56 CONSTRUCTION AND MANAGEMENT OF SMALL GASWORKS. 



seven-eighths of the district under an excessive pressure, to 

 ensure that the remaining one-eighth gets a sufficient supply, 

 3r to keep the whole district under full evening pressure for 

 the benefit of one consumer who uses the gas throughout 

 the night. It may mean more pipe, but an extra half mile 

 or so of pipe is well spent if it saves an excessive pressure 

 over the bulk of the district 



Admitting the full necessity for having pipes large 

 enough, there is no sense in waste, and it is not good 

 engineering to put down a 6-inch pipe where a 4-inch will 

 answer every purpose. The conditions of supply in an 

 average district lead up to a very complicated problem that 

 can only be treated very superficially. In theory, the 

 governor outlet pressure was supposed to represent that 

 obtaining all over the district, and possibly it did so when 

 the number of consumers was small and the requirement 

 per head much lower than at present. The actual pressure 

 at the inlet of a consumer's meter will be the governor 

 pressure, less a variable quantity represented by the force 

 required to drive the gas from the works to the point of 

 consumption. When the demand is small, the difference 

 is negligible, but as the demand becomes large in propor- 

 tion to the size of the pipe, a point is reached at which the 

 driving pressure increases by leaps and bounds. In theory, 

 also, the governor at the works is a machine by which the 

 pressure can be regulated in proportion to the consumption. 

 When the demand increased, more pressure was put on, 

 which, in effect, was a rough and ready way of providing 

 more driving pressure. So long as gas was required for 

 lighting only, it was possible to keep in touch with the con 

 sumption in this manner. It is also possible to provide for 

 other periodical requirements, and there are few gasworks 

 that do not consider, in addition to the evening demand, 



