REGULATION OF TURBINES 517 



also to overcome the pipe resistance, with the result that the possible 

 acceleration of the supply column is reduced. . 



Next consider the action of the governor. In reply to a demand for 

 energy, denoted by a reduction in the speed of rotation, the governor 

 attempts to open the turbine gates. These may be very massive, possess- 

 ing considerable inertia, and may in addition, through working submerged 

 in water containing solid matter in suspension, offer considerable frictional 

 resistance to rotation. 



The governor itself is thus quite incapable of giving the required motion, 

 and some form of relay becomes necessary. A device which was often 

 adopted in the earlier days, but which is now practically obsolete, con- 

 sisted in a system of fast and loose pulleys, mounted on one shaft and 

 driven from a countershaft by means of two belts, one open and the other 

 crossed. 



The position of these belts, one of which is always riding on the loose 

 pulley, is regulated by the governor, and as in consequence the open or 

 crossed belt comes to ride on one of the fixed pulleys, the direction of 

 rotation of this shaft changes. Its rotation causes the turbine gates to 

 open or close and thus regulates the speed of the wheel. 



Two types of a more modern mechanical relay device are shown in 

 Figs. 228 and 247. In the latter, 1 a double ratchet is worked by a link, 

 as shown, from a lay shaft belt-driven from the turbine shaft. A ratchet 

 wheel, which is mounted on a second lay shaft by which the turbine gate 

 is directly operated, is wholly or partially masked by a plate whose position 

 depends on the height of the governor. Thus, under normal conditions 

 of working, the plate covers the wheel so as to put both pawls out of gear. 

 Any increase in speed then raises the governor, rotates the guard plate, 

 and allows one pawl to gear with the ratchet wheel, rotating the lay shaft 

 and closing the turbine gates. A decrease in speed causes the second 

 pawl to be put into gear, and thus produces an opposite rotation of the 

 lay shaft and an opening of the gates. 



With any such type of mechanical device, however, some considerable 

 time is required to open a sluice gate, and while for such a purpose 

 as driving textile machinery, where the changes of load are relatively 

 small, this type fulfils the requirements, yet for electric driving for 

 lighting and power transmission, where a constant speed is required with 

 very large and sudden variations in load, the mechanical relay, except 

 in combination with a large and costly flywheel, is unsatisfactory. 



In such a case the hydraulic relay provides the only satisfactory 

 1 By courtesy of Messrs. Gilbert Gilkes & Co., Ltd., Kendal. 



