Pipes and Governors. Gas piping is so closely allied to plumbing, since iron pipe has come into general use, that a brief notice of this branch is not out of place in connection with matters pertaining to plumbing. Coal gas is only about one-half the specific weight of air. The weight of natural gas is somewhat less than that of coal gas. The distribution of pressures which prevails in a closed system - the pressure of the fluid due to applied pressure being equal at every point - should not be lost sight of in considering the ordinary method of distributing gas over a city or through a building in closed pipes.

Pressures. The most economical pressure at which to consume gas is five-tenths of an inch water pressure. As no town is strictly level, and the friction of the pipe requires some head of pressure to overcome it, the pressure in the mains is necessarily carried above the point at which the best results are obtained. This is generally counteracted by not turning on the full amount at the burner. In towns varying greatly in the level of different portions, it is economy to use automatic governors to control the pressure of the gas in the mains to different levels. This is also true of exceedingly tall buildings in cities whose areas maintain about the same level. One governor for a modern office building is not enough unless the building stands at a low level, in which case the supply to the upper floors may be controlled by one governor situated on one of the upper floors, say midway between the top floor and the average street level.

Gas Meters. Large pipe should not be notched into joists in the middle; it weakens the joists. All pipes should be laid with a decline, toward the meter when possible, otherwise in such a way that they will drain toward a fixture or drip. The meter should be placed in a position easily accessible, and where it may be read without the use of an artificial light. It is connected in the house main on the street side of the first branch. A dry meter - the kind now almost universally employed - is, shown in Fig. 99.

Fig. 99. "Dry" Gas Meter..

Different meters vary but little in the arrangement of the dials. In large meters, there are as many as five or more dials; but those used for dwelling houses usually have but three. Fig. 100 shows the common form of index in a dry meter. The small index hand D, on the upper dial, is not taken into consideration when reading the meter, but is used merely for testing. The three dials, which record the consumption of gas, are marked A, B, and C; and in each, a complete revolution of the index hand denotes 1,000,10,000, and 100,000 cubic feet, respectively. The index hands do not move in the same direction. When the hands are pointing upward, A and C move from left to right, while B moves in the opposite direction, Annex two cyphers at the right of the figures indicated when taking the statement of a meter. The left-hand index shown in Fig 100 reads 48,700. Suppose, after being used for a time, the hands should have the positions shown in the right-hand dial. This would read G4,900; and the amount of gas used during the interval would equal the difference in the readings: 64,900 - 48,700 = 16,200 cubic feet. Meters so invariably register in favor of the consumer after being in use only a few weeks, that the companies are by law permitted to set them 3 per cent fast when new. The route chosen for gas pipes should be the warmest consistent with convenience and economy. Coal gas will freeze - that is, the moisture in it will, in severe weather, form a network of frost that checks or stops the flow. Coal gas and natural gas are practically fixed. There is little trouble from condensation, even from coal gas, after it reaches the residence. There is sufficient reason, however, to incline the pipe and to avoid trapping any portion so that it will not drain. If a pipe runs through a cold place, a drip should be put in at some convenient point where it can be emptied if necessary. No offsets should be made in a way to favor choking the pipe by the products of corrosion falling down vertical parts. No fixture or bracket opening should be less than 3/8-inch; no rising main less than 3/4-inch, All openings for fixtures should have straight threads, and the pipe or fittings should be well secured, perpendicular to the wall passed through, so that they will not wobble, push in, or pull out. Ceiling drops should be cemented in the joint at the line, so that they will not unscrew when the cap is removed or a fixture taken down.

Fig. 100. Common Form of Index on "Dry" Gas Meter. Two Readings are Shown..

The making of intelligent working diagrams for gas or water fitting, is not difficult. Though important, comparatively few have given it due attention. When plans are accurate, the usual work of making figures to show what length the pipes are, may be dispensed with by employing self-measuring ruled sheets in conjunction with the method of diagramming here described. Diagramming systematically and with all lines approximately proportional in length, saves time in distributing the pipe. There is no wondering whether a piece runs down or up, or as to which room a bracket light looks into, or whether a piece of pipe belongs in a horizontal or in a vertical position. A properly made diagram indicates these points clearly, and also what pieces belong in the same plane. There should never be any confusion as to which pieces have been cut and which not, when getting out the pipe. Symbols can be made to show what pieces have been cut and what size they are. The symbols found by practice to answer this purpose best, are as follows: When a 1/4-inch piece is cut, a common check mark is put beside the line on the diagram, showing that it is 1/4 inch and has been cut. For a 3/8-inch piece, a short, straight mark like the letter I, placed across the line, is used. For a 1/2-inch piece, two connected marks like V are made across the line. For 3/4-inch pieces, three connected marks, like the capital N, are made across the line. For 1-inch pieces, four connected marks, like the capital letter M, are used across the line. For 1 1/4-inch pieces, five connected marks, like the capital W with one extra leg, are used. Each short, straight mark represents a quarter-inch in the diameter of the pipe, except in the case of 3/8-inch pipe. For nipples that are too short to put the symbols on, draw a waved arrow from the nipple, and put the symbol upon it. Fig. 101 shows the symbols described, with corresponding sizes of pipe marked beneath them.