STEAM BOILERS 153 



increases as the temperature becomes lower. Below 40 F. the 

 oil is so sluggish that it can scarcely be forced to the burners 

 by the oil pump. Consequently, in all localities where low 

 temperatures are likely to occcur, provision must be made for 

 heating oil fuel, so that it may flow readily through the pump 

 and the pipes. The flow of oil from the storage tank to the 

 pump may be facilitated by surrounding the end of the suc- 

 tion pipe with a coil through which steam is led. The oil in 

 the vicinity of the pipe is thus heated and made more fluid. 

 Oftentimes, the oil is heated after leaving the pump, to aid in 

 obtaining better operation of the burners. In any case, how- 

 ever, the heating must not be carried to a temperature suffi- 

 cient to cause decomposition. The temperature at which the 

 decomposition begins depends on the nature and source of 

 the oil. Ordinarily the oil is not heated beyond a tempera- 

 ture of about 140 F. 



Construction of Oil Tanks. The size of the boiler plant 

 will determine the character of the oil-storage tanks. For 

 plants of small or medium size, the tanks used are generally 

 cylindrical in shape, built of steel plates, and coated with a 

 protective covering of tar. For large plants, rectangular tanks 

 made of reinforced concrete are frequently used. The penetra- 

 tive properties of petroleum necessitate tight joints, and conse- 

 quently it is advisable to entrust the construction of a steel 

 tank to a boilermaker. The rivet holes should be drilled rather 

 than punched, so that the rivets will properly fill them, and the 

 seams should be calked. There should be no openings in the 

 bottom, ends, or sides of the tank; all inlets and outlets should 

 be in the top. The manhole opening should be of such size 

 as to permit ready entrance to the tank when required, and 

 reinforcing flanges of steel or wrought iron should be riveted 

 to the tank at the various openings. Concrete tanks are 

 usually made with partitions, so that deposits of sediment or 

 of viscous matter may be removed at intervals without inter- 

 fering with the continuity of the fuel supply. 



Fittings for Oil Tank. Even at ordinary temperatures, oil 

 undergoes a slow process of evaporation, during which gases 

 are evolved; consequently, every oil-storage tank should be 

 fitted with a ventilating pipe to permit the escape of the gases 



