INTAKES 103 



top of each bay an adjustable iron comb catches the debris col- 

 lected by the rakes and drops it on the floor. 



Influence of Ice. In cold climates, where it is impracticable 

 to reduce the entering velocity of water to a sufficient extent to 

 allow the surface to freeze over, and where considerable quan- 

 tities of anchor or frazil ice are likely to be swept against the racks, 

 adherence to the racks may be reduced either by maintaining the 

 portion of. the racks above the water surface at a temperature 

 above freezing by housing or otherwise, or by constructing the 

 exposed portions of the racks of wood, concrete or other non- 

 conductors of heat, the portion below the water being of steel. 

 Electric heaters have been used in some cases for the purpose of 

 preventing clogging of the racks, and it has also been proposed to 

 so arrange the bars composing the rack that a low-voltage electric 

 current may be sent through them in series, thus heating them 

 sufficiently to prevent the adherence of ice. 



In order to prevent trouble from ice in the wheel casings, it is 

 essential that effective water-seals be provided in the tailrace 

 discharge to prevent the entrance of cold air. 



For further information on precautions to be taken against ice 

 troubles, the reader is refered to the N.E.L.A. Prime Mover 

 Committee's Report for 1917. 



