Εικόνες σελίδας
PDF
Ηλεκτρ. έκδοση

CAST-IRON PIPE.

23

WEIGHT OF CAST-IRON PIPE PER FOOT IN POUNDS.

These weights are for plain pipe. For hautboy pipe add 8 in. in length for each joint. For copper add }; for lead, ; for welded iron, add y's, or multiply by 1.0667.

[graphic]
[ocr errors]
[ocr errors]
[ocr errors]
[blocks in formation]

1 11

In. In. In. In. In. In. Ft. Ft. In. Lb.
1.
.40 .068 .27 .85

1.27 14.15 9.440 .057 .24 27 .54 .088 .36 1.14 1.70 10.50 7.075 .104 .42 18 .67.091 .49 1.55 2.12 7.67 5.657 .192 .56 18

.84 .109 .62 1.96 2.65 6.13 4.502 .305 .84 14 74 1.05 .113 .82

2.59

3.30 4.64 3.637 .533 1.13 14 1.31 .134 1.05 3.29 4.13 3.66 2.903 .863 1.67 111 1.66 .140 1.38 4.33 5.21 2.77 2.301

1.496 2.26 111 112 1.90 .145 1.61 5.06 5.97 2.37 2.010 2.038 2.69 111 2 2.37 .154 2.07 6.49 7.46

1.85 1.611 3.355 3.67 111 272 2.87 .204 2.47 7.75 9.03 1.55 1.328 4.783 5.77 8 3 3.50.217 3.07 9.64 11.00 1.24 1.091 7.388 7.55 8 372 4.00'226 3.55 11.15 12.57 1.08 0.955 9.887 9.05 8

4.50 .237 4.03 12.65 14.14 .95 0.849 12.730 10.73 8 442 5.00 .247 4.51 14.15 15.71 .85 0.765 15.939 12.49 8 5

5.56 .259 5.04 15.85 17.47 .78 0.629 19.990 14.56 8 6

6.62, .280 6.06 19.05 20.81 .63 0.577 28.889 18.77 8 7 7.62 .301 7.02 22.06 23.95 .54 0.505 38.737 23.41 8 8 8.62.322 7.98 25.08 27.10 .48 0.444 50.039 28.35 8 9 9.69.344 9.00 28.28 30.43 .42 0.394 63.633 34.088 10 10.75 .366 10.02 31.47 33.77 .38 0.355 78.838 40.64 8

4

FLUXES FOR SOLDERING OR WELDING.

Iron

Borax Tinned iron

Resin Copper and brass

Sal ammoniac

Zinc

Chloride of zinc Lead

Tallow or resin Lead and tin pipes

Resin and sweet oil

Steel.-Pulverize together 1 part of sal ammoniac and 10 parts of borax and fuse until clear. When solidified, pulverize to powder.

STEAM TABLES. Whenever the pressure of saturated steam is changed, there are other properties that change with it. These properties are the following:

1. The temperature of the steam, or, what is the same thing, the boiling point.

2. The number of B. T. U. required to raise a pound of water from 32° (freezing) to the boiling point corresponding to the given pressure. This is called the heat of the liquid.

3. The number of B. T. U. required to change the water at the boiling temperature into steam at the same temperature. This is called the latent heat of vaporization, or, simply, the latent heat.

4. The number of heat units required to change a pound of water at 320 to steam of the required temperature and pressure. This is called the total heat of vaporization, or, simply, the total heat.

It is plain that the total heat is the sum of the heat of the liquid and the latent heat. That is, total heat heat of liquid + latent heat.

5. The specific volume of the steam at the given pressure; that is, the number of cubic feet occupied by a pound of steam of the given pressure.

6. The density of the steam; that is, the weight of 1 cubic foot of the steam at the given pressure.

All the above properties are different for different pressures. For example, if steam boils under atmospheric pressure, the temperature is 212°; the heat of the liquid is 180.531 B. T. U.; the latent heat, 966.069 B. T. U.; the total heat, 1,146.6 B. T. U. A pound of steam at this pressure occupies 26.37 cu. ft., and a cubic foot of the steam weighs about .037928 lb. When the pressure is 70 lb. per sq. in. above vacuum, the temperature is 302.774°; the heat of the liquid is 272.657 B. T. U.; the latent heat is 901.629 B. T. U.; the total heat is 1,174.286 B. T. U. A pound of the steam occupies 6.076 cu. ft., and a cubic foot of the steam weighs .164584 lb.

