Engineering Overview
In abrasive blasting, the nozzle orifice acts as a restricted opening. To maintain a specific **Blasting Pressure (PSI)**, the compressor must deliver a specific **Volume (CFM)** of air. If the compressor cannot meet the CFM demand of the nozzle, the pressure will drop, leading to slower cleaning speeds and wasted media.
CFM vs PSI Demand Chart
| Nozzle Size | 80 PSI (CFM) | 100 PSI (CFM) | 120 PSI (CFM) | Min HP |
|---|---|---|---|---|
| 5 mm (#3) | 45 | 54 | 63 | 15 HP |
| 6.5 mm (#4) | 81 | 94 | 108 | 25 HP |
| 8 mm (#5) | 137 | 161 | 185 | 40 HP |
| 9.5 mm (#6) | 196 | 230 | 264 | 60 HP |
| 11 mm (#7) | 254 | 300 | 346 | 75 HP |
| 12.5 mm (#8) | 338 | 396 | 454 | 100 HP |
*HP requirements based on Rotary Screw performance at 4 CFM per HP.
Technical Selection Guide
Nozzle: 6.5mm (#4)
Comp: APEX-30
Use: Precision / Light Maintenance
Nozzle: 8mm (#5)
Comp: APEX-45
Use: Structural Steel / Fabrication
Nozzle: 9.5mm (#6)
Comp: APEX-75
Use: Shipyards / High-Volume Tanks
Pressure Drop Logic
Every 50ft of 1" blast hose causes a pressure drop of approx 2-3 PSI. Using a **Vertical Air Receiver** near the blast zone acts as a buffer, ensuring the nozzle maintains peak PSI during continuous duty cycles.
The Moisture Threat
High CFM creates high friction heat in the air lines. Without a high-capacity **Moisture Separator**, condensation will form, causing abrasive to damp-clump and stop the technical flow of media.
Frequently Asked Questions
What CFM do I need for a #6 blast nozzle?
A #6 nozzle (9.5mm bore) at 7 bar requires 180-210 CFM. Rule: each mm of nozzle bore needs approximately 30-35 CFM. #4 (6.4mm): 100-120 CFM. #8 (12.7mm): 350-400 CFM. Going below these figures causes pressure drop below 4 bar — blast quality degrades severely.
What compressor HP is needed for sandblasting?
HP to CFM ratio: 1 HP produces approximately 4 CFM for rotary screw compressors. #6 nozzle (200 CFM) needs ~50 HP. #8 nozzle (350 CFM) needs ~90 HP. Piston compressors deliver less CFM per HP. Always oversize the compressor by 20% — pressure drop from hose length and wear reduces effective output over time.
Why does CFM decrease at higher altitudes?
At higher altitudes, air density is lower. Every 1,000m elevation above sea level reduces compressor output by approximately 10%. A 450 CFM compressor at 1,500m elevation delivers only ~380 CFM. For mountain or high-altitude projects, specify larger compressor capacity or run at lower pressure.