The Water Tower at Elgin, Ill.
The water tower illustrated herewith is that connected with the water supply system at Elgin, Ill. This tower consists of a steel tank thirty feet by ninety-five feet inside dimensions, bolding nearly 500,000 gallons of water, supported by a hollow pedestal, twenty feet in height, made of concrete faced with stone. It was originally intended to locate on ground twenty feet higher, but as it was impossible to get ground and right of way a location at the lower level was necessary. The extreme cost of the metal work for the lower twenty feet, which was thus made necessary, however, was greater than the fund available would permit of, and with the regular flat foundation would have amounted to fully $15,000. The engineer was, therefore, obliged to devise some less expensive method of finishing the tower, and his studies led to the selection of a pedestal with flat top and containing the dome shaped room ns shown in the cut.
The pedestal is faced with rough, hard lime stone, coursed ami tied by headers in the concrete, and extending from the ground surface up to the cut stone coping. The foundation is annular, and all surplus material is avoided by centering placed in the thickest portion. The quiescent load |ier square feet on the earth,which is hard gravel, is about three tons, and the maximum load on any portion of the concrete is eight tons per square feet of section. The thickness of the concrete at the centre of the dome is three feet, and at the thinnest point at the sides is four feet 0 inches.
The concrete was formed by mixing dry 011c part of Ilylerhoff German Portland Cement with three parts clean, sharp sand, and forming them intoastiff mortar. Three parts clean, coarse, screened gravel were then welt wetted and mixed thoroughly with the mortar. The whole was then tamped solidly into place in six-inch layers. The tower is anchored to the concrete, as shown, by rods passing through and held by nuts and washers inside. The centering consisted simply of meridional arches formed of one inch by six inch fencing stuff, spaced three feet, and covered by one inch by six inch stuff tacked on—no tying or bracing was placed or needed. The floor is of concrete. The total settlement when filled was less than oneeighth of an inch. The cost of the concrete per cubic yard in place was practically $5.50, and the total cost completed was alxiut $5500.
The work is interesting as being, so far as we know, the first time that a dome of concrete lias been so heavily loaded, and as showing the great strength of concrete structures where the material is carefully placed and properly made. There are other water towers supported upon concrete bases or pedestals, but none of them compare in size with this, and in none has the dome top been used. The work has stood the test of three years, and is in perfect condition.
In the inner chamber of the tower, placed in the elbow of the supply main, is a valve which opens or closes automatically, so that when it is desired, for fire or any other reason, the stand-pipe may be closed off from the mains. Subsequently the valve may be opened again, the whole operation being controlled by the engineer at the pumping station.
The valve proper acts horizontally ; it is annular in shape, twenty inches long, and when closed bears against a seat at each end. Its spindle is continued at the rear end, and has on it a piston working in the small cylinder shown in the drawing.
The boiler feed-pump at the pumping station, about 800 feet distant, is connected with this cylinder by a iJjMnch pipe. This pipe, after connecting with the cylinder, is continued and connected with the stand-pipe, and between the cylinder and the stand-pipe is placed a check valve, which opens with pressure from the stand-pipe, but closes with pressure from the feed-pump. The difference in area of the two ends of the valve proper is the difference between a I7j£ and an i8^-inch circle, and it is so arranged that under ordinary conditions the pressure in the mains always keeps the valve open. The area of the piston on the end of the spindle is just sufficient to overcome this difference.
The designer of the Elgin water tower was Chester B. Davis, hydraulic engineer, of Chicago, and the part of the tower above the pedestal was built by the Shickle, Harrison & Howard Iron and Pipe Company of St. Louis at a cost, including con nections, of $14,287.