HORSE-POWER OF LOCOMOTIVES.
When people wish to find the horse-power developed by a locomotive, the indicator is generally employed, and the calculations made from the diagram. Others figure out locomotive horse-power as they do that of other engines. By this method, the engine whose traction we have been investigating might have the horse-power calculated as follows:—
| 226.98 | square inches piston area. |
| 80 | pounds mean pressure. |
| ——— | |
| 18158.4 | piston pressure. |
| 4 | feet piston travel each revolution. |
| ——— | |
| 72633.6 | |
| 2 | cylinders. |
| ———— | |
| 145267.2 | |
| 145 | revolutions per minute. |
| ———— | |
| 20063944 | ÷ 33000 = 608 horse-power when running at a speed of 30 miles an hour. |
No allowance has been made for frictional losses in any of these calculations.
One horse-power is equivalent to the work performed in raising 33,000 pounds one foot high in one minute. One pound raised 33,000 feet high, or 330 pounds raised 100 feet high, would amount to the same thing. One horse-power is usually spoken of as 33,000 foot-pounds; and engineers in this country always calculate work by foot-pounds,—that is, so many pounds raised a certain number of feet. To indicate the capacity of any prime motor, the foot-pounds of work it is capable of raising in a given time must be stated. Although the work is often done without any thing being raised vertically, the power represented would be capable of raising the equivalent weight in the stated time.