These properties have been determined by direct experiment for all ordinary steam pressures. They are given in the table of the properties of saturated steam, pages 29-31.

EXPLANATION OF THE TABLE. Column 1 gives the pressures from 1 to 300 lb. These pressures are above vacuum. The steam gauges fitted on steam boilers register the pressure above the atmosphere. That is, if the steam is at atmospheric pressure, 14.7 lb. per sq. in., the gauge registers 0. Consequently, the atmospheric pressure must be added to the reading of the gauge to obtain the pressure above vacuum. In using the table, care must be taken not to use the gauge pressures without first adding 14.7 lb. per sq. in.

Pressures registered above vacuum are called absolute pressures. The pressures given in column 1 are absolute. Absolute pressure per square inch = gauge pressure per square inch + 14.7.

Column 2 gives the temperature of the steam when at the pressure shown in column 1.

Column 3 gives the heat of the liquid. It will be noticed that the values in column 3 may be obtained approximately by subtracting 32o from the temperature in column 2. If the specific heat of water were exactly 1.00, it would, of course, take exactly 212 — 32 = 180 B. T. U. to raise a pound of water from 32° to 212o. But experiment shows that the specific heat of water is slightly greater than 1.00 when the temperature of the water is above 620, and it therefore takes 180.531 B. T. U. to raise a pound of water from 32° to 2120.

Column 4 gives the latent heat of vaporization, which is seen to decrease slightly as the pressure increases.

Column 5 gives the total heat of vaporization. The values in column 5 may be obtained by adding together the corresponding values in columns 3 and 4.

Column 6 gives the weight of a cubic foot of steam in pounds. As would be expected, the steam becomes denser as the pressure rises, and weighs more per cubic foot.

Column 7 gives the number of cubic feet occupied by 1 pound of steam at the given pressure. It will be noticed that the corresponding values of columns 6 and 7 multiplied together always produce 1. Thus, for 31.3 pounds pressure, gauge, .11088 X 9.018 = 1.000, nearly.

Column 8 gives the ratio of the volume of a pound of steam at the given pressure, and the volume of a pound of water at 39.2o. The values in column 8 may be obtained by dividing 62.425, the weight of a cubic foot of water at 39.2°, by the numbers in column 6.

EXAMPLES ON THE USE OF THE STEAM TABLE. EXAMPLE 1.-Calculate the heat required to change 5 lb. of water at 320 into steam at 92 lb. pressure above vacuum.

SOLUTION.–From column 5, the total heat of 1 lb. at 92 lb. pressure is 1,180.045 B. T. U.

1,180.045 X 5 = 5,900.225 B. T. U. EXAMPLE 2.-How many heat units are required to raise 83 lb. of water from 3:20 to 2500 F.?

SOLUTION.-Looking in column 3, the heat of the liquid of 1 lb. at 250.2930 is 219.261 B. T. U. 219.261 - .293 218.968 B. T. U. = heat of liquid for 250°. Then, for 8 lb. it is 218.968 X 8 = 1,861.228 B. T. U.

EXAMPLE 3.-How many foot-pounds of work will it require to change 60 lb. of boiling water at 80 lb. pressure, absolute, into steam of the same pressure ?

SOLUTION.-Looking under column 4, the latent heat of vaporization is 895.108; that is, it takes 895.108 B. T. U. to change 1 lb. of water at 80 lb. pressure into steam of the same pressure. Therefore, it takes 895.108 X 60 53,706.48 B. T. U. to perform the same operation on 60 lb. of water.

53,706.48 X 778 = 41,783,641.44 ft.-lb. EXAMPLE 4.–Find the volume occupied by 14 lb. of steam at 30 lb., gauge pressure.

SOLUTION.- 30 lb., gauge pressure 30 + 14.7 = 44.7, absolute pressure. The nearest pressure in the table is 44 lb., and the volume of a pound of steam at that pressure is 9.403 cu. ft. The volume of a pound at 46 lb. pressure is 9.018 cu. ft. 9.403 – 9.018 .385 cu. ft., the difference in volume for a

.385 difference in pressure of 2 lb. = .1925 cu. ft., the differ

2 ence in volume for a difference in pressure of 1 lb. .1925 X.7 = .135 cu. ft., the difference in volume for a difference in pressure of.7 lb. Therefore, 9.403 —.135 9.268 cu. ft. is the volume of 1 lb. of steam at 44.7 lb. pressure. The .135 cu. ft.

« ΠροηγούμενηΣυνέχεια »