Fig. 983.—Cross section of wrought iron pipe conduit laid in hydraulic cement.
The pipe connections consist of a taper screw thread coupling which can be easily made up as the pipes are laid, and which forms a tight joint.
The pipes in each tier are usually laid from ½ to ¾ of their diameter apart, and when the first tier is in place, the spaces between and around the pipes are filled in with concrete which is carried up over the pipes to a depth of about one-half a diameter to form the bed for another tier of pipes.
Ques. What is the principal object of the top covering of planks.
Ans. To protect the conduit against the tools of workmen making later excavations.
Practical experience shows that workmen will dig through concrete without stopping to investigate as to the character of the obstruction, but under similar circumstances, will invariably turn away from wood.
Ques. How are the pipes treated before being laid?
Ans. They are dipped in tar to protect the outside surface from rust.
Ques. What is the most satisfactory form of lined iron pipe?
Ans. Pipe lined with cement. The internal surfaces of these pipes are usually covered with a lining of pure Rosendale cement about ⅝ inch thick and containing no sand. The internal surface of the cement lining does not offer much friction to the introduction or withdrawal of the conductors.