This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
All large risers should be exposed, and it is desirable to keep all piping accessible as far as possible so that it may be easily reached for repairs. All horizontal pipes should be run with an even though slight grade toward the riser, and all sags in the pipes must be avoided to prevent the collection of water, and for this reason they should be well supported. Floor boards over all horizontal pipes should be fastened down with screws so that they may be removed for inspection of the pipes. When it becomes necessary to trap a pipe, a drip with a drain cock must be put in, but this should always be avoided under floors or in other inaccessible places. When pipes under floors run across the timbers, the latter should be cut into near the ends, or where supported upon partitions, in order to avoid weakening the timbers. All branch outlet pipes should be taken from the side or top of the running lines, and bracket pipes should be run up from below instead of dropping from above. Never drop a center pipe from the bottom of a running line; always take such an outlet from the side of the pipe. Where possible it is better to carry up a main riser near the center of the building, as the distributing pipes will be smaller than if carried up at one end. Where this is done the timbers will not require so much cutting, and the flow of gas will be more uniform throughout the system.
When a building has different heights of post it is always better to have an independent riser for each height rather than to drop a system of piping from a higher to a lower post and grading to a lower point and establishing drip pipes. Drips in a building should be avoided if possible and the whole system of piping be so arranged that any condensed gas will flow back through the system and into the service pipe. All outlet pipes should be securely fastened in position, so that there will be no possibility of their moving when the fixtures are attached. Center pipes should rest on a solid support fastened to the floor timbers near the top. The pipe should be securely fastened to the support to prevent movement side wise. The drop must be perfectly plumb and pass through a guide fastened near the bottom of the timbers in order to hold it rigidly in position. (See arrangement, Fig. 31.)
Unless otherwise directed, outlets for brackets should be placed 5 1/2 feet from the floor except in the cases of hallways and bathrooms, where it is customary to place them 6 feet from the floor. Upright pipes should be plumb, so that nipples which project through the walls will be level; the nipples should not project more than 3/4 inch from the face of the plastering. Lathes and plaster together are usually about 3/4 inch thick, so the nipples should project about 1 1/2 inches from the face of the studding.
Gas pipes should never be placed on the bottoms of floor timbers that are to be lathed and plastered, because they are inaccessible in case of leakage or alterations.
All risers and distributing pipes, and all branches to bracket and center lights should be of sufficient size to supply the total number of burners indicated on the plans. Mains and branches should be proportioned according to the number of lights they are to supply, and not the number of outlets.
No pipe should be less than 3/8 inch in diameter, and this size should not be used for more than two-bracket lights. No pipe for a chandelier should be less than 1/2 inch up to four burners, and it should be at least 3/4 inch for more than four burners. The following table gives sizes of supply pipes for different numbers of burners and lengths of run.
Size of Pipe. Inches.
Greatest Length of Run.
Greatest Number of Burners to be Supplied.