238 



HYDRAULIC EQUIPMENT 



As compared to plate steel, cast-iron casings have certain ad- 

 vantages, such as the lack of rigidity of the plate steel, its danger of 

 local weaknesses at the riveted joints, possibility of corrosion and 

 leakage developing undetected, especially corrosion on the outside 

 surface. Cast casings have, furthermore, the advantage that 

 they may be tested in the shops to a hydrostatic pressure well in 

 excess of that which they can ever be subjected to after installa- 



FIG. 129. Wooden Forms for Concrete Turbine Casings. 



tion. On account of their strength and rigidity, they can also 

 serve as an excellent bed plate for the entire unit. 



For low heads, and especially with large turbines, the casings 

 are usually molded in the concrete foundations of the power-house 

 by means of wooden forms (Fig. 129). If the casings are large 

 enough and the head high enough to produce serious stresses in 

 the concrete, they may be made of metal and imbedded in the 

 concrete. The principal controlling factor in this case is 'the 

 relative cost of such casings as compared with the cost of adequate 

 reinforcing steel for the concrete, which would be required if the 

 metal lining were omitted. 



