the dotted lines. In this position the ring strikes abell-crank lever, which trips, by means of a simple auxiliarymechanism and the tension rod L (Fig. 122), the throttle valveon the main steam supply pipe. The rod L is connected to thecrank D, which operates to release the spring S, pulling up thegear and throwing out the hook G, which holds the valve released by this emergency ring mechanism, the valvedescends upon its seat with a very positive motion due to its. Fig. 123. Details of Spring Type of Emergency Stop. own weight and the unbalanced pressure on the area of thevalve stem. Fig. 123 shows a little different arrangement for tripping thevalve. The free end of a spiral spring is thrown out by centrifu-gal force and strikes a bell-crank lever in very much the sameway as the ring does. The emergency valve is opened by meansof the hand wheel shown at the bottom of the figure. No turbine should be kept in operation unless it is known thatthis speed limiting device is in reliable condition. Governor. Curtis turbines are governed by a method com-monly known as cutting out nozzles. By this method the 240 THE STEAM TURBINE number of nozzles which are open for the discharge of steam isregulated according to the requirements of the load. This methodis described and typical Curtis governors and valve gears areillustrated in Ch
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