Diameter of Cylinder. | 21⁄4 | 3 | 4 | 5 | 6 | 7 |
Stroke. | 6 | 6 | 6 | 6 | 6 | 6 |
Revolutions Per Minute. | 150 | 150 | 140 | 140 | 130 | 130 |
Piston Speed in Feet Per Minute. | 150 | 150 | 140 | 140 | 130 | 130 |
Cubic Feet of Free Air Per Minute. | 2 | 3 | 6 | 9 | 12 | 17 |
Working Pressure. | 150 | 150 | 100 | 100 | 100 | 100 |
Horse Power Required. | 5⁄8 | 3⁄4 | 11⁄2 | 2 | 21⁄2 | 4 |
| Pipes. | ||||||
Suction. | 3⁄4 | 1 | 11⁄2 | 2 | 2 | 21⁄2 |
Discharge. | 3⁄4 | 1 | 11⁄2 | 11⁄2 | 11⁄2 | 11⁄2 |
| Dimensions. | ||||||
Length. | 22″ | 22″ | 24″ | 30″ | 36″ | 36″ |
Width. | 13″ | 14″ | 15″ | 16″ | 18″ | 191⁄2″ |
Height. | 32″ | 331⁄2″ | 38″ | 401⁄2″ | 43″ | 44″ |
Diameter of Cylinder. | 21⁄4 | 3 | 4 | 5 | 6 | 7 |
Stroke. | 6 | 6 | 6 | 6 | 6 | 6 |
Revolutions Per Minute. | 150 | 150 | 140 | 140 | 130 | 130 |
Piston Speed in Feet Per Minute. | 150 | 150 | 140 | 140 | 130 | 130 |
Cubic Feet of Free Air Per Minute. | 2 | 3 | 6 | 9 | 12 | 17 |
Working Pressure. | 100 | 100 | 90 | 85 | 60 | 60 |
Horse Power Required. | 1⁄2 | 5⁄8 | 11⁄4 | 13⁄4 | 2 | 21⁄2 |
| Pipes. | ||||||
Suction. | 3⁄4 | 1 | 11⁄2 | 2 | 2 | 21⁄2 |
Discharge. | 3⁄4 | 1 | 11⁄2 | 11⁄2 | 11⁄2 | 11⁄2 |
| Dimensions. | ||||||
Length. | 16″ | 16″ | 16″ | 24″ | 24″ | 30″ |
Width. | 13″ | 14″ | 14″ | 14″ | 14″ | 18″ |
Height. | 28″ | 291⁄2″ | 331⁄2″ | 371⁄2″ | 371⁄2″ | 42″ |
With increase in altitude the barometric or atmospheric pressure falls from 14.7 pounds per square inch at sea level to about 10 pounds at 10,000 feet above sea level. Since the density of the air decreases with its pressure it is obvious that at such an altitude the total weight of air handled by a given displacement is considerably less than at sea level; and that to fill any volume—a rock drill cylinder, for instance—with air compressed to 90 pounds, a greater free-air displacement will be necessary than would be required at sea level. The relative capacities of a given displacement to do work—as through rock drills or pumps—at varying altitudes are figured in the following table:
Capacities at Varying Heights above Sea Level.
| Feet above Sea Level | Barometer Inches | Relative Capacities |
|---|---|---|
| 0 | 30.00 | 1.000 |
| 500 | 29.42 | .983 |
| 1000 | 28.87 | .967 |
| 1500 | 28.33 | .954 |
| 2000 | 27.79 | .938 |
| 2500 | 27.27 | .924 |
| 3000 | 26.76 | .909 |
| 3500 | 26.25 | .894 |
| 4000 | 25.75 | .879 |
| 4500 | 25.26 | .867 |
| 5000 | 24.78 | .856 |
| 6000 | 23.85 | .827 |
| 7000 | 22.95 | .800 |
| 8000 | 22.10 | .772 |
| 9000 | 21.22 | .750 |
| 10000 | 20.43 | .725 |
| 12000 | 18.92 | .677 |
The fact that the heating effect of compressing air from an initial pressure of 10 pounds absolute to 90 pounds gauge pressure is theoretically equivalent to that of compression to 132 pounds at sea level, makes a two-stage arrangement more imperative in high level work than under ordinary conditions.
Fig. 373.
COMPOUNDING OR TWO-STAGE COMPRESSION.
The two-stage or multi-stage system of air compression is used generally for high pressure work. The system is most usefully employed between 40 and 120 pounds gauge pressure. For the moderate working pressure of 90 to 100 lbs., the two-stage compression has demonstrated its efficiency chiefly for the reason, that the heat generated in the last half of the stroke of a single compressor is by the two-stage process greatly reduced.
Further compounding, for pressures above 100 pounds, becomes quite necessary to secure the advantages named hereafter; the two-stage has proved advantageous up to 500 lbs., three-stage up to 1,000 lbs., and four-stage compression up to 3,000 lbs.