434 ELECTRICAL EQUIPMENT 



give trouble due to the pipe coils being clogged up or destroyed in 

 three ways: 



1st. Corrosion due to air in the water. 



2d. Corrosion due to acids or alkali in the water. 



3d. Deposit of solid matter from the water. 



The special grade of iron used in the manufacture of cooling 

 coils offers much greater resistance to corrosion than ordinary 

 steel does. On this account, it is only under exceptionally severe 

 conditions that it is economical to take the extra precaution of 

 using copper coils; brass being considered inferior to copper. 



Iron coils will not be noticeably corroded by the air ordinarily 

 held in suspension in the water. If the cooling water is taken from 

 a supply of shallow or rapidly moving water, such water is likely to 

 contain an abnormal amount of ah- which will rapidly attack the 

 inner surface of the cooling coil. When it is suspected that the 

 water contains acid or alkali it should be analyzed arid the results 

 referred to the experts for advice. A one-gallon sample is neces- 

 sary for a proper analysis. 



When there is an excessive quantity of alkali or earth salts in 

 solution, the heating of the water will cause a deposit of this salt 

 previously in solution. Such an action will, of course, take place 

 regardless of the material of the cooling coil and can be best 

 guarded against by operating with a rapid flow of water with its 

 resulting low temperature and flushing action. When the water 

 has much suspended solid matter, that is, if it is muddy, it should 

 be filtered, or in less severe cases protection could be obtained by a 

 rapid flow of water. The deposit of such solids in the water will 

 become more rapid as the surface is roughened by deposit or cor- 

 rosion, due to the increased resistance in the path of the outer 

 portion of the column of water. 



Wrought-iron cooling pipe is ordinarily made of extra heavy 

 lap-welded inch or inch and one-half pipe, withstanding a test 

 pressure of 1000 pounds per square inch. Copper coils, on the 

 other hand, are mostly designed to withstand a test pressure of 

 250 pounds per square inch and are. therefore, not as desirable as 

 iron coils from a mechanical standpoint. 



The coils, which may be constructed in single or multiple 

 layers, are placed inside the upper part of the tank and are usually 

 bolted to the same By means of a three-way valve at the inlet 



