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Page:Popular Science Monthly Volume 18.djvu/339

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and can be used anywhere in a house without annoyance, as they run with almost no noise. They occupy but small space, the boiler-casing being in the smallest size but sixteen inches in diameter and three feet in height. The base of the machine has air-spaces to prevent the heat from burning the floor. The construction and operation of the pumping-engine will be clear from an inspection of the cut. The heater B surrounds the boiler C C, which is made with pendent water-tubes G G, among which the burning gases circulate on their way to the smokestack. The gas burns from a double argand burner H, the supply being automatically controlled by the steam-pressure in an ingenious manner. At I, a valve is placed in the gas-pipe which is operated by the lever l, the longer end of which is pressed up by the spring M. A tube, o, leads from the boiler to a chamber in which works the diaphragm-piston r, attached to the shorter end of the lever L. If the pressure in the boiler increases, it is transmitted to the piston which rises and partially closes the valve I, diminishing the supply of gas. A lessening of the boiler-pressure produces the reverse effect of increasing the gas-supply. The amount of fuel consumed is thus accurately proportioned to the amount of steam generated by the engine itself. This allows the gas to be kept burning while no work is being done, and consequently no steam used without there being the slightest danger of an explosion, a feature of great value in a power-engine when it is used intermittently, but needs to be in constant readiness. In the larger sizes in which coal is used, the fire is regulated by means of an automatic damper operated in a similar manner to the valve controlling the gas-supply.

The feeding of water to the boiler is also controlled by a very simple automatic arrangement. The feed-water chamber is placed at the top of the heater-shell, where it is exposed to the heat of the issuing products of combustion. A pipe, h, is open to both the pump and this chamber. So long as the feed-water heater is but partially filled, water continues to be forced into it by the pump; but, when it becomes full, no more can enter until a portion of it has passed into the boiler. The admittance to this latter is controlled by a float mechanism, E, F, D, operating a valve at the base of the boiler through the medium of the rod o. The float E is a flat, inverted vessel, which is partially submerged when the boiler is full. A weight, D, at the other extremity of the lever F, is then able to keep the valve closed; but, as the level of the water sinks, the float drops and the valve is opened by the rod o, the pressure produced by the pump forcing water from the feed heater into the boiler. By these two devices, the one controlling the heat by the steam-pressure so as to keep that pressure constant, and the other regulating the amount of water in the boiler, this steam engine becomes nearly as safe, and gives as little trouble, as any of the simpler forms of heat-engine using hot air or gas. For still further security a safety-valve is placed in the pipe leading from the boiler,