96 CONSTRUCTION AND MANAGEMENT OF SMALL GASWORKS. 



depended upon to pass nearly double its nominal capacity. 

 But it can only do this at a sacrifice of pressure, and we 

 have already noticed that there may be no margin for this. 

 For example, with a pressure of 20-tenths at the inlet of 

 meter, /.?., b + c= 20-tenths and ^ = 5-tenths, ^=20-5 = 

 i5-tenths. But if b is increased to 8-tenths, c falls to 

 i2-tenths, too close to the point at which incandescent 

 burners begin to flicker to be safe. 



The hourly consumption of any gas appliance can usually 

 be ascertained from the maker's list, but a little actual 

 experience with a test meter will soon put anyone in a 

 position to prepare an estimate of the maximum consump- 

 tion. It is no uncommon thing to find a geyser, cooker, 

 gas fire, and, say, six lighting burners, coupled up to a fairly 

 long f-inch service and lo-light meter. If it happens 

 that two out of the three fuel appliances are required at 

 one time, during the evening, the pressure, ^, at the 

 lighting burners is bound to fall, and they will flicker and 

 bob, to the great annoyance of the users. The most that 

 can be expected from 40 feet of f-inch service and a 

 xo-light meter, while maintaining pressure, c, at a proper 

 figure, is 80 to 90 cubic feet per hour barely sufficient 

 for the geyser alone. The following is an example of a 

 maximum consumption estimate : 



Cubic Feet 



Geyser, forty No. 2 flat- flames .... 80 



Cooker ......... 50 



Gas fire 20 



Six incandescent burners, say ..... 25 



Total . . 175 



Having arrived at this figure, a table of the quantities of 

 gas supplied through pipes of various lengths and sizes may 



