524 HYDRAULICS AND ITS APPLICATIONS 



is impracticable the turbine must be mounted in a closed casing, and be 

 supplied through a pipe line. The provision of a stand pipe is here out 

 of the question, inertia effects being guarded against by the provision of a 

 relief valve placed near the turbine casing. A sudden demand for water 

 is met by the accelerating effect of the suction tube, and under these 

 circumstances it is possible to get fairly accurate governing. 



Where a stand pipe is adopted in any plant with a view to preventing 

 inertia effects, the freezing of the water which is spilt over the top of the 

 pipe may prove detrimental to the working of the plant. To avoid this it 

 becomes preferable to use the stand pipe in connection with a pressure 

 regulator or relief valve, the latter taking charge of any rise in pressure, 

 and venting the supply pipe, while the sole function of the stand pipe is 

 to take charge of any fall in pressure on an increasing load. 



Effect of Gates and Governor Connections. Whatever the type of plant, a 

 well-designed system of gates and gate connections is essential for close 

 speed regulation. 



In all connections simplicity, directness, and freedom from backlash are 

 essential, while close regulation is not to be expected from any multiply- 

 ing gear which needs several turns of a worm or spur wheel to close the 

 turbine gates. 



The gates themselves should be as light, well balanced, and frictionless 

 as possible. Of the two types of gate in common use, viz., the sliding 

 cylinder gate and that consisting of a system of pivoted guide vanes, the 

 latter conforms most nearly to these requirements. To give good results 

 these guides should be pivoted near their centres, so as to be approxi- 

 mately in balance under the action of the supply water. If this condition 

 is not satisfied, a large force is required to cause motion, while the gate 

 connections need to be of massive proportions, and the consequent large 

 weight and inertia of these connections makes quick regulation difficult o 

 attainment. 



In the enclosed Thomson turbine, and in enclosed turbines of tl 

 Francis type fitted with this type of guide, the guide spindles are passe 

 through stuffing- boxes in the turbine casing, and the whole governin 

 mechanism, with the exception of the guides and their pivot bearings, 

 removed from the action of the water. In the American type of mixe 

 flow turbine, when fitted with pivoted guides, these are usually rotate 

 either by means of an annular gear wheel, which gears with pinion 

 mounted on the guide- spindles, and which is rotated by means of a lin 

 coupled to an eccentric which receives its own motion from the rela 

 mechanism, or a series of links mounted on the guide spindles ai 



