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TABLE 6

FACTORS OF EVAPORATION

212 1.027 | 1.030 1.032 1.035 1.037 | 1.039 1.041 | 1.043 1.047 200° 1.039 1.042 1.045 | 1.047 1.050 1.052 1.054 1.056 1.059 191° 1.049 1.052 1.054 1.057 1.059 1.061 1.063 | 1.065 1.069 182° | 1.058 1.061 1.064 1.066 1.069 1.071 | 1.073 1.075 1.078 173° 1.067 1.070 1.073 1.076 1.078 1.080 1.082 1.054 1.087 164° 1.077 1.080 1.083 1.085 1.087 1.090 1.091 | 1.093 1.097 152 1.089 1.092 1.095 1.098 | 1.100 I, 102 1.104 1.100 1.109 143° | 1.099 I. 102 1.105 | 1. 107

1. 109
I,III 1.113 | 1,115

I.119 134° 1. 108

I. III 1.1.4 1.116 1.119 I. 121 1.123 1.125 I. 128 125° | 1,118 I. 121 1.123

IJ28

1.130 1.132 1.134 1.137 113° 1.130 1.133 1.136 | 1.138 1.140 | 1.143 | 1.145 I.146 | 1.150 104° 1,138 1.142 1.145 1.148 1.150 1.152 1.154 1.156 1.159 95 1.149 | 1.152 1.154 1.157 1. 159 | 1.161 1.163 1.165 1,169 86° 1,158 1. 161 1.164 1.166 1,169 1.171 | 1.173 1.174 1.178 77° | 1.167 1.170 1.173 1.176 1.178 1.180 1.182 1,184 1.187 65° | 1.180 1.183 1,186 1.188 1.190 1.192 1.194 | 1.196 1.200 56° 1.189 1.192 1.195 1.197 1.200 1. 202 1.204 1.206 1.209 47° | 1.199 1. 201 1.204 | 1.207 1.209 1.2II 1.213 | 1.215

1.218 38° 1.208 1.211 1.214

1.216 1.218 1.220 1, 222 1.224

I. 126

1.228

Second, water evaporated per pound of coal actual conditions = water apparently evaporated divided by coal consumed = 9.65 lbs. No accurate estimate regarding the quality of the coal or the efficiency of the boiler can be made from this figure (9.65 lbs.). It can be used, however, in estimating the cost of fuel for generating the steam; as, for instance, if the boiler is supplying steam to an engine that uses 30 lbs. of steam per horse power per hour, it will require 30 – 9.65 = 3. I lbs. of coal per horse power per hour; the “actual conditions under which the boiler is being operated being the pressure of steam required by the engine and the temperature of the feed water.

Third, water evaporated per pound of coal from and at 212° = water evaporated into dry steam from and at 212° divided by coal consumed = 10.61 lbs. This figure is the proper one to use in comparing the relative economic values of different varieties of coal tested with the same boiler or boilers.

Fourth, water evaporated per pound of combustible from and at 212° = water evaporated into dry steam from and at 212° divided by weight of combustible = 11.81 lbs. This result is the one to be used for ascertaining the efficiency of the boiler, and the percentage of efficiency is found by dividing the heat absorbed by the boiler per pound of combustible by the heat value of one pound of combustible. The average heat value of bituminous and semi-bituminous coals is not far from 15,000 heat units per pound of combustible. In the evaporation of 11.81 pounds of water from and at 212° the heat absorbed was 11.81 % 965.7 = 11,404.9 heat units. The efficiency of e boiler therefore was

11,404.9 X 100
15,000

76 per cent. In like manner to ascertain the efficiency of the boiler and furnace as a whole, the water evaporated from and at 212° per pound of coal is taken. Thus, 10.61 x 965.7 = 10,246 heat units absorbed from each pound of coal. Now assuming that there were 13,500 heat units in each pound of the coal used in the test, the per cent of efficiency of boiler and furnace was

75.9. Fifth, water evaporated per pound of dry coal from and at 212° = water evaporated into dry steam from and at 212° divided by coal corrected for moisture. Thus, 117,788 + 10,878 = 10. S2 lbs. This result is useful for calculating the results of tests of the same grade

10.246 X 100

13,500

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of coal, but differing in the degree of moisture in each.

Sixth. Boiler horse power. The latest decision of the American Society of Mechanical Engineers (than whom there is no better authority) regarding the horse power of a boiler is as follows: "The unit of commercial horse power developed by a boiler shall be taken as 3472 units of evaporation per hour. That is, 3472 lbs. of water evaporated per hour from a feed temperature of 212° into steam of the same temperature. This standard is equivalent to 33,317 B. T. U. per hour. It is also practically equivalent to an evaporation of 30 lbs. of water from a feed water temperature of 100° F. into steam of 70 lbs. gauge pressure."

According to this rule the horse power developed by the boiler during the test under consideration = water evaporated into dry steam from and at 212°, 117,788 lbs + 12 hrs. + 34.5 = 284.5 horse power.

QUESTIONS 1. What is the primary object of an evaporation test?

2. Name four other important points which can be determined by evaporation tests.

3. In making a test of the efficiency of the boiler and furnace, what precautions should be observed?

4. How is the heating surface of water tube boilers estimated?

5. What length of time should a test be conducted ?

6. In case the boiler is fed by an injector, what precautions are necessary?

7. If the steam contains any moisture, what should be done?

8. How is the weight of combustible determined?

9. What is a calorimeter, and for what purpose is it used?

10. By what other method may the moisture in the steam be estimated approximately?

11. What should be done with the percentage of moisture in the coal?

12. How is the chimney draft measured? 13. Describe a draft gauge.

14. Give the formula for ascertaining the efficiency of the boiler and setting.

15. If the test is to determine the efficiency of the poiler alone, what factors are used?

16. If a series of tests is made for comparing different varieties of coal, what should be done?

17. What is meant by equivalent evaporation?

18. Why should the results of all tests be computed from and at 212°?

19. What is a factor of evaporation?
20. How is it determined?
21. What is a boiler horse power?

22. How many heat units per hour is this equiv. alent to?

CHAPTER VI

VALVES AND VALVE SETTING Valves and valve setting-Importance of correct adjustment-The

D slide valve-Single valve engines - Four valve enginesVarious positions of the slide valve during one revolutionRelative positions of the crank pin and eccentric during the stroke-Valve diagrams-Placing the engine on the centerAdjusting the length of eccentric rod—Measuring the inside and outside lap_Setting the valve-Fixed cut off enginesVariable automatic cut off-Factors affecting the distribution of the steam-Why the four valve engine is the most economical—Description of corliss valves and valve gear and directions for adjusting the same. Valves and Valve Setting. It goes without saying that e.'ery man who aspires to be an engineer should endeavor to thoroughly acquaint himself with the principles governing the action of valves as well as the details of valve setting. But it must be remembered that this knowledge can not be acquired in a day or a week, or even months. True, a man may be able to learn some of the alphabet of valve lore in a comparatively short time, but the more practical experience he has in the work the more will he realize the supreme need of mastering all the details of the process.

The common D slide valve, simple as it appears, is capable of furnishing problems over which savants have puzzled themselves

The development of the full amount of power of which the engine is capable, its efficiency and economical use of steam, and its regular and quiet action are, in the largest degree, dependent upon the correct adjustment of its valve or valves.

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