NATURAL GAS 393 



Wroup;ht iron pipos 6 inches and less in diameter are usual- 

 ly connected by collars with threaded joints. Recently the 

 joints for the larger diameters have been made of sleeves of a 

 larger diameter, between which and the pipe rubber packing 

 is forced by flanges drawn together by bolts. This variety of 

 joint is satisfactory in ever}^ way, and has a number of advan- 

 tages over the screw couplings for larger diameters. It over- 

 comes the trouble due to the expansion and contraction of the 

 pipe line without a resort to fine bends; it enables the pipe to 

 swing more or less; it adjusts itself to the inequalities of the 

 surface ; it cheapens the first cost, because no threads have to 

 be cut; it is not so easily injured in transportation, and it is 

 efficient in preventing disintegration by electrolysis in locali- 

 ties where electric roads are operated. Usually the main hne 

 pressure is reduced near the city or town line to a pressure of 

 from 20 to 50 pounds, and the gas is fed into an intermediate 

 system of pipes supplying the regulators that deliver the natu- 

 ral gas into the mains from which the consumers are supplied. 



In the cities and towns there are two methods of distri- 

 bution. The more common system is called the low pressure 

 system, and usually carries a pressure of from 3^ to 7 ounces 

 to the square inch. This system consists of a series of pipes 

 from 2 to 12 inches in diameter laid in the street at a depth of 

 from 2^- to 3 feet, the largest sizes being placed in the localities 

 of the greatest consumption. To these pipes are connected 

 the service pipes, which are usually from 1 to 1 J inches in diam- 

 eter, and lead into the consumers' houses. Between the 

 high pressure lines and the low% automatic regulators are 

 placed, adjusted by weights and diaphragms, in such a manner 

 that the pressure remains almost constant, even when more 

 or less natural gas is conveyed from the high to the low pres- 

 sure. A series of liquid seals are used in connection with most 

 of the regulators, which prevent any pressure over 16 ounces 

 on the low side from getting into the dwellings ; the Uquid seals 

 will blow out when such pressure is reached. 



Another system is that of placing a reducing valve inside 

 or near each house, this valve being connected with a smaller 

 pipe conveying a higher pressure which is reduced by an in- 

 dividual regulator to a pressure of from 4 to 6 ounces. The 



