THE BOILER 



fuel, such as pine kindling wood is used, very little should 

 be allowed in the fire-box, and the fire carefully watched. 

 Enough dirt, sand or ashes should be at hand to check 

 the fire at any instant. The pressure must be closely 

 watched, and if it shows a tendency to rise too rapidly, 

 or go too high, the fire must be covered. The pop-valve 

 will open at the point at which it is set, in the same way as 

 for steam pressure. 



Amount of Pressure. It is not advisable to test an 

 old boiler which was designed to carry one hundred and 

 thirty pounds or less at a greater pressure than one hun- 

 dred and fifty pounds, as higher pressures are apt to 

 strain and weaken the boiler. When a boiler has been 

 tested at one hundred and fifty pounds cold water pressure, 

 it may be used at a working pressure of one hundred and 

 twenty-five pounds. It has been common to make the 

 pressure for the hydraulic test greater than the desired 

 working pressure by fifty per cent., but many engineers 

 now believe that this strains a boiler unnecessarily and 

 consequently such high test pressures are not recom- 

 mended except where required by law. 



Sweating. Inexperienced operators in starting a fire 

 in a new boiler are sometimes deceived by the appearance 

 of moisture on the tube-sheets which they take to be leak- 

 age. However, this is nothing but the moisture in the 

 gases passing through the tubes collecting on the cold 



