[Illustration: FIG. 36.--Steel Penstocks at Chamblay Power-house.]
The Garvin’s Falls station, on the Merrimac River, rests on arches of stone masonry through which the tail-water passes, and the brick walls are water-proofed to an elevation eight feet above the floor. At twenty feet above the floor the twenty-four-inch brick walls on the two longer sides are reduced to eight inches in thickness, thus forming benches each sixteen inches wide on which the crane travels. Arches of stone masonry support the twenty-four-inch brick walls of the station at Red Bridge, on the Chicopee River, and these walls on the two longer sides decrease in thickness to twelve inches at an elevation of twenty-one feet above the floor, thus forming benches twelve inches wide for the ends of the crane.
One concrete wall of the Santa Ana station is 2.5 feet thick to a distance of 13.5 feet above the floor, and then shrinks to a thickness of 1.5 feet, corresponding to that of the opposite wall, thus forming a bench twelve inches wide for one end of the crane. The other end of the crane in this case is supported by an I-beam on a row of iron columns.
It is not uncommon to locate horizontal turbines in a room separate from that occupied by the generators to which they are direct-connected, in order to protect the latter from water in the event of a break in penstocks or wheel cases. In cases of this sort the shafts connecting wheels and generators pass through the wall between them. The horizontal turbines may be located at the bottom of a canal whose water presses against the wall through which the wheel shafts pass, or they may be contained in iron cases at the ends of penstocks. In this latter case an extension of the station is often provided for a wheel room to contain these cases. Such wheel rooms are long, narrow, low-roofed and parallel to the generator rooms of their stations. The floors of these wheel rooms are at nearly the same levels as the floors of generator rooms, but elevations of their roofs above the floors are much less than like elevations in the main parts of the stations. The Garvin’s Falls, Red Bridge, and Apple River stations have wheel rooms of the type just described. With impulse-wheels to which water passes in planes at right angles to their shafts it is desirable, in order to avoid changes in the direction of water pipes, that direct-connected wheels and generators occupy the same room, and this is the arrangement at the Colgate, Electra, Santa Ana, Mill Creek, and many other power-houses using such equipments. The area of a wheel room may frequently be reduced at stations operating direct-connected horizontal-pressure turbines under low heads by placing the wheels at the bottom of the canal which has one side of the station or generator room for a retaining wall. This plan was adopted at the Birchem Bend plant with a head of fourteen feet, and at the Sault Ste. Marie station where the head of water is about twenty feet. Vertical wheels direct-connected to generators must be directly underneath the main room of their station, and may be in a canal over which the station is built, in a wheel room that forms its lower part, or in a wheel pit and supplied with water through penstocks, as at the Niagara Falls plants.