124 STEAM BOILERS 



Rule II. For tubular boilers, either horizontal or vertical, 

 multiply the product of the square of the diameter in feet and 

 the length in feet by 1.9. 



Rule in. For water-tube boilers, multiply the heating sur- 

 face in square feet by .4- 



Rule IV. For boilers not covered by the foregoing rules, 

 multiply the grate surface in square feet by 12. 



Rule V. // the coal consumption in pounds per hour is 

 known, it may be taken as representing the number of gallons 

 evaporated per hour. 



No standard method of designating the size of an injector is 

 followed by all makers; therefore, such an instrument must be 

 selected from the lists of capacities published by the different 

 makers. 



Location of Injector. An injector must always be placed in 

 the position recommended by the maker. There must always 

 be a stop-valve in the steam-supply pipe to the injector. 

 While lifting injectors, when working as such, scarcely need a 

 stop-valve in the suction pipe, it is advisable to supply it. 

 When the water flows to the injector under pressure, a stop- 

 valve in the water-supply pipe is a necessity. A stop-valve 

 and a check-valve must be placed in the feed-delivery pipe, 

 with the stop-valve next to the boiler. The check-valve 

 should never be omitted, even if the injector itself is supplied 

 with one. No valve should ever be placed in the overflow 

 pipe, nor should the overflow be connected directly to the 

 overflow pipe, but a funnel should be placed on the latter so 

 that the water can be seen. This direction does not apply to 

 the inspirator or to any other injector that has a hand-operated, 

 separate overflow valve. In the inspirator, the overflow pipe 

 is connected directly to the overflow, but the end of the pipe 

 must be open to the air. In general, where the injector lifts 

 water it is not advisable to have a foot-valve in the suction 

 pipe, as it is desirable that the injector and pipe may drain 

 themselves when not in use. A strainer should be placed on 

 the end of the suction pipe. 



Steam Supply to Injector. The steam for the injector must 

 be taken from the highest part of the boiler, as it must be 

 sup'plied with dry steam. Under no consideration should the 



