When pipes are not in a straight line, they are said to be out of alignment. Want of alignment sometimes causes trouble by throwing excessive strains on the flanges at the joints of stop valves, separators, etc. This trouble is brought about, as a rule, by forcing the flanges together by means of their joining bolts instead of fitting them carefully into place. The flanges of modern steel pipes and valves are usually of ample thickness, and if they do not come together fairly, they should be taken down and replaced. A thin ring of metal may be put in to make up the length, if necessary.

When erecting heavy pipes, every length of piping should be placed in position and properly supported and leveled by its own slings and brackets. Then it will usually be found that several lengths have to be altered before the flange faces come into alignment. Not until this has been done and every pair of flanges inspected by some responsible person, should the various lengths be bolted together permanently.

When a number of small or moderate-sized engines are connected with the same pipe system and stand on the same foundation, or in the same building, it is sometimes difficult to prevent the pipes from vibrating and at the same time insure the necessary freedom for expansion and contraction. Installations of this kind should therefore be arranged in such a way that the pipes arc quite free to move in one direction, parallel with their length, while movement in other directions should be restricted so far as possible.

High-speed engines are those whose fly-wheels rotate at a high speed; i.e., make a large number of revolutions per minute. Such engines are less expensive to operate than low-speed engines, because the power of an engine depends upon area of its piston, the mean pressure of steam, and the speed at which its fly-wheel rotates. Therefore by doubling the speed, an engine may be built very much smaller and cheaper per horse-power. Engines of this type are used for driving electrical machinery, which requires high speed of rotation and uniform angular velocity.