STEAM BOILERS 123 



combined with the use of high-class materials and fit- 

 tings and the judicious placing of cut-out and by-pass valves. 

 Drainage is best effected by arranging the piping so that all 

 the water of condensation will flow by gravity toward a point 

 close to the delivery end of the pipe, and then providing a drip 

 pipe at that point. A trap may be placed at the end of the 

 drip pipe for automatic draining. 



BOILER FEEDING AND FEEDWATER 

 INJECTORS 



Classification of Injectors. Injectors may be divided into 

 two general classes, namely, non-lifting and lifting injectors. 

 Non-lifting injectors are intended for use where there is a head 

 of water available. When the water comes to a non-lifting 

 injector under pressure, as from a city main, it can be placed 

 in almost any convenient position close to the boiler. Lifting 

 injectors are of two distinct types, called automatic injectors 

 and positive injectors. As positive injectors generally have 

 two sets of tubes, they are frequently called double-tube inject- 

 ors. Automatic injectors are so called from the fact that they 

 will automatically start again in case the jet of water is broken 

 by jarring or other means. Positive, or double-tube, injectors 

 are provided with two sets of tubes, one set of which is used for 

 lifting the water, and the other set for forcing the water thus 

 delivered to it into the boiler. A positive injector has a wider 

 range than an automatic injector and will handle a hotter 

 feed-water supply; it will also lift water to a greater height than 

 the automatic injector. 



Size of Injector. Most engineers prefer to select a size of 

 injector having a capacity per hour about one-half greater 

 than the maximum evaporation per hour in order to have some 

 reserve capacity. The maximum evaporation, when not 

 known, may be estimated in U. S. gallons by one of the follow- 

 ing rules, which hold good for ordinary combustion rates 

 under natural draft: 



Rule I. For plain cylindrical boilers, multiply the Product of 

 the length and diameter in feet by 1.3. 



