140 STEAM BOILERS 



Heaters of the open exhaust-steam type have the advantage 

 of bringing the exhaust steam in direct contact with the feed- 

 water; some of the exhaust steam is condensed, thus effecting 

 a saving in feedwater, and sediment and scale-forming ingre- 

 dients, except sulphates of lime and magnesia, are precipitated 

 or will settle to the bottom of the heater. The oil in the 

 exhaust steam must be intercepted by special oil extractors, 

 filters, or skimmers, generally combined with the heater and, by 

 automatic regulation, sufficient fresh feedwater must be added 

 to make up the total quantity required. When the system is 

 properly arranged, all live-steam drips and discharges from 

 traps are led to the heater. 



BOILER TRIALS 



Purposes of Boiler Trials. A boiler trial, or boiler test, 

 as it is often called, may be made for one or more of several 

 purposes, the method of conducting the trial depending largely 

 on its purpose. The boiler trial may vary from the simplest 

 one, in which the only observations are the fuel burned and the 

 water fed to the boiler in a stated period of time, to the elabo- 

 rate standard boiler trial, in which special apparatus and sev- 

 eral skilled observers are essential. The object of a boiler 

 trial may be to determine the efficiency of the boiler under 

 given conditions; the comparative value of different boilers 

 working under the same conditions; the comparative value of 

 fuel; or the evaporative power, or horsepower, of the boiler. 



Observations During Trial. The essential operations of a 

 boiler trial are the weighing of the feedwater and fuel, and 

 the observations of the steam pressure, temperature of feed- 

 water, and various other less important pressures and tempera- 

 tures. In conducting a boiler trial, the various observations 

 of temperatures, pressures, etc. should be made simultaneously 

 at intervals of about 15 min. 



Weighing the Coal. The coal supplied to the furnace is 

 weighed out in lots of 500 or 600 Ib. It is a convenient plan 

 to have a box with one side open placed on a platform scale. 

 A weight is then placed on the scale beam sufficient to balance 

 the box. The scale may then be set at 500 or 600 Ib., the coal 



