Air Flow is Critical for Your Blast Operation (cont.)
To determine the size compressor needed, add the air requirements of all equipment, plus a 50 percent reserve. If there is a possibility you might switch to a larger nozzle or add air-powered tools, choose a compressor to accommodate those potential demands. A CESCO representative can recommend the size and type of system best suited for your application.
Compressors should be equipped with efficient air intake filters to trap the dust that might cause excessive engine wear.Also, compressors must have shutdown devices to prevent overheating. Overheating can damage engine parts, but more important, it produces carbon monoxide (CO), an odorless, colorless, deadly gas. Where compressors supply helmet breathing air, CO can kill the blast operators.
Very important to the supply of air to blasting systems is the size and type of air outlets furnished with compressors.
To help regulate airflow, many compressors outlet valves have internal slotted plugs about half the size of the valve opening.
A 1-inch (25mm) valve actually has a ½-inch (12.5mm) air passageway, far too small to supply a blast machine.
The quick disconnect couplings fitted to air hose also cause restriction. Coupling size refers to the pipe thread – not the internal diameter. Most ¾-inch (19mm) couplings have ½-inch (12.5mm) inner diameters (ID); 1-inch (25mm) couplings have ¾-inch (19mm) IDs.
Do not use restrictive air valves or quick disconnect couplings, except with small, low production blast machines.
Compressor Air and Abrasive Consumption Estimates
| Nozzle Orifice |
Pressure at the Nozzle (psi) | Air (In cfm) Abrasive & HP requirements |
|||||||
| 50 | 60 | 70 | 80 | 90 | 100 | 125 | 150 | ||
| No. 2 (1/8") |
11 .57 67 2.5 |
13 .77 77 3 |
15 .88 88 3.5 |
17 1.01 101 4 |
18.5 1.12 112 4.5 |
20 1.23 123 5 |
25 1.52 152 5.5 |
30 1.82 182 6.6 |
Air (cfm) Abrasive (cu.ft./hr & Lbs/hr) Compressor hp |
| No. 3 (3/16") |
26 1.5 150 6 |
30 1.71 171 7 |
33 1.96 196 8 |
38 2.16 216 9 |
41 2.38 238 10 |
45 2.64 264 10 |
55 3.19 319 12 |
62 3.83 383 14 |
Air (cfm) Abrasive (cu.ft./hr & Lbs/hr) Compressor hp |
| No. 4 (1/4") |
47 2.68 268 11 |
54 3.12 312 12 |
61 3.54 354 14 |
68 4.08 408 16 |
74 4.48 448 17 |
81 4.94 494 18 |
98 6.08 608 22 |
118 7.30 730 26 |
Air (cfm) Abrasive (cu.ft./hr & Lbs/hr) Compressor hp |
| No. 5 (5/16") |
77 4.68 468 18 |
89 5.34 534 20 |
101 6.04 604 23 |
113 6.72 672 26 |
126 7.40 740 28 |
137 8.12 812 31 |
168 9.82 982 37 |
202 11.78 1178 44 |
Air (cfm) Abrasive (cu.ft./hr & Lbs/hr) Compressor hp |
| No. 6 (3/8") |
108 6.68 668 24 |
126 7.64 764 28 |
143 8.64 864 32 |
161 9.60 960 36 |
173 10.52 1052 39 |
196 11.52 1152 44 |
237 13.93 1393 52 |
284 16.72 1672 62 |
Air (cfm) Abrasive (cu.ft./hr & Lbs/hr) Compressor hp |
| No. 7 (7/16") |
147 8.96 896 33 |
170 10.32 1032 38 |
194 11.76 1176 44 |
217 13.12 1312 49 |
240 14.48 1448 54 |
254 15.84 1584 57 |
314 19.31 1931 69 |
377 23.17 2317 83 |
Air (cfm) Abrasive (cu.ft./hr & Lbs/hr) Compressor hp |
| No. 8 (1/2") |
195 11.60 1160 44 |
224 13.36 1336 50 |
252 15.12 1512 56 |
280 16.80 1680 63 |
309 18.56 1856 69 |
338 20.24 2024 75 |
409 24.59 2459 90 |
491 29.51 2951 108 |
Air (cfm) Abrasive (cu.ft./hr & Lbs/hr) Compressor hp |
Pressure Loss in Compressor Air Line
| ID | Pressure Loss | Production Loss |
| 3/4" | 11.1 psi | 16.6% |
| 1" | 2.4 psi | 3.6% |
| 1-1/4" | 0.7 psi | 1.0% |
| 1-1/2" | 0.2 psi | 0.3% |
| Based on 150 cfm @ 100 psi through 50 feet of compressor air hose | ||
| For maximum efficiency, provide large air lines from the compressor to the blast machine. Place the compressor as near as possible to the blast operation. Use the largest air hose available. | ||
Minimum Compressor Air Line Diameter
| Nozzle No. | Nozzle Orifice Size | Minimum Air Line ID |
| No. 3 | 3/16" (5.0mm) | 1" (25.0mm) |
| No. 4 | 1/4" (6.5mm) | 1" (25.0mm) |
| No. 5 | 5/16" (8.0mm) | 1-1/4" (32.0mm) |
| No. 6 | 3/8" (9.5mm) | 1-1/2" (38.0mm) |
| No. 7 | 7/16" (11.0mm) | 2" (50.0mm) |
| No. 8 | 1/2" (12.5mm) | 2" (50.0mm) |
| No. 10 | 5/8" (16.0mm) | 2-1/2" (64.0mm) |
| No. 12 | 3/4" (19.0) | 3" (76.0mm) |
Effects of Nozzle Wear on Air Consumption
| Nozzle No. | Orifice Size | Air Flow in CFM |
Increase in Air Consumption |
| No. 4 | 1/4" (6.5mm) | 81 cfm | |
| No. 5 | 5/16" (8.0mm) | 137 cfm | 69% more than No.4 |
| No. 6 | 3/8" (9.5mm) | 196 cfm | 43% more than No.5 |
| No. 7 | 7/16" (11.0mm) | 254 cfm | 29% more than No.6 |
| No. 8 | 1/2" (12.5mm) | 338 cfm | 33% more than No.7 |
Blast System Air Volume Estimates
| Nozzle | Size of Orifice |
Volume of Air |
Plus Helmet |
Plus 50% (reserve) |
Minimum Air Required |
| No. 4 | 1/4" 6.5mm |
81 2.3 |
20 0.5 |
50 1.4 |
151 cfm 4.2 m3/min |
| No. 5 | 5/16" 8.0mm |
137 3.9 |
20 0.5 |
79 2.2 |
236 cfm 6.6m3/min |
| No.6 | 3/8" 9.5mm |
196 5.5 |
20 0.5 |
108 3.0 |
324 cfm 9.0 m3/min |
| No. 7 | 7/16" 11.0mm |
254 7.2 |
20 0.5 |
137 3.9 |
411 cfm 11.6 m3/min |
| No. 8 | 1/2" 12.5mm |
338 9.6 |
20 0.5 |
179 5.0 |
537 cfm 16.1 m3/min |
