In installing pipes and metal fittings of all kinds it is absolutely necessary to make proper provision for expansion. (See Chapter IX (Heat And Expansion. 100. Generation And Movement Of Heat), " Heat and Expansion.") When steam is turned on the temperature is raised and the pipes expand. Pieces of curved pipe called bends are usually used to take up the expansion and prevent the joints from leaking. When steam is suddenly admitted to a pipe partly filled with cold water, the water is set in violent motion and travels the length of the pipe in the form of waves often with sufficient velocity to break a valve or other obstruction in its path. The extent of the break will depend upon the manner in which the valve is opened. If opened suddenly, a violent explosion is almost certain to follow, but if opened very gradually, while there may be a certain amount of noise and vibration, no serious results will occur.
Engines are usually placed in a house separate from the boiler, although it is a good plan to have them near so as to avoid the necessity of laying great lengths of steam pipe. Steam pipes are made of wrought iron or steel with flanged joints. The pipes conducting the steam from the boiler to the engines are covered with non-conducting material, such as asbestos, to prevent the escape of heat. Draw-off cocks are placed in convenient positions along the pipe to draw off the water formed from condensed steam.