| Chapter 19 - Compressed Air |
| Number |
Topic |
Rule of Thumb |
| 19.01 |
Power |
The horsepower required for a stationary single-stage electric compressor is approximately 28% that of its capacity, expressed in cfm (sea level at 125 psig). Source: Lyman Scheel |
| 19.02 |
Power |
The horsepower required for a portable diesel air compressor is approximately 33% that of its capacity, expressed in cfm (sea level at 125 psig). Source: Franklin Matthias |
| 19.03 |
Power |
To increase the output pressure of a two-stage compressor from 100 to 120 psig requires a 10% increase in horsepower (1% for each 2 psig). Source: Ingersoll-Rand |
| 19.04 |
Air Intake |
The area of the intake duct should be not less than ½ the area of the low-pressure cylinder of a two-stage reciprocating compressor. Source: Lewis and Clark |
| 19.05 |
Cooling |
A series flow of 2.5 to 2.8 USGPM of cooling water is recommended per 100 CFM of compressor capacity for the typical two-stage mine air compressor (jackets and intercooler). Source: Compressed Air and Gas Institute (CAGI) |
| 19.06 |
Cooling |
A parallel flow of 1.25 USGPM of cooling water is recommended per 100 CFM of compressor capacity for the aftercooler of a typical two-stage mine air compressor. Source: CAGI |
| 19.07 |
Cooling |
Approximately 2½% of the cooling water will be lost due to evaporation with each cycle through a cooling tower. Source: Jack de la Vergne |
| 19.08 |
Receiver |
The primary receiver capacity should be six times the compressor capacity per second of free air for automatic valve unloading. Source: Atlas Copco |
| 19.09 |
Receiver |
The difference between automatic valve unloading and loading pressure limits should not be less than 0.4 bar. Source: Atlas Copco |
| 19.10 |
Air Line Losses |
At 100 psi, a 6-inch diameter airline will carry 3,000 cfm one mile with a loss of approximately 12 psi. Source: Franklin Matthias |
| 19.11 |
Air Line Losses |
At 100 psi, a 4-inch diameter airline will carry 1,000 cfm one mile with a loss of approximately 12 psi. Source: Franklin Matthias |
| 19.12 |
Air Line Losses |
A line leak or cracked valve with an opening equivalent to 1/8-inch (3 mm) diameter will leak 25 cfm (42m3/min.) at 100 psig (7 bars). Source: Lanny Pasternack |
| 19.13 |
Air Line Losses |
In a well-managed system, the air leaks should not exceed 15% of productive consumption. Source: Lanny Pasternack |
| 19.14 |
Air Line Losses |
Many older mines waste as much as 70% of their compressed air capacity through leakage. Source: Robert McKellar |
| 19.15 |
Air Line Losses |
Drilling requires a 25-psi air-drop across the bit for cooling to which must be added the circulation loss for bailing of cuttings in the borehole at a velocity of 5,000 fpm, or more. Source: Reed Tool |
| 19.16 |
Air Line Losses |
Except in South Africa, pneumatic drills are usually designed to operate at 90 psig (6.2 bars). Their drilling speed will be reduced by 30% at 70 psig (4.8 bars). Source: Christopher Bise |
| 19.17 |
Air Line Losses |
A line oiler reduces the air pressure by 5 psi. Source: Ingersoll-Rand |
| 19.18 |
Air Line Losses |
An exhaust muffler can increase the required air pressure by 5 psi, or more. Source: Morris Medd |
| 19.19 |
Air Line Losses |
A constant speed compressor designed to be fed at 60 cycles (hertz) will operate at 50 cycles, but experience a reduction in capacity of about 17%. Source: Jack de la Vergne |
| 19.20 |
Altitude |
A constant speed compressor (or booster) underground will require 1% more horsepower for every 100m of depth below sea level. Source: Atlas Copco |
| 19.21 |
Altitude |
Auto-compression will increase the gage pressure of a column of air in a mineshaft by approximately 10% for each 3,000 feet of depth (11% for each 1,000m). Source: Jack de la Vergne |
| 19.22 |
Altitude |
The compressed air from a constant speed compressor will have 1% less capacity to do useful work for every 100m above sea level that it is located. Source: Atlas Copco |