All About Engines

98 All About Engines ing principle. Two tubes, one of brass and the other of iron, are connected with a small brass vessel containing two compartments separated by a valve. The brass tube is connected at the other end with Fig. 54.—Geipel steam trap the steam pipe, and the iron tube leads to a waste pipe or drain. So long as steam is in the brass tube it is hotter than the iron and, having a higher rate of expansion, the brass tube causes the small brass box to bend upwards. The valve rod is then pressing against the lever above, and is held down on its seat. But as water collects in the brass tube the temperature falls, its length decreases, the valve rod falls away from the lever, and the valve opens. Water is then imme- diately blown into the iron tube, and steam again enters the brass one, with the result of closing the valve. Most other forms of trap depend upon a float. The water from the steam pipes drains into a box, and as it collects it raises a float which opens a valve and permits the water to escape. In these and other ways water is prevented from reaching the engine. Superheated Steam But the most effective plan is to raise the tem- perature of the steam from ioo° Fahr, to 300° Fahr, above the temperature it reaches in the boiler. The value of superheated steam in the engine will be ex- plained in Chapter V. Here it will suffice to say that