106 



STEAM BOILERS 



moved to and fro by an eccentric on the shaft s, so as 

 rock the grates back and forth; the grates thus gradually 

 move the burning fuel downwards. The ashes and clinkers 

 are discharged from the lower grate bar on to the dumping 

 grate e. A guard / may be raised, as shown by the dotted 

 lines, so as to prevent coke or coal from falling from the grate 

 bars into the ash-pit when the dumping grate is lowered. Air 

 for burning the gases is admitted in small jets through holes in 

 the air tile g, and the mixture of gas and air is burned in the 





FIG. 



hot chamber between the firebrick arch h and the bed of burning 

 coke below. 



Underfeed Stoker. The stoker shown in Fig. f> illustrates 

 the principle of operation and the construction of the under- 

 feed stoker. Coal is fed into the hopper a, from which it is 

 drawn by the spiral conveyer b and forced into the magazine d. 

 The incoming supply of fresh coal forces the fuel upwards to the 

 surface and over the sides of the magazine on the grates, where 

 it is burned. A blower forces air through a pipe / into the 



