254 COALFLKLDS AND COLL1KRIKS OK AUSTRALIA. 



strength. The tubes are expanded into the headers, and all 

 joints are kept away from exposure to the direct heat of the 

 fire. The water and steam drum is of sufficient capacity to 

 prevent any sudden fluctuation in pressure or water level. 

 At the lower end of the inclined tubes, the bottom of the 

 headers are connected by other tubes to a mud drum, which is 

 removed from the action of the fire, and which receives the im- 

 purities deposited from the water. The boiler is suspended 

 from wrought-iron girders, resting on iron columns entirely 

 independent of the brickwork. This prevents any straining 

 of the boiler from unequal expansion between it and the en- 

 closing walls, and permits the brickwork to be repaired or 

 removed, if necessary, without disturbing the boiler. The 

 combustion chamber, built round the boiler has soot doors 



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Eig. 162. Babcock and Wilcox Feed Water Heater. 



left in it, and the direction of the draught is controlled by a 

 baffle wall built across it, so the combustion of the gases has 

 a chance to be completed before coming away to the stack. 

 The products of combustion from the grate rise up between 

 the tubes into that portion of the combustion chamber below 

 the steam and water drum. They then pass onwards between 

 the tubes under the baffle wall and up between the rear end 

 of the tubes towards the flue. The tubes, which are supported 

 between their ends by fire brick distance pieces, divide the 

 water into small volumes, which are quickly raised to a high 

 temperature. The mingled steam and heated water rise up- 

 wards to the steam and water drum, where the steam separates 

 and is drawn off in a dry state at the far end of the drum. 

 The water flows to the rear and down the lower end of the 



