SPEED REGULATION OF TURBINES 



525 



connected by levers to a central ring, which is rotated by means of the 

 relay. In either case the gearing is usually placed inside the casing, and 

 while accurate speed regulation is possible with either design, the 

 submerged gearing needs to be designed on more substantial lines to 

 compensate for its inaccessibility for examination. 



Sliding cylinder gates are commonly moved through a couple of parallel 

 drawbars terminating in racks, which gear with pinions on a shaft 

 perpendicular to the wheel axis, this latter shaft deriving its motion from 

 the relay mechanism by one or other of the devices shown in Figs. 228, 

 234A, and 249. Where this type of gate is fitted to a vertical shaft 

 machine, it often becomes advisable to balance the weight of the gate and 



Fia. 251. Direct Relay Governing Mechanism for Sliding Cylinder Gate. 



its drawbars by means of a counterbalance weight, in which case a suit- 

 able type of connection is shown in Fig. 251. 



For successful governing, the gate should consist of a plain cylinder. 

 If provided with fingers, as indicated by the dotted lines in Fig. 230, the 

 water pressure on the upper side of these is largely in excess of that on 

 their lower face. This necessitates a very heavy counterbalance weight, 

 possessing considerable inertia, and increases the force necessary to start 

 and stop the motion of the gate, while the weight and cost of the connect- 

 ing links necessary to withstand the stress become excessive. Without 

 the balance weight the steady resistance produced by the unbalanced 

 pressure produces an excessive stress on the gate connections. In either 

 case the very slight addition to part-gate efficiency is totally insufficient 

 to compensate for the increased difficulty in governing. 



