MOTIVE POWER IN MANUFACTORIES 91 



The buckets, framed by the shrouding, should be curved or elbowed and not radial. They should 

 have a capacity three times as large as the volume of water actually carried, a depth of 10 inches to 

 12 inches and a distance apart, from center to center, of 12 inches. 



Ventilated buckets, having holes in the bottom and allowing air to escape, have an increased effect. 



It is difficult to transform the slow speed of an overshot into the rapid speed required for a circular 

 saw. Transformation is either by countershaft or by cog wheel. 



II. The breast wheel has an effective power of from 45 to 65 per cent, is best applied to falls of from 

 5 feet to 15 feet and to a discharge of from 5 to 80 cubic feet per second. While in the overshot the water 

 works by weight only, it works in the breast wheel largely by impact. 



The velocity of wheel should he such as to fill the buckets to 0'5 or 0'6 of their volume. The buckets 

 here are usually called blades and must be ventilated. 



The wheel runs in a curb or mantle, formed by the inclined and incased end of the sluiceway. 



The distance of the blades, from center to center, should equal the depth of the shrouding, both being 

 from 10 inches to 15 inches. The clearance between the curb and the shrouding must be at least \., inch. 



"High breast" wheels are semi-overshot and "low breast" wheels are semi-undershot wheels. 



The "flutter" wheel is a low breast wheel of small diameter and high speed. It is largely used in 

 the Appalachians for sawmill purposes where water is plentiful and fall about 20 feet. 



III. Undershot or current wheels have an efficiency of from 27 to 45 per cent only and are usually kept 

 anchored in rapid streams, so as to be independent of the water gauge. There are no buckets, but long 

 blades instead. 



The diameter of the wheel is from 13 feet to \6\oieei; there are usually 12 blades, the depth of 

 which is 3 feet to 4 feet. The blades should be completely submerged when passing underneath the axle. 



IV. Turbines have an efficiency of 60 to 80 per cent. Usually the water does not work so much by 

 weight, as by impact, pressure, reaction and suction. 



The speed in turbines is much higher than in vertical wheels; it is well adapted for circular sawmills. 



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 pressing from above; 



(c) Inward flow turbines, water fed from the perimeter; 



(d) Reaction turbines, working after the principle of a lawn sprinkler; 



(e) Impulse turbines, principle of flutter wheels. 



Modern turbines are worked both by impact and reaction and, if possible, by suction. 



The advantages of watermills are: -No fuel, no fireman, no engineer, no explosion, less insurance, 

 possibility of using dust and slabs commercially, &c. 



The disadvantages are: -Usually small power, small speed, and small capacity; power less controllable 

 and less reliable than steam-power, and not portable. 



The small capacity of a watermill does not justify a large outlay for good sawmill machinery. 



(D) STEAM. 



I. Boilers. Tubular boilers are universally used. Diameter of tubes is measured outside, including metal. 



(a) Boilers in common use are designated as:- 



1. Internally fired boilers, when firebox and waterbox are comprised by one and the same steel 

 shell; so all portable boilers and all locomotive boilers. Common forms are the Cornish, the 

 Lancashire, and the Galloway. In the locomotive boiler, the firebox is surrounded by a waterleg. 



