Page:The New International Encyclopædia 1st ed. v. 20.djvu/432

* WATER-WORKS. 362 WATER-WORKS. includes reservoirs, tanks, aud standpipes, and more rarely even the pumping plant. The pipe system eunsists of one or more trunk mains and numerous branches and sub-branches, continually diminishing in size. Pipes are commonly di- vided into mains and services, the former includ- ing all the pipes laid in the streets and the lat- ter the small pipes laid from the street mains to the several buildings supplied. A trunk line which simply feeds other street pipes, but no service pipes, is called a supply main. The latter term is also applied to pipe lines which convey water from a source of supply to the distributing system or to a reservoir feeding the latter. Where water is pumped through such a pipe line it is called a force main. Mains are most com- monly of cast iron. Wood is also used. Wrought- iron pipe, coated and lined with cement, ^vas ex- tensively used some years ago, but most of it has been replaced with cast iron, on account of the frequent failures which occurred. Steel pipes made from thin plates, riveted both circuuifer- entially and longitudinally, have been used for large supply and force mains since about 1800, superseding the wrought-iron pipe of an earlier date. (See Pipes.) The size of main pipes depends upon the volume and velocity of the ^vater conveyed. Cast-iron pipes range from 4 to 48 inches in diameter, with occasional sizes up to 72 inches. Steel and wood supply mains and steel force mains may be built of almost any size. Bored wood pipes are generally confined to relatively small sizes. Pipes which are to afford fire protection should never be less than four inches in diameter, and that size should be restricted- to a few' kundred feet on a short street with only one fire hydrant. In the best dis- tributing systems the area served is gridironed with pipes of liberal size, so arranged that any section may be fed from several directions and pipes in ease of lieavy local draughts for extin- guishing fires. Service-pipes are mo.st commonly of lead or wrought iron. Lead is more expensive than iron, but its flexibility, smooth interior sur- face, relative non-corrosiveness. and great dura- bility are in its favor. Its chief objection, aside from high first cost, is the ease with which it de- composes when exposed to certain waters. (See Quality, above.) Plain wrought-iron pipe cor- rodes so rapidly as to be out of the question. Galvanized, or zinc-coated, wrouglit-iron pipe is fairly durable when used for some waters, but corrodes so rapidly with others as to become al- most tilled with rust after only a few years. Among the various other methods of treating wrought-iron pipe, besides galvanizing, a japan, or baked varnish, coating has been employed of late. Wrought-iron service pipes are quite fre- quently lined with lead, tin, or cement to avoid corrosion and clogging and to give the smooth in- ner surface which is a quality of such materials. Valves are used in distributing systems to control the flow of water to and through the mains and from the mains to the house services. The latter are generally called corporalion cocks, and are set at or near the curb, with a service hox for protection and access. The usual type of valve consists of either a disk or wedge, which is lifted vertically or slid horizontallj- l)y means of a screw rovl and proper gearing. The latter. in the case of large size.?, may be worked by hydraulic pressure from the water main in which the valve is set. 'alves are also operated by electricity, particularly when it is desired to open or shut them from a distance. A free use of valves throughout a distributing sj'stem con- tributes greatly to the reliability of the water- works service and the ease of making repairs to the pipe system. Check valves close against a backward flow of water and are used on pumping mains and for the protection of meters against back pressure. Reilueing valves are automatic devices for relieving the lower levels of a city from excessive pressure where proper division into high and low service is impracticable. The Venturi principle (see Water ^Ieters) is oc- casionally profited by to reduce the cost of valves on large mains. That is to say, a 48-inch main may be gradually contracted to 30 inches, and a valve of that size placed, then the main be in- creased by degrees to its former size. A slight loss of pressure, only, will result, and where there is pressure enough and to spare a consider- able sum of money may be saved. Hydr.xts consist of a valve set at or near the curb line, on a branch pipe. A vertical tube or barrel extends from the valve to and generally above the ground Ccrp- Nozzle Closed t Barrel- yalye Bod Wedcre -Shaped 6a-fe Valve with Bronze Face --^ level, with one and more often two or more nozzles for the attachment of fire hose. Hydrants should rarely if ever be placed more than steamer Nozzle rMO feet apart, and in closel}' built busi- ness sections may need to be much closer together. Meters are self- registering devices for measuring the quantity of water supplied to a whole city, a section of it, or a single con- sumer. They aft'ord the most equitable if not the only fair nu'ans for dividing the cost of the water service between the several consumers, and are most effi- cient agents for the detection of leaks and the prevention of waste. Their con- struction and opera- tion is described in the article Water ]Ieters. They are set in the line of the service pipe, just inside the cellar or house line; or, where there is no danger of frost, at a convenient point on the house service, as bene«th the side- walk. In the latter case dial extensions are attached to the registering mechanism, so as to bring (he dial U]) wherc it may be read with ease. Waste Prevention is essential to economy of operation of a wafer- works plant. As s f:ible water supplies become more scarce and distant, the conservation of quanfity becomes almost as essential as the preservation of the purify of water. The first step in wasta prevention is good Jnlet -from Water Main-> Babbit Metal Valve Seat- BKLTIU.N THRODOH A WATER- WORKS HYDRANT.