Note.—The best way of jointing hydraulic pipes has been the subject of much practical experiment. A gutta percha ring has been universally adopted as the best means of preserving the joint watertight. Modified form of this joint is made by casting a projection on the pipe beyond the flange, the bell and spigot being formed on this projection. The effect is to increase the depth and the strength of the flange, without an increase of its section at the junction between the flange and the pipe.
Much might be said regarding duplicate pipe systems, both for and against. The general practice is coming to be that of subdividing into units, while in smaller plants the duplicate system is used. The service and conditions govern the method of piping, which should be such in every instance as to prevent a shut down due to accident in some part of the system.
All the fittings in the pipe system of a plant should be of the best quality, and the piping for high pressures should be extra heavy to withstand the test of time and usage. Water pipes, when of commercial wrought iron, should be galvanized.
In laying out a line of piping or in replacing a portion of an existing line the measurements should be taken from center to center of the various fittings; the allowance for the threaded part of the pipe can be made after the center-to-center and over-all measurements have been made and before the pipe is cut. Experience teaches what to allow for the threaded part on different sizes of pipe. The accompanying engraving gives an illustration of how the measurements on a pipe system are made.
As, for example, A represents the distance, center-to-center, from elbow to tee; B, from the starting place to center of elbow; C, the distance, center-to-center, of the two elbows; D, from the starting place to the center of the globe valve; E, the center of the globe valve to the center of the tee, and F, from the center of the tee to the center of the elbow.
G shows the center of the elbow to the center of the union; H, from the center of the union to the center of the tee, and I, from the center of the tee to the center of the elbow; J, from the center of the elbow to the center of the coupling, and K, from the center of the coupling to the final tee; all as indicated by the arrow heads and crosses.