FOREST UTILIZATION 43 



The diameter of the wheel is from 13 feet to i6j^ feet; 

 usually 12 blades, the depth of which is 3 feet to 4 feet. 

 The blades should be completely submerged when pass- 

 ing underneath the axle. 



IV. Turbines have an efficiency of 60% to 80%. The water 

 does not work by weight, but by impact, pressure, reac- 

 tion and suction. 

 The speed is much higher than in vertical wheels and hence 



is well adapted for circular saw mills. 



A turbine, however, is badly affected by variations of water 

 supply and suffers from debris and sand and ice. The 

 effect of the water is greatest when the turbine is 

 entirely under water, the flow of water filling the curved 

 channel completely. 

 Turbines are : 



(a) Outward flow turbines, water fed from near 



the center. 



(b) Downward flow turbines, water fed and press- 



ing from above. 



(c) Inward flow turbines, water fed from the perim- 



eter. 



(d) Reaction turbines, working after the principle 



of a lawn sprinkler. 



(e) Impulse turbines, principle of flutter wheels. 



Modern turbines are worked both by im- 

 pact and reaction and, if possible, by suc- 

 tion. 



A g-inch turbine, furnishing 14 horsepower, 

 costs $250, plus $100 for setting it in 

 masonry. 



The advantages of water mills are : no fuel, no fireman, no 

 engineer, no explosion, less insurance, possibility of 

 using dust and slabs for stable bedding, laths etc. 

 Disadvantages are: usually small power, small speed and 

 small capacity. Power less controllable, less reliable 

 than steam power and not portable. 



Small capacity does not justify a large outlay for good saw- 

 mill machinery. 

 D. Steam mills. 



For circular saws, the number of horsepower required is 

 about = 1/3 the diameter of the saw. For example, a 4&- 

 inch circular saw requires 16 horsepower. Ten horsepower 

 are said to manufacture 5,000 b. feet daily in circular saw- 

 mills, and 30 horsepower will cut 30,000 b. feet daily. Every 

 additional horsepower should increase the capacity by 1,000 

 b. feet. 



In large mills each horsepower ought to manufacture 1,000 b. 

 feet ; in small mills only 500 b. feet. 



