does not add any practical resistance. They gave the following approximate formula for diameters of pipes, which they say is practically accurate for sizes over 2½ inches:
![{\displaystyle d=0.184{\sqrt[{5}]{w^{2}L\div pD}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/2ffc5dc3d6a60b46726f9547125de8e173060d4e)
in which d equals the diameter in inches; w, the weight of steam, to be delivered in pounds per minute; L, the length of the pipe in feet; D, the density or weight in pounds per cubic foot, and p, the difference in pressure in pounds per square inch between the ends of the pipe. Transposed, this formula becomes:
From this it will be seen that, other things being equal, the delivery is proportional to the square root of the fifth power of the diameter.
The accompanying table, Table V, is calculated from this formula, assuming p = 1 pound per square inch difference of pressure and D = 0.04, which is the density of steam at a pressure of about one pound above the atmosphere. In this table allowance is made also for two globe valves and two elbows to each length of pipe. The square feet of surface each pipe would supply, allowing 0.30 pound of steam per square foot per hour (0.005 pound per minute), which is very liberal for direct radiation, is also given in the table. This table is chiefly interesting when compared with Table II, but may be of value for long mains where the building to be heated is at a distance from the plant. It should be noticed, however, that the greatest resistance is due to the elbows and valves. For example, the 8-inch pipe, 600 feet long, with two elbows and
| w = wt. of steam delivered per min. per 1 lb. difference of pressure. | ||||||
| R = sq. ft. of radiation supplied at 0.005 lb. per sq. ft. per min. | ||||||
| Diameter, in. | Length of pipe allowing for 2 valves and 2 elbows, feet. | |||||
|---|---|---|---|---|---|---|
| 100 | 200 | 400 | 600 | 1000 | ||
| 3 | w | 8.5 | 7.7 | 6.9 | 6.3 | 5.5 |
| 3 | R | 1,700 | 1,540 | 1,380 | 1,22 | 1,100 |
| 4 | w | 15.0 | 14.2 | 12.9 | 12. | 10.6 |
| 4 | R | 3,000 | 2,840 | 2,580 | 2,400 | 2,120 |
| 6 | w | . . . . | 33. | 31. | 29. | 26.2 |
| 6 | R | . . . . | 6,600 | 6,200 | 5,800 | 5,240 |
| 8 | w | . . . . | 59.5 | 56.5 | 54. | 49. |
| 8 | R | . . . . | 11,900 | 11,300 | 10,800 | 9,800 |
| 10 | w | . . . . | 95. | 90.4 | 87. | 81. |
| 10 | R | . . . . | 19,000 | 18,080 | 17,400 | 16,200 |
| 12 | w | . . . . | 138. | 132. | 138. | 120. |
| 12 | R | . . . . | 27,600 | 26,400 | 25,600 | 24,000 |
