CONTENTS--Design and construction of safety valves, check valves, water cocks, water gauges and steam gauges.
The efficiency of a model boiler depends somewhat upon its fittings, such as safety valves, stop valves, check valves, et cetera. A poorly constructed, leaky valve or boiler fitting of any kind is just as bad as a leak in the boiler and will cause a serious reduction in the working pressure. Therefore, it is quite necessary that a valve or fitting of any kind be made very accurately to insure maximum efficiency. Probably the most important fitting on a model boiler is the safety valve. There are many types of valves, each with its advantages and its disadvantages. In some cases, one type of valve is more adaptable for a certain boiler than another. A properly designed and regulated valve will blow off when the critical pressure is reached in the boiler; below this pressure it should not leak or "weep" in the least. After the valve functions, it should return to its normal position immediately the pressure has fallen beyond the danger-point. Such a valve is not very easy to construct, although the model maker, at first thought, may think that it does not present any difficulties whatsoever. In designing safety valves the model maker must bear in mind the fact that the interior surface of the valve plug determines the pressure at which it will blo woff—the larger the surface, the lower the pressure needed, and vice versa.
