Every blast cabinet, blast room or portable pot that disappoints does so for the same reason: the compressor can’t feed the nozzle. Air consumption is set by nozzle bore and pressure, not by the size of the pot or the cabinet, and a nozzle that starts at 3/8″ is a 7/16″ nozzle after a few hundred hours of wear. Below are Kresco’s published air consumption tables for suction (siphon) and pressure systems, with the abrasive consumption that goes with each pressure setting, followed by how to use them to size a compressor. Kresco marks 100 PSI at the nozzle as the optimal working pressure for high-volume, fast cleaning.
Suction (Siphon) Systems: CFM by Nozzle and Pressure
Suction guns such as the Kresco G5 and SH5 pair a nozzle with an air jet roughly half its bore (1/4″ nozzle with 1/8″ jet, 3/8″ with 3/16″, and so on). The figures are compressed air required in cubic feet per minute.
| Nozzle ID | 40 PSI | 50 PSI | 60 PSI | 70 PSI | 80 PSI | 100 PSI |
|---|---|---|---|---|---|---|
| 1/4″ | 12 | 15 | 17 | 19 | 21 | 26 |
| 5/16″ | 19 | 23 | 27 | 30 | 34 | 42 |
| 3/8″ | 27 | 33 | 38 | 43 | 48 | 58 |
| 7/16″ | 38 | 46 | 52 | 60 | 65 | 80 |
| 1/2″ | 49 | 58 | 67 | 76 | 85 | 94 |
Kresco air consumption table for suction systems. The published table shows 52 CFM for 1/2″ at 60 PSI, which is a misprint; the manual’s figure of 67 CFM is used above.
Pressure Systems: CFM and Abrasive lb/h by Nozzle and Pressure
Pressure cabinets, blast rooms and portable pots push media through the hose at line pressure. Each cell shows CFM of compressed air over pounds of abrasive per hour.
| Nozzle ID | 40 PSI | 50 PSI | 60 PSI | 70 PSI | 80 PSI | 90 PSI | 100 PSI | 120 PSI |
|---|---|---|---|---|---|---|---|---|
| 1/8″ | 10 69 lb | 13 77 lb | 14 82 lb | 15 110 lb | 17 127 lb | 19 140 lb | 20 154 lb | 25 192 lb |
| 3/16″ | 22 140 lb | 26 166 lb | 30 192 lb | 33 220 lb | 38 243 lb | 41 268 lb | 45 297 lb | 55 363 lb |
| 1/4″ | 41 276 lb | 49 329 lb | 55 369 lb | 61 398 lb | 68 460 lb | 74 504 lb | 81 556 lb | 97 666 lb |
| 5/16″ | 65 394 lb | 76 462 lb | 88 528 lb | 101 680 lb | 113 756 lb | 126 832 lb | 137 910 lb | 152 1,010 lb |
| 3/8″ | 91 620 lb | 109 744 lb | 126 860 lb | 143 970 lb | 161 1,080 lb | 173 1,184 lb | 196 1,296 lb | 220 1,454 lb |
| 7/16″ | 124 840 lb | 149 908 lb | 170 1,160 lb | 194 1,320 lb | 217 1,476 lb | 240 1,630 lb | 254 1,782 lb | 300 2,104 lb |
| 1/2″ | 165 1,103 lb | 195 1,305 lb | 224 1,500 lb | 252 1,700 lb | 280 1,890 lb | 309 2,088 lb | 338 2,277 lb | 392 2,640 lb |
| 5/8″ | 260 1,600 lb | 308 1,875 lb | 356 2,140 lb | 404 2,422 lb | 452 2,690 lb | 504 2,973 lb | 548 3,250 lb | 611 3,623 lb |
Kresco air consumption table for pressure systems; lower pressures (20–35 PSI) are omitted here. Abrasive figures are typical for a mineral-abrasive density and move with media choice and metering valve setting.
How to Size the Compressor
- Pick the nozzle by the job, not the compressor. A 3/8″ nozzle is the workhorse for blast rooms; 1/4″ to 5/16″ for pressure cabinets; 1/4″ for most suction cabinets.
- Read CFM at 100 PSI. One 3/8″ pressure nozzle at 100 PSI needs 196 CFM. Rule of thumb: a rotary screw compressor delivers roughly 4–5 CFM per horsepower, so that single nozzle wants a 40–50 HP machine to itself.
- Add every other air user that runs at the same time: the operator’s supplied-air respirator, the dust collector’s pulse cleaning, the blast pot’s own controls, blow-off guns and anything else on the header.
- Add 30–50% for nozzle wear. A 3/8″ nozzle that has worn to 7/16″ needs 254 CFM at 100 PSI. Kresco’s maintenance guides tell you to check bore with a drill bit and replace the nozzle when the next size up slides in.
- Keep the pressure at the nozzle, not the compressor. Long or undersized hose, small fittings and 1-1/4″ piping all eat pressure. Kresco measured 34 PSI of loss on a standard 1-1/4″ pot system against 7–10 PSI with 1-1/2″ MaxBlast piping; every PSI lost at the nozzle costs about 1.5% in production.
- Dry the air. Wet air clumps media and plugs metering valves; point-of-use desiccant dryers and water separators protect the whole system.
Worked Example
Two operators in a blast room, each on a 3/8″ nozzle at 100 PSI: 2 × 196 = 392 CFM. Two supplied-air respirators (budget about 15–25 CFM each per the respirator maker’s spec) and the pot and collector controls add roughly 50 CFM: 442 CFM. Add 30% wear margin: about 575 CFM, which is a 125–150 HP compressor, or two 75 HP machines. That number drives the blast room quote as much as the room size does.
Related Reading
- PowerBlast suction and pressure cabinets
- SBP pressure blast pots and the MaxBlast 1-1/2″ upgrade
- Blast rooms and the maintenance checklist (nozzle drill-bit test)
- Blast media selection chart
Not sure what your plant air can support? Send us your compressor nameplate and the parts you blast or call (847) 833-7010 and we’ll size the system to the air you have, or tell you what air the system needs.
