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Airflow

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
(Resource: Clemco Blast Off 2(Your Guide to Safe and Efficient Abrasive Blasting)