It is important to see that no blisters or ragged pipes go into the returns, and also to make sure that the ends are not “burred in” with a dull pipe cutter wheel so as to form a place of lodgment for loose matter in the pipe to stop against.
Figs. 135-137.
Experiments recently made on the strength of bent pipes have developed some things not commonly known, or at least not recognized, that is, the strain on the inside of the angles, due to the effort of the pipes to straighten themselves under pressure. The problem is one of considerable intricacy, resolvable, however, by computation, and is a good one for practice. In the experiment referred to, a copper pipe of 63⁄4 in. bore, 3⁄16 in. thick, was used. The angle was 90 degrees, and the legs about 16 in. long from the center. At a pressure of 912 pounds to an inch, the deflection of the pipe was nearly 3⁄8 in., showing an enormous strain on the inner side, in addition to the pressure.
Steam valves should be connected in such a manner that the valve closes against the constant steam pressure.
Interesting experiments show that the loss by condensation in carrying steam one mile is 5 per cent. of the capacity of the main, and a steam pressure of seventy-five pounds carried in five miles of mains, ending at a point one-half mile from the boiler house only shows a loss of pressure of two pounds.
In steam warming it is necessary to bring the water to a boiling point to get any heat whatever; in hot water warming, a low temperature will radiate a corresponding amount of heat.
Never use a valve in putting in a low pressure apparatus if it is possible to get along without it. All the valves or cocks that are actually required in a well-proportioned low pressure apparatus are, a cock to blow off the water and clean out the return pipes, another to turn on the feed water. Of course the safety valves, gauge cocks, and those to shut fire regulators and such as are a part of the boiler, are not included in this “point.”