This tank may also be used as an indicator where varying quantities of water are used, to show the amount of water in any batch. For this purpose, set the ball for the maximum capacity, allow the tank to fill, and open the tank valve. The pointer on the outside will go downward as the water falls in the tank; and a glance at the gauge will show, at any instant, how much water has run out. • The "Koehring" water-measuring tank is a simple mechanism containing neither float nor moving parts. It consists of a cylindrical steel tank mounted horizontally, near one end of which a 2-inch pipe with a long running thread passes down through the tank into a 21/2-inch brass pipe to which a special three-way valve is fitted at the end. Within the tank is an oblong hole cut into the 2-inch threaded pipe, through which water flows into the mixer drum, and which, by being raised or lowered to any desired height, controls the amount of water to each batch mixed in the drum. The tank will always fill up to the top, a vertical check-valve allowing the air to escape, and closing when the water comes in contact with it. When it is de sired to put the water into the mixer drum, the lever on the three-way valve is given a quarter turn, which shuts off the supply and allows the water in the tank to flow out into the mixer through the oblong hole. If more water is de sired, it is only necessary to screw down the threaded pipe. On account of the large pipe the flow of 'water from the tank into the mixer is very rapid.
The feed-hose is connected with the three way valve by a pipe, and from this inch pipe there is also a connection to supply the water for boiler, so that only one feed-hose is required.
In the "McKelvey" Mixer, shown in Plate 8 (at top), the drum, which is chain-driven, is fed and discharged while in motion, without changing its position or direction. Blades in the
interior assist in the mixing of the ingredients for the batch, and the discharge is controlled by a lever on the drum, The "Snell" Mixer (Plate 8, lower figure) is also a rotary machine, but of the open-drum type. The drum is its distinctive feature. In the smaller machines, this is cylindrical in form and made in one piece; but in the larger ma chines, only the base of the drum is cylindrical, a conical top being riveted thereto, which gives a diminshed opening and facilitates discharge in small space. The interior of the drum is per fectly smooth, except for five small blades riveted to its sides, at right angles to the bottom and parallel to one another.
When in operation, the drum is tilted at an angle of 45 degrees. The small blades not only carry the material to the top and then let it fall, but also effect a pouring process, which is ac knowledged to be effective in mixing. The time required for loading, mixing, and discharging, it is claimed, is normally two minutes. The drum may be loaded directly from wheelbarrows run up onto the low loading platform. The mate rial remains in full view all the time, for inspec tion during the mixing process. Discharge is effected by tilting the drum. In the case of the smaller machines, this is done by hand, the drum being balanced so that little power is required. With the larger machines, the tilting is accom plished by means of a power-driven worm gear controlled from the loading platform. Both loading and discharge may be effected while the machine is in operation.
In the "Polygon" Mixer (Plate 9, top fig ure), the shape of the drum is depended upon, as it revolves, to effect the mixing of the batch. A rapid endwise, sidewise, and crosswise move ment is set up, the materials being thrown from each end and side toward and past the center alternately, while the drum is constantly turn ing. The dumping chute, which is raised or lowered as required, is readily controlled, so that as large or as small a quantity of concrete as may be desired can be taken out; and both charg ing and discharging can be done while the machine is running at full speed.