Fibre Conduits.—This form of conduit consists of pipes made of wood pulp impregnated with a bituminous preservative and insulating compound. These pipes are laid in concrete in a manner similar to iron pipe. Fibre conduits are made in sizes ranging from 1 inch to 4 inches in diameter and from 2½ to 5 feet in length, with walls ranging from ¼ to ½ inch in thickness.
Ques. Name the three types of fibre conduit.
Ans. The socket joint type, as shown in [fig. 984], the sleeve type, [fig. 985], and the screw joint type, [fig. 986].
Ques. What is the usual method of laying the socket joint type of fibre conduit?
Ans. After the trench has been dug to the required width and depth, depending upon the number or pipes to be placed in a tier and the number of tiers, a bed of concrete about 3 inches deep is placed on the bottom and a line drawn on one side for the alignment of the first line of pipes. The other lines of pipe or ducts are laid parallel to the first line, and are separated from it and from each other by means of ¼ inch or ½ inch wooden or iron pegs. The pipes are well grouted and covered with a layer of concrete to the depth of ¼ or ½ inch, and the next tier laid in place in the same manner. When the final tier of pipes has been installed, it is covered with a layer of concrete about 2 to 3 inches deep.
Fig. 985.—Sleeve joint type of fibre. Both the socket type ([fig. 984]), and the sleeve type here shown are easily aligned without the use of a mandrel.
Ques. What is done when it is necessary to cut a length of pipe to break joints, or to enter a manhole?
Ans. The remaining part of the length may be utilized by using a fibre conduit sleeve having an inside diameter ½ inch greater than the pipe being used on the system.