168 APPLICATION OF STANDARDIZATION AND GRAPHICAL 



The spots indicated on the diagrams give the actual number in the case of some 

 standard designs actually worked out, and it will be noted that at various points 

 a step occurs in the curve. This step is due to the fact that when the point is 

 reached where, due to the increase in size of the boiler, it becomes possible to add 

 another horizontal row of tubes, the number of tubes is increased somewhat rapidly. 



As regards the length of the tubes, this is of course dependent upon the length 

 of the boiler, depth of combustion chamber, and depth of water space back of the 

 combustion chamber. 



It would appear that by definitely settling upon certain desired characteristics 

 of boilers, i. e., the ratio of heating to grate surface and the ratio of area through 

 tubes to grate surface, the lengths of a complete series of boilers could be kept 

 down to very few different dimensions, which would result in the possibility of 

 keeping the tubes of certain standard lengths, possibly only three or four lengths 

 being required, which would enable both the manufacturers and boiler-makers to 

 keep stocks of tubes for ready use. 



It would also have the further advantage that the lengths of furnace could be 

 kept standard, and there is no reason why these should not be made to standard 

 dimensions throughout, which again would make possible the standardization of fur- 

 nace fittings. 



Anyone familiar with repair-shop practice knows that unless each vessel is pro- 

 vided with patterns for the side bars for each furnace, whenever it becomes neces- 

 sary to renew same, new patterns have to be made and fitted to each furnace, which 

 in itself constitutes a serious economic waste. 



Lastly, the boilermaker would be benefited by the fact that all longitudinal stays 

 could be made of standard dimensions. 



COMBUSTION CHAMBERS. 



The depth of combustion chambers used in connection with these diagrams has 

 been plotted on Plate 57. The proportions given are quite sufficient for coal burning 

 and generally should be sufficient when burning oil, although some designers prefer to 

 use a greater depth in the latter case. 



It should be kept in mind that the dimensions given are inside dimensions, and 

 the actual depth used should be stated in even inches, which will somewhat simplify 

 the calculations for allowable pressures on plates, stays and girders, etc. 



HEATING AND GRATE SURFACE. 



Based upon the dimensions for furnaces and combustion chambers given by 

 Plate 57 and upon the number of tubes given by Plate 58, the diagrams for heating 

 surface, grate surface and area through tubes have been constructed. 



By reference to Plates 59, 60 and 61 it is possible to quickly estimate how much 

 heating surface may be expected from a boiler of certain dimensions or, knowing 

 the heating surface required, what size boiler is needed. In this connection the 



