STEAM BOILERS 161 



level are conducive to economy in the use of a fuel is to be found 

 in the fact that with these conditions in a properly designed 

 plant there will be a fairly steady temperature in the furnace, 

 which, under normal conditions, is sufficiently high to insure 

 a thorough ignition of the volatile matter in the coal. Now, 

 with a constant demand for steam, a fluctuation in the steam 

 pressure is caused by a change in the furnace temperature, 

 assuming the feedwater supply to be constant, and whenever 

 the steam pressure is down, the furnace temperature is low at 

 the same time. In consequence of this, large quantities of the 

 volatile matter in the coal often escape unconsumed and cause 

 a serious loss of heat. Furthermore, with a steady steam pres- 

 sure the stresses on the boiler are constant, and herlce the life 

 of the boiler will be increased and repair bills will be smaller 

 than otherwise. 



Maintenance of Uniform Pressure. During the period of 

 time between the cleaning of the fires, the pressure may be car- 

 ried nearly uniform by observing the following instructions: 

 Manipulate the feed apparatus so that just the necessary 

 amount of water constantly enters the boiler and thus main- 

 tains a constant level. Intermittent feeding is practiced under 

 certain local conditions, as, for example, where there is an injec- 

 tor or a pump that is so large that it would be impossible to run 

 it continuously without increasing the height of the water level. 

 In such a case, stop feeding just before firing; that is, do not 

 feed while firing nor resume feeding until the new fire begins to 

 make steam, as indicated by the rise of pressure on the gauge. 

 If the pressure tends to rise above the standard or normal 

 pressure, partly close the dampers and increase the quantity 

 of feed, assuming in this case that no damper regulator is fitted 

 and that hence the damper is regulated by hand. A damper 

 regulator, systematic firing, and proper feeding are essential 

 for carrying a practically uniform pressure. Should the pres- 

 sure continue to rise, throw on more green fuel, close the 

 damper, increase the feed, and only as a last resort open 

 the furnace door. 



A uniform steam pressure cannot be kept without proper 

 firing. To maintain such a pressure the following directions 

 should be observed: Keep the fire uniformly thick; allow no 



